SRF2015 - List of Keywords (cavity)

Paper	Title	Other Keywords	Page
MOAA01	FRIB Project: Moving to Production Phase	SRF, solenoid, cryomodule, linac	1
	K. Saito, H. Ao, N.K. Bultman, E.E. Burkhardt, F. Casagrande, S. Chouhan, C. Compton, J.L. Crisp, K.D. Davidson, K. Elliott, F. Feyzi, A.D. Fox, P.E. Gibson, L. Hodges, K. Holland, G. Kiupel, S.M. Lidia, I.M. Malloch, D. Miller, S.J. Miller, D. Morris, D. Norton, J. Popielarski, L. Popielarski, A.P. Rauch, R.J. Rose, T. Russo, S. Shanab, M. Shuptar, S. Stark, G.J. Velianoff, D.R. Victory, J. Wei, T. Xu, T. Xu, Y. Yamazaki, Q. Zhao, Z. Zheng FRIB, East Lansing, Michigan, USA S.K. Chandrasekaran Fermilab, Batavia, Illinois, USA A. Facco INFN/LNL, Legnaro (PD), Italy K. Hosoyama, M. Masuzawa KEK, Ibaraki, Japan R.E. Laxdal TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada M.X. Xu IMP/CAS, Lanzhou, People's Republic of China
	Funding: Work supported by the U.S. Department of Energy Office of Science under Cooperative Agreement DE-SC0000661 The Facility for Rare Isotope Beams (FRIB) is based upon a high power heavy ion driver linac under construction at Michigan State University under a cooperative agreement with the US DOE. The construction of conventional facilities already started in the summer, 2013, and the accelerator production began from the summer, 2014. FRIB will accelerate all the stable ion beams from proton to uranium beyond a beam energy of 200 MeV/u and up to a beam power of 400 kW to produce a great number of various rare isotopes using SRF linac. The FRIB SRF driver linac makes use of four kinds of SRF structures. Totally 332 two gap cavities and 48 cryomodules are needed. All SRF hardware components have been validated and are now moving to production. The SRF infrastructure also has been constructed in MSU campus. This talk will present FRIB project and challenges regarding SRF technologies. The status of SRF linac hardware validation and their production, SRF infrastructure status and plan shall be addressed. The information that can be relevant for future large scale proton/ion SRF linacs will also be provided.
	Slides MOAA01 [2.754 MB]
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MOAA02	Recent Progress with EU-XFEL	cryomodule, linac, operation, cryogenics	14
	D. Reschke DESY, Hamburg, Germany
	The superconducting accelerator of the European XFEL consists of the injector part and the main linac. The injector includes one 1.3 GHz accelerator module and one 3.9 GHz third-harmonic module, while the main linac will consist of 100 accelerator modules, operating at an average design gradient of 23.6 MV/m. The fabrication and surface treatment by industry as well as RF acceptance tests of the required 808 superconducting 1.3 GHz cavities are close to an end by the time of SRF15. The accelerator module assembly, testing and installation in the tunnel is in full swing. First steps of commissioning have been made. The status and results of cavity and module RF tests at 1.3 GHz and 3.9 GHz are presented.
	Slides MOAA02 [2.903 MB]
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MOAA04	Overview of Recent SRF Developments for ERLs	SRF, gun, linac, cryomodule	24
	S.A. Belomestnykh BNL, Upton, Long Island, New York, USA S.A. Belomestnykh Stony Brook University, Stony Brook, USA
	Funding: Work is supported by Brookhaven Science Associates, LLC under contract No. DE-AC02-98CH10886 with the US DOE. This talk reviews SRF technology for Energy Recovery Linacs (ERLs). In particular, recent developments and results reported at the ERL2015 Workshop are highlighted. The talk covers facilities under construction, commissioning or operation, such as cERL at KEK, BERLinPro at HZB and R&D ERL at BNL, as well as facilities in the development phase. Future perspectives will be discussed.
	Slides MOAA04 [5.376 MB]
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MOBA03	Sensitivity of Niobium Superconducting RF Cavities to Magnetic Field	vacuum, niobium, impedance, SRF	34
	D. Gonnella, J.J. Kaufman, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	One important characteristic of nitrogen-doped cavities is their very high sensitivity to increased residual surface resistance from trapped ambient magnetic flux. We have performed a systematic study on the losses by trapped flux, and their dependence on the mean-free-path (MFP) of the niobium RF penetration layer. Cavities with a wide range of MFP values were tested in uniform ambient magnetic fields to measure trapped magnetic flux and resulting increase in RF surface resistance. MFP values were determined from surface impedance measurements. It was found that larger mean free paths lead to lower sensitivity to trapped magnetic flux.
	Slides MOBA03 [1.817 MB]
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MOBA04	High-Q Operation of SRF Cavities: The Impact of Thermocurrents on the RF Surface Resistance	simulation, shielding, niobium, operation	37
	J.M. Köszegi, J. Knobloch, O. Kugeler HZB, Berlin, Germany
	For CW applications much effort is being expended to minimize the power dissipation (surface resistance) of niobium cavities. Previous studies have shown that residual resistance can be reduced by performing a thermal cycle, a procedure of warming up a cavity after initial cooldown to about 20K and cooling it down again. It was postulated that thermocurrents during cooldown generate additional trapped magnetic flux that impacts the cavity quality factor. Here, we present a more extensive study that includes measurements of two additional passband modes and that confirms the effect. A change in surface resistance of more than a factor seven was observed. In this paper, we also discuss simulations that support the claim. While the layout of the cavity LHe tank system is cylindrically symmetric, we show that the temperature dependence of the material parameters results in a non-symmetric current distribution.
	Slides MOBA04 [2.830 MB]
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MOBA05	Nature of Quality Factor Degradation in SRF Cavities due to Quench	superconductivity, simulation, electron, cryogenics	41
	M. Checchin Fermilab, Batavia, Illinois, USA
	Superconductive quench is a well-known phenomenon that causes magnetic flux trapping in superconducting accelerating cavities increasing the radio-frequency surface resistance. This paper is addressed to the understanding of the quench-induced losses nature. We present the proof that the real origin of quench-related quality factor degradation is consequence only of ambient magnetic field trapped at the quench spot. Also, we show how the quality factor can be fully recovered after it was highly deteriorated quenching several times in presence of external magnetic field. Such phenomenon was found to be completely reliable up to certain values of applied magnetic field, above that the cavity quality factor cannot be fully recovered anymore.
	Slides MOBA05 [2.742 MB]
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MOBA06	N Doping: Progress in Development and Understanding	niobium, superconductivity, factory, injection	48
	A. Grassellino Fermilab, Batavia, Illinois, USA
	Significant progress was made recently with N2 doped cavities. This talk will summarize all developments with N-doped Nb cavity work at FNAL in the past two years.
	Slides MOBA06 [7.704 MB]
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MOBA08	Niobium Impurity-Doping Studies at Cornell and CM Cool-Down Dynamic Effect on Q0	cryomodule, SRF, niobium, superconductivity	55
	M. Liepe, B. Clasby, R.G. Eichhorn, B. Elmore, F. Furuta, G.M. Ge, D. Gonnella, T. Gruber, D.L. Hall, G.H. Hoffstaetter, J.J. Kaufman, P.N. Koufalis, J.T. Maniscalco, T.I. O'Connell, P. Quigley, D.M. Sabol, J. Sears, E.N. Smith, V. Veshcherevich Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	As part of a multi-laboratory research initiative on high Q0 niobium cavities for LCLS-II and other future CW SRF accelerators, Cornell has conducted an extensive research program during the last two years on impurity-doping of niobium cavities and related material characterization. Here we give an overview of these activities, and present results from single-cell studies, from vertical performance testing of nitrogen-doped nine-cell cavities, and from cryomodule testing of nitrogen-doped nine-cell cavities.
	Slides MOBA08 [8.983 MB]
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MOPB001	RF Performance of Ingot Niobium Cavities of Medium-Low Purity	SRF, vacuum, operation, radio-frequency	61
	G. Ciovati, P. Dhakal, P. Kneisel, G.R. Myneni, J.K. Spradlin JLab, Newport News, Virginia, USA
	Funding: This manuscript has been authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. Superconducting radio-frequency cavities made of ingot niobium with residual resistivity ratio (RRR) greater than 250 have proven to have similar or better performance than fine-grain Nb cavities of the same purity, after standard processing. The high purity requirement contributes to the high cost of the material. As superconducting accelerators operating in continuous-wave typically require cavities to operate at moderate accelerating gradients, using lower purity material could be advantageous not only to reduce cost but also to achieve higher Q0-values, because of the well-known dependence of the BCS-surface resistance on mean free path. In this contribution we present the results from cryogenic RF tests of 1.3-1.5 GHz single-cell cavities made of ingot Nb of medium (RRR=100-150) and low (RRR=60) purity from different suppliers. Cavities made of medium-purity ingots routinely achieved peak surface magnetic field values greater than 70 mT with Q0-values above 1.5·10¹⁰ at 2 K. The performance of cavities made of low-purity ingots were affected by significant pitting of the surface after chemical etching.
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MOPB002	Observation of High Field Q-Slope in 3 GHz Nb Cavities	niobium, SRF, radiation, feedback	66
	G.V. Eremeev, F.E. Hannon JLab, Newport News, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. A degradation of the unloaded quality factor is commonly observed above about 100 mT in elliptical niobium cavities. The cause of this degradation has not been fully understood yet, but the empirically found solution of heating to about 100-120 C for 24-48 hrs. eliminates the degradation in electropolished fine grain or large grain niobium cavities. While numerous experiments related to this phenomenon have been done at 1.3 GHz and 1.5 GHz, little data exists at other frequencies, and the frequency dependence of this degradation is not clear. We have measured the unloaded quality factor of 3 GHz fine grain niobium cavities, which were chemically polished as the final treatment before RF tests in a vertical Dewar and observed the characteristic degradation in two cavities. The measurement of the quality factor degradation at different bath temperatures points to a field-dependent rather than a temperature-related effect.
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MOPB003	Superconducting Cavity for the Measurements of Frequency, Temperature, RF Field Dependence of the Surface Resistance	plasma, coupling, cryogenics, experiment	70
	H. Park, S.U. De Silva, J.R. Delayen ODU, Norfolk, Virginia, USA H. Park JLab, Newport News, Virginia, USA
	In order to better understand the contributions of the various physical processes to the surface resistance of superconductors the ODU Center for Accelerator Science is developing a half-wave resonator capable of operating between 325 MHz and 1.3 GHz. This will allow the measurement of the temperature and rf field dependence of the surface resistance on the same surface over the range of frequency of interest for particle accelerators and identify the various sources of power dissipation.
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MOPB004	Understanding the Field Dependence of the Surface Resistance in Nitrogen-Doped Cavities	simulation, radio-frequency, vacuum, impedance	74
	P.N. Koufalis, D. Gonnella, M. Liepe, J.T. Maniscalco, I. Packtor Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: NSF Grant PHYS-1416318 An important limiting factor in the performance of superconducting radio frequency (SRF) cavities in medium and high field gradients is the intrinsic quality factor and, thus, the surface resistance of the cavity. The exact dependence of the surface resistance on the magnitude of the RF field is not well understood. We present an analysis of experimental data of LT1-3 and LT1-4, 1.3 GHz single-cell nitrogen-doped cavities prepared and tested at Cornell. Most interestingly, the cavities display anti-Q slopes in the medium-field region (i.e. Rs decreases with increasing accelerating field). We extract the temperature dependent surface resistances of the cavities, analyze field dependencies, and compare with theoretical predictions. These comparisons and analyses provide new insights into the field dependence of the surface resistance and improve our understanding of the mechanisms behind the effect.
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MOPB005	Developing a Setup to Measure Field Dependence of BCS Surface Resistance	solenoid, niobium, radio-frequency, software	77
	J.T. Maniscalco, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: NSF/DOE The temperature-dependent part of the microwave surface resistance of superconducting radio-frequency (SRF) cavities has been shown experimentally to depend on the strength of the applied magnetic surface field. Several theories have recently been proposed to describe this phenomenon. In this paper we present work on the development of a microwave cavity setup for measuring the field-dependence with an applied DC magnetic field.
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MOPB007	Temperature Excursions in Nb Sheets With Imbedded Delamination Cracks	SRF, radiation, status, radio-frequency	82
	P. Xu, N.T. Wright MSU, East Lansing, Michigan, USA T.R. Bieler Michigan State University, East Lansing, Michigan, USA C. Compton FRIB, East Lansing, Michigan, USA
	Funding: Work supported by US DOE Cooperative Agreement DE-SC0000661 and Michigan State University. Delamination cracks can form in rolled Nb sheets, and between layers with different micro-structures. Such cracks cause resistance to heat conduction from the RF surface to the liquid He bath. A delamination crack can negate the advances in manufacturing processes that have enhanced the thermal conductivity of Nb. Here, temperature excesses are calculated as functions of crack size and location, and the power dissipated at an imperfection in the RF surface. A disk shape of Nb sheet is modeled as having adiabatic sides. A hemispherical defect is located on the RF surface at the center of this section. A crack is modeled as a void within the Nb disk. The Kapitza resistance between the Nb surface and liquid He is varied. The results indicate that an incipient crack leads to a decrease in the magnetic flux required to cause thermal breakdown. The decrease in the field is gradual with increasing crack radius, until the crack radius nearly equals the section radius, after which the field required for breakdown decreases sharply. To a lesser extent, the field strength for thermal breakdown also decreases with increased crack depth.
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MOPB008	Theoretical Field Limit and Cavity Surface Conditions: Nano-Scale Topography and Sub-millimeter Pit	factory, simulation, radio-frequency, framework	86
	T. Kubo KEK, Ibaraki, Japan
	The recent two theoretical papers,* are briefly introduced. The former addresses the superheating field (Bs) suppression due to nano-defects distributing almost continuously on the cavity surface. We introduce a model of the nano-defect. An analytical formula for Bs suppression factor is derived. By using the formula, suppression factors of bulk or multilayer superconductors and those after various surface processing technologies can be evaluated. An application to the dirty Nb processed by EP is also presented as an example. The latter address the magnetic field enhancement (MFE) at the sub-millimeter pit on the surface of cavity, which is thought to cause quench. There exists the famous well-type pit model, but many of pits are not well-type but have gentle slopes. Impacts of the slope angle on MFE have not been well understood. We introduce a model that can describe a pit with an arbitrary slope angle. A formula to evaluate the MFE factor is derived. A pit with a gentle slope angle yields a much smaller MFE factor than the well-type pit. The formula can be applied to the calculation of MFE factors of real pits with arbitrary slope angles. T. Kubo, Prog. Theor. Exp. Phys. 2015,063G01(2015). ** T. Kubo, Prog. Theor. Exp. Phys. 2015,073G01(2015).
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MOPB009	Model of Flux Trapping in Cooling Down Process	target, interface, experiment, framework	90
	T. Kubo KEK, Ibaraki, Japan
	Recent findings that cooling conditions affect an amount of trapped magnetic flux attract much attention as a way to achieve a high-Q0 by SRF cavity,,*. Q0~210¹¹ has already been achieved by the full flux expulsion***. While much experimental studies have been conducted, not much theoretical progress followed on it. In this paper, I introduce a simple model that can explain how trapped fluxoids are expelled in cooling process. J.M.Vogt et al., PRSTAB 16, 102002 (2013) A.Romanenko et al., JAP 115, 184903 (2014) J.M.Vogt et al., PRSTAB 18, 042001 (2015) ***A.Romanenko et al., APL 105, 234103 (2014)
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MOPB010	Field-Dependent Surface Resistance for Superconducting Niobium Accelerating Cavities: The Case of N-Doping	niobium, data-analysis, electron, superconductivity	95
	W. Weingarten Private Address, SERGY, France R.G. Eichhorn Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	The dependence of the Q-value on the RF field (Q-slope) for superconducting RF cavities is actively studied in various accelerator laboratories. Although remedies against this dependence have been found, the physical cause still remains obscure. A rather straightforward two-fluid model description of the Q-slope in the low and high field domains is extended to the case of the recently experimentally identified increase of the Q-value with the RF field obtained by so-called "N-doping”. This paper was initiated when one of the authors (W.W., retiree from CERN) visited Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, NY.
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MOPB011	How Uniform Are Cool-Downs?	interface, simulation, niobium, factory	100
	J.A. Robbins, R.G. Eichhorn Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Since the last SRF conference it has become clear that achieving extremely high quality factors of SRF cavities depend on the cool-down scenario. While some findings favor a fast cool-down, others suggest a slow cycle to be advantageous, and many variations to that have been investigated: the role of thermocurrents, amount of ambient magnetic field and flux trapping. This paper will investigate, how uniformly different cool-down procedures are and if they can explain the more efficient magnetic flux expulsion.
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MOPB013	Simulation of Geometry Dependent Flux Trapping	simulation, factory, superconducting-cavity, focusing	105
	J. May-Mann, R.G. Eichhorn Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Trapping or expulsion of ambient magnetic field has become an important factor in the performance of superconducting cavities with very high Q. As experimental data is limited, we set up a numerical field calculation model to study this effect in more details. We will report, how the cavity orientation, the movement of the transition to superconductivity front, and the orientation of the magnetic field contributes to the amount of magnetic field being vulnerable for trapping.
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MOPB014	Magnetic Flux Expulsion in Horizontally Cooled Cavities	interface, SRF, distributed, simulation	110
	M. Martinello, M. Checchin, A. Grassellino, O.S. Melnychuk, A. Romanenko, D.A. Sergatskov Fermilab, Batavia, Illinois, USA M. Checchin Illinois Institute of Technology, Chicago, Illlinois, USA J. Zasadzinski IIT, Chicago, Illinois, USA
	Funding: Work supported by the US Department of Energy, Office of High Energy Physics The cool down details of superconducting accelerating cavities are crucial parameters that have to be optimize in order to obtain very high quality factors. The temperature all around the cavity is monitored during its cool down across the critical temperature, in order to visualize the different dynamics of fast and slow cool-down, which determine considerable difference in terms of magnetic field expulsion and cavity performance. The study is performed placing a single cell 1.3 GHz elliptical cavity perpendicularly to the helium cooling flow, which is representative of how SRF cavities are cooled in an accelerator. Hence, the study involves geometrical considerations regarding the cavity horizontal configuration, underling the different impact of the various magnetic field components on the surface resistance. Experimental data also proves that under established conditions, flux lines are concentrated at the cavity top, in the equatorial region, leading to temperature rise.
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MOPB015	Trapped Flux Surface Resistance Analysis for Different Surface Treatments	niobium, resonance, superconductivity, instrumentation	115
	M. Martinello, M. Checchin, A. Grassellino, O.S. Melnychuk, S. Posen, A. Romanenko, D.A. Sergatskov Fermilab, Batavia, Illinois, USA M. Checchin Illinois Institute of Technology, Chicago, Illlinois, USA J. Zasadzinski IIT, Chicago, Illinois, USA
	Funding: Work supported by the US Department of Energy, Office of High Energy Physics The trapped flux surface resistance is one of the main contributions on cavity losses which appears when cavities are cooled in presence of external magnetic field. The study is focused on the understanding of the different parameters which determine the trapped flux surface resistance, and how this change as a function of different surface treatments. The study is performed on 1.3 GHz niobium cavities processed with different surface treatments after the 800 C bake: electro-polishing (EP), 120 C baking, and N-doping varying the time of the Nitrogen exposure. The trapped flux surface resistance normalized for the trapped magnetic flux is then analyzed as a function of the mean free path in order to find the surface treatment which minimized the trapped flux sensitivity.
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MOPB018	Introduction of Precisely Controlled Microstructural Defects into SRF Cavity Niobium Sheets and Their Impact on Local Superconducting Properties	niobium, SRF, electron, superconductivity	120
	M. Wang, T.R. Bieler, D. Kang Michigan State University, East Lansing, Michigan, USA C. Compton FRIB, East Lansing, Michigan, USA D.C. Larbalestier, A. Polyanskii, Z-H. Sung ASC, Tallahassee, Florida, USA P.J. Lee NHMFL, Tallahassee, Florida, USA
	Funding: Research supported by DOE/OHEP (contract number DE-FG02-09ER41638 at MSU and DE-SC0009960 at FSU) and the State of Florida. When SRF cavity shapes are formed from Nb sheets, the metallurgical processing introduces microstructural defects such as dislocations and low-angle grain boundaries that can serve as pinning centers for magnetic flux that may degrade cavity performance. Therefore, the relationship between magnetic flux behavior and microstructural defects in carefully strained SRF Nb sheet was investigated. Laue X-ray and EBSD-OIM crystallographic analyses of large grain ingot slices were used to characterize microstructural defects and then predict which grains and sample orientations will produce desired model defects due to tensile deformation. Grain orientations were chosen to favor specific slip systems, which generate dislocations with special angles with respect to the sample surface. Nb bicrystals were also prepared to investigate the effects of grain boundaries on flux pinning. The generated defect structures were confirmed by OIM and TEM. Cryogenic magneto-optical imaging was used to directly observe the penetration of magnetic flux into the deformed Nb. These model samples have deformation that is similar to that expected in typical cavity forming processes.
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MOPB019	Horizontal Testing and Thermal Cycling of an N-Doped Tesla Type Cavity	shielding, pick-up, factory, EPICS	125
	O. Kugeler, J. Knobloch, J.M. Köszegi HZB, Berlin, Germany A. Grassellino, O.S. Melnychuk, A. Romanenko, D.A. Sergatskov Fermilab, Batavia, Illinois, USA
	An N-doped TESLA type cavity treated at FERMILAB has been tested in the HoBiCaT horizontal test stand. Temperatures and magnetic fields occuring during the superconducting transition were recorded at various positions and directions on the outer cavity surface. Several thermal cycling runs were performed yielding different Q0 factors just like in undoped cavities. The resulting residual and BCS resistance values were correlated to the thermal and magnetic conditions during cooldown.
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MOPB023	Detectors Sensing Second Events Induced by Thermal Quenches of SRF Cavities in He II	SRF, detector, instrumentation, diagnostics	135
	M. Fouaidy, F. Dubois, D. Longuevergne, O. Pochon, J.-F. Yaniche IPN, Orsay, France
	SRF bulk Nb cavities are often limited by quench due to anomalous losses (heating due normal defects or Field Emission). We continued R&D on Quench Detectors (QD) activity for locating quench in SRF cavities via 2nd sound in superfluid helium. We investigated 2 kinds of QD: Capacitive OST (COST) and Low Response time resistive Thermometers (LRT). A test stand operating in LHe (Temperature: T0) was used for the characterization of the QD by means of precise experimental simulation of SRF cavity quench (pulsed heat flux qP). For improving spatial resolution of QD, smaller COSTs were developed and tested. We investigated the dynamic response of QD as function of different parameters (heater size/geometry, T0, qP) and data are reported. Further, a 2nd Sound Resonator (SSR), with a pair of COSTs at its 2 extremities as 2nd Sound Generator (SSG) and Detector (SSD) respectively and housing also a low heat capacity heater (SSG) and a LRT (SSD) assembly was developed. The first experimental data obtained, with SSR operated in resonating mode or in a shock wave mode are presented. The results concerning locating of quenches in QWR and spoke cavities are discussed.
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MOPB024	SRF Cavity Breakdown Calculation Procedure Using FEA-Software	simulation, cathode, SRF, niobium	140
	R.A. Kostin, A. Kanareykin Euclid TechLabs, LLC, Solon, Ohio, USA I.V. Gonin Fermilab, Batavia, Illinois, USA E.N. Zaplatin FZJ, Jülich, Germany
	SRF cavity thermal breakdown can be analyzed analytically using thermodynamics equation. This technique is suitable for simple geometries when surface magnetic field variation can be omitted. Thermal radiation effect which is crucial for SRF gun calculations is also hard to implement properly because of complicated geometry. All of these can be overcome by using multiphysics FEA-software. This paper shows the procedure of cavity thermal breakdown calculation in coupled multiphysics analysis with dependable parameters.
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MOPB027	Modifications of Superconducting Properties of Niobium Caused by Nitrogen Doping of Ultra-High Quality Factor Cavities	niobium, SRF, superconductivity, vacuum	144
	A. Vostrikov, A. Grassellino, A. Romanenko Fermilab, Batavia, Illinois, USA L. Horyn, Y.K. Kim, A. Vostrikov University of Chicago, Chicago, Illinois, USA T. Murat University of Wisconsin-Madison, Madison, USA
	We have performed detailed studies using DC and AC magnetometry and electrical resistivity measurements of niobium samples prepared using different nitrogen doping recipes. We compare the results to the samples prepared by standard preparation techniques such as EP with and without additional 120C baking to get insight into driving factors of the lowered quench field in N-doped SRF cavities.
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MOPB028	Preservation of Very High Quality Factors of 1.3 GHz Nine Cell Cavities From Bare Vertical Test to Dressed Horizontal Test	cryomodule, factory, shielding, HOM	149
	A. Grassellino, S. Aderhold, M. Checchin, A.C. Crawford, C.J. Grimm, A. Hocker, M. Martinello, O.S. Melnychuk, J.P. Ozelis, S. Posen, A.M. Rowe, D.A. Sergatskov, N. Solyak, R.P. Stanek, G. Wu Fermilab, Batavia, Illinois, USA D. Gonnella Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA J.M. Köszegi HZB, Berlin, Germany M. Liepe Cornell University, Ithaca, New York, USA
	In this contribution we will report quality factor evolution of several different nine cell N doped cavities with very high Q. The evolution of the quality factor will be reported from bare to dressed in vertical test to dressed in horizontal test with unity coupling to dressed in horizontal test and CM-like environment/configuration (with RF ancillaries). Cooling studies and optimal cooling regimes will be discussed for both vertical and horizontal tests and comparisons will be drawn also for different styles titanium vessels. Studies of sensitivities to magnetic field in final horizontal configuration have been performed by applying a field around the dressed cavity and varying the cooling; parameters required for a very good flux expulsion will be presented.
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MOPB030	Measurements of Thermal Impedance on Superconducting Radiofrequency Cavities	impedance, SRF, niobium, operation	154
	P. Dhakal, G. Ciovati, G.R. Myneni JLab, Newport News, Virginia, USA
	Funding: This manuscript has been authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. The thermal impedance of niobium plays an important role in the stability of the superconducting radio frequency cavities used in particle accelerators. During the operation of SRF cavities, the RF power dissipated on the inner surface of the cavities and the heat transport to the helium bath depend on the thermal conductivity of niobium and the Kapitza conductance of the interface between the niobium and superfluid helium. Here, we present the results of measurements done on samples as well as on SRF cavities made of both ingot and fine-grain Nb to explore the effect of the surface preparation and crystal structure on the thermal impedance.
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MOPB033	LCLS-II SRF Cavity Processing Protocol Development and Baseline Cavity Performance Demonstration	cryomodule, SRF, linac, vacuum	159
	M. Liepe, P. Bishop, H. Conklin, R.G. Eichhorn, F. Furuta, G.M. Ge, D. Gonnella, T. Gruber, D.L. Hall, G.H. Hoffstaetter, J.J. Kaufman, G. Kulina, J.T. Maniscalco, T.I. O'Connell, P. Quigley, D.M. Sabol, J. Sears, V. Veshcherevich Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA M. Checchin, A.C. Crawford, A. Grassellino, C.J. Grimm, A. Hocker, M. Martinello, O.S. Melnychuk, J.P. Ozelis, A. Romanenko, A.M. Rowe, D.A. Sergatskov, W.M. Soyars, R.P. Stanek, G. Wu Fermilab, Batavia, Illinois, USA E. Daly, G.K. Davis, M.A. Drury, J.F. Fischer, A.D. Palczewski, C.E. Reece JLab, Newport News, Virginia, USA M.C. Ross SLAC, Menlo Park, California, USA
	Funding: Work supported, in part, by the US DOE and the LCLS-II Project under U.S. DOE Contract No. DE-AC05-06OR23177 and DE-AC02-76SF00515. The ”Linac Coherent Light Source-II” Project will construct a 4 GeV CW superconducting RF linac in the first kilometer of the existing SLAC linac tunnel. The baseline design calls for 280 1.3 GHz nine-cell cavities with an average intrinsic quality factor Q0 of 2.7·10¹⁰ at 2K and 16 MV/m accelerating gradient. The LCLS-II high Q0 cavity treatment protocol utilizes the reduction in BCS surface resistance by nitrogen doping of the RF surface layer, which was discovered originally at FNAL. Cornell University, FNAL, and TJNAF conducted a joint high Q0 R&D program with the goal of (a) exploring the robustness of the N-doping technique and establishing the LCLS-II cavity high Q0 processing protocol suitable for production use, and (b) demonstrating that this process can reliably achieve LCLS-II cavity specification in a production acceptance testing setting. In this paper we describe the LCLS-II cavity protocol and analyze combined cavity performance data from both vertical and horizontal testing at the three partner labs, which clearly shows that LCLS-II specifications were met, and thus demonstrates readiness for LCLS-II cavity production.
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MOPB035	Nature and Implication of Found Actual Particulates on the Inner Surface of Cavities in a Full-Scale Cryomodule Previously Operated With Beams	cryomodule, ion, vacuum, operation	164
	R.L. Geng, J.F. Fischer, E.A. McEwen, O. Trofimova JLab, Newport News, Virginia, USA
	Field emission in an SRF cavity is often the result of small foreign particulates lodging on the cavity inner surface. To avoid these particulate field emitters, careful cleaning and handling of individual cavities and clean room assembly of cavity strings are common practice. Despite these elaborate processes, some particulates persist to stay on the final surface of a beam-ready cavity. Moreover, as will be shown in this contribution, new particulates accumulate after a cryomodule is placed in the accelerator tunnel. The nature of these accumulated particulates on the inner surface of a beam-accelerating cavity is largely unknown for two reasons: (1) lack of access to such surfaces; (2) lack of a workable procedure for investigation without destroying the cavity. In this contribution, we report the first study on found actual particulates on the inner surface of 5-cell CEBAF cavities in a full-scale cryomodule previously operated with beam. The nature of the studied particulates is presented. The implication of the findings will be discussed in view of reliable and efficient operation of CEBAF and future large-scale SRF accelerators.
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MOPB036	TOF-SIMS Study of Nitrogen Doping Niobium Samples	niobium, experiment, vacuum, ion	169
	Z.Q. Yang, L. Lin, X.Y. Lu, W.W. Tan, D.Y. Yang, J. Zhao PKU, Beijing, People's Republic of China
	Nitrogen doping treatment with the subsequent electropolishing (EP) of the niobium superconducting cavity can significantly increase the cavity’s quality factor up to a factor of 3. The nitrogen doping experiment has been successfully repeated and demonstrated. But the mechanism of the nitrogen doping effect remains unclear. Nitrogen doping study on niobium samples was carried out in Peking University. The niobium samples were manual processed to avoid heat generation. The experiment condition is close to that of the Fermilab. After the nitrogen doping treatment, the samples were mildly electropolished with the thickness of 1.3μm, 1.9μm, 3.3μm, 4.2μm, 5.1μm, 5.9μm and 7.0μm. The time of flight secondary ion mass spectrometry (TOF-SIMS) measurements show that the samples directly after nitrogen doping have a much higher nitrogen concentration in the depth of about 90nm. When the EP removal is larger than 1.3μm, the samples’ impurity elements is remarkably reduced and their distribution is similar to each other. Also the measured results to some extent prove that EP removal can introduce H to the niobium surface.
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MOPB039	Analysis of BCS RF Loss Dependence on N-Doping Protocols	niobium, SRF, linac, operation	174
	A.D. Palczewski, P. Dhakal, C.E. Reece JLab, Newport News, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177 with supplemental funding from the LCLS-II Project U.S. DOE Contract No. DE-AC02-76SF00515. We present a study on two parallel-path SRF cavities (one large grain and one fine grain, 1.3 GHz) which seeks to explain the correlation between the amount of nitrogen on the inner surface of a “nitrogen doped” SRF cavity and the change in the temperature dependant (packaged into term BCS) RF losses. For each doping/EP, the cavities were tested at multiple temperatures (2.0 K to 1.5 K in 0.1 K steps) to create a Q0 vs. Eacc vs. T matrix which then could be used to extract temperature dependant and independent components. After each test, the cavities were thermally cycled to 120 K and then re-cooled and retested to assess if evidence of hydrogen migration might appear even at a small level. In addition, TD-5 was also tested at fixed low field (Q0 vs. T) to fit standard BCS theory. In parallel, SIMS data was taken on like-treated samples to correlate the amount of nitrogen within the RF surface to the change in the temperature dependant fitting parameter “A”.** [] H.Tian et al., contributed to SRF2015.
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MOPB040	Performance of Dressed Cavities for the Jefferson Laboratory LCLS-II Prototype Cryomodule - With Comparison to the Pre-Dressed Performance	HOM, cryomodule, hardware, linac	178
	A.D. Palczewski, G.K. Davis JLab, Newport News, Virginia, USA F. Furuta, G.M. Ge, D. Gonnella, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177 with supplemental funding from the LCLS-II Project U.S. DOE Contract No. DE-AC02-76SF00515. Initial vertical RF test results and quench studies for six of the eight undressed 9 cell cavities slated for use in the Jefferson laboratory LCLS-II prototype cryomodule were presented at IPAC2015. For the final string 2 more cavities AES029 and AES030 (work done at Cornell) are being processed and tested for qualification before helium vessel welding. In addition, AES034 (initial R&D treatment) is being reworked with the current production protocol after a surface reset to improve the overall performance. After final qualification all 8 cavities will be welded into helium vessels and equipped with HOM couplers. In this paper we will present the final undressed and dressed vertical RF data comparing the changes in the surface resistance before their installation in the cryomodule string. A.D. Palczewski et al. Quench Studies of Six High Temperature Nitrogen Doped 9 Cell Cavities for use in the LCLS-II Prototype Cryo-module at Jefferson Laboratory, Proc. IPAC2015, WEPWI019, 2015.
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MOPB041	Cryomodule Testing of Nitrogen-Doped Cavities	cryomodule, HOM, SRF, linac	182
	D. Gonnella, B. Clasby, R.G. Eichhorn, B. Elmore, F. Furuta, G.M. Ge, D.L. Hall, Y. He, G.H. Hoffstaetter, J.J. Kaufman, P.N. Koufalis, M. Liepe, J.T. Maniscalco, T.I. O'Connell, P. Quigley, D.M. Sabol, E.N. Smith, V. Veshcherevich Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA A. Grassellino, C.J. Grimm, J.P. Holzbauer, O.S. Melnychuk, Y.M. Pischalnikov, A. Romanenko, W. Schappert, D.A. Sergatskov Fermilab, Batavia, Illinois, USA A.D. Palczewski, C.E. Reece JLab, Newport News, Virginia, USA
	Funding: DOE and the LCLS-II High Q Project The Linac Coherent Light Source-II (LCLS-II) is a new FEL x-ray source that is planned to be constructed in the existing SLAC tunnel. In order to meet the required high Q0 specification of 2.7x10¹⁰ at 2 K and 16 MV/m, nitrogen-doping has been proposed as a preparation method for the SRF cavities in the linac. In order to test the feasibility of these goals, four nitrogen-doped cavities have been tested at Cornell in the Horizontal Test Cryomodule (HTC) in five separate tests. The first three tests consisted of cavities assembled in the HTC with high Q input coupler. The fourth test used the same cavity as the third but with the prototype high power LCLS-II coupler installed. Finally, the fifth test used a high power LCLS-II coupler, cavity tuner, and HOM antennas. Here we report on the results from these tests along with a systematic analysis of change in performance due to the various steps in preparing and assembling LCLS-II cavities for cryomodule operation. These results represent one of the final steps to demonstrate readiness for full prototype cryomodule assembly for LCLS-II.
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MOPB042	Fundamental Studies on Doped SRF Cavities	niobium, vacuum, simulation, SRF	187
	D. Gonnella, T. Gruber, J.J. Kaufman, P.N. Koufalis, M. Liepe, J.T. Maniscalco, B. Yu Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: NSF Recently, doping with nitrogen has been demonstrated to help SRF cavities reach significantly higher intrinsic quality factors than with standard procedures. However, the quench fields of these cavities have also been shown to be frequently reduced. Here we report on fundamental studies of doped cavities, investigating the source of reduced quench field and exploring alternative dopants. We have focused on studying the quench of nitrogen-doped cavities with temperature mapping and measurements of the flux penetration field using pulsed power to investigate maximum fields in nitrogen doped cavities. We also report on studies of cavities doped with other gases such as helium. These studies have enabled us to shed light on the mechanisms behind the higher Q and lower quench fields that have been observed in cavities doped with impurities.
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MOPB045	Study of Slip and Deformation in High Purity Single Crystal Nb for Accelerator Cavities	experiment, niobium, SRF, factory	191
	D. Kang, D.C. Baars, T.R. Bieler Michigan State University, East Lansing, Michigan, USA C. Compton FRIB, East Lansing, Michigan, USA A. Mapar, F. Pourboghrat MSU, East Lansing, Michigan, USA
	Funding: This work was supported by the U.S. Department of Energy, Office of High Energy Physics, through Grant No. DE-FG02-09ER41638. High purity Nb has been used to build accelerator cavities over the past couple decades, and there is a growing interest in using ingot Nb as an alternative to the fine grain sheets. Plastic deformation governed by slip is complicated in body-centered cubic metals like Nb. Besides the crystal orientation with respect to the applied stress (Schmid effect), slip is also affected by other factors including temperature, strain rate, strain history, and non-Schmid effects such as twinning/anti-twinning asymmetry and non-glide shear stresses. A clear understanding of slip is an essential step towards modeling the deep drawing of large grain ingot slices, hence predicting the final microstructure/performance of cavities. Two groups of single crystals, with and without a prior heat treatment, were deformed to 40% engineering strain in uniaxial tension. Differences in flow stresses and active slip systems between the two groups were observed, likely due to the removal of preexisting dislocations. Crystal plasticity modeling of the stress-strain behavior suggests that the non-Schmid effect is small in Nb, and that the deep drawing process might be approximated with a Schmid model.
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MOPB047	Secondary Electron Yield of Electron Beam Welded Areas of SRF Cavities	electron, gun, niobium, vacuum	196
	M. Basovic, S. Popović, M. Tomovic, L. Vušković ODU, Norfolk, Virginia, USA F. Čučkov, A. Samolov University of Massachusetts Boston, Boston, Massachusetts, USA
	Secondary Electron Emission (SEE) is a phenomenon that contributes to the total electron activity inside the Superconducting Radiofrequency (SRF) cavities during the accelerator operation. SEE is highly dependent on the state of the surface. During electron beam welding process, significant amount of heat is introduced into the material causing the microstructure change of Niobium (Nb). Currently, all simulation codes for field emission and multipacting are treating the inside of the cavity as a uniform, homogeneous surface. Due to its complex shape and fabricating procedure, and the sensitivity of the SEE on the surface state, it would be interesting to see if the Secondary Electron Yield (SEY) parameters vary in the surface area on and near the equator weld. For that purpose, we have developed experimental setup that can measure accurately the energy distribution of the SEY of coupon-like like samples. To test the influence of the weld area on the SEY of Nb, dedicated samples are made from a welded plate using electron beam welding parameters common for cavity fabrication. SEY data matrix of those samples will be presented.
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MOPB049	High Flux Three Dimensional Heat Transport in Superfluid Helium and Its Application to a Trilateration Algorithm for Quench Localization With OSTs	detector, experiment, niobium, software	201
	T. Junginger TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada P. Horn TU Dresden, Dresden, Germany T. Koettig, K.C. Liao, A. Macpherson CERN, Geneva, Switzerland B.J. Peters KIT, Karlsruhe, Germany
	Oscillating superleak transducers of second sound can be used to localize quench spots on superconducting cavities by trilateration. However propagation speeds faster than the velocity of second sound are usually observed imped- ing the localization. Dedicated experiments show that the fast propagation cannot be correlated to the dependence of the velocity on the heat flux density, but rather to boiling effects in the vicinity of the hot spot. 17 OSTs were used to detect quenches on a 704MHz one-cell elliptical cavity. Two different algorithms for quench localization have been tested and implemented in a computer program enabling direct crosschecks. The new algorithm gives more consis- tent results for different OST signals analyzed for the same quench spot.
	Poster MOPB049 [0.901 MB]
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MOPB051	Muon Spin Rotation on Treated Nb Samples in Parallel Field Geometry	SRF, polarization, detector, niobium	210
	S. Gheidi UBC, Vancouver, B.C., Canada T.J. Buck, T. Junginger, R.E. Laxdal, G. Morris TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada M. Dehn TUM/Physik, Garching bei München, Germany R. Kiefl UBC & TRIUMF, Vancouver, British Columbia, Canada
	MuSR is a powerful tool to probe local magnetism and hence can be used to diagnose the entry of magnetic flux in superconductors. First measurements on SRF samples were done with an external DC field applied perpendicular to the sample1 (transverse geometry) with the muons applied to the sample face. Here the results are strongly impacted by demagnetization, pinning strength and edge effects. A new spectrometer has been developed to allow sample testing with a field varying from 0 to 300mT applied along the sample face (parallel geometry) analogous to rf fields in SRF resonators. The geometry is characterized by a small demagnetization factor reducing the impact of pinning and edge effects on field of first flux entry. The beamline installation and first results comparing transverse and parallel results will be presented. 1 Grassellino et al. Muon spin rotation studies of niobium for superconducting rf applications. Phys. Rev. ST Accel. Beams, 16:062002, Jun 2013.
	Poster MOPB051 [0.719 MB]
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MOPB052	Determination of Bulk and Surface Superconducting Properties of N2-Doped Cold Worked, Heat Treated and Electro-polished SRF Grade Niobium	SRF, superconductivity, niobium, operation	214
	S. Chetri, D.C. Larbalestier, Z-H. Sung ASC, Tallahassee, Florida, USA P. Dhakal JLab, Newport News, Virginia, USA P.J. Lee NHMFL, Tallahassee, Florida, USA
	Funding: Support for this work at FSU was from US DOE Award# DE-SC0009960 and the State of Florida Additional support for the National High Magnetic Field Laboratory facilities is from the NSF: NSF-DMR-1157490 Nitrogen-doped cavities show significant performance improvement in the medium accelerating field regime due to a lowered RF surface resistivity. However, the mechanism of enhancement has not been clearly explained. Our experiments explore how N2-doping influences Nb bulk and surface superconducting properties, and compare the N2-doped properties with those obtained previously with conventionally treated samples. High purity Nb-rod was mechanically deformed and post treated based on a typical SRF cavity treatment recipe. The onset of flux penetration at Hc1, and the upper and the surface critical fields, Hc2 and Hc3, were characterized by magnetic hysteresis and AC susceptibility techniques. The surface depth profile responsible for superconductivity was examined by changing AC amplitude in AC susceptibility, and the microstructure was directly observed with EBSD-OIM. We are also investigating surface chemistry for detailed composition using XPS. We have found that N2-doping at 800 °C significantly reduces the Hc3/Hc2 ratio towards the ideal value of ~1.7, and conclude that AC susceptibility is capable of following changes to the surface properties induced by N2-doping.
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MOPB055	Characterization of Nitrogen Doping Recipes for the Nb SRF Cavities	niobium, SRF, cryogenics, electron	223
	Y. Trenikhina, A. Grassellino, O.S. Melnychuk, A. Romanenko Fermilab, Batavia, Illinois, USA
	For the future development of the nitrogen doping technology, it’s vital to understand the mechanisms behind the performance benefits of N-doped cavities as well as the performance limitations, such as quench field. Following various doping recipes, cavity cutouts and flat niobium samples have been evaluated with XRD, SEM, SIMS and TEM in order to relate structural and compositional changes in the niobium near-surface to SRF performance. Annealing of Nb cavities with nitrogen for various durations and at various temperatures lead to a layer containing inclusions of non-superconducting Nb nitride phases, followed by unreacted Nb with an elevated N-interstitials concentration. We found that EP of the N-treated cavities removes the unwanted niobium nitride phases, confirming that performance benefits are originating from the elevated concentration of N interstitials. The role of low temperature Nb hydride precipitants in the performance limitation of N-doped cavities was evaluated by TEM temperature dependent studies. Finally, extended characterization of the original cavity cutouts from the N-doped RF tested cavity sheds some light on quenching mechanisms.
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MOPB057	Crystal Plasticity Modeling of Single Crystal Nb	experiment, niobium, SRF, software	228
	A. Mapar, F. Pourboghrat MSU, East Lansing, Michigan, USA T.R. Bieler, D. Kang Michigan State University, East Lansing, Michigan, USA C. Compton FRIB, East Lansing, Michigan, USA
	Funding: This work was supported by the U.S. Department of Energy, Office of High Energy Physics, through Grant No. DE-FG02-09ER41638. Deformation behavior of niobium (Nb) is not thoroughly studied, although it is widely used in manufacturing superconducting cavities. This deficiency of knowledge limits the predictibality in raw material properties for fine grain sheets, which are less anisotropic and easier to deform uniformly than large grain sheets. Studies on modeling and simulation of deformation of Nb are also limited. Therefore design of a new manufacturing procedure becomes a costly process, because models predicting the deformation of Nb are not accurate. A polycrystal is an aggregate of single crystals. Tensile tests were performed on single crystal with different orientations, to study the deformation behavior of Nb. A number of crystal plasticity models were developed, calibrated and finally used to predict the deformation of single crystal tensile samples. This study compares the predictions of these models. This provides a foundation for physically realistic polycrystal deformation models.
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MOPB059	Field Emission Investigation of Centrifugal-Barrel-Polished Nb Samples	site, vacuum, survey, electron	237
	S. Lagotzky, G. Müller Bergische Universität Wuppertal, Wuppertal, Germany A. Navitski DESY, Hamburg, Germany A.L. Prudnikava, Y. Tamashevich University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
	Funding: This work was funded by BMBF project 05H12PX6. Actual and future SRF-accelerators require high accelerating gradient Eacc and quality factor Q0, which are often limited by enhanced field emission (EFE)* caused by surface roughness or particulates. Various expensive surface preparation techniques (e.g. BCP, EP, HPR etc.) have been developed to obtain the required surface quality and remove the emitters. Recently, centrifugal barrel polishing (CBP) has been reconsidered to obtain a comparable surface roughness as EP with less effort. We have started to investigate Nb samples, which were prepared as coupons in a single cell 1.3 GHz cavity by an optimized five step CBP process with a final dry ice cleaning. EFE maps showed the first emitter (1 nA) at 60 MV/m, and 32 emitters at 110 MV/m. SEM/EDX analysis of the emitting sites revealed many Al2O3 inclusions with sharp edges. Therefore, subsequent BCP (~20 μm removal) was applied to the sample. Surface analysis as well as EFE characterization of CBP treated Nb coupons with/without BCP step will be presented. D. Reschke et al., THPP021, LINAC14. A. Navitski et al., PRSTAB 16, 112001 (2013). *C.A. Cooper, L.D. Cooley, Supercond. Sci. Technol. 26, 015011 (2013).
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MOPB060	A GPU Based 3D Particle Tracking Code for Multipacting Simulation	GPU, simulation, gun, SRF	242
	T. Xin Stony Brook University, Stony Brook, USA S.A. Belomestnykh, I. Ben-Zvi, J.C. Brutus, V. Litvinenko, I. Pinayev, J. Skaritka, Q. Wu, B. P. Xiao BNL, Upton, Long Island, New York, USA
	Funding: This work was carried out at Brookhaven Science Associates, LLC under Contracts No. DE-AC02-98CH10886 and at Stony Brook University under grant DE-SC0005713 with the U.S. DOE. A new GPU based 3D electron tracking code is developed at BNL and benchmarked with both popular existing parallel tracking code and experimental results. The code takes advantage of massive concurrency of GPU cards to track electrons under RF field in 3D Tetrahedron meshed structures. Approximately ten times of FLOPS can be achieved by utilizing GPUs compare to CPUs with same level of power consumption. Different boundary materials can be specified and the 3D EM field can be imported from the result of Omega3P calculation. CUDA_OpenGL interop was implemented so that the emerging of multipactors can be monitored in real time while the simulation is undergoing. Code also has GPU farm version that can run on multiple GPUs to further increase the turnover of multipacting simulation.
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MOPB061	Suppression of Upstream Field Emission in RF Accelerators	electron, cryomodule, SRF, site	246
	F. Marhauser, S.V. Benson, D. Douglas JLab, Newport News, Virginia, USA L.J.P. Ament ASML US Inc., Wilton, CT, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177 So-called electron loading is the primary cause for cavity performance limitations in modern RF accelerating cavities. In superconducting RF cavities in particular, the onset of parasitic electron effects may start at field levels as low as a few MV/m. Electron loading can be attributed to mainly three phenomena: field emission, multiple impact electron amplification, and RF electrical breakdown. Field emission has been a persistent issue despite advances in SRF technology, whereas RF electrical breakdown and multipacting can be controlled by appropriate cavity design choices. Field emission becomes a major concern when the electrons emitted are captured by the accelerating RF field and directed along the beam axis through a series of cavities or even entire cryomodules. Consequently, electrons can accumulate energy comparable to that of the main beam over similar distances. This can represent a considerable dark current, which can travel downstream or upstream depending on the field-emitting site of origin. In this paper, a method is presented that can significantly suppress the upstream field emission by design.
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MOPB063	Design of the Superconducting LINAC for SARAF	cryomodule, solenoid, cryogenics, linac	250
	C. Madec CEA, Gif-sur-Yvette, France N. Bazin, L. Boudjaoui, R. Cubizolles, G. Ferrand, P. Hardy, C. Pes, N. Sellami CEA/IRFU, Gif-sur-Yvette, France P. Bertrand GANIL, Caen, France P. Brédy, B. Gastineau, N. Pichoff CEA/DSM/IRFU, France
	CEA is committed to delivering a Medium Energy Beam Transfer line and a superconducting linac (SCL) for SARAF accelerator in order to accelerate 5mA beam of either protons from 1.3 MeV to 35 MeV or deuterons from 2.6 MeV to 40.1 MeV. The SCL consists 4 cryomodules equipped with warm diagnostics. The first two identical cryomodules host 6 half-wave resonator (HWR) low beta cavities (β = 0.091), 176 MHz. As the last two identical welcome 7 HWR high-beta cavities (β = 0.181), 176 MHz. The beam is focused through the superconducting solenoids located between cavities housing steering coils. A Beam Position Monitor is placed upstream each solenoid. A diagnostic box containing a beam profiler, a bunch length monitor and a vacuum pump will be inserted between 2 consecutive cryomodules. The HWR cavities, the solenoid package and the cryomodules are being designed. These studies will be presented in this poster.
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MOPB065	Recent Measurements on the SC 325 MHz CH-Cavity	ion, linac, heavy-ion, controls	255
	M. Busch, M. Amberg, M. Basten, F.D. Dziuba, H. Podlech, U. Ratzinger IAP, Frankfurt am Main, Germany M. Amberg HIM, Mainz, Germany
	Funding: Work supported by GSI, BMBF Contr. No. 06FY7102 At the Institute for Applied Physics (IAP), Frankfurt University, a sc 325 MHz CH-Cavity has been designed and fabricated. Successful tests at 4 K and 2 K with gradients up to 14.1 MV/m have been performed. The cavity is destined for a 11.4 AMeV 10 mA ion beam at the GSI UNILAC, Darmstadt. Consisting of 7 gaps and a geometrical beta of 0.16 this resonator is designed to provide a gradient of 5 MV/m. Novel features of this structure comprise a compact design, low electric peak fields, improved surface processing possibilities and power coupling. In addition a tuner system based on mechanically deformable bellow tuners attached inside the cavity and driven either by a stepping motor or a piezo actuator will keep the cavity on resonance. This contribution reports about the latest measurements on the cavity with the recently attached helium vessel and a renewed surface processing.
	Poster MOPB065 [1.270 MB]
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MOPB066	R&D Status of the New Superconducting CW Heavy Ion LINAC@GSI	linac, simulation, ion, operation	258
	M. Basten, M. Busch, F.D. Dziuba, D. Mäder, H. Podlech, M. Schwarz IAP, Frankfurt am Main, Germany M. Amberg, K. Aulenbacher, M. Miski-Oglu HIM, Mainz, Germany W.A. Barth, V. Gettmann, M. Heilmann, S. Mickat GSI, Darmstadt, Germany
	To keep the ambitious Super Heavy Element (SHE) physics program at GSI competitive a superconducting (sc) continuous wave (cw) high intensity heavy ion LINAC is currently under progress as a multi-stage R&D program of GSI, HIM and IAP. The baseline linac design consists of a high performance ion source, a new low energy beam transport line, an (cw) upgraded High Charge State Injector (HLI), and a matching line (1.4 MeV/u) which is followed by the new sc-DTL LINAC for post acceleration up to 7.3 MeV/u. In the present design the new cw-heavy ion LINAC comprises constant-beta sc Crossbar-H-mode (CH) cavities operated at 217 MHz. The advantages of the proposed beam dynamics concept applying a constant beta profile are easy manufacturing with minimized costs as well as a straightforward energy variation. An important milestone will be the full performance test of the first CH cavity (Demonstrator), in a horizontal cryo module with beam. An advanced demonstrator setup comprising a string of cavities and focussing elements is proposed to build from 10 short CH-cavities with 8 gaps. The corresponding simulations and technical layout of the new cw heavy ion LINAC will be presented. W. Barth et al., Further R&D for a new Superconducting cw Heavy Ion LINAC@GSI, IPAC2014, THPME004 **M. Schwarz et al., Beam Dynamics for the sc cw Heavy Ion Linac at GSI, IPAC2015, THPF025
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MOPB067	Steps Towards Superconducting CW-LINAC for Heavy Ions at GSI	linac, ion, heavy-ion, quadrupole	262
	M. Miski-Oglu, M. Amberg, K. Aulenbacher, V. Gettmann HIM, Mainz, Germany W.A. Barth, M. Heilmann, S. Mickat, S. Yaramyshev GSI, Darmstadt, Germany M. Basten, D. Bänsch, F.D. Dziuba, H. Podlech, U. Ratzinger IAP, Frankfurt am Main, Germany
	Providing heavy ion beams for the ambitious experiment program at GSI, the Universal Linear Accelerator (UNILAC) serves as a powerful high duty factor (25%) accelerator. Beam time availability for SHE-research will be decreased due to the limitation of the UNILAC providing a proper beam for FAIR simultaneously. To keep the GSI-SHE program competitive on a high level, a standalone sc cw-LINAC in combination with the upgraded GSI High Charge State injector is planned to build. In preparation for this the first linac section (financed by HIM and partly by HGF-ARD-initiative) will be tested in 2015 as a demonstrator. After successful testing the construction of an extended cryomodule comprising two further, but shorter CH cavities is foreseen to test until end of 2017. In this contribution the measurement of the beam parameters at the entrance of CW-Demonstartor, the preliminary simulation of beam dynamics for the first stage of advanced demonstrator will be presented. As a final R&D step towards an entire linac an advanced cryo module comprising up to five CH cavities is envisaged for 2019 serving for first user experiments at the coulomb barrier.
	Poster MOPB067 [2.807 MB]
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MOPB068	Pulsed SC Ion Linac as an Injector to Booster of Electron Ion Collider	ion, linac, operation, proton	265
	P.N. Ostroumov, Z.A. Conway, B. Mustapha ANL, Argonne, USA B. Erdelyi Northern Illinois University, DeKalb, Illinois, USA
	Funding: This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics, under contract number DE-AC02-06CH11357. The electron-ion collider (EIC) being developed at JLAB requires a new ion accelerator complex (IAC). The IAC includes a new linac and a booster accelerator facility. The new facility is required for the acceleration of ions from protons to lead for colliding beam experiments with electrons in the EIC storage ring. Originally, we proposed a pulsed linac which is based upon a NC front end, < 5 MeV/u, with a SC section for energies > 5 MeV/u and capable of providing 285 MeV protons and ~100 MeV/u lead ions for injection into the IAC booster. A recent cost optimization study of the IAC suggested that lower injection energy into the booster may reduce the overall project cost with ~120 MeV protons and ~40 MeV/u lead ions. Stronger space charge effects in the booster caused by lower injection energy will be mitigated by the booster design. In this paper we discuss both linac options.
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MOPB069	Superconducting Linac Upgrade Plan for the Second Target Station Project at SNS	cryomodule, linac, HOM, accelerating-gradient	268
	S.-H. Kim, M. Doleans, J. Galambos, M.P. Howell ORNL, Oak Ridge, Tennessee, USA J.D. Mammosser ORNL RAD, Oak Ridge, Tennessee, USA
	Funding: This work was supported by SNS through UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. DOE. The beam power of the Linac for the Second Target Station (STS) at the Spallation Neutron Source (SNS) will be doubled to 2.8 MW. For the energy upgrade seven additional cryomodules will be installed in the reserved space at the end of the linac tunnel to produce the linac output energy of 1.3 GeV. The cryomodules for STS will have some changes that do not require changes of overall layout based on the lessons learned from operational experience over the last 10 years and the high beta spare cryomodule developed in house. The average macro-pulse beam current for the STS will be 38 mA that is about 40 % increase from that for the present 1.4 MW operation. Plans for the existing cryomodules to support higher beam current for the STS is also presented in this paper.
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MOPB070	Preliminary Conceptual Design of the CEPC SRF System	HOM, SRF, collider, booster	272
	J.Y. Zhai, J. Gao, T.M. Huang, Z.C. Liu, Z.H. Mi, P. Sha, Y. Sun, H.J. Zheng IHEP, Beijing, People's Republic of China S.A. Belomestnykh BNL, Upton, Long Island, New York, USA S.A. Belomestnykh Stony Brook University, Stony Brook, USA C. Pagani INFN/LASA, Segrate (MI), Italy C. Pagani Università degli Studi di Milano & INFN, Segrate, Italy
	CEPC is a circular electron positron collider operating at 240 GeV center-of-mass energy as a Higgs factory, recently proposed by the Chinese high energy physics community. The CEPC study group, together with the FCC and ILC community, will contribute to the development of future high energy colliders and experiments which will ensure that the elementary particle physics remain a vibrant and exciting field of fundamental investigation for decades to come. Superconducting RF (SRF) system is one of the most important technical systems of CEPC and is a key to achieving its design energy and luminosity. It will dominate, with the associated RF power source and cryogenic system, the overall machine cost, efficiency and performance. The CEPC SRF system will be one of the largest and most powerful SRF accelerator installations in the world. The preliminary conceptual design of the CEPC SRF system is summarized in this paper, including the machine layout, key parameter choices and some critical issues such as HOM damping, emphasizing the new technology requirement and R&D focuses.
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MOPB071	Technology Readiness Levels Applied to Current SRF Accelerator Technology for ADS	SRF, cryomodule, proton, TRIUMF	276
	R. Edinger PAVAC, Richmond, B.C., Canada R.E. Laxdal, L. Yang TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada
	Accelerator Driven Systems (ADS) are comprised of high power accelerators supplying a proton beam to a reactor vessel. The reactor vessel could contain fuels such as used uranium nuclear fuels or Thorium. The proton beam will be used to produce Neutrons by spallation in the reactor vessel. Technology readiness levels (TRL’s) can be used to chart technology status with respect to end goal and as such can be used to outline a road map to complete an ADS system. TRL1 defines basic principles observed and reported, whereas TRL9 is defined as system ready for full scale deployment. SRF technology when applied to ADS reflects a mix of TRL levels since worldwide many SRF Accelerators are in operation. The paper will identify the building blocks of an ADS accelerator and analyze each for technical readiness for industrial scale deployment. The integrated ADS structure is far more complex than the individual systems, but the use of proven sub-systems allows to build SRF accelerators that could deliver the beam required. An analysis of the technical readiness of SRF technology for ADS will be presented.
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MOPB072	Characterization of Surface Defects on EXFEL Series and ILC-Higrade Cavities	niobium, SRF, laser, radiation	281
	A. Navitski, E. Elsen, V. Myronenko, J. Schaffran, O. Turkot DESY, Hamburg, Germany Y. Tamashevich University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
	Funding: BMBF project 05H12GU9, Alexander von Humboldt Foundation, CRISP (No. 283745) and ”Construction of New Infrastructures-Preparatory Phase” ILC-HiGrade (No. 206711) of the EU 7th FP7/2007-2013 Programme. Inspection of the inner cavity surface by an optical system is an inexpensive and useful means for surface control and identification of critical or suspicious features. Optical inspection of around 100 EXFEL series and ILC-HiGrade cavities has been performed recently using the high-resolution OBACHT system. It is a semi-automated tool based on the Kyoto camera. To gain information about the 3D topography of surface features or defects, a replica technique has been applied additionally. This is a non-destructive surface-study method reaching resolution down to 1 μm by imprinting the details of the surface onto a hardened rubber. The footprint is subsequently investigated with a microscope or profilometer. Based on these studies, several defects on the surface have been found and classified. Most of the cavity failures leading e.g. to field limitations below 20 MV/m have been identified and corresponding feedback given to the production cycle. Typical surface features and defects as well as their influence on the cavity performance will be presented and discussed.
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MOPB073	Surface Analyses and Optimization of Centrifugal Barrel Polishing of Nb Cavities	niobium, SRF, laser, embedded	286
	A. Navitski, E. Elsen, B. Foster DESY, Hamburg, Germany B. Foster, A.L. Prudnikava, Y. Tamashevich University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
	Funding: BMBF project 05H12GU9, Alexander von Humboldt Foundation, and CRISP (No. 283745). Centrifugal barrel polishing (CBP) is an acid-free surface-polishing technique based on abrasive media. It considerably reduces the usage of chemicals in the preparation of Nb cavities, typically leaving only a final light electropolishing (EP) and achieves considerably smaller roughness than in chemical treatments alone. CBP addresses in particular the removal of pits, welding spatters, deep scratches, and foreign material inclusions that occasionally occur in the production process. A mirror-smooth surface without chemical contamination is also an important enabling step for thin films. Recent results indicate, however, the need of further optimizations, mainly to reduce the surface damaged layer as well as the pollution by the polishing media. A dedicated study of the CBP process using a “coupon” cavity facilitates better polishing characterisation and optimisation by direct measurements of the roughness, removal rate, and removal profile as well as the amount of contamination left behind and determination of a best combination of the CBP and chemical polishing. Results of the coupon-studies and perspectives of the optimizations will be presented and discussed.
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MOPB074	CERN’s Bulk Niobium High Gradient SRF Programme: Developments and Recent Cold Test Results	niobium, cathode, radiation, SRF	291
	A. Macpherson, K.G. Hernández-Chahín, C. Jarrige, P. Maesen, F. Pillon, K.M. Schirm, R. Torres-Sanchez, N. Valverde Alonso CERN, Geneva, Switzerland K.G. Hernández-Chahín DCI-UG, León, Mexico
	Recent results from the bulk niobium high-gradient cavity development program at CERN are presented, with particular focus on test results for the 704 MHz bulk niobium 5-cell elliptical cavity prototypes produced for the Superconducting Proton Linac (SPL) project. Successive cold tests of bare cavities have been used to refine the cavity preparation and testing process, with all steps done in-house at CERN. Current performance results are discussed with reference to observables such as ambient magnetic field, field emission levels, and quenches.
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MOPB075	Experiences on Retreatment of EU-XFEL Series Cavities at DESY	controls, status, feedback, linac	296
	A. Matheisen, N. Krupka, S. Saegebarth, P. Schilling, N. Steinhau-Kühl, B. van der Horst DESY, Hamburg, Germany
	For the European XFEL (EU-XFEL), two industrial companies are responsible for the manufacture and surface preparation of the eight hundred superconducting cavities. The companies had to strictly follow the XFEL specification and document all production and preparation steps. No performance guaranties were required. Each cavity delivered by industry to DESY is tested in a vertical test at 2K. Resonators not reaching the performances defined for application at the EU-XFEL linear accelerator modules or showing leakage during cold RF tests have undergone a subsequent retreatment at DESY. Nearly 20% of the cavity production required retreatment, most of them by an additional high pressure rinsing. Some cavities received additional chemical treatment by BCP flash after the initial HPR did not cure the problem. The analysis of retreatments and quality control data available from the retreatment sequences and the workflow of retreatment will be presented.
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MOPB076	Horizontal RF Test of a Fully Equipped 3.9 GHz Cavity for the European XFEL in the DESY AMTF	HOM, operation, cryomodule, controls	301
	C.G. Maiano, C. Albrecht, R. Bospflug, J. Branlard, L. Butkowski, T. Delfs, J. Eschke, A. Gössel, F. Hoffmann, M. Hüning, K. Jensch, R. Jonas, R. Klos, D. Kostin, W. Maschmann, A. Matheisen, U. Mavrič, W.-D. Möller, C. Müller, K. Mueller, B. Petersen, P. Pierini, J. Rothenburg, O. Sawlanski, M. Schmökel, A.A. Sulimov, E. Vogel DESY, Hamburg, Germany A. Bosotti, M. Moretti, R. Paparella, P. Pierini, D. Sertore INFN/LASA, Segrate (MI), Italy E.R. Harms Fermilab, Batavia, Illinois, USA C.R. Montiel ANL, Argonne, Illinois, USA S. Pivovarov BINP SB RAS, Novosibirsk, Russia
	In order to validate the cavity package concept before the module preparation for the European XFEL Injector, one 3.9 GHz cavity, complete with magnetic shielding, power coupler and frequency tuner was tested in a specially designed single cavity cryomodule in one of the caves of the DESY Accelerator Module Test Facility (AMTF). The cavity was tested in high power pulsed operation up to the quench limit of 24 MV/m, above the vertical test qualifications and all subsystems under test (coupler, tuner, waveguide tuners, LLRF system) were qualified to design performances.
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MOPB077	Vertical Tests of XFEL 3rd Harmonic Cavities	vacuum, HOM, operation, instrumentation	306
	D. Sertore, M. Bertucci, A. Bosotti, J.F. Chen, C.G. Maiano, P. Michelato, L. Monaco, M. Moretti, R. Paparella, P. Pierini INFN/LASA, Segrate (MI), Italy A. Matheisen, M. Schmökel DESY, Hamburg, Germany C. Pagani Università degli Studi di Milano & INFN, Segrate, Italy
	The 10 cavities of the EXFEL 3rd Harmonic Cryomodule have been tested and qualified, before integration in the He-tank, in our upgraded Vertical Test stand. In this paper, we report the measured RF performance of these cavities together with the main features of the test facility.
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MOPB078	Mode Sensitivity Analysis of 704.4 MHz Superconducting RF Cavities	HOM, operation, linac, dipole	311
	K. Papke, F. Gerigk, S. Horvath-Mikulas, S. Papadopoulos, E. Pilicer, F. Pillon CERN, Geneva, Switzerland U. van Rienen Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
	Due to the large variety of beam patterns considered for the superconducting proton linac (SPL) at CERN it is likely that the frequencies of some HOMs are close to machine lines during operation. Hence, in the interest of developing a method to shift HOM frequencies away from machine lines, we study the influence of cavity detuning and re-tuning (e.g. by Lorentz forces, field flatness tuning, frequency tuning during operation) on HOMs. The sensitivity of HOMs with respect to the fundamental mode was studied for a mono-cell and for 5-cell high-beta SPL cavities operating at 704.4 MHz. First, the variation of the HOMs during the flat-field tuning was measured. In this process, several detuning and re-tuning cycles were made to estimate the range of possible HOM frequency shifts. Secondly the effect of the frequency tuner on the HOMs is presented and finally the frequency shifts of all modes due to the cool down.
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MOPB079	Analysis of the Test Rate for European XFEL Series Cavities	vacuum, database, site, status	316
	J. Schaffran, S. Aderhold, D. Reschke, L. Steder, N. Walker DESY, Hamburg, Germany L. Monaco INFN/LASA, Segrate (MI), Italy
	The main part of the superconducting European XFEL linear accelerator consists of 100 accelerator modules each containing eight RF-cavities. Before the installation to a module, all of these cavities will be tested at cryogenic temperatures in a vertical cryostat in the accelerator module test facility (AMTF) at DESY. This paper discusses the average vertical test rate at the present status. It should be 1 in the ideal case, but actually it’s observed to be approximately 1.5. Classification and analysis concerning the reasons for this deviation are given as well as suggestions for a reduction of the test rate for future production cycles.
	Poster MOPB079 [0.632 MB]
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MOPB080	Update and Status of Test Results of the XFEL Series Accelerator Modules	cryomodule, radiation, linac, status	319
	M. Wiencek, K. Kasprzak, A. Zwozniak IFJ-PAN, Kraków, Poland D. Kostin, D. Reschke, N. Walker DESY, Hamburg, Germany
	The European X-ray Free Electron Laser is under construction at DESY, Hamburg. During preparation for tunnel installation 100 Cryomodules are tested in a dedicated facility on the DESY campus. Up to now around 50 cryomodules have been measured at 2K. This paper describes the current status of the measurements, especially single cavity limitations. In addition we present a comparison between the vertical test results of the individual cavities and the corresponding performance measurements of the cavities once assembled into the accelerator string inside the cryomodule.
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MOPB083	Cooling Front Measurement of a 9-Cell Cavity via the Multi-Cell Temperature-Mapping System at Cornell University	SRF, experiment, electronics, linac	324
	G.M. Ge, R.G. Eichhorn, F. Furuta Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Cooling speed significantly affects flux trapping of a SRF cavity, which will determine the residual resistance and the quality factor of the cavity. We measured the temperature distribution of a 9-cell cavity at different cooling speeds by the multi-cell T-map system of Cornell University. This paper proposed a method to evaluate the formation of a normal conducting island at different cooling speed. The fast cool-down and slow cool-down has been compared. We conclude that the slow cool-down freezes less normal conducting islands.
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MOPB084	Performance of Nitrogen-Doped 9-Cell SRF Cavities in Vertical Tests at Cornell University	SRF, superconducting-RF, linac, HOM	328
	G.M. Ge, R.G. Eichhorn, B. Elmore, F. Furuta, D. Gonnella, T. Gruber, G.H. Hoffstaetter, J.J. Kaufman, M. Liepe, T.I. O'Connell, J. Sears, E.N. Smith Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Cornell University treated five LCLS-II 9-cell cavities by nitrogen-doping recipe. In this paper, we reported the performance of these 9-cell cavities. In the treatments, the nitrogen recipes are slightly different. The cavities have been firstly doped under high nitrogen pressure; after the vertical tests some of the cavities has been reset the surface and re-doped under light nitrogen pressure. The detail of the cavity preparation and test results will be shown. The comparison of the different recipes will be discussed.
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MOPB085	Efforts of the Improvement of Cavity Q-Value by Plasma Cleaning Technology: Plan and Results From Cornell University	plasma, experiment, SRF, ECR	333
	G.M. Ge, F. Furuta, G.H. Hoffstaetter, M. Liepe, J. Sears, V. Veshcherevich Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	We reported the plasma works at Cornell University. The plasma has been generated for 1) surface cleaning to reduce field emission; 2) the cavity quality factor improvement. The experiment design, including RF design, the gas type and pressure selection, the external DC magnetic field calculation, had been discussed. The plasma experiment set-up by using a 1.3GHz single-cell cavity is shown. Argon and helium plasma was successfully ignited in the cavity; the results of the plasma processing will be displayed.
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MOPB086	Update and Status of Vertical Test Results of the European XFEL Series Cavities	status, linac, cryomodule, niobium	337
	N. Walker, D. Reschke, J. Schaffran, L. Steder DESY, Hamburg, Germany L. Monaco INFN/LASA, Segrate (MI), Italy M. Wiencek IFJ-PAN, Kraków, Poland
	The series production by two industrial vendors of the 800 1.3-GHz superconducting cavities for the European XFEL has been on-going since the beginning of 2013 and will conclude towards the end of this year. As of publication some 740 cavities (~93%) have been produced at an average rate of 6 cavities per week. As part of the acceptance testing, all cavities have undergone at least one vertical RF test at 2K at the AMTF facility at DESY. The acceptance criterion for module assembly is based on the concept of a “usable gradient”, which is defined as the maximum field taking into account Q0 performance and allowed thresholds for field emission, as well as breakdown limits. Approximate 20% of the cavities have undergone further surface treatment in the DESY infrastructure to improve their usable gradient performance. In this paper we present the performance statistics of the vertical test results, as well as an analysis of the limiting criteria for the usable gradient, and finally the impact of the surface retreatment on both usable gradient and Q0.
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MOPB087	Integrated High-Power Tests of Dressed N-doped 1.3 GHz SRF Cavities for LCLS-II	HOM, cryomodule, resonance, vacuum	342
	N. Solyak, T.T. Arkan, B.E. Chase, A.C. Crawford, E. Cullerton, I.V. Gonin, A. Grassellino, C.J. Grimm, A. Hocker, J.P. Holzbauer, T.N. Khabiboulline, O.S. Melnychuk, J.P. Ozelis, T.J. Peterson, Y.M. Pischalnikov, K.S. Premo, A. Romanenko, A.M. Rowe, W. Schappert, D.A. Sergatskov, R.P. Stanek, G. Wu Fermilab, Batavia, Illinois, USA
	New auxiliary components have been designed and fabricated for the 1.3 GHz SRF cavities comprising the LCLS-II linac. In particular, the LCLS-II cavity’s helium vessel, high-power input coupler, higher-order mode (HOM) feedthroughs, magnetic shielding, and cavity tuning system were all designed to meet LCLS-II specifications. Integrated tests of the cavity and these components were done at Fermilab’s Horizontal Test Stand (HTS) using several kilowatts of continuous-wave (CW) RF power. The results of the tests are summarized here.
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MOPB088	HOM Measurements on the ARIEL eLINAC Cryomodules	HOM, simulation, cryomodule, linac	347
	P. Kolb, R.E. Laxdal, Y. Ma, Z.Y. Yao, V. Zvyagintsev TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada
	The ARIEL eLINAC is a 50 MeV, 10 mA electron LINAC designed for the creation of rare isotopes via photo-fission. Future upgrade plans include the addition of a recirculating beam line to allow for either further energy increase of the beam beyond 50 MeV or to operate a free electron laser in an energy recovery mode. For both recirculating LINAC and ERL the higher order modes (HOM) have to be sufficiently suppressed to prevent beam-break-up. The design of the 1.3 GHz nine-cell cavity incorporated this requirement by including beam line absorbers on both ends of each cavity and an asymmetric beam pipe configuration on the cavity to allow trapped modes to propagate to the beam line absorbers. Measurements of the higher order modes on the completed injector cryomodule and the first cavity in the accelerating cryomodules will be shown and compared to simulations.
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MOPB089	1.3 GHz Cavity Test Program for ARIEL	cryomodule, induction, TRIUMF, vacuum	350
	P. Kolb, P.R. Harmer, J.J. Keir, D. Kishi, D. Lang, R.E. Laxdal, H. Liu, Y. Ma, T. Shishido, B.S. Waraich, Z.Y. Yao, V. Zvyagintsev TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada E. Bourassa, R.S. Orr, D. Trischuk University of Toronto, Toronto, Ontario, Canada T. Shishido KEK, Ibaraki, Japan
	The ARIEL eLINAC is a 50 MeV 10 mA electron LINAC. Once finished, five cavities will each provide 10MV of effective accelerating voltage. At the present time two cavities have been installed and successfully accelerated been above specifications of 10 MV/m at a Q0 of 10¹⁰. The next cavities are already in the pipeline and being processed. In addition, one additional cavity has been produced for our collaboration with VECC, India. This cavity has been tested and installed in a cryomodule identical to the eLINAC injector cryomodule. New developments for single cell testing at TRIUMF are a T-mapping system developed in collaboration with UoT and vertical EP for single cells. The progress of the performance after each treatment step has been measured and will be shown. measured and will be shown.
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MOPB090	Analysis of Degraded Cavities in Prototype Modules for the European XFEL	accelerating-gradient, SRF, cryogenics, radiation	355
	S. Aderhold Fermilab, Batavia, Illinois, USA S. Aderhold, D. Kostin, A. Matheisen, A. Navitski, D. Reschke DESY, Hamburg, Germany
	In-between the fabrication and the operation in an accelerator the performance of superconducting RF cavities is typically tested several times. Although the assembly is done under very controlled conditions in a clean room, it is observed from time to time that a cavity with good performance in the vertical acceptance test shows deteriorated performance in the accelerator module afterwards. This work presents the analysis of several such cavities that have been disassembled from modules of the prototype phase for the European XFEL for detailed investigation like additional rf tests, optical inspection and replica.
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MOPB092	Economics of Electropolishing Niobium SRF Cavities in Eco-Friendly Aqueous Electrolytes Without Hydrofluoric Acid	SRF, niobium, accelerating-gradient, cathode	359
	E.J. Taylor, T.D. Hall, M.E. Inman, S.T. Snyder Faraday Technology, Inc., Clayton, Ohio, USA D. Holmes AES, Medford, New York, USA A.M. Rowe Fermilab, Batavia, Illinois, USA
	A major challenge for industrialization of SRF cavity fabrication and processing is developing a supply chain to meet the high production demands of the ILC prior to establishment of a long term market need. Conventional SRF cavity electropolishing is based on hydrofluoric-sulfuric acid mixtures. In comparison, FARADAYIC® Bipolar EP applies pulse reverse electrolysis in dilute sulfuric acid-water solutions without hydrofluoric acid and offers substantial savings in operating and capital costs. Based on a preliminary economic analysis of the cavity processing requirements associated with the ILC, we project the cost of FARADAYIC® Bipolar EP to be about 27% that of the Baseline EP. In terms of tangible cost savings, the cost per cavity for the FARADAYIC® Bipolar EP and Baseline EP are \1,293 and \4,828, respectively. The “eco-friendly” intangible cost savings are generally accepted although the cost savings in terms of material degradation and maintenance are difficult to quantify at this time. Continued development and validation of FARADAYIC® Bipolar EP on nine cell cavities will contribute greatly to the industrialization of SRF accelerator technology. Work supported by DOE Grant Nos. DE-SC0011235 and DE-SC0011342 and DOE Purchase Order No. 594128.
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MOPB093	Vertical Electropolishing Studies at Cornell	cathode, SRF, niobium, target	364
	F. Furuta, B. Elmore, G.M. Ge, T. Gruber, G.H. Hoffstaetter, D.K. Krebs, J. Sears Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA T.D. Hall, M.E. Inman, S.T. Snyder, E.J. Taylor Faraday Technology, Inc., Clayton, Ohio, USA H. Hayano, T. Saeki KEK, Ibaraki, Japan Y.I. Ida, K.N. Nii MGH, Hyogo-ken, Japan
	Vertical Electro-Polishing (VEP) has been developed and applied on various SRF R&Ds at Cornell as primary surface process of Nb. Recent achievements had been demonstrated with nitrogen doped high-Q cavities for LCLS-II. Five 9-cell cavities processed with VEP and nitrogen doping at Cornell showed the high average Qo value of 3.0·10¹⁰ at 16MV/m, 2K, during vertical test. this achievement satisfied the required cavity specification values of LCLS-II(2.7·10¹⁰ at 16MV/m, 2K). We will report the details of these achievements and new VEP collaboration projects between Cornell and companies.
	Poster MOPB093 [4.364 MB]
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MOPB094	Inspection and Repair Techniques for the EXFEL Superconducting 1.3 GHz Cavities at Ettore Zanon S.p.A: Methods and Results	operation, accelerating-gradient, electron, controls	368
	G. Massaro, G. Corniani, N. Maragno Ettore Zanon S.p.A., Schio, Italy A. Matheisen, A. Navitski DESY, Hamburg, Germany P. Michelato, L. Monaco INFN/LASA, Segrate (MI), Italy
	The quality control of the inner surface of superconducting RF cavities is essential in order to assure high accelerating gradient and quality factor. Ettore Zanon S.p.A. (EZ) has implemented in the serial production an optical system that use an high-resolution camera, in order to detect various types of defects. This system is added to a grinding machine, that was specifically designed and built to repair imperfections of the cavities inner surface. This inspection and repair system is applied to recover performance limited cavities of the 1.3 GHz European XFEL project, where surface irregularities are detected, either by the Obacht inspection system at Desy or the optical system at EZ. The optical system and the grinding procedure are qualified using two series cavities limited in gradient and showing different types of surface defects. The performances of these cavities have been recovered to reach the specifications of the project. Until now, all the series XFEL cavities built by EZ, repaired with this technique, have shown an accelerating gradient well above the EXFEL goal.
	Poster MOPB094 [0.795 MB]
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MOPB095	SRF Cavity Processing and Chemical Etching Development for the FRIB Linac	SRF, linac, controls, operation	373
	I.M. Malloch, E.S. Metzgar, L. Popielarski FRIB, East Lansing, Michigan, USA M.J. LaVere MSU, East Lansing, Michigan, USA
	Funding: This material is based upon work supported by the U.S. Department of Energy Office of Science under Cooperative Agreement DE SC0000661, the State of Michigan and Michigan State University. In preparation of a rigorous superconducting RF (SRF) cavity processing and test plan for the production of the Facility for Rare Isotope Beams (FRIB) driver linac, a state-of-the-art chemical etching tool has been installed in the FRIB coldmass production facility. This paper seeks to summarize the etching equipment design, installation, and validation program and subsequent etching results for a variety of SRF cavity types and etching configurations. Bulk etching, light etching, and custom (frequency tuning) etching results for different FRIB cavities are discussed. Special emphasis is placed on the etching removal uniformity and frequency tuning reliability of these processes.
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MOPB096	Vertical Electro-Polishing at TRIUMF	cathode, TRIUMF, operation, niobium	378
	J.J. Keir, P.R. Harmer, D. Lang, R.E. Laxdal, T. Shishido, R. Smith TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada T. Shishido KEK, Ibaraki, Japan
	A setup for electropolishing of a superconducting niobium single-cell cavity has been installed at TRIUMF. A vertical method was selected to make the setup compact. To increase removal speed at the equator and remove hydrogen bubbles at the iris surface, 4 cathode paddles were rotated in the cavity cell during electropolishing. We will report on our first electropolishing result.
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MOPB098	Improvement of Temperature Control During Nb 9-Cell SRF Cavity Vertical Electro-Polishing (VEP) and Progress of VEP Quality	experiment, cathode, controls, SRF	381
	K.N. Nii, V. Chouhan, Y.I. Ida, T.Y. Yamaguchi MGH, Hyogo-ken, Japan H. Hayano, S. Kato, H. Monjushiro, T. Saeki, M. Sawabe KEK, Ibaraki, Japan K. Ishimi MGI, Chiba, Japan
	Marui Galvanizing Co.,Ltd. has been developing Nb 9-cell SRF cavity vertical electro-polishing (VEP) facility and technique for mass production in collaboration with KEK. Our first 9-cell cavity VEP facility was not enough to control temperature during VEP, so the polishing quality was not so high. In this article, we will report the progress of temperature distribution and polishing quality due to the improvement of temperature control system of electrolyte and cavity during VEP.
	Poster MOPB098 [0.988 MB]
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MOPB100	Cathode Geometry and Flow Dynamics Impact on Vertical Electropolishing of Superconducting Niobium Cavities	cathode, niobium, simulation, operation	385
	L.M.A. Ferreira CERN, Geneva, Switzerland
	CERN has now a fully operating vertical electropolishing installation, which has been used for the processing of 704 MHz high-beta five-cell Superconducting Proton Linac (SPL) niobium cavities. This installation relies only on the electrolyte circulation (HF/H2SO4) for power dissipation, evacuation of gases and homogeneous finishing; thus, parameters like cathode geometry, electrolyte flow and temperature become even more crucial when compared with horizontal electropolishing installations. Based on computational simulations performed with Comsol Multiphysics® and on a methodology developed at CERN, it is possible to assess the impact of the different cathode geometries as well as of the flow on the etching rate distribution. The data obtained with two different cathode geometries are presented: electrolyte velocity distribution, etching rate distribution, average current density and minimum working potential. One geometry was defined through a purely electrochemical approach while the second was defined to minimise the difference between the maximum and the minimum electrolyte speed inside the cavity; in both cases, the influence of the electrolyte flow was taken into account.
	Poster MOPB100 [1.794 MB]
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MOPB101	Electropolishing of Niobium SRF Cavities in Eco-Friendly Aqueous Electrolytes Without Hydrofluoric Acid	niobium, SRF, cathode, target	390
	M.E. Inman, T.D. Hall, S. Lucatero, S.T. Snyder, E.J. Taylor Faraday Technology, Inc., Clayton, Ohio, USA F. Furuta, G.H. Hoffstaetter Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA J.D. Mammosser ORNL, Oak Ridge, Tennessee, USA A.M. Rowe Fermilab, Batavia, Illinois, USA
	Electropolishing of niobium cavities is conventionally conducted in high viscosity electrolytes consisting of concentrated sulfuric and hydrofluoric acids. This use of dangerous and ecologically damaging chemicals requires careful attention to safety protocols to avoid harmful worker exposure and environmental damage. We present an approach for electropolishing of niobium materials based on pulse reverse waveforms, enabling the use of low viscosity aqueous dilute sulfuric acid electrolytes without hydrofluoric acid, or aqueous near-neutral pH salt solutions without any acid. Results will be summarized for both cavity and coupon electropolishing for bulk and final polishing steps. With minimal optimization of pulse reverse waveform parameters we have demonstrated the ability to electropolish single-cell niobium SRF cavities and achieve at least equivalent performance compared to conventionally processed cavities. Cavities are electropolished in a vertical orientation filled with electrolyte and without rotation, offering numerous advantages from an industrial processing perspective. Shielding, external cooling and high surface area cathodes are adaptable to the bipolar EP process. Work supported by DOE Grant Nos. DE-SC0011235 and DE-SC0011342 and DOE Purchase Order No. 594128.
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MOPB102	Comments on Electropolishing at Ettore Zanon SpA at the End of EXFEL Production	niobium, controls, cathode, acceleration	394
	M. Rizzi, G. Corniani Ettore Zanon S.p.A., Schio, Italy A. Matheisen DESY, Hamburg, Germany P. Michelato INFN/LASA, Segrate (MI), Italy
	In 2013 a new horizontal Electropolishing facility was developed and implemented by Ettore Zanon SpA (EZ) for the treatment of cavities for the European XFEL series production. More than 300 cavities have been treated. Electropolishing has been used for two applications: bulk removal and recovering of cavities with surface defects. Treatment settings have been analysed and compared with cavities performances to verify possible influences of the various parameters. Main parameters considered are treatment time, voltage and current, that together define average thickness removal. We present here the results of these investigation. The facility and process in use are also presented, together with possible next upgrade of the system, facing the new production of cavities for the LCLSII project.
	Poster MOPB102 [1.535 MB]
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MOPB103	Vertical Electro-Polishing at DESY of a 1.3 GHz Gun Cavity for CW Application	gun, acceleration, injection, SRF	399
	N. Steinhau-Kühl, R. Bandelmann, D. Kostin, A. Matheisen, M. Schmökel, J.K. Sekutowicz DESY, Hamburg, Germany
	Superconducting gun cavities for cw operation in accelerators are under study. In 2003 a three-and-a-half cell gun cavity was chemically treated with buffered chemical polishing and tested successfully in a collaboration between Helmholtz-Zentrum Dresden-Rossendorf and DESY. For several years a 1.3-GHz 1.6-cell resonator has been under study, which has been built and tested at DESY and elsewhere. For further studies and optimization the gun cavity needed to be electro-polished, which was conducted at DESY for the first time using vertical electro-polishing. The technical set-up for the vertical electro-polishing and high pressure rinsing as well as the processing parameters applied and the adaptation of the existing infrastructure to the 1.6-cell geometry at DESY are presented.
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MOPB104	Flux Expulsion Variation in SRF Cavities	niobium, factory, cryogenics, SRF	404
	S. Posen, M. Checchin, A.C. Crawford, A. Grassellino, M. Martinello, O.S. Melnychuk, A. Romanenko, D.A. Sergatskov Fermilab, Batavia, Illinois, USA
	Treating a cavity with nitrogen doping significantly increases Q₀ at medium fields, reducing cryogenic costs for high duty factor linear accelerators such as LCLS II. N-doping also makes cavities more sensitive to increased residual resistance due to trapped magnetic flux, making it critical to either have extremely effective magnetic shielding, or to prevent flux from being trapped in the cavity during cooldown. In this paper, we report on results of a study of flux expulsion. We discuss possible ways in which flux can be pinned in the inner surface, outer surface, or bulk of a cavity, and we present experimental results studying these mechanisms. We show that grain structure appears to play a key role and that a cavity that expelled flux poorly changed to expelling flux well after a high temperature furnace treatment. We further show that after furnace treatment, this cavity exhibited a significant improvement in quality factor when cooled in an external magnetic field. We conclude with implications for SRF accelerators with high Q₀ requirements.
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MOPB105	Symmetric Removal of Niobium Superconducting RF Cavity in Vertical Electropolishing	cathode, experiment, accumulation, niobium	409
	V. Chouhan, Y.I. Ida, K.N. Nii, T.Y. Yamaguchi MGH, Hyogo-ken, Japan H. Hayano, S. Kato, H. Monjushiro, T. Saeki, M. Sawabe KEK, Ibaraki, Japan K. Ishimi MGI, Chiba, Japan
	Vertical electropolishing (VEP) leads several advantages over horizontal EP in respect of easy operation and mechanism of an EP system resulting in lower cost. However, till yet VEP always resulted inhomogeneous removal of a niobium (Nb) cavity along its length and bubble traces especially on the top iris of a vertically set cavity. In this work we performed lab EP and VEP experiments in order to study and solve these two problems. A coupon cavity which contains 6 disk type Nb coupons positioned at beam pipes, irises and equator was vertically electropolished to optimize VEP parameters so as to get almost uniform removal of Nb and a smooth surface of the cavity without bubble traces. Our patented unique i-Ninja cathode having 4 wings was used with an optimized rotation speed to get homogeneous removal of Nb. The homogeneous removal and the surface without bubble traces might be result of a uniform thickness of a viscous layer on the surface of the cavity cell and no accumulation of hydrogen bubbles on the top iris surface. The surfaces of the coupons were studied in detail with surface analytical tools.
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MOPB106	Analysis of High Pressure Rinsing Characteristics for SRF Cavities	target, experiment, SRF, niobium	414
	Y. Jung, M.O. Hyun, M.J. Joung IBS, Daejeon, Republic of Korea J. Kim, J. Seo Vitzrotech Co., Ltd., Ansan City, Kyunggi-Do, Republic of Korea
	High pressure rinsing (HPR) treatment has been widely used in the SRF cavity fabrication. This well- known process helps remove effectively undesirable emission tips from the inner surface of cavities, which are responsible for a different level's multipaction and hellium quenching. Also, the HPR treatment can clean or polish the RF (Radio Frequency) surface, which is critically sensitive to an applied magnetic field, by removing contaminants such as an organic oil, a remnant metal debris and dirty etchants from the cavity surface. Consequently, the HPR treatment contributes to improve quality factor during the cavity operation both by decreasing various field emission sites and by removing defects from the cavity surface. In this paper, we performed HPR experiments by using a simplified cavity structure, intentionally painted with a pattern on the inner surface. Therefore, we report how the surface treatment by HPR was carried out as functions of the distance between a target to be cleaned and a nozzle, and a water pressure.
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MOPB110	The Transfer of Improved Cavity Processing Protocols to Industry for LCLS-II: N-Doping and Electropolishing	cathode, niobium, controls, superconductivity	418
	C.E. Reece, F. Marhauser, A.D. Palczewski JLab, Newport News, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177 with supplemental funding from the LCLS-II Project U.S. DOE Contract No. DE-AC02-76SF00515. Based on the R&D efforts of colleagues at FNAL, Cornell, and JLab, the LCLS-II project adopted a modification to the rather standard niobium SRF cavity surface processing protocol that incorporates a high temperature diffusion doping with nitrogen gas. This change was motivated by the resulting higher Q0 and the prospect of significantly lower cryogenic heat load for LCLS-II. JLab is responsible for managing the cavity procurement for the LCLS-II project. The first phase of the procurement action is to transfer the nitrogen-doping protocol to the industrial vendors. We also seek to exploit improvements in understanding of the niobium electropolishing process as part of the production processing of the TESLA-style LCLS-II cavities. We report on the technology transfer activities and progress toward the envisaged performance demonstration of vendor-processed cavities.
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MOPB111	Furnace N2 Doping Treatments at Fermilab	vacuum, SRF, controls, PLC	423
	M. Merio, M. Checchin, A.C. Crawford, A. Grassellino, M. Martinello, A.M. Rowe, M. Wong Fermilab, Batavia, Illinois, USA M. Checchin, M. Martinello Illinois Institute of Technology, Chicago, Illlinois, USA
	Funding: Operated by Fermi Research Alliance, LLC under Contract No. De-AC02-07CH11359 with the United States Department of Energy. The Fermilab SRF group regularly performs Nitrogen (N2) doping heat treatments on superconducting cavities in order to improve their Radio Frequency (RF) performances. This paper describes the set up and operations of the Fermilab vacuum furnaces, with a major focus on the implementation and execution of the N2 doping recipe. The cavity preparation will be presented, N2 doping recipes will be analyzed and heat treatment data will be reported in the form of plot showing temperature, total pressure and partial pressures over time. Finally possible upgrades and improvements of the furnace and the N2 doping process are discussed.
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MOPB112	SRF Quality Assurance Studies and Their Application to Cryomodule Repairs at SNS	cryomodule, vacuum, HOM, hardware	428
	J.D. Mammosser, R. Afanador, D.L. Barnhart, B. DeGraff, B.S. Hannah, J. Saunders, P.V. Tyagi ORNL RAD, Oak Ridge, Tennessee, USA C.M. Campbell Omega Technical Services, Oak Ridge, Tennessee, USA M. Doleans, D.K. Hensley, S.-H. Kim ORNL, Oak Ridge, Tennessee, USA
	Funding: This work was supported by SNS through UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. DOE. Many of the SRF activities involve interactions to cavities which presents risk for particulate contamination to RF surfaces. In order to understand and reduce contamination in cavities during cleaning, vacuum pumping and purging, and in-situ cryomodule repairs, a Quality Assurance (QA) studies were initiated to evaluate these activities and improve them where possible. This paper covers the results of investigations on the effectiveness of the SNS ultrasonic cleaning systems, particulate control during pumping and purging, procedure development for in-situ cryomodule repairs, the application of these studies to the repair of a linac cryomodule, and discussion of further improvement in these areas.
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MOPB113	Study of the Evolution of Artificial Defects on the Surface of Niobium During Electrochemical and Chemical Polishing	SRF, controls, laser, operation	433
	L. Monaco, P. Michelato INFN/LASA, Segrate (MI), Italy A. Navitski, J. Schaffran, W. Singer DESY, Hamburg, Germany C. Pagani Università degli Studi di Milano & INFN, Segrate, Italy A.L. Prudnikava, Y. Tamashevich University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
	The presence of defects on the inner surface of Nb superconducting RF structures might limit its final performance. For this reason, strict requirements are imposed during mechanical production of the cavities, specifically on the quality control of the inner surface of components, to avoid the presence of defects or scratches. Nevertheless, some defects may remain also after control or can arise from the following production steps. Understanding the evolution of the defect might shine new insight on its origin and help in defining possible repair techniques. This paper reports the topographical evolution of defects on a Nb sample polished with the standard recipe used for the 1.3 GHz cavities of the EXFEL project. Various artificial defects of different shape, dimensions, and thicknesses/depths, with geometrical characteristics similar to the one that may occur during the machining and handling of cavities, have been “ad hoc” produced on the sample of the same material used for the cell fabrication. Analysis shows the evolution of the shape and profile of the defects at the different polishing steps.
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MOPB115	Surface Studies of Plasma Processed Nb Samples	plasma, vacuum, SRF, ion	438
	P.V. Tyagi, R. Afanador, B. DeGraff, M. Doleans, B.S. Hannah, M.P. Howell, S.-H. Kim, J.D. Mammosser, C.J. McMahan, J. Saunders, S.E. Stewart ORNL, Oak Ridge, Tennessee, USA
	Funding: This work is supported by SNS through UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. DOE. Contaminants present at top surface of superconducting radio frequency (SRF) cavities can act as field emitters and restrict the cavity accelerating gradient. A room temperature in-situ plasma processing technology for SRF cavities aiming to clean hydrocarbons from inner surface of cavities has been recently developed at the Spallation Neutron Source (SNS). Surface studies of the plasma processed Nb samples by Secondary ion mass spectrometry (SIMS) and Scanning Kelvin Probe (SKP) showed that the NeO2 plasma processing is very effective to remove carbonaceous contaminants from top surface and improves the surface work function by 0.5 to 1.0 eV. M. Doleans et al., Proc. 2013 SRF, Paris, France. P. V. Tyagi, et al., Proc. Linac14, Geneva, Switzerland. **M. Doleans et al., These proceedings.
	Poster MOPB115 [0.524 MB]
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MOPB116	Developments of Horizontal High Pressure Rinsing for SuperKEKB SRF Cavities	vacuum, factory, operation, SRF	443
	Y. Morita, K. Akai, T. Furuya, A. Kabe, S. Mitsunobu, M. Nishiwaki KEK, Ibaraki, Japan
	The Q factors of the eight superconducting accelerating cavities gradually degraded during the long-term operation of the KEKB accelerator. Since we will re-use those SRF cavities for the SuperKEKB, the performance degradation will be a serious problem. Several cavities degraded their performance significantly at high accelerating fields. The Q degradation is still acceptable for the 1.5 MV operations at SuperKEKB. However, further degradation will make the operation difficult. In order to recover the cavity performance, we developed horizontal high pressure water rinsing (HHPR). This method uses a horizontal high pressure water nozzle and inserts it directly into the cavity module. We applied this method to two degraded cavities and their degraded Q factors recovered above 10⁹ at around 2 MV. In this paper we will present the HHPR method, high power test results after the HHPR and the residual gas analysis.
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MOPB117	Identification and Evaluation of Contamination Sources During Clean Room Preparation of SRF Cavities	experiment, hardware, SRF, superconductivity	448
	L. Zhao, G.K. Davis, A.V. Reilly JLab, Newport News, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contracts DE-AC05-06OR23177 and DE-AC02-76SF00515 for the LCLS-II Project. Particles are one possible cause of field emission issues in SRF cavity operations. During clean room cavity preparation, several processes could contribute to the generation of particles. One of them is friction between hardware during assembly and disassembly. It is important to understand the behaviours that generate and propagate particles into cavities. Using a single cell cavity, particle shedding between flanges and other materials have been tested. The number of particles is recorded with an airborne particle counter, and the generated particles are examined with microscope. The migration of particles into a cavity due to different movements is studied. Suggestions are made to reduce particle generation and prevent contamination of the cavity interior area.
	Poster MOPB117 [2.832 MB]
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MOPB118	Cleanliness and Vacuum Acceptance Tests for the UHV Cavity String of the XFEL Linac	vacuum, operation, controls, cryomodule	452
	S. Berry, O. Napoly, B. Visentin CEA/DSM/IRFU, France C. Boulch, C. Cloué, C. Madec, T. Trublet CEA/IRFU, Gif-sur-Yvette, France D. Henning, L. Lilje, A. Matheisen, M. Schmökel DESY, Hamburg, Germany
	The main linac of the European XFEL will consist of 100 accelerator modules, i.e. 800 superconducting accelerator cavities operated at a design gradient of 23.6MV/m. In this context CEA-Saclay built an assembly facility designed to produce one module per week, ready to be tested at DESY. The facility overcame the foreseen production rate. We would like to highlight and discuss the critical fields: cleanliness and vacuum. A new assembly method to protect final assembly against particulates contamination has been implemented on the production line. Impact on cryomodule RF test is presented. Particle transport measurements on components used for the European XFEL accelerator module are presented. The results indicate that the nominal operation of the automated pumping and venting units will not lead to particle transport. Vacuum acceptance tests are of major interest: leak tests and residual gas analysis (RGA) are used to control the absence of air leak and contamination. The RGA specifications have been slightly relaxed to ensure the production rate.
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TUAA02	Commissioning of the SRF Linac for ARIEL	cryomodule, linac, TRIUMF, electron	457
	V. Zvyagintsev, Z.T. Ang, T. Au, S. Calic, K. Fong, P.R. Harmer, B. Jakovljevic, J.J. Keir, D. Kishi, P. Kolb, S.R. Koscielniak, A. Koveshnikov, C. Laforge, D. Lang, M.P. Laverty, R.E. Laxdal, Y. Ma, A.K. Mitra, N. Muller, R.R. Nagimov, W.R. Rawnsley, R.W. Shanks, R. Smith, B.S. Waraich, L. Yang, Z.Y. Yao, Q. Zheng TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada
	This paper is reporting commissioning results for the SRF linac of ARIEL facility at TRIUMF. The paper is focused on the SRF challenges: cavity design and performance, ancillaries design and preparation, cryomodule design and performance, RF system and final beam test results.
	Slides TUAA02 [4.004 MB]
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TUAA03	BESSY VSR: A Novel Application of SRF for Synchrotron Light Sources	damping, SRF, HOM, storage-ring	462
	A.V. Vélez, H.-W. Glock, P. Goslawski, A. Jankowiak, J. Knobloch, A. Neumann, M. Ries, G. Wüstefeld HZB, Berlin, Germany
	CW SRF Cavities have been used very successfully in the past in synchrotron light sources to provide high power acceleration. Here we present a novel application of higher harmonic systems of two frequencies (1.5 GHz and 1.75 GHz) to generate a beating of accelerating voltage. With such a system it is possible to store "standard" (some 10 ps long) and "short" (ps and sub-ps long) pulses simultaneously in the light source. This opens up brand new possibilities for light source users to perform dynamic and high-resolution experiments at the same facility. The demands on the SRF system and RF control are substantial and a new design, based on waveguide damping, is currently being developed. This system will be used for a major upgrade of the BESSY-II facility to the BESSY Variable Pulse Storage Ring (BESSY-VSR) for a next-generation storage-ring light source. We will discuss the concept, challenges and designs for BESSY-VSR.
	Slides TUAA03 [2.103 MB]
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TUAA04	Rapid Growth of SRF in India	niobium, linac, SRF, electron	467
	D. Kanjilal IUAC, New Delhi, India
	Funding: Funding received from Ministry of Higher Education through University Grants Commission of India and from Department of Atomic Energy are gratefully acknowledged. The talk shall summarize the recent advances in the SRF program in various research centres in India. The SRF related activities at Inter-University Accelerator Centre (IUAC) at Delhi , Raja Ramanna Centre for Advanced Technology (RRCAT) at Indore, Bhabha Atomic Research Centre (BARC) and Tata Institute of Fundamental Research (TIFR) both at Mumbai, and Variable Energy Cyclotron Centre (VECC) at Kolkata shall be addressed. In particular indigenous niobium resonator fabrication and test facilities of IUAC operational for more than a decade which have been used extensively for development, fabrication and utilization of various types of resonators will be discussed. The results from the commissioning of the full three linac modules having eight niobium quarter wave resonators in each module of the heavy ion linac at IUAC for regular scheduled experiments will be presented. The technology and infrastructure developments at RRCAT, BARC, TIFR and VECC for fabrication, processing and tests of future cavities will be discussed.
	Slides TUAA04 [5.918 MB]
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TUAA06	Recent Progress of ESS Spoke and Elliptical Cryomodules	cryomodule, SRF, cryogenics, linac	474
	G. Olry IPN, Orsay, France
	The ESS accelerator high level requirements are to provide a 2.86 ms long proton pulse at 2 GeV at repetition rate of 14 Hz. This represents 5 MW of average beam power with a 4% duty cycle on target. In a framework of collaboration between IPN Orsay, CEA Saclay and ESS, prototype spoke and medium and high beta elliptical cavities and cryomodules have been studied, constructed and tested. After a description of the ESS project and the accelerator layout, this paper will focus on the recent progress towards realization of the detailed design, the manufacturing of the first components of the prototype cryomodules and the first test results of some of the main critical elements such as SRF cavities and cold tuning systems.
	Slides TUAA06 [17.400 MB]
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TUBA01	Status of the SRF Systems at HIE-ISOLDE	cryomodule, vacuum, cryogenics, solenoid	481

Paper

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Page

MOAA01

FRIB Project: Moving to Production Phase

SRF, solenoid, cryomodule, linac

1

K. Saito, H. Ao, N.K. Bultman, E.E. Burkhardt, F. Casagrande, S. Chouhan, C. Compton, J.L. Crisp, K.D. Davidson, K. Elliott, F. Feyzi, A.D. Fox, P.E. Gibson, L. Hodges, K. Holland, G. Kiupel, S.M. Lidia, I.M. Malloch, D. Miller, S.J. Miller, D. Morris, D. Norton, J. Popielarski, L. Popielarski, A.P. Rauch, R.J. Rose, T. Russo, S. Shanab, M. Shuptar, S. Stark, G.J. Velianoff, D.R. Victory, J. Wei, T. Xu, T. Xu, Y. Yamazaki, Q. Zhao, Z. Zheng
FRIB, East Lansing, Michigan, USA
S.K. Chandrasekaran
Fermilab, Batavia, Illinois, USA
A. Facco
INFN/LNL, Legnaro (PD), Italy
K. Hosoyama, M. Masuzawa
KEK, Ibaraki, Japan
R.E. Laxdal
TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada
M.X. Xu
IMP/CAS, Lanzhou, People's Republic of China

Funding: Work supported by the U.S. Department of Energy Office of Science under Cooperative Agreement DE-SC0000661
The Facility for Rare Isotope Beams (FRIB) is based upon a high power heavy ion driver linac under construction at Michigan State University under a cooperative agreement with the US DOE. The construction of conventional facilities already started in the summer, 2013, and the accelerator production began from the summer, 2014. FRIB will accelerate all the stable ion beams from proton to uranium beyond a beam energy of 200 MeV/u and up to a beam power of 400 kW to produce a great number of various rare isotopes using SRF linac. The FRIB SRF driver linac makes use of four kinds of SRF structures. Totally 332 two gap cavities and 48 cryomodules are needed. All SRF hardware components have been validated and are now moving to production. The SRF infrastructure also has been constructed in MSU campus. This talk will present FRIB project and challenges regarding SRF technologies. The status of SRF linac hardware validation and their production, SRF infrastructure status and plan shall be addressed. The information that can be relevant for future large scale proton/ion SRF linacs will also be provided.

Slides MOAA01 [2.754 MB]

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MOAA02

Recent Progress with EU-XFEL

cryomodule, linac, operation, cryogenics

14

D. Reschke
DESY, Hamburg, Germany

The superconducting accelerator of the European XFEL consists of the injector part and the main linac. The injector includes one 1.3 GHz accelerator module and one 3.9 GHz third-harmonic module, while the main linac will consist of 100 accelerator modules, operating at an average design gradient of 23.6 MV/m. The fabrication and surface treatment by industry as well as RF acceptance tests of the required 808 superconducting 1.3 GHz cavities are close to an end by the time of SRF15. The accelerator module assembly, testing and installation in the tunnel is in full swing. First steps of commissioning have been made. The status and results of cavity and module RF tests at 1.3 GHz and 3.9 GHz are presented.

Slides MOAA02 [2.903 MB]

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MOAA04

Overview of Recent SRF Developments for ERLs

SRF, gun, linac, cryomodule

24

S.A. Belomestnykh
BNL, Upton, Long Island, New York, USA
S.A. Belomestnykh
Stony Brook University, Stony Brook, USA

Funding: Work is supported by Brookhaven Science Associates, LLC under contract No. DE-AC02-98CH10886 with the US DOE.
This talk reviews SRF technology for Energy Recovery Linacs (ERLs). In particular, recent developments and results reported at the ERL2015 Workshop are highlighted. The talk covers facilities under construction, commissioning or operation, such as cERL at KEK, BERLinPro at HZB and R&D ERL at BNL, as well as facilities in the development phase. Future perspectives will be discussed.

Slides MOAA04 [5.376 MB]

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MOBA03

Sensitivity of Niobium Superconducting RF Cavities to Magnetic Field

vacuum, niobium, impedance, SRF

34

D. Gonnella, J.J. Kaufman, M. Liepe
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

One important characteristic of nitrogen-doped cavities is their very high sensitivity to increased residual surface resistance from trapped ambient magnetic flux. We have performed a systematic study on the losses by trapped flux, and their dependence on the mean-free-path (MFP) of the niobium RF penetration layer. Cavities with a wide range of MFP values were tested in uniform ambient magnetic fields to measure trapped magnetic flux and resulting increase in RF surface resistance. MFP values were determined from surface impedance measurements. It was found that larger mean free paths lead to lower sensitivity to trapped magnetic flux.

Slides MOBA03 [1.817 MB]

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MOBA04

High-Q Operation of SRF Cavities: The Impact of Thermocurrents on the RF Surface Resistance

simulation, shielding, niobium, operation

37

J.M. Köszegi, J. Knobloch, O. Kugeler
HZB, Berlin, Germany

For CW applications much effort is being expended to minimize the power dissipation (surface resistance) of niobium cavities. Previous studies have shown that residual resistance can be reduced by performing a thermal cycle, a procedure of warming up a cavity after initial cooldown to about 20K and cooling it down again. It was postulated that thermocurrents during cooldown generate additional trapped magnetic flux that impacts the cavity quality factor. Here, we present a more extensive study that includes measurements of two additional passband modes and that confirms the effect. A change in surface resistance of more than a factor seven was observed. In this paper, we also discuss simulations that support the claim. While the layout of the cavity LHe tank system is cylindrically symmetric, we show that the temperature dependence of the material parameters results in a non-symmetric current distribution.

Slides MOBA04 [2.830 MB]

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MOBA05

Nature of Quality Factor Degradation in SRF Cavities due to Quench

superconductivity, simulation, electron, cryogenics

41

M. Checchin
Fermilab, Batavia, Illinois, USA

Superconductive quench is a well-known phenomenon that causes magnetic flux trapping in superconducting accelerating cavities increasing the radio-frequency surface resistance. This paper is addressed to the understanding of the quench-induced losses nature. We present the proof that the real origin of quench-related quality factor degradation is consequence only of ambient magnetic field trapped at the quench spot. Also, we show how the quality factor can be fully recovered after it was highly deteriorated quenching several times in presence of external magnetic field. Such phenomenon was found to be completely reliable up to certain values of applied magnetic field, above that the cavity quality factor cannot be fully recovered anymore.

Slides MOBA05 [2.742 MB]

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MOBA06

N Doping: Progress in Development and Understanding

niobium, superconductivity, factory, injection

48

A. Grassellino
Fermilab, Batavia, Illinois, USA

Significant progress was made recently with N2 doped cavities. This talk will summarize all developments with N-doped Nb cavity work at FNAL in the past two years.

Slides MOBA06 [7.704 MB]

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MOBA08

Niobium Impurity-Doping Studies at Cornell and CM Cool-Down Dynamic Effect on Q0

cryomodule, SRF, niobium, superconductivity

55

M. Liepe, B. Clasby, R.G. Eichhorn, B. Elmore, F. Furuta, G.M. Ge, D. Gonnella, T. Gruber, D.L. Hall, G.H. Hoffstaetter, J.J. Kaufman, P.N. Koufalis, J.T. Maniscalco, T.I. O'Connell, P. Quigley, D.M. Sabol, J. Sears, E.N. Smith, V. Veshcherevich
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

As part of a multi-laboratory research initiative on high Q0 niobium cavities for LCLS-II and other future CW SRF accelerators, Cornell has conducted an extensive research program during the last two years on impurity-doping of niobium cavities and related material characterization. Here we give an overview of these activities, and present results from single-cell studies, from vertical performance testing of nitrogen-doped nine-cell cavities, and from cryomodule testing of nitrogen-doped nine-cell cavities.

Slides MOBA08 [8.983 MB]

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MOPB001

RF Performance of Ingot Niobium Cavities of Medium-Low Purity

SRF, vacuum, operation, radio-frequency

61

G. Ciovati, P. Dhakal, P. Kneisel, G.R. Myneni, J.K. Spradlin
JLab, Newport News, Virginia, USA

Funding: This manuscript has been authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
Superconducting radio-frequency cavities made of ingot niobium with residual resistivity ratio (RRR) greater than 250 have proven to have similar or better performance than fine-grain Nb cavities of the same purity, after standard processing. The high purity requirement contributes to the high cost of the material. As superconducting accelerators operating in continuous-wave typically require cavities to operate at moderate accelerating gradients, using lower purity material could be advantageous not only to reduce cost but also to achieve higher Q0-values, because of the well-known dependence of the BCS-surface resistance on mean free path. In this contribution we present the results from cryogenic RF tests of 1.3-1.5 GHz single-cell cavities made of ingot Nb of medium (RRR=100-150) and low (RRR=60) purity from different suppliers. Cavities made of medium-purity ingots routinely achieved peak surface magnetic field values greater than 70 mT with Q0-values above 1.5·10¹⁰ at 2 K. The performance of cavities made of low-purity ingots were affected by significant pitting of the surface after chemical etching.

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MOPB002

Observation of High Field Q-Slope in 3 GHz Nb Cavities

niobium, SRF, radiation, feedback

66

G.V. Eremeev, F.E. Hannon
JLab, Newport News, Virginia, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
A degradation of the unloaded quality factor is commonly observed above about 100 mT in elliptical niobium cavities. The cause of this degradation has not been fully understood yet, but the empirically found solution of heating to about 100-120 C for 24-48 hrs. eliminates the degradation in electropolished fine grain or large grain niobium cavities. While numerous experiments related to this phenomenon have been done at 1.3 GHz and 1.5 GHz, little data exists at other frequencies, and the frequency dependence of this degradation is not clear. We have measured the unloaded quality factor of 3 GHz fine grain niobium cavities, which were chemically polished as the final treatment before RF tests in a vertical Dewar and observed the characteristic degradation in two cavities. The measurement of the quality factor degradation at different bath temperatures points to a field-dependent rather than a temperature-related effect.

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MOPB003

Superconducting Cavity for the Measurements of Frequency, Temperature, RF Field Dependence of the Surface Resistance

plasma, coupling, cryogenics, experiment

70

H. Park, S.U. De Silva, J.R. Delayen
ODU, Norfolk, Virginia, USA
H. Park
JLab, Newport News, Virginia, USA

In order to better understand the contributions of the various physical processes to the surface resistance of superconductors the ODU Center for Accelerator Science is developing a half-wave resonator capable of operating between 325 MHz and 1.3 GHz. This will allow the measurement of the temperature and rf field dependence of the surface resistance on the same surface over the range of frequency of interest for particle accelerators and identify the various sources of power dissipation.

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MOPB004

Understanding the Field Dependence of the Surface Resistance in Nitrogen-Doped Cavities

simulation, radio-frequency, vacuum, impedance

74

P.N. Koufalis, D. Gonnella, M. Liepe, J.T. Maniscalco, I. Packtor
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: NSF Grant PHYS-1416318
An important limiting factor in the performance of superconducting radio frequency (SRF) cavities in medium and high field gradients is the intrinsic quality factor and, thus, the surface resistance of the cavity. The exact dependence of the surface resistance on the magnitude of the RF field is not well understood. We present an analysis of experimental data of LT1-3 and LT1-4, 1.3 GHz single-cell nitrogen-doped cavities prepared and tested at Cornell. Most interestingly, the cavities display anti-Q slopes in the medium-field region (i.e. Rs decreases with increasing accelerating field). We extract the temperature dependent surface resistances of the cavities, analyze field dependencies, and compare with theoretical predictions. These comparisons and analyses provide new insights into the field dependence of the surface resistance and improve our understanding of the mechanisms behind the effect.

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MOPB005

Developing a Setup to Measure Field Dependence of BCS Surface Resistance

solenoid, niobium, radio-frequency, software

77

J.T. Maniscalco, M. Liepe
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: NSF/DOE
The temperature-dependent part of the microwave surface resistance of superconducting radio-frequency (SRF) cavities has been shown experimentally to depend on the strength of the applied magnetic surface field. Several theories have recently been proposed to describe this phenomenon. In this paper we present work on the development of a microwave cavity setup for measuring the field-dependence with an applied DC magnetic field.

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MOPB007

Temperature Excursions in Nb Sheets With Imbedded Delamination Cracks

SRF, radiation, status, radio-frequency

82

P. Xu, N.T. Wright
MSU, East Lansing, Michigan, USA
T.R. Bieler
Michigan State University, East Lansing, Michigan, USA
C. Compton
FRIB, East Lansing, Michigan, USA

Funding: Work supported by US DOE Cooperative Agreement DE-SC0000661 and Michigan State University.
Delamination cracks can form in rolled Nb sheets, and between layers with different micro-structures. Such cracks cause resistance to heat conduction from the RF surface to the liquid He bath. A delamination crack can negate the advances in manufacturing processes that have enhanced the thermal conductivity of Nb. Here, temperature excesses are calculated as functions of crack size and location, and the power dissipated at an imperfection in the RF surface. A disk shape of Nb sheet is modeled as having adiabatic sides. A hemispherical defect is located on the RF surface at the center of this section. A crack is modeled as a void within the Nb disk. The Kapitza resistance between the Nb surface and liquid He is varied. The results indicate that an incipient crack leads to a decrease in the magnetic flux required to cause thermal breakdown. The decrease in the field is gradual with increasing crack radius, until the crack radius nearly equals the section radius, after which the field required for breakdown decreases sharply. To a lesser extent, the field strength for thermal breakdown also decreases with increased crack depth.

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MOPB008

Theoretical Field Limit and Cavity Surface Conditions: Nano-Scale Topography and Sub-millimeter Pit

factory, simulation, radio-frequency, framework

86

T. Kubo
KEK, Ibaraki, Japan

The recent two theoretical papers*,** are briefly introduced. The former addresses the superheating field (Bs) suppression due to nano-defects distributing almost continuously on the cavity surface*. We introduce a model of the nano-defect. An analytical formula for Bs suppression factor is derived. By using the formula, suppression factors of bulk or multilayer superconductors and those after various surface processing technologies can be evaluated. An application to the dirty Nb processed by EP is also presented as an example. The latter address the magnetic field enhancement (MFE) at the sub-millimeter pit on the surface of cavity, which is thought to cause quench**. There exists the famous well-type pit model, but many of pits are not well-type but have gentle slopes. Impacts of the slope angle on MFE have not been well understood. We introduce a model that can describe a pit with an arbitrary slope angle. A formula to evaluate the MFE factor is derived. A pit with a gentle slope angle yields a much smaller MFE factor than the well-type pit. The formula can be applied to the calculation of MFE factors of real pits with arbitrary slope angles.
* T. Kubo, Prog. Theor. Exp. Phys. 2015,063G01(2015).
** T. Kubo, Prog. Theor. Exp. Phys. 2015,073G01(2015).

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MOPB009

Model of Flux Trapping in Cooling Down Process

target, interface, experiment, framework

90

T. Kubo
KEK, Ibaraki, Japan

Recent findings that cooling conditions affect an amount of trapped magnetic flux attract much attention as a way to achieve a high-Q0 by SRF cavity*,**,***. Q0~2*10¹¹ has already been achieved by the full flux expulsion****. While much experimental studies have been conducted, not much theoretical progress followed on it. In this paper, I introduce a simple model that can explain how trapped fluxoids are expelled in cooling process.
*J.M.Vogt et al., PRSTAB 16, 102002 (2013)
**A.Romanenko et al., JAP 115, 184903 (2014)
***J.M.Vogt et al., PRSTAB 18, 042001 (2015)
****A.Romanenko et al., APL 105, 234103 (2014)

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MOPB010

Field-Dependent Surface Resistance for Superconducting Niobium Accelerating Cavities: The Case of N-Doping

niobium, data-analysis, electron, superconductivity

95

W. Weingarten
Private Address, SERGY, France
R.G. Eichhorn
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

The dependence of the Q-value on the RF field (Q-slope) for superconducting RF cavities is actively studied in various accelerator laboratories. Although remedies against this dependence have been found, the physical cause still remains obscure. A rather straightforward two-fluid model description of the Q-slope in the low and high field domains is extended to the case of the recently experimentally identified increase of the Q-value with the RF field obtained by so-called "N-doping”.
This paper was initiated when one of the authors (W.W., retiree from CERN) visited Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, NY.

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MOPB011

How Uniform Are Cool-Downs?

interface, simulation, niobium, factory

100

J.A. Robbins, R.G. Eichhorn
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Since the last SRF conference it has become clear that achieving extremely high quality factors of SRF cavities depend on the cool-down scenario. While some findings favor a fast cool-down, others suggest a slow cycle to be advantageous, and many variations to that have been investigated: the role of thermocurrents, amount of ambient magnetic field and flux trapping. This paper will investigate, how uniformly different cool-down procedures are and if they can explain the more efficient magnetic flux expulsion.

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MOPB013

Simulation of Geometry Dependent Flux Trapping

simulation, factory, superconducting-cavity, focusing

105

J. May-Mann, R.G. Eichhorn
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Trapping or expulsion of ambient magnetic field has become an important factor in the performance of superconducting cavities with very high Q. As experimental data is limited, we set up a numerical field calculation model to study this effect in more details. We will report, how the cavity orientation, the movement of the transition to superconductivity front, and the orientation of the magnetic field contributes to the amount of magnetic field being vulnerable for trapping.

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MOPB014

Magnetic Flux Expulsion in Horizontally Cooled Cavities

interface, SRF, distributed, simulation

110

M. Martinello, M. Checchin, A. Grassellino, O.S. Melnychuk, A. Romanenko, D.A. Sergatskov
Fermilab, Batavia, Illinois, USA
M. Checchin
Illinois Institute of Technology, Chicago, Illlinois, USA
J. Zasadzinski
IIT, Chicago, Illinois, USA

Funding: Work supported by the US Department of Energy, Office of High Energy Physics
The cool down details of superconducting accelerating cavities are crucial parameters that have to be optimize in order to obtain very high quality factors. The temperature all around the cavity is monitored during its cool down across the critical temperature, in order to visualize the different dynamics of fast and slow cool-down, which determine considerable difference in terms of magnetic field expulsion and cavity performance. The study is performed placing a single cell 1.3 GHz elliptical cavity perpendicularly to the helium cooling flow, which is representative of how SRF cavities are cooled in an accelerator. Hence, the study involves geometrical considerations regarding the cavity horizontal configuration, underling the different impact of the various magnetic field components on the surface resistance. Experimental data also proves that under established conditions, flux lines are concentrated at the cavity top, in the equatorial region, leading to temperature rise.

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MOPB015

Trapped Flux Surface Resistance Analysis for Different Surface Treatments

niobium, resonance, superconductivity, instrumentation

115

M. Martinello, M. Checchin, A. Grassellino, O.S. Melnychuk, S. Posen, A. Romanenko, D.A. Sergatskov
Fermilab, Batavia, Illinois, USA
M. Checchin
Illinois Institute of Technology, Chicago, Illlinois, USA
J. Zasadzinski
IIT, Chicago, Illinois, USA

Funding: Work supported by the US Department of Energy, Office of High Energy Physics
The trapped flux surface resistance is one of the main contributions on cavity losses which appears when cavities are cooled in presence of external magnetic field. The study is focused on the understanding of the different parameters which determine the trapped flux surface resistance, and how this change as a function of different surface treatments. The study is performed on 1.3 GHz niobium cavities processed with different surface treatments after the 800 C bake: electro-polishing (EP), 120 C baking, and N-doping varying the time of the Nitrogen exposure. The trapped flux surface resistance normalized for the trapped magnetic flux is then analyzed as a function of the mean free path in order to find the surface treatment which minimized the trapped flux sensitivity.

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MOPB018

Introduction of Precisely Controlled Microstructural Defects into SRF Cavity Niobium Sheets and Their Impact on Local Superconducting Properties

niobium, SRF, electron, superconductivity

120

M. Wang, T.R. Bieler, D. Kang
Michigan State University, East Lansing, Michigan, USA
C. Compton
FRIB, East Lansing, Michigan, USA
D.C. Larbalestier, A. Polyanskii, Z-H. Sung
ASC, Tallahassee, Florida, USA
P.J. Lee
NHMFL, Tallahassee, Florida, USA

Funding: Research supported by DOE/OHEP (contract number DE-FG02-09ER41638 at MSU and DE-SC0009960 at FSU) and the State of Florida.
When SRF cavity shapes are formed from Nb sheets, the metallurgical processing introduces microstructural defects such as dislocations and low-angle grain boundaries that can serve as pinning centers for magnetic flux that may degrade cavity performance. Therefore, the relationship between magnetic flux behavior and microstructural defects in carefully strained SRF Nb sheet was investigated. Laue X-ray and EBSD-OIM crystallographic analyses of large grain ingot slices were used to characterize microstructural defects and then predict which grains and sample orientations will produce desired model defects due to tensile deformation. Grain orientations were chosen to favor specific slip systems, which generate dislocations with special angles with respect to the sample surface. Nb bicrystals were also prepared to investigate the effects of grain boundaries on flux pinning. The generated defect structures were confirmed by OIM and TEM. Cryogenic magneto-optical imaging was used to directly observe the penetration of magnetic flux into the deformed Nb. These model samples have deformation that is similar to that expected in typical cavity forming processes.

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MOPB019

Horizontal Testing and Thermal Cycling of an N-Doped Tesla Type Cavity

shielding, pick-up, factory, EPICS

125

O. Kugeler, J. Knobloch, J.M. Köszegi
HZB, Berlin, Germany
A. Grassellino, O.S. Melnychuk, A. Romanenko, D.A. Sergatskov
Fermilab, Batavia, Illinois, USA

An N-doped TESLA type cavity treated at FERMILAB has been tested in the HoBiCaT horizontal test stand. Temperatures and magnetic fields occuring during the superconducting transition were recorded at various positions and directions on the outer cavity surface. Several thermal cycling runs were performed yielding different Q0 factors just like in undoped cavities. The resulting residual and BCS resistance values were correlated to the thermal and magnetic conditions during cooldown.

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MOPB023

Detectors Sensing Second Events Induced by Thermal Quenches of SRF Cavities in He II

SRF, detector, instrumentation, diagnostics

135

M. Fouaidy, F. Dubois, D. Longuevergne, O. Pochon, J.-F. Yaniche
IPN, Orsay, France

SRF bulk Nb cavities are often limited by quench due to anomalous losses (heating due normal defects or Field Emission). We continued R&D on Quench Detectors (QD) activity for locating quench in SRF cavities via 2nd sound in superfluid helium. We investigated 2 kinds of QD: Capacitive OST (COST) and Low Response time resistive Thermometers (LRT). A test stand operating in LHe (Temperature: T0) was used for the characterization of the QD by means of precise experimental simulation of SRF cavity quench (pulsed heat flux qP). For improving spatial resolution of QD, smaller COSTs were developed and tested. We investigated the dynamic response of QD as function of different parameters (heater size/geometry, T0, qP) and data are reported. Further, a 2nd Sound Resonator (SSR), with a pair of COSTs at its 2 extremities as 2nd Sound Generator (SSG) and Detector (SSD) respectively and housing also a low heat capacity heater (SSG) and a LRT (SSD) assembly was developed. The first experimental data obtained, with SSR operated in resonating mode or in a shock wave mode are presented. The results concerning locating of quenches in QWR and spoke cavities are discussed.

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MOPB024

SRF Cavity Breakdown Calculation Procedure Using FEA-Software

simulation, cathode, SRF, niobium

140

R.A. Kostin, A. Kanareykin
Euclid TechLabs, LLC, Solon, Ohio, USA
I.V. Gonin
Fermilab, Batavia, Illinois, USA
E.N. Zaplatin
FZJ, Jülich, Germany

SRF cavity thermal breakdown can be analyzed analytically using thermodynamics equation. This technique is suitable for simple geometries when surface magnetic field variation can be omitted. Thermal radiation effect which is crucial for SRF gun calculations is also hard to implement properly because of complicated geometry. All of these can be overcome by using multiphysics FEA-software. This paper shows the procedure of cavity thermal breakdown calculation in coupled multiphysics analysis with dependable parameters.

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MOPB027

Modifications of Superconducting Properties of Niobium Caused by Nitrogen Doping of Ultra-High Quality Factor Cavities

niobium, SRF, superconductivity, vacuum

144

A. Vostrikov, A. Grassellino, A. Romanenko
Fermilab, Batavia, Illinois, USA
L. Horyn, Y.K. Kim, A. Vostrikov
University of Chicago, Chicago, Illinois, USA
T. Murat
University of Wisconsin-Madison, Madison, USA

We have performed detailed studies using DC and AC magnetometry and electrical resistivity measurements of niobium samples prepared using different nitrogen doping recipes. We compare the results to the samples prepared by standard preparation techniques such as EP with and without additional 120C baking to get insight into driving factors of the lowered quench field in N-doped SRF cavities.

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MOPB028

Preservation of Very High Quality Factors of 1.3 GHz Nine Cell Cavities From Bare Vertical Test to Dressed Horizontal Test

cryomodule, factory, shielding, HOM

149

A. Grassellino, S. Aderhold, M. Checchin, A.C. Crawford, C.J. Grimm, A. Hocker, M. Martinello, O.S. Melnychuk, J.P. Ozelis, S. Posen, A.M. Rowe, D.A. Sergatskov, N. Solyak, R.P. Stanek, G. Wu
Fermilab, Batavia, Illinois, USA
D. Gonnella
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
J.M. Köszegi
HZB, Berlin, Germany
M. Liepe
Cornell University, Ithaca, New York, USA

In this contribution we will report quality factor evolution of several different nine cell N doped cavities with very high Q. The evolution of the quality factor will be reported from bare to dressed in vertical test to dressed in horizontal test with unity coupling to dressed in horizontal test and CM-like environment/configuration (with RF ancillaries). Cooling studies and optimal cooling regimes will be discussed for both vertical and horizontal tests and comparisons will be drawn also for different styles titanium vessels. Studies of sensitivities to magnetic field in final horizontal configuration have been performed by applying a field around the dressed cavity and varying the cooling; parameters required for a very good flux expulsion will be presented.

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MOPB030

Measurements of Thermal Impedance on Superconducting Radiofrequency Cavities

impedance, SRF, niobium, operation

154

P. Dhakal, G. Ciovati, G.R. Myneni
JLab, Newport News, Virginia, USA

Funding: This manuscript has been authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
The thermal impedance of niobium plays an important role in the stability of the superconducting radio frequency cavities used in particle accelerators. During the operation of SRF cavities, the RF power dissipated on the inner surface of the cavities and the heat transport to the helium bath depend on the thermal conductivity of niobium and the Kapitza conductance of the interface between the niobium and superfluid helium. Here, we present the results of measurements done on samples as well as on SRF cavities made of both ingot and fine-grain Nb to explore the effect of the surface preparation and crystal structure on the thermal impedance.

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MOPB033

LCLS-II SRF Cavity Processing Protocol Development and Baseline Cavity Performance Demonstration

cryomodule, SRF, linac, vacuum

159

M. Liepe, P. Bishop, H. Conklin, R.G. Eichhorn, F. Furuta, G.M. Ge, D. Gonnella, T. Gruber, D.L. Hall, G.H. Hoffstaetter, J.J. Kaufman, G. Kulina, J.T. Maniscalco, T.I. O'Connell, P. Quigley, D.M. Sabol, J. Sears, V. Veshcherevich
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
M. Checchin, A.C. Crawford, A. Grassellino, C.J. Grimm, A. Hocker, M. Martinello, O.S. Melnychuk, J.P. Ozelis, A. Romanenko, A.M. Rowe, D.A. Sergatskov, W.M. Soyars, R.P. Stanek, G. Wu
Fermilab, Batavia, Illinois, USA
E. Daly, G.K. Davis, M.A. Drury, J.F. Fischer, A.D. Palczewski, C.E. Reece
JLab, Newport News, Virginia, USA
M.C. Ross
SLAC, Menlo Park, California, USA

Funding: Work supported, in part, by the US DOE and the LCLS-II Project under U.S. DOE Contract No. DE-AC05-06OR23177 and DE-AC02-76SF00515.
The ”Linac Coherent Light Source-II” Project will construct a 4 GeV CW superconducting RF linac in the first kilometer of the existing SLAC linac tunnel. The baseline design calls for 280 1.3 GHz nine-cell cavities with an average intrinsic quality factor Q0 of 2.7·10¹⁰ at 2K and 16 MV/m accelerating gradient. The LCLS-II high Q0 cavity treatment protocol utilizes the reduction in BCS surface resistance by nitrogen doping of the RF surface layer, which was discovered originally at FNAL. Cornell University, FNAL, and TJNAF conducted a joint high Q0 R&D program with the goal of (a) exploring the robustness of the N-doping technique and establishing the LCLS-II cavity high Q0 processing protocol suitable for production use, and (b) demonstrating that this process can reliably achieve LCLS-II cavity specification in a production acceptance testing setting. In this paper we describe the LCLS-II cavity protocol and analyze combined cavity performance data from both vertical and horizontal testing at the three partner labs, which clearly shows that LCLS-II specifications were met, and thus demonstrates readiness for LCLS-II cavity production.

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MOPB035

Nature and Implication of Found Actual Particulates on the Inner Surface of Cavities in a Full-Scale Cryomodule Previously Operated With Beams

cryomodule, ion, vacuum, operation

164

R.L. Geng, J.F. Fischer, E.A. McEwen, O. Trofimova
JLab, Newport News, Virginia, USA

Field emission in an SRF cavity is often the result of small foreign particulates lodging on the cavity inner surface. To avoid these particulate field emitters, careful cleaning and handling of individual cavities and clean room assembly of cavity strings are common practice. Despite these elaborate processes, some particulates persist to stay on the final surface of a beam-ready cavity. Moreover, as will be shown in this contribution, new particulates accumulate after a cryomodule is placed in the accelerator tunnel. The nature of these accumulated particulates on the inner surface of a beam-accelerating cavity is largely unknown for two reasons: (1) lack of access to such surfaces; (2) lack of a workable procedure for investigation without destroying the cavity. In this contribution, we report the first study on found actual particulates on the inner surface of 5-cell CEBAF cavities in a full-scale cryomodule previously operated with beam. The nature of the studied particulates is presented. The implication of the findings will be discussed in view of reliable and efficient operation of CEBAF and future large-scale SRF accelerators.

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MOPB036

TOF-SIMS Study of Nitrogen Doping Niobium Samples

niobium, experiment, vacuum, ion

169

Z.Q. Yang, L. Lin, X.Y. Lu, W.W. Tan, D.Y. Yang, J. Zhao
PKU, Beijing, People's Republic of China

Nitrogen doping treatment with the subsequent electropolishing (EP) of the niobium superconducting cavity can significantly increase the cavity’s quality factor up to a factor of 3. The nitrogen doping experiment has been successfully repeated and demonstrated. But the mechanism of the nitrogen doping effect remains unclear. Nitrogen doping study on niobium samples was carried out in Peking University. The niobium samples were manual processed to avoid heat generation. The experiment condition is close to that of the Fermilab. After the nitrogen doping treatment, the samples were mildly electropolished with the thickness of 1.3μm, 1.9μm, 3.3μm, 4.2μm, 5.1μm, 5.9μm and 7.0μm. The time of flight secondary ion mass spectrometry (TOF-SIMS) measurements show that the samples directly after nitrogen doping have a much higher nitrogen concentration in the depth of about 90nm. When the EP removal is larger than 1.3μm, the samples’ impurity elements is remarkably reduced and their distribution is similar to each other. Also the measured results to some extent prove that EP removal can introduce H to the niobium surface.

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MOPB039

Analysis of BCS RF Loss Dependence on N-Doping Protocols

niobium, SRF, linac, operation

174

A.D. Palczewski, P. Dhakal, C.E. Reece
JLab, Newport News, Virginia, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177 with supplemental funding from the LCLS-II Project U.S. DOE Contract No. DE-AC02-76SF00515.
We present a study on two parallel-path SRF cavities (one large grain and one fine grain, 1.3 GHz) which seeks to explain the correlation between the amount of nitrogen on the inner surface of a “nitrogen doped” SRF cavity and the change in the temperature dependant (packaged into term BCS) RF losses. For each doping/EP, the cavities were tested at multiple temperatures (2.0 K to 1.5 K in 0.1 K steps) to create a Q0 vs. Eacc vs. T matrix which then could be used to extract temperature dependant and independent components. After each test, the cavities were thermally cycled to 120 K and then re-cooled and retested to assess if evidence of hydrogen migration might appear even at a small level. In addition, TD-5 was also tested at fixed low field (Q0 vs. T) to fit standard BCS theory. In parallel, SIMS data was taken on like-treated samples to correlate the amount of nitrogen within the RF surface to the change in the temperature dependant fitting parameter “A”.**
[**] H.Tian et al., contributed to SRF2015.

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MOPB040

Performance of Dressed Cavities for the Jefferson Laboratory LCLS-II Prototype Cryomodule - With Comparison to the Pre-Dressed Performance

HOM, cryomodule, hardware, linac

178

A.D. Palczewski, G.K. Davis
JLab, Newport News, Virginia, USA
F. Furuta, G.M. Ge, D. Gonnella, M. Liepe
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177 with supplemental funding from the LCLS-II Project U.S. DOE Contract No. DE-AC02-76SF00515.
Initial vertical RF test results and quench studies for six of the eight undressed 9 cell cavities slated for use in the Jefferson laboratory LCLS-II prototype cryomodule were presented at IPAC2015*. For the final string 2 more cavities AES029 and AES030 (work done at Cornell) are being processed and tested for qualification before helium vessel welding. In addition, AES034 (initial R&D treatment) is being reworked with the current production protocol after a surface reset to improve the overall performance. After final qualification all 8 cavities will be welded into helium vessels and equipped with HOM couplers. In this paper we will present the final undressed and dressed vertical RF data comparing the changes in the surface resistance before their installation in the cryomodule string.
*A.D. Palczewski et al. Quench Studies of Six High Temperature Nitrogen Doped 9 Cell Cavities for use in the LCLS-II Prototype Cryo-module at Jefferson Laboratory, Proc. IPAC2015, WEPWI019, 2015.

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MOPB041

Cryomodule Testing of Nitrogen-Doped Cavities

cryomodule, HOM, SRF, linac

182

D. Gonnella, B. Clasby, R.G. Eichhorn, B. Elmore, F. Furuta, G.M. Ge, D.L. Hall, Y. He, G.H. Hoffstaetter, J.J. Kaufman, P.N. Koufalis, M. Liepe, J.T. Maniscalco, T.I. O'Connell, P. Quigley, D.M. Sabol, E.N. Smith, V. Veshcherevich
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
A. Grassellino, C.J. Grimm, J.P. Holzbauer, O.S. Melnychuk, Y.M. Pischalnikov, A. Romanenko, W. Schappert, D.A. Sergatskov
Fermilab, Batavia, Illinois, USA
A.D. Palczewski, C.E. Reece
JLab, Newport News, Virginia, USA

Funding: DOE and the LCLS-II High Q Project
The Linac Coherent Light Source-II (LCLS-II) is a new FEL x-ray source that is planned to be constructed in the existing SLAC tunnel. In order to meet the required high Q0 specification of 2.7x10¹⁰ at 2 K and 16 MV/m, nitrogen-doping has been proposed as a preparation method for the SRF cavities in the linac. In order to test the feasibility of these goals, four nitrogen-doped cavities have been tested at Cornell in the Horizontal Test Cryomodule (HTC) in five separate tests. The first three tests consisted of cavities assembled in the HTC with high Q input coupler. The fourth test used the same cavity as the third but with the prototype high power LCLS-II coupler installed. Finally, the fifth test used a high power LCLS-II coupler, cavity tuner, and HOM antennas. Here we report on the results from these tests along with a systematic analysis of change in performance due to the various steps in preparing and assembling LCLS-II cavities for cryomodule operation. These results represent one of the final steps to demonstrate readiness for full prototype cryomodule assembly for LCLS-II.

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MOPB042

Fundamental Studies on Doped SRF Cavities

niobium, vacuum, simulation, SRF

187

D. Gonnella, T. Gruber, J.J. Kaufman, P.N. Koufalis, M. Liepe, J.T. Maniscalco, B. Yu
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: NSF
Recently, doping with nitrogen has been demonstrated to help SRF cavities reach significantly higher intrinsic quality factors than with standard procedures. However, the quench fields of these cavities have also been shown to be frequently reduced. Here we report on fundamental studies of doped cavities, investigating the source of reduced quench field and exploring alternative dopants. We have focused on studying the quench of nitrogen-doped cavities with temperature mapping and measurements of the flux penetration field using pulsed power to investigate maximum fields in nitrogen doped cavities. We also report on studies of cavities doped with other gases such as helium. These studies have enabled us to shed light on the mechanisms behind the higher Q and lower quench fields that have been observed in cavities doped with impurities.

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MOPB045

Study of Slip and Deformation in High Purity Single Crystal Nb for Accelerator Cavities

experiment, niobium, SRF, factory

191

D. Kang, D.C. Baars, T.R. Bieler
Michigan State University, East Lansing, Michigan, USA
C. Compton
FRIB, East Lansing, Michigan, USA
A. Mapar, F. Pourboghrat
MSU, East Lansing, Michigan, USA

Funding: This work was supported by the U.S. Department of Energy, Office of High Energy Physics, through Grant No. DE-FG02-09ER41638.
High purity Nb has been used to build accelerator cavities over the past couple decades, and there is a growing interest in using ingot Nb as an alternative to the fine grain sheets. Plastic deformation governed by slip is complicated in body-centered cubic metals like Nb. Besides the crystal orientation with respect to the applied stress (Schmid effect), slip is also affected by other factors including temperature, strain rate, strain history, and non-Schmid effects such as twinning/anti-twinning asymmetry and non-glide shear stresses. A clear understanding of slip is an essential step towards modeling the deep drawing of large grain ingot slices, hence predicting the final microstructure/performance of cavities. Two groups of single crystals, with and without a prior heat treatment, were deformed to 40% engineering strain in uniaxial tension. Differences in flow stresses and active slip systems between the two groups were observed, likely due to the removal of preexisting dislocations. Crystal plasticity modeling of the stress-strain behavior suggests that the non-Schmid effect is small in Nb, and that the deep drawing process might be approximated with a Schmid model.

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MOPB047

Secondary Electron Yield of Electron Beam Welded Areas of SRF Cavities

electron, gun, niobium, vacuum

196

M. Basovic, S. Popović, M. Tomovic, L. Vušković
ODU, Norfolk, Virginia, USA
F. Čučkov, A. Samolov
University of Massachusetts Boston, Boston, Massachusetts, USA

Secondary Electron Emission (SEE) is a phenomenon that contributes to the total electron activity inside the Superconducting Radiofrequency (SRF) cavities during the accelerator operation. SEE is highly dependent on the state of the surface. During electron beam welding process, significant amount of heat is introduced into the material causing the microstructure change of Niobium (Nb). Currently, all simulation codes for field emission and multipacting are treating the inside of the cavity as a uniform, homogeneous surface. Due to its complex shape and fabricating procedure, and the sensitivity of the SEE on the surface state, it would be interesting to see if the Secondary Electron Yield (SEY) parameters vary in the surface area on and near the equator weld. For that purpose, we have developed experimental setup that can measure accurately the energy distribution of the SEY of coupon-like like samples. To test the influence of the weld area on the SEY of Nb, dedicated samples are made from a welded plate using electron beam welding parameters common for cavity fabrication. SEY data matrix of those samples will be presented.

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MOPB049

High Flux Three Dimensional Heat Transport in Superfluid Helium and Its Application to a Trilateration Algorithm for Quench Localization With OSTs

detector, experiment, niobium, software

201

T. Junginger
TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada
P. Horn
TU Dresden, Dresden, Germany
T. Koettig, K.C. Liao, A. Macpherson
CERN, Geneva, Switzerland
B.J. Peters
KIT, Karlsruhe, Germany

Oscillating superleak transducers of second sound can be used to localize quench spots on superconducting cavities by trilateration. However propagation speeds faster than the velocity of second sound are usually observed imped- ing the localization. Dedicated experiments show that the fast propagation cannot be correlated to the dependence of the velocity on the heat flux density, but rather to boiling effects in the vicinity of the hot spot. 17 OSTs were used to detect quenches on a 704MHz one-cell elliptical cavity. Two different algorithms for quench localization have been tested and implemented in a computer program enabling direct crosschecks. The new algorithm gives more consis- tent results for different OST signals analyzed for the same quench spot.

Poster MOPB049 [0.901 MB]

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MOPB051

Muon Spin Rotation on Treated Nb Samples in Parallel Field Geometry

SRF, polarization, detector, niobium

210

S. Gheidi
UBC, Vancouver, B.C., Canada
T.J. Buck, T. Junginger, R.E. Laxdal, G. Morris
TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada
M. Dehn
TUM/Physik, Garching bei München, Germany
R. Kiefl
UBC & TRIUMF, Vancouver, British Columbia, Canada

MuSR is a powerful tool to probe local magnetism and hence can be used to diagnose the entry of magnetic flux in superconductors. First measurements on SRF samples were done with an external DC field applied perpendicular to the sample1 (transverse geometry) with the muons applied to the sample face. Here the results are strongly impacted by demagnetization, pinning strength and edge effects. A new spectrometer has been developed to allow sample testing with a field varying from 0 to 300mT applied along the sample face (parallel geometry) analogous to rf fields in SRF resonators. The geometry is characterized by a small demagnetization factor reducing the impact of pinning and edge effects on field of first flux entry. The beamline installation and first results comparing transverse and parallel results will be presented.
1 Grassellino et al. Muon spin rotation studies of niobium for superconducting rf applications.
Phys. Rev. ST Accel. Beams, 16:062002, Jun 2013.

Poster MOPB051 [0.719 MB]

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MOPB052

Determination of Bulk and Surface Superconducting Properties of N2-Doped Cold Worked, Heat Treated and Electro-polished SRF Grade Niobium

SRF, superconductivity, niobium, operation

214

S. Chetri, D.C. Larbalestier, Z-H. Sung
ASC, Tallahassee, Florida, USA
P. Dhakal
JLab, Newport News, Virginia, USA
P.J. Lee
NHMFL, Tallahassee, Florida, USA

Funding: Support for this work at FSU was from US DOE Award# DE-SC0009960 and the State of Florida Additional support for the National High Magnetic Field Laboratory facilities is from the NSF: NSF-DMR-1157490
Nitrogen-doped cavities show significant performance improvement in the medium accelerating field regime due to a lowered RF surface resistivity. However, the mechanism of enhancement has not been clearly explained. Our experiments explore how N2-doping influences Nb bulk and surface superconducting properties, and compare the N2-doped properties with those obtained previously with conventionally treated samples. High purity Nb-rod was mechanically deformed and post treated based on a typical SRF cavity treatment recipe. The onset of flux penetration at Hc1, and the upper and the surface critical fields, Hc2 and Hc3, were characterized by magnetic hysteresis and AC susceptibility techniques. The surface depth profile responsible for superconductivity was examined by changing AC amplitude in AC susceptibility, and the microstructure was directly observed with EBSD-OIM. We are also investigating surface chemistry for detailed composition using XPS. We have found that N2-doping at 800 °C significantly reduces the Hc3/Hc2 ratio towards the ideal value of ~1.7, and conclude that AC susceptibility is capable of following changes to the surface properties induced by N2-doping.

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MOPB055

Characterization of Nitrogen Doping Recipes for the Nb SRF Cavities

niobium, SRF, cryogenics, electron

223

Y. Trenikhina, A. Grassellino, O.S. Melnychuk, A. Romanenko
Fermilab, Batavia, Illinois, USA

For the future development of the nitrogen doping technology, it’s vital to understand the mechanisms behind the performance benefits of N-doped cavities as well as the performance limitations, such as quench field. Following various doping recipes, cavity cutouts and flat niobium samples have been evaluated with XRD, SEM, SIMS and TEM in order to relate structural and compositional changes in the niobium near-surface to SRF performance. Annealing of Nb cavities with nitrogen for various durations and at various temperatures lead to a layer containing inclusions of non-superconducting Nb nitride phases, followed by unreacted Nb with an elevated N-interstitials concentration. We found that EP of the N-treated cavities removes the unwanted niobium nitride phases, confirming that performance benefits are originating from the elevated concentration of N interstitials. The role of low temperature Nb hydride precipitants in the performance limitation of N-doped cavities was evaluated by TEM temperature dependent studies. Finally, extended characterization of the original cavity cutouts from the N-doped RF tested cavity sheds some light on quenching mechanisms.

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MOPB057

Crystal Plasticity Modeling of Single Crystal Nb

experiment, niobium, SRF, software

228

A. Mapar, F. Pourboghrat
MSU, East Lansing, Michigan, USA
T.R. Bieler, D. Kang
Michigan State University, East Lansing, Michigan, USA
C. Compton
FRIB, East Lansing, Michigan, USA

Funding: This work was supported by the U.S. Department of Energy, Office of High Energy Physics, through Grant No. DE-FG02-09ER41638.
Deformation behavior of niobium (Nb) is not thoroughly studied, although it is widely used in manufacturing superconducting cavities. This deficiency of knowledge limits the predictibality in raw material properties for fine grain sheets, which are less anisotropic and easier to deform uniformly than large grain sheets. Studies on modeling and simulation of deformation of Nb are also limited. Therefore design of a new manufacturing procedure becomes a costly process, because models predicting the deformation of Nb are not accurate. A polycrystal is an aggregate of single crystals. Tensile tests were performed on single crystal with different orientations, to study the deformation behavior of Nb. A number of crystal plasticity models were developed, calibrated and finally used to predict the deformation of single crystal tensile samples. This study compares the predictions of these models. This provides a foundation for physically realistic polycrystal deformation models.

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MOPB059

Field Emission Investigation of Centrifugal-Barrel-Polished Nb Samples

site, vacuum, survey, electron

237

S. Lagotzky, G. Müller
Bergische Universität Wuppertal, Wuppertal, Germany
A. Navitski
DESY, Hamburg, Germany
A.L. Prudnikava, Y. Tamashevich
University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany

Funding: This work was funded by BMBF project 05H12PX6.
Actual and future SRF-accelerators require high accelerating gradient Eacc and quality factor Q0, which are often limited by enhanced field emission (EFE)* caused by surface roughness or particulates**. Various expensive surface preparation techniques (e.g. BCP, EP, HPR etc.) have been developed to obtain the required surface quality and remove the emitters. Recently, centrifugal barrel polishing (CBP) has been reconsidered to obtain a comparable surface roughness as EP with less effort***. We have started to investigate Nb samples, which were prepared as coupons in a single cell 1.3 GHz cavity by an optimized five step CBP process with a final dry ice cleaning. EFE maps showed the first emitter (1 nA) at 60 MV/m, and 32 emitters at 110 MV/m. SEM/EDX analysis of the emitting sites revealed many Al2O3 inclusions with sharp edges. Therefore, subsequent BCP (~20 μm removal) was applied to the sample. Surface analysis as well as EFE characterization of CBP treated Nb coupons with/without BCP step will be presented.
*D. Reschke et al., THPP021, LINAC14.
**A. Navitski et al., PRSTAB 16, 112001 (2013).
***C.A. Cooper, L.D. Cooley, Supercond. Sci. Technol. 26, 015011 (2013).

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MOPB060

A GPU Based 3D Particle Tracking Code for Multipacting Simulation

GPU, simulation, gun, SRF

242

T. Xin
Stony Brook University, Stony Brook, USA
S.A. Belomestnykh, I. Ben-Zvi, J.C. Brutus, V. Litvinenko, I. Pinayev, J. Skaritka, Q. Wu, B. P. Xiao
BNL, Upton, Long Island, New York, USA

Funding: This work was carried out at Brookhaven Science Associates, LLC under Contracts No. DE-AC02-98CH10886 and at Stony Brook University under grant DE-SC0005713 with the U.S. DOE.
A new GPU based 3D electron tracking code is developed at BNL and benchmarked with both popular existing parallel tracking code and experimental results. The code takes advantage of massive concurrency of GPU cards to track electrons under RF field in 3D Tetrahedron meshed structures. Approximately ten times of FLOPS can be achieved by utilizing GPUs compare to CPUs with same level of power consumption. Different boundary materials can be specified and the 3D EM field can be imported from the result of Omega3P calculation. CUDA_OpenGL interop was implemented so that the emerging of multipactors can be monitored in real time while the simulation is undergoing. Code also has GPU farm version that can run on multiple GPUs to further increase the turnover of multipacting simulation.

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MOPB061

Suppression of Upstream Field Emission in RF Accelerators

electron, cryomodule, SRF, site

246

F. Marhauser, S.V. Benson, D. Douglas
JLab, Newport News, Virginia, USA
L.J.P. Ament
ASML US Inc., Wilton, CT, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177
So-called electron loading is the primary cause for cavity performance limitations in modern RF accelerating cavities. In superconducting RF cavities in particular, the onset of parasitic electron effects may start at field levels as low as a few MV/m. Electron loading can be attributed to mainly three phenomena: field emission, multiple impact electron amplification, and RF electrical breakdown. Field emission has been a persistent issue despite advances in SRF technology, whereas RF electrical breakdown and multipacting can be controlled by appropriate cavity design choices. Field emission becomes a major concern when the electrons emitted are captured by the accelerating RF field and directed along the beam axis through a series of cavities or even entire cryomodules. Consequently, electrons can accumulate energy comparable to that of the main beam over similar distances. This can represent a considerable dark current, which can travel downstream or upstream depending on the field-emitting site of origin. In this paper, a method is presented that can significantly suppress the upstream field emission by design.

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MOPB063

Design of the Superconducting LINAC for SARAF

cryomodule, solenoid, cryogenics, linac

250

C. Madec
CEA, Gif-sur-Yvette, France
N. Bazin, L. Boudjaoui, R. Cubizolles, G. Ferrand, P. Hardy, C. Pes, N. Sellami
CEA/IRFU, Gif-sur-Yvette, France
P. Bertrand
GANIL, Caen, France
P. Brédy, B. Gastineau, N. Pichoff
CEA/DSM/IRFU, France

CEA is committed to delivering a Medium Energy Beam Transfer line and a superconducting linac (SCL) for SARAF accelerator in order to accelerate 5mA beam of either protons from 1.3 MeV to 35 MeV or deuterons from 2.6 MeV to 40.1 MeV. The SCL consists 4 cryomodules equipped with warm diagnostics. The first two identical cryomodules host 6 half-wave resonator (HWR) low beta cavities (β = 0.091), 176 MHz. As the last two identical welcome 7 HWR high-beta cavities (β = 0.181), 176 MHz. The beam is focused through the superconducting solenoids located between cavities housing steering coils. A Beam Position Monitor is placed upstream each solenoid. A diagnostic box containing a beam profiler, a bunch length monitor and a vacuum pump will be inserted between 2 consecutive cryomodules. The HWR cavities, the solenoid package and the cryomodules are being designed. These studies will be presented in this poster.

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MOPB065

Recent Measurements on the SC 325 MHz CH-Cavity

ion, linac, heavy-ion, controls

255

M. Busch, M. Amberg, M. Basten, F.D. Dziuba, H. Podlech, U. Ratzinger
IAP, Frankfurt am Main, Germany
M. Amberg
HIM, Mainz, Germany

Funding: Work supported by GSI, BMBF Contr. No. 06FY7102
At the Institute for Applied Physics (IAP), Frankfurt University, a sc 325 MHz CH-Cavity has been designed and fabricated. Successful tests at 4 K and 2 K with gradients up to 14.1 MV/m have been performed. The cavity is destined for a 11.4 AMeV 10 mA ion beam at the GSI UNILAC, Darmstadt. Consisting of 7 gaps and a geometrical beta of 0.16 this resonator is designed to provide a gradient of 5 MV/m. Novel features of this structure comprise a compact design, low electric peak fields, improved surface processing possibilities and power coupling. In addition a tuner system based on mechanically deformable bellow tuners attached inside the cavity and driven either by a stepping motor or a piezo actuator will keep the cavity on resonance. This contribution reports about the latest measurements on the cavity with the recently attached helium vessel and a renewed surface processing.

Poster MOPB065 [1.270 MB]

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MOPB066

R&D Status of the New Superconducting CW Heavy Ion LINAC@GSI

linac, simulation, ion, operation

258

M. Basten, M. Busch, F.D. Dziuba, D. Mäder, H. Podlech, M. Schwarz
IAP, Frankfurt am Main, Germany
M. Amberg, K. Aulenbacher, M. Miski-Oglu
HIM, Mainz, Germany
W.A. Barth, V. Gettmann, M. Heilmann, S. Mickat
GSI, Darmstadt, Germany

To keep the ambitious Super Heavy Element (SHE) physics program at GSI competitive a superconducting (sc) continuous wave (cw) high intensity heavy ion LINAC is currently under progress as a multi-stage R&D program of GSI, HIM and IAP*. The baseline linac design consists of a high performance ion source, a new low energy beam transport line, an (cw) upgraded High Charge State Injector (HLI), and a matching line (1.4 MeV/u) which is followed by the new sc-DTL LINAC for post acceleration up to 7.3 MeV/u. In the present design the new cw-heavy ion LINAC comprises constant-beta sc Crossbar-H-mode (CH) cavities operated at 217 MHz. The advantages of the proposed beam dynamics concept applying a constant beta profile are easy manufacturing with minimized costs as well as a straightforward energy variation**. An important milestone will be the full performance test of the first CH cavity (Demonstrator), in a horizontal cryo module with beam. An advanced demonstrator setup comprising a string of cavities and focussing elements is proposed to build from 10 short CH-cavities with 8 gaps. The corresponding simulations and technical layout of the new cw heavy ion LINAC will be presented.
* W. Barth et al., Further R&D for a new Superconducting cw Heavy Ion LINAC@GSI, IPAC2014, THPME004
**M. Schwarz et al., Beam Dynamics for the sc cw Heavy Ion Linac at GSI, IPAC2015, THPF025

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MOPB067

Steps Towards Superconducting CW-LINAC for Heavy Ions at GSI

linac, ion, heavy-ion, quadrupole

262

M. Miski-Oglu, M. Amberg, K. Aulenbacher, V. Gettmann
HIM, Mainz, Germany
W.A. Barth, M. Heilmann, S. Mickat, S. Yaramyshev
GSI, Darmstadt, Germany
M. Basten, D. Bänsch, F.D. Dziuba, H. Podlech, U. Ratzinger
IAP, Frankfurt am Main, Germany

Providing heavy ion beams for the ambitious experiment program at GSI, the Universal Linear Accelerator (UNILAC) serves as a powerful high duty factor (25%) accelerator. Beam time availability for SHE-research will be decreased due to the limitation of the UNILAC providing a proper beam for FAIR simultaneously. To keep the GSI-SHE program competitive on a high level, a standalone sc cw-LINAC in combination with the upgraded GSI High Charge State injector is planned to build. In preparation for this the first linac section (financed by HIM and partly by HGF-ARD-initiative) will be tested in 2015 as a demonstrator. After successful testing the construction of an extended cryomodule comprising two further, but shorter CH cavities is foreseen to test until end of 2017. In this contribution the measurement of the beam parameters at the entrance of CW-Demonstartor, the preliminary simulation of beam dynamics for the first stage of advanced demonstrator will be presented. As a final R&D step towards an entire linac an advanced cryo module comprising up to five CH cavities is envisaged for 2019 serving for first user experiments at the coulomb barrier.

Poster MOPB067 [2.807 MB]

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MOPB068

Pulsed SC Ion Linac as an Injector to Booster of Electron Ion Collider

ion, linac, operation, proton

265

P.N. Ostroumov, Z.A. Conway, B. Mustapha
ANL, Argonne, USA
B. Erdelyi
Northern Illinois University, DeKalb, Illinois, USA

Funding: This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics, under contract number DE-AC02-06CH11357.
The electron-ion collider (EIC) being developed at JLAB requires a new ion accelerator complex (IAC). The IAC includes a new linac and a booster accelerator facility. The new facility is required for the acceleration of ions from protons to lead for colliding beam experiments with electrons in the EIC storage ring. Originally, we proposed a pulsed linac which is based upon a NC front end, < 5 MeV/u, with a SC section for energies > 5 MeV/u and capable of providing 285 MeV protons and ~100 MeV/u lead ions for injection into the IAC booster. A recent cost optimization study of the IAC suggested that lower injection energy into the booster may reduce the overall project cost with ~120 MeV protons and ~40 MeV/u lead ions. Stronger space charge effects in the booster caused by lower injection energy will be mitigated by the booster design. In this paper we discuss both linac options.

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MOPB069

Superconducting Linac Upgrade Plan for the Second Target Station Project at SNS

cryomodule, linac, HOM, accelerating-gradient

268

S.-H. Kim, M. Doleans, J. Galambos, M.P. Howell
ORNL, Oak Ridge, Tennessee, USA
J.D. Mammosser
ORNL RAD, Oak Ridge, Tennessee, USA

Funding: This work was supported by SNS through UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. DOE.
The beam power of the Linac for the Second Target Station (STS) at the Spallation Neutron Source (SNS) will be doubled to 2.8 MW. For the energy upgrade seven additional cryomodules will be installed in the reserved space at the end of the linac tunnel to produce the linac output energy of 1.3 GeV. The cryomodules for STS will have some changes that do not require changes of overall layout based on the lessons learned from operational experience over the last 10 years and the high beta spare cryomodule developed in house. The average macro-pulse beam current for the STS will be 38 mA that is about 40 % increase from that for the present 1.4 MW operation. Plans for the existing cryomodules to support higher beam current for the STS is also presented in this paper.

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MOPB070

Preliminary Conceptual Design of the CEPC SRF System

HOM, SRF, collider, booster

272

J.Y. Zhai, J. Gao, T.M. Huang, Z.C. Liu, Z.H. Mi, P. Sha, Y. Sun, H.J. Zheng
IHEP, Beijing, People's Republic of China
S.A. Belomestnykh
BNL, Upton, Long Island, New York, USA
S.A. Belomestnykh
Stony Brook University, Stony Brook, USA
C. Pagani
INFN/LASA, Segrate (MI), Italy
C. Pagani
Università degli Studi di Milano & INFN, Segrate, Italy

CEPC is a circular electron positron collider operating at 240 GeV center-of-mass energy as a Higgs factory, recently proposed by the Chinese high energy physics community. The CEPC study group, together with the FCC and ILC community, will contribute to the development of future high energy colliders and experiments which will ensure that the elementary particle physics remain a vibrant and exciting field of fundamental investigation for decades to come. Superconducting RF (SRF) system is one of the most important technical systems of CEPC and is a key to achieving its design energy and luminosity. It will dominate, with the associated RF power source and cryogenic system, the overall machine cost, efficiency and performance. The CEPC SRF system will be one of the largest and most powerful SRF accelerator installations in the world. The preliminary conceptual design of the CEPC SRF system is summarized in this paper, including the machine layout, key parameter choices and some critical issues such as HOM damping, emphasizing the new technology requirement and R&D focuses.

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MOPB071

Technology Readiness Levels Applied to Current SRF Accelerator Technology for ADS

SRF, cryomodule, proton, TRIUMF

276

R. Edinger
PAVAC, Richmond, B.C., Canada
R.E. Laxdal, L. Yang
TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada

Accelerator Driven Systems (ADS) are comprised of high power accelerators supplying a proton beam to a reactor vessel. The reactor vessel could contain fuels such as used uranium nuclear fuels or Thorium. The proton beam will be used to produce Neutrons by spallation in the reactor vessel. Technology readiness levels (TRL’s) can be used to chart technology status with respect to end goal and as such can be used to outline a road map to complete an ADS system. TRL1 defines basic principles observed and reported, whereas TRL9 is defined as system ready for full scale deployment. SRF technology when applied to ADS reflects a mix of TRL levels since worldwide many SRF Accelerators are in operation. The paper will identify the building blocks of an ADS accelerator and analyze each for technical readiness for industrial scale deployment. The integrated ADS structure is far more complex than the individual systems, but the use of proven sub-systems allows to build SRF accelerators that could deliver the beam required. An analysis of the technical readiness of SRF technology for ADS will be presented.

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MOPB072

Characterization of Surface Defects on EXFEL Series and ILC-Higrade Cavities

niobium, SRF, laser, radiation

281

A. Navitski, E. Elsen, V. Myronenko, J. Schaffran, O. Turkot
DESY, Hamburg, Germany
Y. Tamashevich
University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany

Funding: BMBF project 05H12GU9, Alexander von Humboldt Foundation, CRISP (No. 283745) and ”Construction of New Infrastructures-Preparatory Phase” ILC-HiGrade (No. 206711) of the EU 7th FP7/2007-2013 Programme.
Inspection of the inner cavity surface by an optical system is an inexpensive and useful means for surface control and identification of critical or suspicious features. Optical inspection of around 100 EXFEL series and ILC-HiGrade cavities has been performed recently using the high-resolution OBACHT system. It is a semi-automated tool based on the Kyoto camera. To gain information about the 3D topography of surface features or defects, a replica technique has been applied additionally. This is a non-destructive surface-study method reaching resolution down to 1 μm by imprinting the details of the surface onto a hardened rubber. The footprint is subsequently investigated with a microscope or profilometer. Based on these studies, several defects on the surface have been found and classified. Most of the cavity failures leading e.g. to field limitations below 20 MV/m have been identified and corresponding feedback given to the production cycle. Typical surface features and defects as well as their influence on the cavity performance will be presented and discussed.

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MOPB073

Surface Analyses and Optimization of Centrifugal Barrel Polishing of Nb Cavities

niobium, SRF, laser, embedded

286

A. Navitski, E. Elsen, B. Foster
DESY, Hamburg, Germany
B. Foster, A.L. Prudnikava, Y. Tamashevich
University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany

Funding: BMBF project 05H12GU9, Alexander von Humboldt Foundation, and CRISP (No. 283745).
Centrifugal barrel polishing (CBP) is an acid-free surface-polishing technique based on abrasive media. It considerably reduces the usage of chemicals in the preparation of Nb cavities, typically leaving only a final light electropolishing (EP) and achieves considerably smaller roughness than in chemical treatments alone. CBP addresses in particular the removal of pits, welding spatters, deep scratches, and foreign material inclusions that occasionally occur in the production process. A mirror-smooth surface without chemical contamination is also an important enabling step for thin films. Recent results indicate, however, the need of further optimizations, mainly to reduce the surface damaged layer as well as the pollution by the polishing media. A dedicated study of the CBP process using a “coupon” cavity facilitates better polishing characterisation and optimisation by direct measurements of the roughness, removal rate, and removal profile as well as the amount of contamination left behind and determination of a best combination of the CBP and chemical polishing. Results of the coupon-studies and perspectives of the optimizations will be presented and discussed.

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MOPB074

CERN’s Bulk Niobium High Gradient SRF Programme: Developments and Recent Cold Test Results

niobium, cathode, radiation, SRF

291

A. Macpherson, K.G. Hernández-Chahín, C. Jarrige, P. Maesen, F. Pillon, K.M. Schirm, R. Torres-Sanchez, N. Valverde Alonso
CERN, Geneva, Switzerland
K.G. Hernández-Chahín
DCI-UG, León, Mexico

Recent results from the bulk niobium high-gradient cavity development program at CERN are presented, with particular focus on test results for the 704 MHz bulk niobium 5-cell elliptical cavity prototypes produced for the Superconducting Proton Linac (SPL) project. Successive cold tests of bare cavities have been used to refine the cavity preparation and testing process, with all steps done in-house at CERN. Current performance results are discussed with reference to observables such as ambient magnetic field, field emission levels, and quenches.

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MOPB075

Experiences on Retreatment of EU-XFEL Series Cavities at DESY

controls, status, feedback, linac

296

A. Matheisen, N. Krupka, S. Saegebarth, P. Schilling, N. Steinhau-Kühl, B. van der Horst
DESY, Hamburg, Germany

For the European XFEL (EU-XFEL), two industrial companies are responsible for the manufacture and surface preparation of the eight hundred superconducting cavities. The companies had to strictly follow the XFEL specification and document all production and preparation steps. No performance guaranties were required. Each cavity delivered by industry to DESY is tested in a vertical test at 2K. Resonators not reaching the performances defined for application at the EU-XFEL linear accelerator modules or showing leakage during cold RF tests have undergone a subsequent retreatment at DESY. Nearly 20% of the cavity production required retreatment, most of them by an additional high pressure rinsing. Some cavities received additional chemical treatment by BCP flash after the initial HPR did not cure the problem. The analysis of retreatments and quality control data available from the retreatment sequences and the workflow of retreatment will be presented.

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MOPB076

Horizontal RF Test of a Fully Equipped 3.9 GHz Cavity for the European XFEL in the DESY AMTF

HOM, operation, cryomodule, controls

301

C.G. Maiano, C. Albrecht, R. Bospflug, J. Branlard, L. Butkowski, T. Delfs, J. Eschke, A. Gössel, F. Hoffmann, M. Hüning, K. Jensch, R. Jonas, R. Klos, D. Kostin, W. Maschmann, A. Matheisen, U. Mavrič, W.-D. Möller, C. Müller, K. Mueller, B. Petersen, P. Pierini, J. Rothenburg, O. Sawlanski, M. Schmökel, A.A. Sulimov, E. Vogel
DESY, Hamburg, Germany
A. Bosotti, M. Moretti, R. Paparella, P. Pierini, D. Sertore
INFN/LASA, Segrate (MI), Italy
E.R. Harms
Fermilab, Batavia, Illinois, USA
C.R. Montiel
ANL, Argonne, Illinois, USA
S. Pivovarov
BINP SB RAS, Novosibirsk, Russia

In order to validate the cavity package concept before the module preparation for the European XFEL Injector, one 3.9 GHz cavity, complete with magnetic shielding, power coupler and frequency tuner was tested in a specially designed single cavity cryomodule in one of the caves of the DESY Accelerator Module Test Facility (AMTF). The cavity was tested in high power pulsed operation up to the quench limit of 24 MV/m, above the vertical test qualifications and all subsystems under test (coupler, tuner, waveguide tuners, LLRF system) were qualified to design performances.

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MOPB077

Vertical Tests of XFEL 3rd Harmonic Cavities

vacuum, HOM, operation, instrumentation

306

D. Sertore, M. Bertucci, A. Bosotti, J.F. Chen, C.G. Maiano, P. Michelato, L. Monaco, M. Moretti, R. Paparella, P. Pierini
INFN/LASA, Segrate (MI), Italy
A. Matheisen, M. Schmökel
DESY, Hamburg, Germany
C. Pagani
Università degli Studi di Milano & INFN, Segrate, Italy

The 10 cavities of the EXFEL 3rd Harmonic Cryomodule have been tested and qualified, before integration in the He-tank, in our upgraded Vertical Test stand. In this paper, we report the measured RF performance of these cavities together with the main features of the test facility.

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MOPB078

Mode Sensitivity Analysis of 704.4 MHz Superconducting RF Cavities

HOM, operation, linac, dipole

311

K. Papke, F. Gerigk, S. Horvath-Mikulas, S. Papadopoulos, E. Pilicer, F. Pillon
CERN, Geneva, Switzerland
U. van Rienen
Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany

Due to the large variety of beam patterns considered for the superconducting proton linac (SPL) at CERN it is likely that the frequencies of some HOMs are close to machine lines during operation. Hence, in the interest of developing a method to shift HOM frequencies away from machine lines, we study the influence of cavity detuning and re-tuning (e.g. by Lorentz forces, field flatness tuning, frequency tuning during operation) on HOMs. The sensitivity of HOMs with respect to the fundamental mode was studied for a mono-cell and for 5-cell high-beta SPL cavities operating at 704.4 MHz. First, the variation of the HOMs during the flat-field tuning was measured. In this process, several detuning and re-tuning cycles were made to estimate the range of possible HOM frequency shifts. Secondly the effect of the frequency tuner on the HOMs is presented and finally the frequency shifts of all modes due to the cool down.

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MOPB079

Analysis of the Test Rate for European XFEL Series Cavities

vacuum, database, site, status

316

J. Schaffran, S. Aderhold, D. Reschke, L. Steder, N. Walker
DESY, Hamburg, Germany
L. Monaco
INFN/LASA, Segrate (MI), Italy

The main part of the superconducting European XFEL linear accelerator consists of 100 accelerator modules each containing eight RF-cavities. Before the installation to a module, all of these cavities will be tested at cryogenic temperatures in a vertical cryostat in the accelerator module test facility (AMTF) at DESY. This paper discusses the average vertical test rate at the present status. It should be 1 in the ideal case, but actually it’s observed to be approximately 1.5. Classification and analysis concerning the reasons for this deviation are given as well as suggestions for a reduction of the test rate for future production cycles.

Poster MOPB079 [0.632 MB]

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MOPB080

Update and Status of Test Results of the XFEL Series Accelerator Modules

cryomodule, radiation, linac, status

319

M. Wiencek, K. Kasprzak, A. Zwozniak
IFJ-PAN, Kraków, Poland
D. Kostin, D. Reschke, N. Walker
DESY, Hamburg, Germany

The European X-ray Free Electron Laser is under construction at DESY, Hamburg. During preparation for tunnel installation 100 Cryomodules are tested in a dedicated facility on the DESY campus. Up to now around 50 cryomodules have been measured at 2K. This paper describes the current status of the measurements, especially single cavity limitations. In addition we present a comparison between the vertical test results of the individual cavities and the corresponding performance measurements of the cavities once assembled into the accelerator string inside the cryomodule.

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MOPB083

Cooling Front Measurement of a 9-Cell Cavity via the Multi-Cell Temperature-Mapping System at Cornell University

SRF, experiment, electronics, linac

324

G.M. Ge, R.G. Eichhorn, F. Furuta
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Cooling speed significantly affects flux trapping of a SRF cavity, which will determine the residual resistance and the quality factor of the cavity. We measured the temperature distribution of a 9-cell cavity at different cooling speeds by the multi-cell T-map system of Cornell University. This paper proposed a method to evaluate the formation of a normal conducting island at different cooling speed. The fast cool-down and slow cool-down has been compared. We conclude that the slow cool-down freezes less normal conducting islands.

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MOPB084

Performance of Nitrogen-Doped 9-Cell SRF Cavities in Vertical Tests at Cornell University

SRF, superconducting-RF, linac, HOM

328

G.M. Ge, R.G. Eichhorn, B. Elmore, F. Furuta, D. Gonnella, T. Gruber, G.H. Hoffstaetter, J.J. Kaufman, M. Liepe, T.I. O'Connell, J. Sears, E.N. Smith
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Cornell University treated five LCLS-II 9-cell cavities by nitrogen-doping recipe. In this paper, we reported the performance of these 9-cell cavities. In the treatments, the nitrogen recipes are slightly different. The cavities have been firstly doped under high nitrogen pressure; after the vertical tests some of the cavities has been reset the surface and re-doped under light nitrogen pressure. The detail of the cavity preparation and test results will be shown. The comparison of the different recipes will be discussed.

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MOPB085

Efforts of the Improvement of Cavity Q-Value by Plasma Cleaning Technology: Plan and Results From Cornell University

plasma, experiment, SRF, ECR

333

G.M. Ge, F. Furuta, G.H. Hoffstaetter, M. Liepe, J. Sears, V. Veshcherevich
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

We reported the plasma works at Cornell University. The plasma has been generated for 1) surface cleaning to reduce field emission; 2) the cavity quality factor improvement. The experiment design, including RF design, the gas type and pressure selection, the external DC magnetic field calculation, had been discussed. The plasma experiment set-up by using a 1.3GHz single-cell cavity is shown. Argon and helium plasma was successfully ignited in the cavity; the results of the plasma processing will be displayed.

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MOPB086

Update and Status of Vertical Test Results of the European XFEL Series Cavities

status, linac, cryomodule, niobium

337

N. Walker, D. Reschke, J. Schaffran, L. Steder
DESY, Hamburg, Germany
L. Monaco
INFN/LASA, Segrate (MI), Italy
M. Wiencek
IFJ-PAN, Kraków, Poland

The series production by two industrial vendors of the 800 1.3-GHz superconducting cavities for the European XFEL has been on-going since the beginning of 2013 and will conclude towards the end of this year. As of publication some 740 cavities (~93%) have been produced at an average rate of 6 cavities per week. As part of the acceptance testing, all cavities have undergone at least one vertical RF test at 2K at the AMTF facility at DESY. The acceptance criterion for module assembly is based on the concept of a “usable gradient”, which is defined as the maximum field taking into account Q0 performance and allowed thresholds for field emission, as well as breakdown limits. Approximate 20% of the cavities have undergone further surface treatment in the DESY infrastructure to improve their usable gradient performance. In this paper we present the performance statistics of the vertical test results, as well as an analysis of the limiting criteria for the usable gradient, and finally the impact of the surface retreatment on both usable gradient and Q0.

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MOPB087

Integrated High-Power Tests of Dressed N-doped 1.3 GHz SRF Cavities for LCLS-II

HOM, cryomodule, resonance, vacuum

342

N. Solyak, T.T. Arkan, B.E. Chase, A.C. Crawford, E. Cullerton, I.V. Gonin, A. Grassellino, C.J. Grimm, A. Hocker, J.P. Holzbauer, T.N. Khabiboulline, O.S. Melnychuk, J.P. Ozelis, T.J. Peterson, Y.M. Pischalnikov, K.S. Premo, A. Romanenko, A.M. Rowe, W. Schappert, D.A. Sergatskov, R.P. Stanek, G. Wu
Fermilab, Batavia, Illinois, USA

New auxiliary components have been designed and fabricated for the 1.3 GHz SRF cavities comprising the LCLS-II linac. In particular, the LCLS-II cavity’s helium vessel, high-power input coupler, higher-order mode (HOM) feedthroughs, magnetic shielding, and cavity tuning system were all designed to meet LCLS-II specifications. Integrated tests of the cavity and these components were done at Fermilab’s Horizontal Test Stand (HTS) using several kilowatts of continuous-wave (CW) RF power. The results of the tests are summarized here.

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MOPB088

HOM Measurements on the ARIEL eLINAC Cryomodules

HOM, simulation, cryomodule, linac

347

P. Kolb, R.E. Laxdal, Y. Ma, Z.Y. Yao, V. Zvyagintsev
TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada

The ARIEL eLINAC is a 50 MeV, 10 mA electron LINAC designed for the creation of rare isotopes via photo-fission. Future upgrade plans include the addition of a recirculating beam line to allow for either further energy increase of the beam beyond 50 MeV or to operate a free electron laser in an energy recovery mode. For both recirculating LINAC and ERL the higher order modes (HOM) have to be sufficiently suppressed to prevent beam-break-up. The design of the 1.3 GHz nine-cell cavity incorporated this requirement by including beam line absorbers on both ends of each cavity and an asymmetric beam pipe configuration on the cavity to allow trapped modes to propagate to the beam line absorbers. Measurements of the higher order modes on the completed injector cryomodule and the first cavity in the accelerating cryomodules will be shown and compared to simulations.

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MOPB089

1.3 GHz Cavity Test Program for ARIEL

cryomodule, induction, TRIUMF, vacuum

350

P. Kolb, P.R. Harmer, J.J. Keir, D. Kishi, D. Lang, R.E. Laxdal, H. Liu, Y. Ma, T. Shishido, B.S. Waraich, Z.Y. Yao, V. Zvyagintsev
TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada
E. Bourassa, R.S. Orr, D. Trischuk
University of Toronto, Toronto, Ontario, Canada
T. Shishido
KEK, Ibaraki, Japan

The ARIEL eLINAC is a 50 MeV 10 mA electron LINAC. Once finished, five cavities will each provide 10MV of effective accelerating voltage. At the present time two cavities have been installed and successfully accelerated been above specifications of 10 MV/m at a Q0 of 10¹⁰. The next cavities are already in the pipeline and being processed. In addition, one additional cavity has been produced for our collaboration with VECC, India. This cavity has been tested and installed in a cryomodule identical to the eLINAC injector cryomodule. New developments for single cell testing at TRIUMF are a T-mapping system developed in collaboration with UoT and vertical EP for single cells. The progress of the performance after each treatment step has been measured and will be shown. measured and will be shown.

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MOPB090

Analysis of Degraded Cavities in Prototype Modules for the European XFEL

accelerating-gradient, SRF, cryogenics, radiation

355

S. Aderhold
Fermilab, Batavia, Illinois, USA
S. Aderhold, D. Kostin, A. Matheisen, A. Navitski, D. Reschke
DESY, Hamburg, Germany

In-between the fabrication and the operation in an accelerator the performance of superconducting RF cavities is typically tested several times. Although the assembly is done under very controlled conditions in a clean room, it is observed from time to time that a cavity with good performance in the vertical acceptance test shows deteriorated performance in the accelerator module afterwards. This work presents the analysis of several such cavities that have been disassembled from modules of the prototype phase for the European XFEL for detailed investigation like additional rf tests, optical inspection and replica.

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MOPB092

Economics of Electropolishing Niobium SRF Cavities in Eco-Friendly Aqueous Electrolytes Without Hydrofluoric Acid

SRF, niobium, accelerating-gradient, cathode

359

E.J. Taylor, T.D. Hall, M.E. Inman, S.T. Snyder
Faraday Technology, Inc., Clayton, Ohio, USA
D. Holmes
AES, Medford, New York, USA
A.M. Rowe
Fermilab, Batavia, Illinois, USA

A major challenge for industrialization of SRF cavity fabrication and processing is developing a supply chain to meet the high production demands of the ILC prior to establishment of a long term market need. Conventional SRF cavity electropolishing is based on hydrofluoric-sulfuric acid mixtures. In comparison, FARADAYIC® Bipolar EP applies pulse reverse electrolysis in dilute sulfuric acid-water solutions without hydrofluoric acid and offers substantial savings in operating and capital costs. Based on a preliminary economic analysis of the cavity processing requirements associated with the ILC, we project the cost of FARADAYIC® Bipolar EP to be about 27% that of the Baseline EP. In terms of tangible cost savings, the cost per cavity for the FARADAYIC® Bipolar EP and Baseline EP are \1,293 and \4,828, respectively. The “eco-friendly” intangible cost savings are generally accepted although the cost savings in terms of material degradation and maintenance are difficult to quantify at this time. Continued development and validation of FARADAYIC® Bipolar EP on nine cell cavities will contribute greatly to the industrialization of SRF accelerator technology.
Work supported by DOE Grant Nos. DE-SC0011235 and DE-SC0011342 and DOE Purchase Order No. 594128.

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MOPB093

Vertical Electropolishing Studies at Cornell

cathode, SRF, niobium, target

364

F. Furuta, B. Elmore, G.M. Ge, T. Gruber, G.H. Hoffstaetter, D.K. Krebs, J. Sears
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
T.D. Hall, M.E. Inman, S.T. Snyder, E.J. Taylor
Faraday Technology, Inc., Clayton, Ohio, USA
H. Hayano, T. Saeki
KEK, Ibaraki, Japan
Y.I. Ida, K.N. Nii
MGH, Hyogo-ken, Japan

Vertical Electro-Polishing (VEP) has been developed and applied on various SRF R&Ds at Cornell as primary surface process of Nb. Recent achievements had been demonstrated with nitrogen doped high-Q cavities for LCLS-II. Five 9-cell cavities processed with VEP and nitrogen doping at Cornell showed the high average Qo value of 3.0·10¹⁰ at 16MV/m, 2K, during vertical test. this achievement satisfied the required cavity specification values of LCLS-II(2.7·10¹⁰ at 16MV/m, 2K). We will report the details of these achievements and new VEP collaboration projects between Cornell and companies.

Poster MOPB093 [4.364 MB]

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MOPB094

Inspection and Repair Techniques for the EXFEL Superconducting 1.3 GHz Cavities at Ettore Zanon S.p.A: Methods and Results

operation, accelerating-gradient, electron, controls

368

G. Massaro, G. Corniani, N. Maragno
Ettore Zanon S.p.A., Schio, Italy
A. Matheisen, A. Navitski
DESY, Hamburg, Germany
P. Michelato, L. Monaco
INFN/LASA, Segrate (MI), Italy

The quality control of the inner surface of superconducting RF cavities is essential in order to assure high accelerating gradient and quality factor. Ettore Zanon S.p.A. (EZ) has implemented in the serial production an optical system that use an high-resolution camera, in order to detect various types of defects. This system is added to a grinding machine, that was specifically designed and built to repair imperfections of the cavities inner surface. This inspection and repair system is applied to recover performance limited cavities of the 1.3 GHz European XFEL project, where surface irregularities are detected, either by the Obacht inspection system at Desy or the optical system at EZ. The optical system and the grinding procedure are qualified using two series cavities limited in gradient and showing different types of surface defects. The performances of these cavities have been recovered to reach the specifications of the project. Until now, all the series XFEL cavities built by EZ, repaired with this technique, have shown an accelerating gradient well above the EXFEL goal.

Poster MOPB094 [0.795 MB]

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MOPB095

SRF Cavity Processing and Chemical Etching Development for the FRIB Linac

SRF, linac, controls, operation

373

I.M. Malloch, E.S. Metzgar, L. Popielarski
FRIB, East Lansing, Michigan, USA
M.J. LaVere
MSU, East Lansing, Michigan, USA

Funding: This material is based upon work supported by the U.S. Department of Energy Office of Science under Cooperative Agreement DE SC0000661, the State of Michigan and Michigan State University.
In preparation of a rigorous superconducting RF (SRF) cavity processing and test plan for the production of the Facility for Rare Isotope Beams (FRIB) driver linac, a state-of-the-art chemical etching tool has been installed in the FRIB coldmass production facility. This paper seeks to summarize the etching equipment design, installation, and validation program and subsequent etching results for a variety of SRF cavity types and etching configurations. Bulk etching, light etching, and custom (frequency tuning) etching results for different FRIB cavities are discussed. Special emphasis is placed on the etching removal uniformity and frequency tuning reliability of these processes.

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MOPB096

Vertical Electro-Polishing at TRIUMF

cathode, TRIUMF, operation, niobium

378

J.J. Keir, P.R. Harmer, D. Lang, R.E. Laxdal, T. Shishido, R. Smith
TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada
T. Shishido
KEK, Ibaraki, Japan

A setup for electropolishing of a superconducting niobium single-cell cavity has been installed at TRIUMF. A vertical method was selected to make the setup compact. To increase removal speed at the equator and remove hydrogen bubbles at the iris surface, 4 cathode paddles were rotated in the cavity cell during electropolishing. We will report on our first electropolishing result.

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MOPB098

Improvement of Temperature Control During Nb 9-Cell SRF Cavity Vertical Electro-Polishing (VEP) and Progress of VEP Quality

experiment, cathode, controls, SRF

381

K.N. Nii, V. Chouhan, Y.I. Ida, T.Y. Yamaguchi
MGH, Hyogo-ken, Japan
H. Hayano, S. Kato, H. Monjushiro, T. Saeki, M. Sawabe
KEK, Ibaraki, Japan
K. Ishimi
MGI, Chiba, Japan

Marui Galvanizing Co.,Ltd. has been developing Nb 9-cell SRF cavity vertical electro-polishing (VEP) facility and technique for mass production in collaboration with KEK. Our first 9-cell cavity VEP facility was not enough to control temperature during VEP, so the polishing quality was not so high. In this article, we will report the progress of temperature distribution and polishing quality due to the improvement of temperature control system of electrolyte and cavity during VEP.

Poster MOPB098 [0.988 MB]

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MOPB100

Cathode Geometry and Flow Dynamics Impact on Vertical Electropolishing of Superconducting Niobium Cavities

cathode, niobium, simulation, operation

385

L.M.A. Ferreira
CERN, Geneva, Switzerland

CERN has now a fully operating vertical electropolishing installation, which has been used for the processing of 704 MHz high-beta five-cell Superconducting Proton Linac (SPL) niobium cavities. This installation relies only on the electrolyte circulation (HF/H2SO4) for power dissipation, evacuation of gases and homogeneous finishing; thus, parameters like cathode geometry, electrolyte flow and temperature become even more crucial when compared with horizontal electropolishing installations. Based on computational simulations performed with Comsol Multiphysics® and on a methodology developed at CERN, it is possible to assess the impact of the different cathode geometries as well as of the flow on the etching rate distribution. The data obtained with two different cathode geometries are presented: electrolyte velocity distribution, etching rate distribution, average current density and minimum working potential. One geometry was defined through a purely electrochemical approach while the second was defined to minimise the difference between the maximum and the minimum electrolyte speed inside the cavity; in both cases, the influence of the electrolyte flow was taken into account.

Poster MOPB100 [1.794 MB]

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MOPB101

Electropolishing of Niobium SRF Cavities in Eco-Friendly Aqueous Electrolytes Without Hydrofluoric Acid

niobium, SRF, cathode, target

390

M.E. Inman, T.D. Hall, S. Lucatero, S.T. Snyder, E.J. Taylor
Faraday Technology, Inc., Clayton, Ohio, USA
F. Furuta, G.H. Hoffstaetter
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
J.D. Mammosser
ORNL, Oak Ridge, Tennessee, USA
A.M. Rowe
Fermilab, Batavia, Illinois, USA

Electropolishing of niobium cavities is conventionally conducted in high viscosity electrolytes consisting of concentrated sulfuric and hydrofluoric acids. This use of dangerous and ecologically damaging chemicals requires careful attention to safety protocols to avoid harmful worker exposure and environmental damage. We present an approach for electropolishing of niobium materials based on pulse reverse waveforms, enabling the use of low viscosity aqueous dilute sulfuric acid electrolytes without hydrofluoric acid, or aqueous near-neutral pH salt solutions without any acid. Results will be summarized for both cavity and coupon electropolishing for bulk and final polishing steps. With minimal optimization of pulse reverse waveform parameters we have demonstrated the ability to electropolish single-cell niobium SRF cavities and achieve at least equivalent performance compared to conventionally processed cavities. Cavities are electropolished in a vertical orientation filled with electrolyte and without rotation, offering numerous advantages from an industrial processing perspective. Shielding, external cooling and high surface area cathodes are adaptable to the bipolar EP process.
Work supported by DOE Grant Nos. DE-SC0011235 and DE-SC0011342 and DOE Purchase Order No. 594128.

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MOPB102

Comments on Electropolishing at Ettore Zanon SpA at the End of EXFEL Production

niobium, controls, cathode, acceleration

394

M. Rizzi, G. Corniani
Ettore Zanon S.p.A., Schio, Italy
A. Matheisen
DESY, Hamburg, Germany
P. Michelato
INFN/LASA, Segrate (MI), Italy

In 2013 a new horizontal Electropolishing facility was developed and implemented by Ettore Zanon SpA (EZ) for the treatment of cavities for the European XFEL series production. More than 300 cavities have been treated. Electropolishing has been used for two applications: bulk removal and recovering of cavities with surface defects. Treatment settings have been analysed and compared with cavities performances to verify possible influences of the various parameters. Main parameters considered are treatment time, voltage and current, that together define average thickness removal. We present here the results of these investigation. The facility and process in use are also presented, together with possible next upgrade of the system, facing the new production of cavities for the LCLSII project.

Poster MOPB102 [1.535 MB]

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MOPB103

Vertical Electro-Polishing at DESY of a 1.3 GHz Gun Cavity for CW Application

gun, acceleration, injection, SRF

399

N. Steinhau-Kühl, R. Bandelmann, D. Kostin, A. Matheisen, M. Schmökel, J.K. Sekutowicz
DESY, Hamburg, Germany

Superconducting gun cavities for cw operation in accelerators are under study. In 2003 a three-and-a-half cell gun cavity was chemically treated with buffered chemical polishing and tested successfully in a collaboration between Helmholtz-Zentrum Dresden-Rossendorf and DESY. For several years a 1.3-GHz 1.6-cell resonator has been under study, which has been built and tested at DESY and elsewhere. For further studies and optimization the gun cavity needed to be electro-polished, which was conducted at DESY for the first time using vertical electro-polishing. The technical set-up for the vertical electro-polishing and high pressure rinsing as well as the processing parameters applied and the adaptation of the existing infrastructure to the 1.6-cell geometry at DESY are presented.

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MOPB104

Flux Expulsion Variation in SRF Cavities

niobium, factory, cryogenics, SRF

404

S. Posen, M. Checchin, A.C. Crawford, A. Grassellino, M. Martinello, O.S. Melnychuk, A. Romanenko, D.A. Sergatskov
Fermilab, Batavia, Illinois, USA

Treating a cavity with nitrogen doping significantly increases Q₀ at medium fields, reducing cryogenic costs for high duty factor linear accelerators such as LCLS II. N-doping also makes cavities more sensitive to increased residual resistance due to trapped magnetic flux, making it critical to either have extremely effective magnetic shielding, or to prevent flux from being trapped in the cavity during cooldown. In this paper, we report on results of a study of flux expulsion. We discuss possible ways in which flux can be pinned in the inner surface, outer surface, or bulk of a cavity, and we present experimental results studying these mechanisms. We show that grain structure appears to play a key role and that a cavity that expelled flux poorly changed to expelling flux well after a high temperature furnace treatment. We further show that after furnace treatment, this cavity exhibited a significant improvement in quality factor when cooled in an external magnetic field. We conclude with implications for SRF accelerators with high Q₀ requirements.

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MOPB105

Symmetric Removal of Niobium Superconducting RF Cavity in Vertical Electropolishing

cathode, experiment, accumulation, niobium

409

V. Chouhan, Y.I. Ida, K.N. Nii, T.Y. Yamaguchi
MGH, Hyogo-ken, Japan
H. Hayano, S. Kato, H. Monjushiro, T. Saeki, M. Sawabe
KEK, Ibaraki, Japan
K. Ishimi
MGI, Chiba, Japan

Vertical electropolishing (VEP) leads several advantages over horizontal EP in respect of easy operation and mechanism of an EP system resulting in lower cost. However, till yet VEP always resulted inhomogeneous removal of a niobium (Nb) cavity along its length and bubble traces especially on the top iris of a vertically set cavity. In this work we performed lab EP and VEP experiments in order to study and solve these two problems. A coupon cavity which contains 6 disk type Nb coupons positioned at beam pipes, irises and equator was vertically electropolished to optimize VEP parameters so as to get almost uniform removal of Nb and a smooth surface of the cavity without bubble traces. Our patented unique i-Ninja cathode having 4 wings was used with an optimized rotation speed to get homogeneous removal of Nb. The homogeneous removal and the surface without bubble traces might be result of a uniform thickness of a viscous layer on the surface of the cavity cell and no accumulation of hydrogen bubbles on the top iris surface. The surfaces of the coupons were studied in detail with surface analytical tools.

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MOPB106

Analysis of High Pressure Rinsing Characteristics for SRF Cavities

target, experiment, SRF, niobium

414

Y. Jung, M.O. Hyun, M.J. Joung
IBS, Daejeon, Republic of Korea
J. Kim, J. Seo
Vitzrotech Co., Ltd., Ansan City, Kyunggi-Do, Republic of Korea

High pressure rinsing (HPR) treatment has been widely used in the SRF cavity fabrication. This well- known process helps remove effectively undesirable emission tips from the inner surface of cavities, which are responsible for a different level's multipaction and hellium quenching. Also, the HPR treatment can clean or polish the RF (Radio Frequency) surface, which is critically sensitive to an applied magnetic field, by removing contaminants such as an organic oil, a remnant metal debris and dirty etchants from the cavity surface. Consequently, the HPR treatment contributes to improve quality factor during the cavity operation both by decreasing various field emission sites and by removing defects from the cavity surface. In this paper, we performed HPR experiments by using a simplified cavity structure, intentionally painted with a pattern on the inner surface. Therefore, we report how the surface treatment by HPR was carried out as functions of the distance between a target to be cleaned and a nozzle, and a water pressure.

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MOPB110

The Transfer of Improved Cavity Processing Protocols to Industry for LCLS-II: N-Doping and Electropolishing

cathode, niobium, controls, superconductivity

418

C.E. Reece, F. Marhauser, A.D. Palczewski
JLab, Newport News, Virginia, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177 with supplemental funding from the LCLS-II Project U.S. DOE Contract No. DE-AC02-76SF00515.
Based on the R&D efforts of colleagues at FNAL, Cornell, and JLab, the LCLS-II project adopted a modification to the rather standard niobium SRF cavity surface processing protocol that incorporates a high temperature diffusion doping with nitrogen gas. This change was motivated by the resulting higher Q0 and the prospect of significantly lower cryogenic heat load for LCLS-II. JLab is responsible for managing the cavity procurement for the LCLS-II project. The first phase of the procurement action is to transfer the nitrogen-doping protocol to the industrial vendors. We also seek to exploit improvements in understanding of the niobium electropolishing process as part of the production processing of the TESLA-style LCLS-II cavities. We report on the technology transfer activities and progress toward the envisaged performance demonstration of vendor-processed cavities.

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MOPB111

Furnace N2 Doping Treatments at Fermilab

vacuum, SRF, controls, PLC

423

M. Merio, M. Checchin, A.C. Crawford, A. Grassellino, M. Martinello, A.M. Rowe, M. Wong
Fermilab, Batavia, Illinois, USA
M. Checchin, M. Martinello
Illinois Institute of Technology, Chicago, Illlinois, USA

Funding: Operated by Fermi Research Alliance, LLC under Contract No. De-AC02-07CH11359 with the United States Department of Energy.
The Fermilab SRF group regularly performs Nitrogen (N2) doping heat treatments on superconducting cavities in order to improve their Radio Frequency (RF) performances. This paper describes the set up and operations of the Fermilab vacuum furnaces, with a major focus on the implementation and execution of the N2 doping recipe. The cavity preparation will be presented, N2 doping recipes will be analyzed and heat treatment data will be reported in the form of plot showing temperature, total pressure and partial pressures over time. Finally possible upgrades and improvements of the furnace and the N2 doping process are discussed.

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MOPB112

SRF Quality Assurance Studies and Their Application to Cryomodule Repairs at SNS

cryomodule, vacuum, HOM, hardware

428

J.D. Mammosser, R. Afanador, D.L. Barnhart, B. DeGraff, B.S. Hannah, J. Saunders, P.V. Tyagi
ORNL RAD, Oak Ridge, Tennessee, USA
C.M. Campbell
Omega Technical Services, Oak Ridge, Tennessee, USA
M. Doleans, D.K. Hensley, S.-H. Kim
ORNL, Oak Ridge, Tennessee, USA

Funding: This work was supported by SNS through UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. DOE.
Many of the SRF activities involve interactions to cavities which presents risk for particulate contamination to RF surfaces. In order to understand and reduce contamination in cavities during cleaning, vacuum pumping and purging, and in-situ cryomodule repairs, a Quality Assurance (QA) studies were initiated to evaluate these activities and improve them where possible. This paper covers the results of investigations on the effectiveness of the SNS ultrasonic cleaning systems, particulate control during pumping and purging, procedure development for in-situ cryomodule repairs, the application of these studies to the repair of a linac cryomodule, and discussion of further improvement in these areas.

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MOPB113

Study of the Evolution of Artificial Defects on the Surface of Niobium During Electrochemical and Chemical Polishing

SRF, controls, laser, operation

433

L. Monaco, P. Michelato
INFN/LASA, Segrate (MI), Italy
A. Navitski, J. Schaffran, W. Singer
DESY, Hamburg, Germany
C. Pagani
Università degli Studi di Milano & INFN, Segrate, Italy
A.L. Prudnikava, Y. Tamashevich
University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany

The presence of defects on the inner surface of Nb superconducting RF structures might limit its final performance. For this reason, strict requirements are imposed during mechanical production of the cavities, specifically on the quality control of the inner surface of components, to avoid the presence of defects or scratches. Nevertheless, some defects may remain also after control or can arise from the following production steps. Understanding the evolution of the defect might shine new insight on its origin and help in defining possible repair techniques. This paper reports the topographical evolution of defects on a Nb sample polished with the standard recipe used for the 1.3 GHz cavities of the EXFEL project. Various artificial defects of different shape, dimensions, and thicknesses/depths, with geometrical characteristics similar to the one that may occur during the machining and handling of cavities, have been “ad hoc” produced on the sample of the same material used for the cell fabrication. Analysis shows the evolution of the shape and profile of the defects at the different polishing steps.

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MOPB115

Surface Studies of Plasma Processed Nb Samples

plasma, vacuum, SRF, ion

438

P.V. Tyagi, R. Afanador, B. DeGraff, M. Doleans, B.S. Hannah, M.P. Howell, S.-H. Kim, J.D. Mammosser, C.J. McMahan, J. Saunders, S.E. Stewart
ORNL, Oak Ridge, Tennessee, USA

Funding: This work is supported by SNS through UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. DOE.
Contaminants present at top surface of superconducting radio frequency (SRF) cavities can act as field emitters and restrict the cavity accelerating gradient. A room temperature in-situ plasma processing technology for SRF cavities aiming to clean hydrocarbons from inner surface of cavities has been recently developed at the Spallation Neutron Source (SNS). Surface studies of the plasma processed Nb samples by Secondary ion mass spectrometry (SIMS) and Scanning Kelvin Probe (SKP) showed that the NeO2 plasma processing is very effective to remove carbonaceous contaminants from top surface and improves the surface work function by 0.5 to 1.0 eV.
*M. Doleans et al., Proc. 2013 SRF, Paris, France.
**P. V. Tyagi, et al., Proc. Linac14, Geneva, Switzerland.
***M. Doleans et al., These proceedings.

Poster MOPB115 [0.524 MB]

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MOPB116

Developments of Horizontal High Pressure Rinsing for SuperKEKB SRF Cavities

vacuum, factory, operation, SRF

443

Y. Morita, K. Akai, T. Furuya, A. Kabe, S. Mitsunobu, M. Nishiwaki
KEK, Ibaraki, Japan

The Q factors of the eight superconducting accelerating cavities gradually degraded during the long-term operation of the KEKB accelerator. Since we will re-use those SRF cavities for the SuperKEKB, the performance degradation will be a serious problem. Several cavities degraded their performance significantly at high accelerating fields. The Q degradation is still acceptable for the 1.5 MV operations at SuperKEKB. However, further degradation will make the operation difficult. In order to recover the cavity performance, we developed horizontal high pressure water rinsing (HHPR). This method uses a horizontal high pressure water nozzle and inserts it directly into the cavity module. We applied this method to two degraded cavities and their degraded Q factors recovered above 10⁹ at around 2 MV. In this paper we will present the HHPR method, high power test results after the HHPR and the residual gas analysis.

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MOPB117

Identification and Evaluation of Contamination Sources During Clean Room Preparation of SRF Cavities

experiment, hardware, SRF, superconductivity

448

L. Zhao, G.K. Davis, A.V. Reilly
JLab, Newport News, Virginia, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contracts DE-AC05-06OR23177 and DE-AC02-76SF00515 for the LCLS-II Project.
Particles are one possible cause of field emission issues in SRF cavity operations. During clean room cavity preparation, several processes could contribute to the generation of particles. One of them is friction between hardware during assembly and disassembly. It is important to understand the behaviours that generate and propagate particles into cavities. Using a single cell cavity, particle shedding between flanges and other materials have been tested. The number of particles is recorded with an airborne particle counter, and the generated particles are examined with microscope. The migration of particles into a cavity due to different movements is studied. Suggestions are made to reduce particle generation and prevent contamination of the cavity interior area.

Poster MOPB117 [2.832 MB]

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MOPB118

Cleanliness and Vacuum Acceptance Tests for the UHV Cavity String of the XFEL Linac

vacuum, operation, controls, cryomodule

452

S. Berry, O. Napoly, B. Visentin
CEA/DSM/IRFU, France
C. Boulch, C. Cloué, C. Madec, T. Trublet
CEA/IRFU, Gif-sur-Yvette, France
D. Henning, L. Lilje, A. Matheisen, M. Schmökel
DESY, Hamburg, Germany

The main linac of the European XFEL will consist of 100 accelerator modules, i.e. 800 superconducting accelerator cavities operated at a design gradient of 23.6MV/m. In this context CEA-Saclay built an assembly facility designed to produce one module per week, ready to be tested at DESY. The facility overcame the foreseen production rate. We would like to highlight and discuss the critical fields: cleanliness and vacuum. A new assembly method to protect final assembly against particulates contamination has been implemented on the production line. Impact on cryomodule RF test is presented. Particle transport measurements on components used for the European XFEL accelerator module are presented. The results indicate that the nominal operation of the automated pumping and venting units will not lead to particle transport. Vacuum acceptance tests are of major interest: leak tests and residual gas analysis (RGA) are used to control the absence of air leak and contamination. The RGA specifications have been slightly relaxed to ensure the production rate.

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TUAA02

Commissioning of the SRF Linac for ARIEL

cryomodule, linac, TRIUMF, electron

457

V. Zvyagintsev, Z.T. Ang, T. Au, S. Calic, K. Fong, P.R. Harmer, B. Jakovljevic, J.J. Keir, D. Kishi, P. Kolb, S.R. Koscielniak, A. Koveshnikov, C. Laforge, D. Lang, M.P. Laverty, R.E. Laxdal, Y. Ma, A.K. Mitra, N. Muller, R.R. Nagimov, W.R. Rawnsley, R.W. Shanks, R. Smith, B.S. Waraich, L. Yang, Z.Y. Yao, Q. Zheng
TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada

This paper is reporting commissioning results for the SRF linac of ARIEL facility at TRIUMF. The paper is focused on the SRF challenges: cavity design and performance, ancillaries design and preparation, cryomodule design and performance, RF system and final beam test results.

Slides TUAA02 [4.004 MB]

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TUAA03

BESSY VSR: A Novel Application of SRF for Synchrotron Light Sources

damping, SRF, HOM, storage-ring

462

A.V. Vélez, H.-W. Glock, P. Goslawski, A. Jankowiak, J. Knobloch, A. Neumann, M. Ries, G. Wüstefeld
HZB, Berlin, Germany

CW SRF Cavities have been used very successfully in the past in synchrotron light sources to provide high power acceleration. Here we present a novel application of higher harmonic systems of two frequencies (1.5 GHz and 1.75 GHz) to generate a beating of accelerating voltage. With such a system it is possible to store "standard" (some 10 ps long) and "short" (ps and sub-ps long) pulses simultaneously in the light source. This opens up brand new possibilities for light source users to perform dynamic and high-resolution experiments at the same facility. The demands on the SRF system and RF control are substantial and a new design, based on waveguide damping, is currently being developed. This system will be used for a major upgrade of the BESSY-II facility to the BESSY Variable Pulse Storage Ring (BESSY-VSR) for a next-generation storage-ring light source. We will discuss the concept, challenges and designs for BESSY-VSR.

Slides TUAA03 [2.103 MB]

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TUAA04

Rapid Growth of SRF in India

niobium, linac, SRF, electron

467

D. Kanjilal
IUAC, New Delhi, India

Funding: Funding received from Ministry of Higher Education through University Grants Commission of India and from Department of Atomic Energy are gratefully acknowledged.
The talk shall summarize the recent advances in the SRF program in various research centres in India. The SRF related activities at Inter-University Accelerator Centre (IUAC) at Delhi , Raja Ramanna Centre for Advanced Technology (RRCAT) at Indore, Bhabha Atomic Research Centre (BARC) and Tata Institute of Fundamental Research (TIFR) both at Mumbai, and Variable Energy Cyclotron Centre (VECC) at Kolkata shall be addressed. In particular indigenous niobium resonator fabrication and test facilities of IUAC operational for more than a decade which have been used extensively for development, fabrication and utilization of various types of resonators will be discussed. The results from the commissioning of the full three linac modules having eight niobium quarter wave resonators in each module of the heavy ion linac at IUAC for regular scheduled experiments will be presented. The technology and infrastructure developments at RRCAT, BARC, TIFR and VECC for fabrication, processing and tests of future cavities will be discussed.

Slides TUAA04 [5.918 MB]

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TUAA06

Recent Progress of ESS Spoke and Elliptical Cryomodules

cryomodule, SRF, cryogenics, linac

474

G. Olry
IPN, Orsay, France

The ESS accelerator high level requirements are to provide a 2.86 ms long proton pulse at 2 GeV at repetition rate of 14 Hz. This represents 5 MW of average beam power with a 4% duty cycle on target. In a framework of collaboration between IPN Orsay, CEA Saclay and ESS, prototype spoke and medium and high beta elliptical cavities and cryomodules have been studied, constructed and tested. After a description of the ESS project and the accelerator layout, this paper will focus on the recent progress towards realization of the detailed design, the manufacturing of the first components of the prototype cryomodules and the first test results of some of the main critical elements such as SRF cavities and cold tuning systems.

Slides TUAA06 [17.400 MB]

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TUBA01

Status of the SRF Systems at HIE-ISOLDE

cryomodule, vacuum, cryogenics, solenoid

481

W. Venturini Delsolaro, L. Arnaudon, K. Artoos, C. Bertone, J.A. Bousquet, N. Delruelle, M. Elias, J.A. Ferreira Somoza, F. Formenti, J. Gayde, J.L. Grenard, Y. Kadi, G. Kautzmann, Y. Leclercq, M. Mician, A. Miyazaki, E. Montesinos, V. Parma, G.J. Rosaz, K.M. Schirm, E. Siesling, A. Sublet, M. Therasse, L. Valdarno, D. Valuch, G. Vandoni, L.R. Williams, P. Zhang
CERN, Geneva, Switzerland

The HIE-ISOLDE project has been approved by CERN in 2009 and gained momentum after 2011. The final energy goal of the upgrade is to boost the radioactive beams of REX-ISOLDE from the present 3 MeV/u up to 10 MeV/u for A/q up to 4.5. This is to be achieved by means of a new superconducting linac, operating at 101.28 MHz and 4.5 K with independently phased quarter wave resonators (QWR). The QWRs are based on the Nb sputtering on copper technology, pioneered at CERN and developed at INFN-LNL for this cavity shape. Transverse focusing is provided by Nb-Ti superconducting solenoids. The cryomodules hosting the active elements are of the common vacuum type. In this contribution we will report on the recent advancements of the HIE-ISOLDE linac technical systems involving SRF technology. The paper is focused on the cavity production, on the experience with the assembly of the first cryomodule (CM1), and on the results of the first hardware commissioning campaign.

Slides TUBA01 [27.129 MB]

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TUBA02

Thermal Contact Resistance at the Nb-Cu Interface

interface, niobium, feedback, superconductivity

488

V. Palmieri
INFN/LNL, Legnaro (PD), Italy
R. Vaglio
UniNa, Napoli, Italy

Funding: Work performed thanks to the financement in Italy by the INFN 5th group for Accelerator and Applied Physics
Niobium thin film sputtered copper cavities are strongly limited for the application in high field accelerators by the unsolved “Q-slope” problem. In the present paper, we examine the different contributions of the niobium film, the copper substrate, the Helium-Copper interface and the Niobium-Copper Interface, proposing the hypothesis that main cause of losses is due to an enhanced thermal boundary resistance RNb/Cu at the Nb/Cu interface, due to poor thermal contact between film and substrate. So, starting from different Q vs Eacc experimental curves from different sources, and using a typical “inverse problem” method, we deduced the corresponding distribution functions generating those curves. Assuming that only a small fraction of the film over the cavity surface is in poor thermal contact with the substrate (or even partially detached), due to bad adhesion problems, we propose as a possible solution of the problem, the possibility to use higher temperatures of deposition and the adoption at the interface of a buffer layer of a material that alloys both with Copper and with Niobium.

Slides TUBA02 [18.852 MB]

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TUBA03

On the Understanding of Q-Slope of Niobium Thin Films

ECR, niobium, ion, SRF

494

S. Aull, T. Junginger, A. Sublet, W. Venturini Delsolaro, P. Zhang
CERN, Geneva, Switzerland
J. Knobloch
HZB, Berlin, Germany
J. Knobloch
University of Siegen, Siegen, Germany
A-M. Valente-Feliciano
JLab, Newport News, Virginia, USA

The Q-slope of niobium coated copper cavities at medium fields is still the limiting factor for the application the Nb/Cu technology in accelerators. This paper presents a dedicated study of a niobium coating with bulk-like characteristics which shows a Q-slope comparable to bulk Nb at 400 MHz and 4 K. Combining the bulk like film with recent findings of the HIE Isolde indicates that the film microstructure and the Nb/Cu interface are the key aspects to understanding the Q-slope.

Slides TUBA03 [3.414 MB]

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TUBA04

Nb3Sn Cavities: Material Characterization and Coating Process Optimization

simulation, SRF, niobium, radio-frequency

501

D.L. Hall, T. Gruber, J.J. Kaufman, M. Liepe, J.T. Maniscalco, S. Posen, B. Yu
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
Th. Proslier
ANL, Argonne, Illinois, USA

Funding: Work supported by DOE grant DE-SC0008431 and NSF grant PHY-141638. Use of CCMR via NSF MRSEC program (DMR-1120296)
Recent progress on vapour diffusion coated Nb3Sn SRF cavities makes this material a very promising alternative for CW medium field SRF applications. In this paper we report on several systematic studies to determine the sources currently limiting the performance of Nb3Sn cavities to determine improved coating parameters to overcome these limitations. These include a detailed study of the sensitivity of Nb3Sn to trapped ambient magnetic flux, a first measurement of the field dependence of the energy gap in Nb3Sn and detailed measurements of the stoichiometry of the obtained Nb3Sn coatings with synchrotron x-ray diffraction and STEM. Initial results from a study on the impact of the coating process parameters on energy gap, Q-slope, and residual resistance, show clear dependencies, and thus directions for process optimization.

Slides TUBA04 [3.872 MB]

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TUBA05

Progress With Multi-Cell Nb3Sn Cavity Development Linked With Sample Materials Characterization

niobium, vacuum, SRF, factory

505

G.V. Eremeev, M.J. Kelley, C.E. Reece
JLab, Newport News, Virginia, USA
M.J. Kelley, U. Pudasaini
The College of William and Mary, Williamsburg, Virginia, USA
J. Tuggle
Virginia Polytechnic Institute and State University, Blacksburg, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
Exploiting both the new Nb3Sn coating system and the materials characterization tools nearby, we report our progress in low-loss Nb3Sn films development. Nb3Sn films a few micrometers thick were grown on Nb coupons as well as single- and multi-cell cavities by the Sn-diffusion technique. Films structure and composition were investigated on coated samples and cavity cutouts with characterization tools including SEM/EDS/EBSD, AFM, XPS, SIMS towards correlating film growth and RF loss to material properties and deposition parameters. Cavity coating efforts focused on establishing techniques for coating progressively more complicated RF structures, and understanding limiting mechanisms in coated cavities. Nb3Sn coated 1.5 GHz 1-cell and 1.3 GHz 2-cell cavities have shown quality factors of 10¹⁰ at 4.3 K, with several cavities reaching above Eacc = 10 MV/m. The dominant limiting mechanisms were low field quenches and quality factor degradation above 8 MV/m. The surface data indicates a near-stoichiometric Nb3Sn consistent with the transition temperature and gap measurements. The Nb3Sn layer is covered with Nb2O5 and SnO2 native oxides and has little memory of the pre-coating surface.

Slides TUBA05 [2.418 MB]

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TUBA06

Increase in Vortex Penetration Field on Nb Ellipsoid Coated With a MbB2 Thin Film

SRF, shielding, superconductivity, radio-frequency

512

T. Tan, M.A. Wolak, X. Xi
Temple University, Philadelphia, USA
L. Civale, T. Tajima
LANL, Los Alamos, New Mexico, USA

Funding: DOE Office of Science/High Energy Physics
Since SRF2013, there has been a remarkable progress in terms of sample measurement. Instead of measuring a flat film that allows magnetic field on both sides of the film, which does not simulate the situation on a SRF cavity correctly, an ellipsoidal bulk Nb (rugby-ball shape with ~8 mm long axis) was coated with a MgB2 film and its vortex penetration field has been measured with a SQUID magnetometer and compared with uncoated samples. After a number of measurements, vortex penetration field has been consistent with maximum critical RF field, superheating field. Here, we show that 100 nm and 200 nm thick MgB2 coating increases the vortex penetration field by up to ~70 mT, e.g., 240 mT (200 nm MgB2 coated Nb) vs. 170 mT (uncoated Nb) at 2.8 K (lowest measurement temperature) with the trend of increasing as temperature goes down. This is consistent with recent theoretical development saying that the increase is possible even without an insulation layer, which makes the coating easier. In this talk, the thickness dependence of the rise and comparison with theory will be shown.

Slides TUBA06 [2.088 MB]

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TUBA08

Growth and Characterization of Multi-Layer NbTiN Films

SRF, ECR, radio-frequency, lattice

516

A-M. Valente-Feliciano, G.V. Eremeev, C.E. Reece, J.K. Spradlin
JLab, Newport News, Virginia, USA
M.C. Burton, R.A. Lukaszew
The College of William and Mary, Williamsburg, Virginia, USA

Significant theoretical interest has stimulated efforts to grow and characterize thin multi-layer superconductor/insulator/superconductor structures for their potential capability of supporting otherwise inaccessible surface magnetic fields in SRF cavities. The technological challenges include realization of high quality superconductors with sharp, clean, transition to high quality dielectric materials and back to superconductor, with careful thickness control of each layer. Choosing NbTiN as the first candidate material, we have developed the tools and techniques that produce such SIS film structures and have begun their characterization. Using DC magnetron sputtering and HiPIMS, NbTiN and AlN can be deposited with nominal superconducting and dielectric parameters. Hc1 enhancement is observed for NbTiN layers with a Tc of 16.9 K for a thickness less than 150 nm. The optimization of the thickness of each type of layer to reach optimum SRF performance is underway. This talk describes this work and the rf performance characteristics observed to date.

Slides TUBA08 [8.536 MB]

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TUPB001

Progress on Superconducting RF Cavity Development With UK Industry

niobium, SRF, superconducting-RF, accelerating-gradient

521

A.E. Wheelhouse, R.K. Buckley, L.S. Cowie, P. Goudket, A.R. Goulden, P.A. McIntosh
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
J.R. Everard, N. Shakespeare
Shakespeare Engineering, South Woodham Ferrers, Essex, United Kingdom

As part of a STFC Industrial Programme Support (IPS) Scheme grant, Daresbury Laboratory and Shakespeare Engineering Ltd have been developing the capability to fabricate, process, and test a 9-cell, 1.3 GHz superconducting RF cavity. The objective of the programme of work is to achieve an accelerating gradient of greater than 20 MV/m at an unloaded quality factor of 1.0 x 10¹⁰ or better. Processes such as the high pressure rinsing and the buffer chemical polishing are being developed at Daresbury Laboratory and the manufacturing of the cavity half cells and beampipes are being optimised by Shakespeare Engineering to enable this target to be achieved. These are discussed in this paper.

Poster TUPB001 [2.155 MB]

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TUPB003

Cavity Procurement and Qualification Plan for LCLS-II

controls, hardware, site, cathode

529

F. Marhauser, E. Daly, J.A. Fitzpatrick
JLab, Newport News, Virginia, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177 with supplemental funding from the LCLS-II Project U.S. DOE Contract No. DE-AC02-76SF00515.
The LCLS-II project aims to build 35 accelerating cryomodules, which are based on the European XFEL design but modified for operation in CW mode. Each cryomodule houses eight TESLA-style nine-cell superconducting radio-frequency cavities. The activities to assemble the first two prototype cryomodules are ongoing at FNAL and JLab. 264 cavities worth of cavities for the remaining 33 cryomodules will be procured from two industrial vendors in similar quantity considering the option to produce spares. The assembly of cavities into the production cryomodules will be distributed among FNAL (16 cryomodules) and JLab (17 cryomodules). In this paper the cavity procurement and qualification plan for the LCLS-II project is detailed.

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TUPB004

Vertical Cavity Test Facility at Fermilab

controls, instrumentation, experiment, SRF

534

O.S. Melnychuk, A. Grassellino, F.L. Lewis, J.P. Ozelis, R.V. Pilipenko, Y.M. Pischalnikov, O.V. Pronitchev, A. Romanenko, D.A. Sergatskov, B. Squires
Fermilab, Batavia, Illinois, USA

After a recent upgrade, the vertical test facility for SRF cavities at Fermilab features a low level RF system capable of testing 325MHz, 650MHz, 1.3GHz, and 3.9GHz cavities, helium liquefying plant, three test cryostats, and the interlock safety system. The cryostats can accommodate measurements of multiple cavities in a given cryogenic cycle in the range of temperatures from 4.2K to 1.4K. We present a description of the components of the vertical test facility. We also discuss cavity instrumentation that is used for diagnostics of cavity ambient conditions and quench characterization.

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TUPB006

The CLS SRF Cryogenic System Upgrade

cryomodule, storage-ring, SRF, cryogenics

539

C.N. Regier
CLS, Saskatoon, Saskatchewan, Canada

The Canadian Light Source currently makes use of a 500 MHz CESR-B type SRF cavity in its storage ring. While the performance of this cavity has generally been good, the reliability of the cryostat and cryogenic system has suffered a few setbacks over the 10 years of operation. The position of CLS as a user facility requires reliable beam to be consistently delivered. For this reason CLS is undertaking an upgrade project to improve system reliability and reduce downtime due to planned and unplanned maintenance. The upgrade is to include a redundant helium compressor, and new cryogenic infrastructure. In addition, the spare CESR-B cryomodule will be installed and operating in the storage ring. This talk reviews the problems with the current system to date, and discusses the proposals for the upgrade of the system.

Poster TUPB006 [0.622 MB]

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TUPB007

Progress in the Elliptical Cavities and Cryomodule Demonstrators for the ESS LINAC

cryomodule, vacuum, cryogenics, linac

544

F. Peauger, C. Arcambal, S. Berry, N. Berton, P. Bosland, E. Cenni, J.-P. Charrier, G. Devanz, F. Éozénou, F. Gougnaud, A. Hamdi, X. Hanus, P. Hardy, V.M. Hennion, T. Joannem, F. Leseigneur, D. Loiseau, C. Madec, L. Maurice, O. Piquet, J. Plouin, J.P. Poupeau, B. Renard, D. Roudier, P. Sahuquet, C. Servouin
CEA/DSM/IRFU, France
C. Darve, N. Elias
ESS, Lund, Sweden
G. Olivier
IPN, Orsay, France

The European Spallation Source (ESS) accelerator is a large superconducting linac under construction in Lund, Sweden. A collaboration between CEA Saclay, IPN Orsay and ESS-AB is established to design the elliptical cavities cryomodule of the linac. It is foreseen to build and test two cryomodule demonstrators within the next two years. We present the design evolution and the fabrication status of the cryomodule components housing four cavities. The latest test results of two prototype cavities are shown. The cryomodule assembly process and the on-going testing infrastructures at CEA Saclay are also described.

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TUPB013

Fermilab Cryomodule Test Stand Design and Plans

cryomodule, cryogenics, controls, SRF

566

E.R. Harms, C.M. Baffes, K. Carlson, B.E. Chase, A.L. Klebaner, M.J. Kucera, J.R. Leibfritz, M.W. McGee, P.S. Prieto, J. Reid, R.P. Stanek, D. Sun, M.J. White
Fermilab, Batavia, Illinois, USA

Funding: Operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy.
A facility dedicated to SRF cryomodule testing is under construction at Fermilab. The test stand has been designed to be flexible enough to cool down and power test full length TESLA-style 8-cavity cryomodules as well cryomodules for low-β acceleration. We describe the design considerations, status, and near future plans for utilization of the test stand.

Poster TUPB013 [5.146 MB]

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TUPB014

First Operation of a Superconducting RF Electron Test Accelerator at Fermilab

electron, gun, operation, superconducting-RF

571

E.R. Harms, R. Andrews, C.M. Baffes, D.R. Broemmelsiek, K. Carlson, D.J. Crawford, N. Eddy, D.R. Edstrom, J.R. Leibfritz, A.H. Lumpkin, S. Nagaitsev, P. Piot, P.S. Prieto, J. Reid, J. Ruan, J.K. Santucci, V.D. Shiltsev, W.M. Soyars, D. Sun, R.M. Thurman-Keup, A. Valishev, A. Warner
Fermilab, Batavia, Illinois, USA

Funding: Operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy.
A test accelerator utilizing SRF technology recently accelerated its first electrons to 20 MeV at Fermilab. Foreseen enhancements will make acceleration to 300 MeV possible at a maximum beam power of 80 kW. A summary of commissioning steps and first experiments as well as current beam parameters compared to design is presented. Plans for expansion and the future physics program are also summarized.

Poster TUPB014 [11.582 MB]

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TUPB015

A New Cleanroom With Facilities for Cleaning and Assembly of Superconducting Cavities at Helmholtz-Institut Mainz

linac, heavy-ion, status, ion

575

F. Schlander, K. Aulenbacher, R.G. Heine
IKP, Mainz, Germany
K. Aulenbacher, W.A. Barth, V. Gettmann, M. Miski-Oglu
HIM, Mainz, Germany
W.A. Barth, S. Mickat
GSI, Darmstadt, Germany

The Helmholtz-Institut Mainz HIM will operate a clean room facility for the assembly and possible re-treatment of superconducting cavities. This is mandatory for several SRF accelerator projects, like the advanced demonstrator for a dedicated sc heavy ion cw-linac at HIM or other projects pursued by research facilities or universities close by. While the installation of the clean room is in progress, the procurement of the appliances is ongoing. The present equipment planned and the current status of the installation will be presented.

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TUPB016

Progress on Superconducting Linac for the RAON Heavy Ion Accelerator

linac, cryomodule, ion, electron

578

H.J. Kim
IBS, Daejeon, Republic of Korea

The RISP (Rare Isotope Science Project) has been proposed as a multi-purpose accelerator facility for providing beams of exotic rare isotopes of various energies. It can deliver ions from proton to uranium. Proton and uranium ions are accelerated upto 600 MeV and 200 MeV/u respectively. The facility consists of three superconducting linacs of which superconducting cavities are independently phased. Requirement of the linac design is especially high for acceleration of multiple charge beams. In this paper, we present the RISP linac design, the prototyping of superconducting cavity and cryomodule.

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TUPB017

1.3 GHz SRF Technology R&D Progress of IHEP

cryomodule, vacuum, cryogenics, HOM

581

J.Y. Zhai, Y.L. Chi, J.P. Dai, X.W. Dai, J. Gao, R. Ge, D.Y. He, T.M. Huang, X. Huang, S. Jin, S.P. Li, H.Y. Lin, B. Liu, Z.C. Liu, Q. Ma, Z.H. Mi, W.M. Pan, X.H. Peng, L.R. Sun, Y. Sun, Z. Xue, S.W. Zhang, Z. Zhang, H. Zhao, T.X. Zhao, H.J. Zheng, Z.S. Zhou
IHEP, Beijing, People's Republic of China

IHEP started the 1.3GHz SRF technology R&D in 2006 and recently enters the stage of integration and industrialization. After successfully making several single cell and 9-cell cavities of different shape and material, we designed and assembled a short cryomodule containing one large grain low loss shape 9-cell cavity with an input coupler and a tuner etc. This module will perform horizontal test in 2016 with the newly commissioned 1.3GHz 5MW klystron and the 2K cryogenic system. Beam test with a DC photocathode gun is also foreseen in the near future. We report here the problems, key findings and improvements in cavity dressing, clean room assembly, cryomodule assembly and the liquid nitrogen cool down test. A fine grain TESLA 9-cell cavity is also under fabrication in a company as the industrialization study.

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TUPB018

Preparation of the 3.9 GHz System for the European XFEL Injector Commissioning

HOM, operation, alignment, vacuum

584

P. Pierini, M. Bertucci, M. Bonezzi, A. Bosotti, J.F. Chen, M. Chiodini, P. Michelato, L. Monaco, M. Moretti, R. Paparella, D. Sertore
INFN/LASA, Segrate (MI), Italy
C. Albrecht, N. Baboi, S. Barbanotti, J. Branlard, Th. Buettner, L. Butkowski, T. Delfs, H. Hintz, F. Hoffmann, M. Hüning, K. Jensch, R. Jonas, R. Klos, D. Kostin, L. Lilje, C.G. Maiano, W. Maschmann, A. Matheisen, U. Mavrič, W.-D. Möller, C. Müller, P. Pierini, J. Prenting, J. Rothenburg, O. Sawlanski, M. Schlösser, M. Schmökel, A.A. Sulimov, E. Vogel
DESY, Hamburg, Germany
E.R. Harms
Fermilab, Batavia, Illinois, USA
C.R. Montiel
ANL, Argonne, Illinois, USA
C. Pagani
Università degli Studi di Milano & INFN, Segrate, Italy

The 3.9 GHz cryomodule and RF system for the XFEL Injector is being assembled and delivered to the underground building in summer 2015, for the injector commissioning in Fall 2015. This contribution outlines the status of the activity and reports the preparation stages of the technical commissioning of the system.

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TUPB020

Recent Status New Superconducting CW Heavy Ion LINAC@GSI

solenoid, linac, heavy-ion, ion

589

V. Gettmann, M. Amberg, K. Aulenbacher, W.A. Barth, M. Miski-Oglu
HIM, Mainz, Germany
M. Amberg, M. Basten, D. Bänsch, F.D. Dziuba, H. Podlech, U. Ratzinger
IAP, Frankfurt am Main, Germany
K. Aulenbacher
IKP, Mainz, Germany
W.A. Barth, M. Heilmann, S. Mickat, S. Yaramyshev
GSI, Darmstadt, Germany

The demonstrator is a prototype of the first section of the proposed cw-LINAC@GSI, comprising a superconducting CH-cavity embedded by two superconducting solenoids. The sc CH-structure is the key component and offers a variety of research and development. The beam focusing solenoids provide maximum fields of 9.3 T at an overall length of 380 mm and a free beam aperture of 30 mm. The magnetic induction of the fringe is minimized to 50 mT at the inner NbTi-surface of the neighboring cavity. The fabrication of the key components is still in progress and is near to completion. After cold performance testing of the RF cavity, the helium jacket will be welded on. The cryostat is partly assembled and will be finished in the next weeks. The test environment is completely prepared. Advanced emittance measurement is foreseen to prepare for best matching of the heavy ion beam from the injector. Integration of the cryostat into the beam line, the first cool down of the module and commissioning of the RF elements will be performed as next steps towards a complete testing of the demonstrator.

Poster TUPB020 [8.595 MB]

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TUPB021

Measurement of the Cavity Performances of Compact ERL Main Linac Cryomodule During Beam Operation

operation, linac, radiation, cryomodule

592

H. Sakai, M. Egi, K. Enami, T. Furuya, S. Michizono, T. Miura, F. Qiu, K. Shinoe, K. Umemori
KEK, Ibaraki, Japan
M. Sawamura
JAEA, Ibaraki-ken, Japan

We developed ERL main linac cryomodule for Compact ERL (cERL) in KEK. The module consists of two 9-cell 1.3 GHz superconducting cavities, two 20 kW high power coupler, two mechanical tuner and three HOM dampers. After construction of cERL recirculation loop, beam operation was started in 2013 Dec. First electron beam of 20 MeV successfully passed the main linac cavities. After adjusting beam optics, energy recovery operation was achieved. Main linac cavity was enough stable for ERL beam operation with digital LLRF system and energy recovery was successfully done with CW 80 uA beam. However, field emission was a problem for long term operation. In this paper, we express the measurement of the cavity performances of long term beam operation.

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TUPB022

Low-Beta SRF Cavity Processing and Testing Facility for the Facility for Rare Isotope Beams at Michigan State University

SRF, vacuum, controls, cryomodule

597

L. Popielarski
NSCL, East Lansing, Michigan, USA
B.W. Barker, C. Compton, K. Elliott, I.M. Malloch, E.S. Metzgar, J. Popielarski, K. Saito, G.J. Velianoff, D.R. Victory, T. Xu
FRIB, East Lansing, Michigan, USA

Funding: This material is based upon work supported by the U.S. Department of Energy Office of Science under Cooperative Agreement DE SC0000661, the State of Michigan and Michigan State University
Major work centers of the new SRF Highbay are fully installed and in use for FRIB pre-production SRF quarter-wave and half-wave resonators, including inspection area, high temperature vacuum furnace for cavity degassing, chemical etching facility and processing and assembly cleanrooms. Pre-production activities focus on optimizing workflow by reducing process time, tracking part status and related data, and identifying bottlenecks. Topics discussed may include; buffered chemical polish (BCP) etching for cavity frequency control, degassing time reduction, automated high pressure rinse, particle control against field emission, pre-production cavity test results and implementation of workflow status programs

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TUPB026

Cryogenic Performance of the HNOSS Test Facility at Uppsala University

cryogenics, operation, vacuum, controls

612

R. Santiago Kern, K.J. Gajewski, L. Hermansson, R.J.M.Y. Ruber
Uppsala University, Uppsala, Sweden
P. Bujard, T. Junquera, J.P. Thermeau
Accelerators and Cryogenic Systems, Orsay, France

Funding: Knut and Alice Wallenbergs foundation
The FREIA Laboratory at Uppsala University, Sweden, is developing part of the RF system and testing the superconducting double spoke cavitites for ESS. During 2014 it was equipped with HNOSS, a versatile horizontal cryostat system for testing superconducting cavities. HNOSS is designed for high power RF testing of up to two superconducting accelerating cavities equipped with helium tank, fundamental power coupler and tuning system. In particular it will be used to characterise the performance of spoke cavities like used in the accelerator for the ESS project. HNOSS is connected to a cryogenic plant providing liquid helium and a sub-atmospheric pumping system enabling operation in the range 1.8 to 4.5~K. We present a brief description of the major components, installation and results from the recent operation and tests.

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TUPB027

Developments on SRF Coatings at CERN

SRF, plasma, simulation, cathode

617

A. Sublet, S. Aull, B. Bártová, S. Calatroni, T. Richard, G.J. Rosaz, M. Taborelli, M. Therasse, W. Venturini Delsolaro, P. Zhang
CERN, Geneva, Switzerland

The thin films techniques applied to Superconducting RF (SRF) has a long history at CERN. A large panel of cavities have been coated from LEP, to LHC. For the current and future projects (HIE-ISOLDE, HL-LHC, FCC) there is a need for further higher RF-performances with focus on minimizing residual resistance Rres and maximizing quality factor Q0 of the cavities. This paper will present CERN’s developments on thin films to achieve these goals through the following main axes of research: The first one concerns the application of different coating techniques for Nb (DC-bias diode sputtering, magnetron sputtering and HiPIMS). Another approach is the investigation of alternative materials like Nb3Sn. These lines of development will be supported by a material science approach to characterize and evaluate the layer properties by means of FIB-SEM, TEM, XPS, XRD, etc. In addition a numerical tool for plasma simulation will be exploited to develop adapted coating systems and optimize the coating process, from plasma generation to thin film growth.

Poster TUPB027 [1.070 MB]

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TUPB030

Recent Results from the Cornell Sample Host Cavity

niobium, SRF, radio-frequency, superconducting-RF

626

J.T. Maniscalco, B. Clasby, T. Gruber, D.L. Hall, M. Liepe
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: DOE/NSF
Many novel materials are under investigation for the future of superconducting radio-frequency accelerators (SRF). In particular, thin-film materials such as Nb3Sn, NbN, SIS multilayers, and also thin-film niobium on copper, may offer improvements in cost efficiency and RF performance over the standard niobium cavities. To avoid the difficulties of depositing thin films on full cavities, Cornell has developed a TE-mode sample host cavity which allows for RF measurements of large, flat samples at fields up to and over 100 mT. We present recent performance results from the cavity, reaching record high fields and quality factor using a niobium calibration plate. We also discuss plans for future collaborations.

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TUPB032

Energetic Condensation Growth of Nb on Cu SRF Cavities

cathode, niobium, SRF, plasma

629

K.M. Velas, S.F. Chapman, I. Irfan, M. Krishnan
AASC, San Leandro, California, USA

Funding: This research is supported by the US DOE via and SBIR grant: DE-SC0011371
Alameda Applied Sciences Corporation (AASC) grows Nb thin films via Coaxial Energetic Deposition (CED) from a cathodic arc plasma. The plasma from the cathode consists exclusively of 60-120eV Nb ions (Nb+ and Nb2+) that penetrate a few monolayers into the substrate and enable sufficient surface mobility to ensure that the lowest energy state (crystalline structure with minimal defects) is accessible to the film. AASC is coating 1.3 GHz SRF cavities using a graded anode to ensure uniform film thickness in the beam tube and elliptical regions. Copper cavities are centrifugal barrel polished and electropolished (done for us by the Fermilab Technical Division, Superconducting RF Development Department and by Thomas Jefferson National Accelerator Facility (JLAB)) before coating, to ensure good adhesion and improved film quality. The Nb coated copper cavities will undergo RF tests at JLAB and at Fermilab to measure Qo vs. E.

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TUPB034

Bulk Niobium Polishing and Electropolishing Steps for Thinfilm Coated Copper SRF Cavities

SRF, ion, plasma, cathode

633

M. Krishnan, S.F. Chapman, I. Irfan, K.M. Velas
AASC, San Leandro, California, USA
J.K. Spradlin, H. Tian
JLab, Newport News, Virginia, USA

Funding: Research supported at AASC by the US DOE via SBIR grant: DE-SC0011371. The JLab effort was provided by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177
Alameda Applied Sciences Corporation (AASC) grows Nb thin films via Coaxial Energetic Deposition (CED) from a cathodic arc plasma. The plasma consists of 60-120eV Nb ions (Nb+ and Nb++) [1] that penetrate a few monolayers into the substrate [2] and enable sufficient surface mobility to ensure that the lowest energy state (crystalline structure with minimal defects) is accessible to the film [3]. One limitation of CED thinfilms is the presence of Nb macroparticles (~0.1-10 microns) that could be deleterious to high field performance of the SRF cavity. One way to remove such macroparticles [4] is to grow a thick film (~3-5 microns), followed by mechanical polishing (MP) using the finest media as might be applied in Centrifugal Barrel Polishing (CBP) to achieve a 0.4 micron surface figure, and an electropolishing (EP) step to remove ~1 micron of Nb that also removes all traces of embedded media in the film. The residual 2-4 micron Nb film should more nearly resemble the surface of a bulk Nb cavity that has been subjected to the same steps. This paper describes experiments conducted on Cu coupons as a prelude to an SRF Cu cavity coating.

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TUPB037

Superconducting NbN-Based Multilayer and NbTiN Thin Films for the Enhancement of SRF Accelerator Cavities

target, lattice, SRF, niobium

638

M.C. Burton, M. Beebe, R.A. Lukaszew, J.M. Riso
The College of William and Mary, Williamsburg, Virginia, USA
C.E. Reece, A-M. Valente-Feliciano
JLab, Newport News, Virginia, USA

Funding: Funded by: Defense Threat Reduction Agency HDTRA1-10-1-0072
Current superconducting radio frequency (SRF) technology, used in various particle accelerator facilities is reliant upon bulk Nb. Due to technological advancements in the processing of bulk Nb cavities, the facilities have reached accelerating fields very close to material-dependent limits, i.e. ~50 MV/m for bulk Nb. One possible solution to overcome this limit proposed by A. Gurevich consists of the deposition of alternating thin layers of superconducting and insulating materials on the interior surface of the cavities which may prevent early field penetration and thus delay high field breakdown*. Some candidate materials proposed for this scheme are NbN and NbTiN. Here we present experimental results correlating film microstructure and surface morphology with superconducting properties on coupon samples made with NbN and NbTiN. We have achieved thin films with close to bulk-like lattice parameters and transition temperatures, while achieving Hc1 values larger than bulk for films thinner than their London penetration depths. We compare results from samples grown utilizing NbTi targets with different stoichiometries and we will show RF measurements from 2” coupon samples.
*A. Gurevich, Appl. Phys. Lett. 88, 012511 (2006).

Poster TUPB037 [0.989 MB]

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TUPB042

Low Energy Muon Spin Rotation and Point Contact Tunneling Applied to Niobium Films for SRF Cavities

niobium, experiment, scattering, data-analysis

656

T. Junginger
TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada
S. Calatroni, G. Terenziani
CERN, Geneva, Switzerland
T. Prokscha, Z. Salman, A. Suter
PSI, Villigen PSI, Switzerland
Th. Proslier
ANL, Argonne, Illinois, USA
G. Terenziani
Sheffield University, Sheffield, United Kingdom
J. Zasadzinski
IIT, Chicago, Illinois, USA

Muon spin rotation (muSR) and point contact tunneling (PCT) are used since several years for bulk niobium studies. Here we present studies on niobium thin film samples of different deposition techniques (diode, magnetron and HIPIMS) and compare the results with RF measurements and bulk niobium results. It is consistently found from muSR and RF measurements that HIPIMS can be used to produce thin films of high RRR. Hints for magnetism are especially found on the HIPIMS samples. These could possibly contribute to the field dependent losses of superconducting cavities, which are strongly pronounced on niobium on copper cavities.

Poster TUPB042 [0.932 MB]

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TUPB044

High Quality Factor Studies in SRF Nb3Sn Cavities

niobium, SRF, radio-frequency, accelerating-gradient

661

D.L. Hall, B. Clasby, H. Conklin, R.G. Eichhorn, T. Gruber, G.H. Hoffstaetter, J.J. Kaufman, M. Liepe
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: Work supported by DOE grant DE-SC0008431 and NSF grant PHY-141638
A significant advantage of Nb3Sn coated on niobium over conventional bulk niobium is the substantial reduction in the BCS losses at equal temperatures of the former relative to the latter. The quality factor of a 1.3 GHz Nb3Sn cavity is thus almost entirely dictated by the residual resistance at temperatures at and below 4.2 K, which, if minimised, offers the ability to operate the cavity in liquid helium at atmospheric pressure with quality factors exceeding 4·10¹⁰. In this paper we look at the impact of the cooldown procedure – which is intrinsically linked to the effect of spatial and temporal gradients – and the impact of external ambient magnetic fields on the performance of a Nb3Sn cavity.

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TUPB045

Surface Analysis and Material Property Studies of Nb3Sn on Niobium for Use in SRF Cavities

niobium, radio-frequency, klystron, electron

665

D.L. Hall, H. Conklin, T. Gruber, J.J. Kaufman, M. Liepe, J.T. Maniscalco, B. Yu
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
Th. Proslier
ANL, Argonne, Illinois, USA

Funding: Work supported by DOE grant DE-SC0008431 and NSF grant PHY-141638. Use of CCMR via NSF MRSEC program (DMR-1120296)
Studies of superconducting Nb3Sn cavities and samples at Cornell University and Argonne National Lab have shown that current state-of-the-art Nb3Sn cavities are limited by material properties and imperfections. In particular, the presence of regions within the Nb3Sn layer that are deficient in tin are suspected to be the cause of the lower than expected peak accelerating gradient. In this paper we present results from a material study of the Nb3Sn layer fabricated using the vapour deposition method, with data collected using AFM, SEM, TEM, EDX, and XRD methods as well as with pulsed RF testing.

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TUPB046

Structure and Composition of Nb3Sn Diffusion Coated Films on Nb

ion, niobium, electron, SRF

669

J. Tuggle, M.J. Kelley
Virginia Polytechnic Institute and State University, Blacksburg, USA
G.V. Eremeev, M.J. Kelley, C.E. Reece
JLab, Newport News, Virginia, USA
M.J. Kelley, H. Xu
The College of William and Mary, Williamsburg, Virginia, USA

Funding: Co-authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. College of William & Mary supported by U.S. DOE Office of High Energy Physics under grant DE-SC-0014475
The structure and composition of Nb3Sn films obtained by diffusion coating niobium coupons and SRF cavities were investigated by x-ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy (SIMS) and scanning electron microscopy (SEM) with energy-dispersive x-ray spectroscopy (EDS) and electron back-scatter diffraction (EBSD), including native surfaces, depth profiles and cross-sections. We find that the native surface oxide is significantly tin-rich, we have measured depth profiles. We find that the grains apparent in the SEM images are individual crystallites having no evident relationship to the substrate or each other.

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TUPB048

Fermilab Nb3Sn R&D Program

niobium, SRF, cryogenics, accelerating-gradient

678

S. Posen, M. Merio, A. Romanenko, Y. Trenikhina
Fermilab, Batavia, Illinois, USA

A substantial program has been initiated at FNAL for R&D on Nb3Sn coated cavities. Since early 2015, design, fabrication, and commissioning has been ongoing on a coating chamber, designed for deposition via vapor diffusion. The volume of the chamber will be large enough to accommodate not just R&D cavities, but full production-style cavities such as TeSLA 9-cells. In this contribution, we overview the development of the chamber and we introduce the R&D program planned for the coming years. We discuss research paths that may yield increased maximum fields and reduced residual resistances as well as new applications that could be explored with larger coated cavities.

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TUPB049

Cutout Study of a Nb3Sn Cavity

niobium, electron, SRF, accelerating-gradient

681

S. Posen, O.S. Melnychuk, A. Romanenko, D.A. Sergatskov, Y. Trenikhina
Fermilab, Batavia, Illinois, USA
D.L. Hall, M. Liepe
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

The first 1.3 GHz single cell Nb₃Sn cavity coated at Cornell was shown in RF measurements at Cornell and FNAL to have poor RF performance. Though subsequent cavities showed much higher quality factors, this cavity exhibited Q₀ on the order of 10⁹ caused by strong heating concentrated in one of the half cells. This paper presents an investigation into the source of this excess heating, for the purpose of process improvement, so that similar degradation can be avoided in future coatings. Through the use of temperature mapping both at Cornell and at FNAL, locations with high and low surface resistance were located, cut out from the cavity, and studied with microscopic tools. We present the RF measurements and temperature maps as well as the microscopic analyses, then conclude with plans for continued studies.

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TUPB050

Secondary Electron Yield of SRF Materials

electron, niobium, SRF, vacuum

686

S. Aull, T. Junginger, H. Neupert
CERN, Geneva, Switzerland
S. Aull, J. Knobloch
University of Siegen, Siegen, Germany
J. Knobloch
HZB, Berlin, Germany

The secondary electron yield (SEY) describes the number of electrons emitted to the vacuum per arriving electron at the surface. For a given geometry, the SEY is the defining factor for multipacting activity. In the quest of superconducting RF materials beyond bulk niobium, we studied the SEY of the currently most important candidates for future SRF applications: Nb3Sn, NbTiN and MgB2. All studies were done on clean but technical surfaces, i.e. on clean surfaces exposed to air and with their native oxides as it would be the case for SRF cavities.

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TUPB054

Local Composition and Topography of Nb3Sn Diffusion Coatings on Niobium

niobium, electron, site, accelerating-gradient

703

U. Pudasaini, M.J. Kelley
The College of William and Mary, Williamsburg, Virginia, USA
G.V. Eremeev, M.J. Kelley, C.E. Reece
JLab, Newport News, Virginia, USA

Funding: Co-authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. College of William & Mary supported by U.S. DOE Office of High Energy Physics under grant DE-SC-0014475.
The potential for energy savings and for increased gradient continues to bring attention to Nb3Sn-coated niobium as a future SRF cavity technology. We prepared these materials by vapor diffusion coating on polycrystalline and single crystal niobium. The effect of changing substrate preparation, coating parameters and post-treatment were examined by AFM and SEM/EDS. The AFM data were analyzed in terms of power spectral density (PSD). We found little effect of pre-coating topography on the result. The PSD’s show some surprising kinship to those obtained from BCP-treated surfaces. SEM/EDS revealed no composition non-uniformities at the micron scale.

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TUPB056

Characterization of Nb3Sn Coated Nb Samples

SRF, electron, ion, niobium

708

Y. Trenikhina, S. Posen, A. Romanenko
Fermilab, Batavia, Illinois, USA
D.L. Hall
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
M. Liepe
Cornell University, Ithaca, New York, USA

Nb3Sn has a great potential to replace traditional Nb for the fabrication of SRF cavities. The higher critical temperature of Nb3Sn potentially allows for an increased operational temperature for SRF cavities, which promises cryogenic cost savings. We present preliminary characterization of Nb3Sn layer grown on flat Nb sample prepared by the same chemical vapor deposition method that is used for the cavity coating. SEM, TEM/EDS, TEM imaging and diffraction characterization was used in order to evaluate any chemical and structural defects that could be responsible for the limited quench field and high residual resistance. Variation of local stoichiometry was found in the Nb3Sn layer, which is in line with previous studies. Regions of decreased Sn content can have a lower Tc in comparison to the stoichiometric composition, which may be responsible for the limited performance. AES investigations of the Nb3Sn surface before and after HF-rinse were done in order to explore the mechanism that is responsible for the performance degradation of HF-rinsed Nb3Sn coated cavities.

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TUPB058

Characterization of Thin Films Using Local Magneometer

experiment, SRF, superconductivity, operation

712

N. Katyan, C.Z. Antoine
CEA/DSM/IRFU, Grenoble, France
C.Z. Antoine
CEA/IRFU, Gif-sur-Yvette, France

Funding: CEA
SIS nanocomposite (Superconductor/Insulator/Superconductor) could improve efficiency of accelerating cavities. The SRF multilayers concept focuses on the enhancement of HC1 using thin layers (d~λ). The use of thin layers makes it easier to avoid avalanche penetration of vortices in case of local defects. Several layers are needed in order to attenuate the external field to values below Nb HC1, decoupled using dielectric layers. We don’t know yet how the predicted properties evolve in realistic conditions; hence it seems reasonable to do their optimization. Two parameters need to be measured to study their behavior in cavity operating conditions: HC1 and Rs surface resistance (especially residual). For that purpose two instruments were developed in Saclay and in Orsay. A local magnetometer allows measuring the vortex penetration on samples without the orientation and edge effects encountered in SQUID magnetometers. Its operating conditions range from 2-40 K, with field up to 150 mT, and upgradation to higher field. A pill-box cavity working on TE011 and TE012 modes with removable sample/top measures surface resistance up to 60 mT based on calorimetric method from 1.6-4.5 K.*
*SRF cavities, 3rd Harmonic Analysis

Poster TUPB058 [1.581 MB]

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TUPB060

Measurements of RF Properties of Thin Film Nb3Sn Superconducting Multilayers Using a Calorimetric Technique

SRF, impedance, radio-frequency, vacuum

720

S.I. Sosa Guitron, J.R. Delayen, A.V. Gurevich
ODU, Norfolk, Virginia, USA
E. Chang Beom, C. Sundahl
University of Wisconsin-Madison, Madison, USA
G.V. Eremeev
JLab, Newport News, Virginia, USA

Funding: DOE Contract No. DE-AC05-06OR23177 DOE Grant No. DE-SC0010081
Results of RF tests of Nb3Sn thin film samples related to the superconducting multilayer coating development are presented. We have investigated thin film samples of Nb3Sn/Al2O3/Nb with Nb3Sn layer thicknesses of 50 nm and 100 nm using a Surface Impedance Characterization system. These samples were measured in the temperature range 4 K-19 K, where significant screening by Nb3Sn layers was observed below 16-17 K, consistent with the bulk critical temperature of Nb3Sn.

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TUPB062

Evaluation of Sc Property Coated on a Surface

ion, vacuum, gun, neutron

723

Y. Iwashita, Y. Fuwa
Kyoto ICR, Uji, Kyoto, Japan
M. Hino
Kyoto University, Research Reactor Institute, Osaka, Japan
T. Kubo, T. Saeki
KEK, Ibaraki, Japan

Funding: This work was supported by JSPS KAKENHI Grant Number 26600142.
We are trying to deposit thin superconducting material on a substrate for higher accelerating field gradients. In order to evaluate the deposit method, surface properties are under measurement. Some results on measurements at DC and a preparation status toward RF measurement will be reported.

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TUPB063

A Multi-Sample Residual Resistivity Ratio System for High Quality Superconductor Measurements

ECR, niobium, feedback, electron

726

J.K. Spradlin, C.E. Reece, A-M. Valente-Feliciano
JLab, Newport News, Virginia, USA

Funding: This work is supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC05-06OR2317.
For developing accelerator cavity materials, superconducting transition temperature (T_C), transition width (ΔTC), and residual resistivity ratio (RRR), are useful parameters to correlate with SRF performance and fabrication processes of bulk, thin film, and novel materials. The RRR gauges the purity and structure of the superconductor based on the temperature dependence of electron scattering in the normal conducting state. Combining a four point probe delta pulse setup with a switch allows multiplexing of the electrical measurements to 32 samples per cooldown cycle. The samples are measured inside of an isothermal setup in a liquid helium (LHe) dewar. The isothermal setup is required for a quasistatic warmup of the samples through TC. This contribution details the current setup for collecting RRR and TC data, the current standard of throughput, measurement quality of the setup, and the improvements underway to increase the system’s resolution and ease of use.

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TUPB064

Superconducting Thin Film Test Cavity Commissioning

vacuum, niobium, cryogenics, resonance

731

P. Goudket, K.D. Dumbell, L. Gurran, O.B. Malyshev, N. Pattalwar, S.M. Pattalwar, R. Valizadeh
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
G. Burt, L. Gurran
Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
G. Burt, L. Gurran
Lancaster University, Lancaster, United Kingdom
P. Goudket, O.B. Malyshev, S.M. Pattalwar, R. Valizadeh
Cockcroft Institute, Warrington, Cheshire, United Kingdom
T.J. Jones, E.S. Jordan
STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom

A radiofrequency (RF) cavity and cryostat dedicated to the measurement of superconducting coatings at GHz frequencies was designed to evaluate surface resistive losses on a flat sample. The test cavity consists of two parts: a cylindrical half-cell made of bulk niobium (Nb) and a flat Nb disc. The two parts can be thermally and electrically isolated via a vacuum gap, whereas the electromagnetic fields are constrained through the use of RF chokes. Both parts are conduction cooled hence the cavity halves are suspended in vacuum during operation. The flat disc can be replaced with a sample, such as a Cu disc coated with a film of niobium or any other superconducting material. The RF test provides simple cavity Q-factor measurements as well as calorimetric measurements of the losses on the sample. The advantage of this method is the combination of a compact cavity with a simple planar sample. The paper describes the RF, mechanical and cryogenic design, and initial commissioning of the system with notes on how any issues arising are to be addressed.

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TUPB065

Cryogenic RF Characterization of Superconducting Materials at SLAC With Hemispherical Cavities

niobium, SRF, factory, cryogenics

735

P.B. Welander, M.A. Franzi, S.G. Tantawi
SLAC, Menlo Park, California, USA

For the characterization of SRF materials, we have commissioned a second-generation, X-band cavity cryostat that can rapidly analyze thin-film coatings or bulk samples. The system operates at 11.4 GHz, at temperatures down to 4 K, and utilizes two interchangeable hemispherical cavities (one Cu, one Nb) that can accommodate 51 mm-diameter samples on the flat side. The cavities are designed to operate with a TE032-like mode where the magnetic field is strongest on the sample surface. As a result, the sample accounts for 33% of the overall cavity loss, despite comprising less than 8% of the total surface area. For low-power testing we utilize a programmable network analyzer, while for high-power testing we connect the cavity to a 50 MW XL-4 klystron. With the Nb cavity we can measure surface resistances down to 0.7 microhm, while with the Cu cavity we can measure quenching fields up to 360 mT. X-band operation permits a compact cavity and cryostat design with a reasonable sample size, while the closed-cycle pulse-tube cryorefrigerator allows for rapid sample cycling. We will discuss cryostat design, cavity modeling, measurement limits, and recent sample testing results.

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TUPB071

Development and Testing of a 325 MHz beta0 = 0.82 Single-Spoke Cavity

linac, vacuum, impedance, cryogenics

744

C.S. Hopper, J.R. Delayen, H. Park
ODU, Norfolk, Virginia, USA
J.R. Delayen, H. Park
JLab, Newport News, Virginia, USA

A single-spoke cavity operating at 325 MHz with geometric beta of 0.82 has been developed and tested. Initial results* showed high levels of field emission which limited the achievable gradient. Several rounds of helium processing significantly improved the cavity performance. Here we discuss the development process and report on the improved results.
*C.S. Hopper, HyeKyoung Park, and J.R. Delayen, “Cryogenic Testing of High-Velocity Spoke Cavities,” Proc. of the 27th Linear Accelerator Conference, Geneva, Switzerland, TUPP109, (2014).

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TUPB072

Report of Vertical Test of the β=0.12 Half-Wave Resonator at RISP

ion, vacuum, TRIUMF, simulation

747

G.-T. Park, H.J. Cha, H. Kim, W.K. Kim
IBS, Daejeon, Republic of Korea
Z.Y. Yao
TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada

β=0.12, f=162.5 MHz half-wave resonator for Rare Isotope Science Project (RISP) was recently tested at TRIUMF. We briefly report the vertical test result: At 2K, the cavity achieved Q₀=2·10⁹ at E_acc=6.4 MV/m and the performance was limited at E_acc=7.8 MV/m by intense field emission. The surface processing was standard: 120 micron buffered chemical polishing followed by high pressure rinsing. After first cold test, 120C baking was done and the corresponding result was also obtained.

Poster TUPB072 [0.414 MB]

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TUPB073

Cold Tests of SSR1 Resonators Manufactured by IUAC for the Fermilab PIP-II Project

niobium, electron, proton, radio-frequency

750

L. Ristori, A. Grassellino, O.S. Melnychuk, D.A. Sergatskov, A.I. Sukhanov
Fermilab, Batavia, Illinois, USA
K.K. Mistri, P.N. Potukuchi, A. Rai, J. Sacharias, S.S.K. Sonti
IUAC, New Delhi, India

In the framework of the Indian Institutions and Fermilab Collaboration (IIFC) within the PIP-II project, two Superconducting Single Spoke Resonators were manufactured at the Inter-University Accelerator Centre (IUAC) in New Delhi and tested at Fermilab. The resonators were subject to the routine series of inspections and later processed chemically by means of Buffered Chemical Polishing, heat-treated at 600 C and cold-tested at Fermilab in the Vertical Test Stand. In this paper we present the findings of the inspections and the results of the cold-tests.

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TUPB074

High-Vacuum Simulations and Measurements on the SSR1 Cryomodule Beam-Line

vacuum, cryomodule, simulation, niobium

754

D. Passarelli, T.H. Nicol, M. Parise, L. Ristori
Fermilab, Batavia, Illinois, USA

Funding: Work supported by Fermi Research Alliance, LLC under Contract No. DEAC02- 07CH11359 with the United States Department of Energy
In order to guarantee an effective cool-down process for the SSR1 cryomodule, a high-vacuum level must be achieved at room temperature in the beam-line before introducing gaseous and liquid helium. The SSR1 cavities in the beamline have a small beam aperture compared to the size of their internal volume. To avoid unnecessary complications for the vacuum piping of the cryomodule cold-mass, a pilot study was conducted on the string prior to processing and qualification of the components to investigate the vacuum level achievable by pumping only through the beam-line. To estimate the pressure distribution inside the cavity string we used a mathematical model implemented in a test-particle Monte-Carlo simulator for ultra-high-vacuum systems.

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TUPB075

Measurements on the Superconducting 217 MHz CH Cavity During the Manufacturing Phase

simulation, operation, resonance, linac

757

F.D. Dziuba, M. Amberg, M. Basten, M. Busch, H. Podlech
IAP, Frankfurt am Main, Germany
M. Amberg, K. Aulenbacher, W.A. Barth, S. Mickat
HIM, Mainz, Germany
K. Aulenbacher
IKP, Mainz, Germany
W.A. Barth, S. Mickat
GSI, Darmstadt, Germany

Funding: GSI, HIM, BMBF Contr. No. 05P12RFRBL
Since in future the existing UNILAC (Universal Linear Accelerator) will be used as an injector for the FAIR (Facility for Antiproton and Ion Research) project, a new superconducting (sc) continuous wave (cw) linac at GSI is proposed to keep the Super Heavy Element (SHE) program at a competitive high level. In this context, a sc 217 MHz crossbar-H-mode (CH) cavity has been designed at the Institute for Applied Physics (IAP), Frankfurt University, and was built at Research Instruments (RI) GmbH, Germany. The cavity serves as a first prototype to demonstrate the reliable operability under a realistic accelerator environment and its successful beam operation will be a milestone on the way to the new linac. In this contribution measurements during the production process of the cavity as well as corresponding simulations will be presented.

Poster TUPB075 [2.476 MB]

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TUPB076

The Multipacting Study of Niobium Sputtered High-Beta Quarter-Wave Resonators for HIE-ISOLDE

electron, simulation, pick-up, niobium

760

P. Zhang, W. Venturini Delsolaro
CERN, Geneva, Switzerland

Funding: This work has been supported partly by a Marie Curie Early Initial Training Network Fellowship of the European Community’s 7th Programme under contract number PITN-GA-2010-264330-CATHI.
Superconducting quarter-Wave Resonators (QWRs) will be used in the superconducting linac upgrade in the frame of HIE-ISOLDE project at CERN. The cavities are made of bulk copper with thin niobium film coated. They will be operated at 101.28 MHz at 4.5 K providing 6 MV/m accelerating gradient with 10 W power dissipation. Multipacting (MP) has been studied for the high-beta (β=10.9%) QWRs and two MP barriers have been found: Eacc at around 0.05MV/m and 1.5MV/m. We have used both CST Microwave Studio & Particle Studio and the parallel codes Omega3P & Track3P developed at SLAC. The results from the two codes are consistent and are in good agreement with cavity vertical cold test results. Both MP barriers can be processed by RF during the cavity cold test.

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TUPB077

The Influence of Cooldown Conditions at Transition Temperature on the Quality Factor of Niobium Sputtered Quarter-Wave Resonators for HIE-ISOLDE

niobium, accelerating-gradient, linac, cathode

765

P. Zhang, G.J. Rosaz, A. Sublet, M. Therasse, W. Venturini Delsolaro
CERN, Geneva, Switzerland

Funding: This work has been supported partly by a Marie Curie Early Initial Training Network Fellowship of the European Community’s 7th Programme under contract number PITN-GA-2010-264330-CATHI.
Superconducting quarter-wave resonators (QWRs) are to be used in the ongoing linac upgrade of the ISOLDE facility at CERN. The cavities are made of niobium sputtered on copper substrates. They will be operated at 101.28 MHz at 4.5 K providing 6 MV/m accelerating gradient with 10 W power dissipation. In recent measurements, we found the thermal gradient along the cavity during the niobium superconducting transition has an impact on the cavity quality factor. On the other hand, the speed of the cooling down through the superconducting transition turned out to have no influence on the cavity Q-factor.

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TUPB078

Developments on a Cold Bead-Pull Test Stand for SRF Cavities

HOM, SRF, factory, operation

770

A.V. Vélez, A. Frahm, J. Knobloch, A. Neumann
HZB, Berlin, Germany

Final tuning and field profile characterization of SRF cavities always takes place at room temperature. However, important questions remains as to what happens when the cavity is cooled to LHe temperature, in particular with multi cell systems. To enable the characterization of cavities in the cold, we have designed and commissioned a "cold bead-pull" test stand at HZB. The present test stand is designed to be integrated in HoBiCaT (Horizontal bi-cavity testing facility) with the ability to provide electric field profile measurements under realistic superconducting conditions (T=1.8K). In this paper mechanical and operational details of the apparatus will be described as well as future plans for the development and usage of this facility.

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TUPB079

Second Sound Quench Detection of Dressed TESLA-Shape SRF Cavities

detector, simulation, SRF, HOM

774

Y. Tamashevich
University of Hamburg, Hamburg, Germany
E. Elsen, A. Navitski
DESY, Hamburg, Germany

A compact detector and numerical algorithm for second sound measurements has been developed. The detector allows precise 3D quench localisation within a single unit and can be used even for cavities with mounted helium tank. The compact device is easily mounted and requires minimum space. It can be used as a part of the standard cold test of cavities. The results obtained with the new detector and a 3D algorithm have been cross-checked by optical inspection and resistor-based temperature mapping. The resolution of the detector is seen to be limited by the sampling rate and the lateral extent of the quench induced heated area on the Nb superconductor.

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TUPB080

Diagnostic Developments at CERN’s SRF Testing Facility

diagnostics, monitoring, SRF, niobium

778

A. Macpherson, S. Aull, A. Benoit, P.F. Fernández López, K.G. Hernández-Chahín, C. Jarrige, P. Maesen, K.M. Schirm, R. Torres-Sanchez, R. Valera Teruel
CERN, Geneva, Switzerland
K.G. Hernández-Chahín
DCI-UG, León, Mexico
T. Junginger
HZB, Berlin, Germany
T. Junginger
TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada

As part of CERN’s re-establishment of an SRF cold testing facility for bulk niobium cavities, diagnostic instrumentation and testing procedures on our vertical cryostat have been upgraded, with particular attention given to quench location, ambient magnetic field control, thermometry and thermal cycling techniques. In addition, preparation and measurement procedures have been addressed, allowing for improved measurement of cavity properties and detailed study of transient effects during the course of cavity testing.

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TUPB081

Multi-Cell Temperature Mapping and Conclusions

SRF, monitoring, controls, cryogenics

783

F. Furuta, R.G. Eichhorn, G.M. Ge, D. Gonnella, D.L. Hartill, G.H. Hoffstaetter, J.J. Kaufman, M. Liepe, E.N. Smith
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Multi-cell temperature mapping (T-map) system has been developed and applied on SRF Nb cavities vertical tests (VT) at Cornell. It has nearly two thousand thermometers and achieved a 1mK resolution of niobium surface temperature rinsing in superfluid helium . We have upgraded the system to be capable of monitoring the temperature profiles of quench spot on cavity. The recent results of T-map during cavity tests and details will be reported.

Poster TUPB081 [4.421 MB]

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TUPB082

Automatic Surface Defect Detection and Sizing for Superconducting Radio Frequency Cavity Using Haar Cascades

niobium, background, radio-frequency, SRF

788

G.V. Eremeev
JLab, Newport News, Virginia, USA
D.C. Iriks
Santa Rosa Junior College, Santa Rosa, USA

Serious albeit tiny surface defects can remain on the surface of superconducting radio frequency (SRF) cavities after polishing and cleaning. These defects reduce the efficiency of cavities and often limit the maximum attainable fields. We applied a Haar cascade artificial vision technique for automated identification, counting, and sizing of defects induced on niobium surface by Nb-H precipitates formed at cryogenic temperatures. The defects were counted and sized by a computer program and also counted and measured manually to estimate detection rate and accuracy of sizing. The overall detection rate was 53%, and the overall false positive rate was 29%. The technique that was used to automatically size the features was found to oversize the features, but oversize them consistently, resulting in a size histogram that represents the defect size distribution on the sample. After scaling the histogram data, the average defect area was found to be 90 square micrometers with the standard deviation of 70 square micrometers.

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TUPB083

Test Characterization of Superconducting Spoke Cavities at Uppsala University

cryogenics, superconductivity, accelerating-gradient, pick-up

791

H. Li, A.K. Bhattacharyya, V.A. Goryashko, L. Hermansson, R.J.M.Y. Ruber, R. Santiago Kern
Uppsala University, Uppsala, Sweden
D.S. Dancila
Uppsala University, Department of Engineering Sciences, Uppsala, Sweden
G. Olry
IPN, Orsay, France

As part of the development of the ESS spoke linac, the FREIA Laboratory at Uppsala University, Sweden, has been equipped with a superconducting cavity test facility. The cryogenic tests of a single and double spoke cavity developed by IPN Orsay have been performed in the new HNOSS horizontal cryostat system. The cavities are equipped with a low power input antenna and a pick-up antenna. Different measurement methods were investigated to measure the RF signal coupling from the cavity. Results from the tests confirm the possibility to transport the cavities from France to Sweden without consequences. We present the methods and preliminary study results of the cavity performance.

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TUPB085

Characterization of Optical Surface Properties of 1.3 GHz SRF Cavities for the European XFEL

background, electron, niobium, SRF

795

M. Wenskat, L. Steder
DESY, Hamburg, Germany

The optical inspection of the inner surface of superconducting rf cavities is a well-established tool at many laboratories. Its purpose is to recognise and understand field limitations and to allow optical quality assurance during cavity production. Within the ILC-HiGrade programme at DESY, as part of the XFEL cavity production, an automated image processing and analysis algorithm has been developed that recognises structural boundaries. The count of features, the length of boundaries and their orientation can be used for characterisation. Appreciable differences are observed depending on the fabrication process at the vendor and the chemical treatment applied. The potential of this framework for automated quality assurance as an integral part of large-scale cavity production will be outlined. In addition, correlations between geometrical surface properties and the maximal accelerating field of twenty cavities have been found. These observations coincide with quench localisation by second sound of two cavities. The distribution of the limiting cell is vendor dependent, indicating weaknesses in the fabrication procedure.

Poster TUPB085 [2.272 MB]

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TUPB087

Development of an X-Ray Fluorescence Probe for Inner Cavity Inspection

detector, niobium, radiation, background

799

M. Bertucci, P. Michelato, L. Monaco, M. Moretti, C. Pagani
INFN/LASA, Segrate (MI), Italy
A. Navitski
DESY, Hamburg, Germany

The development of an x-ray fluorescence probe for detection of foreign material inclusions of the inner surface of 1.3 GHz tesla-type Niobium cavities is here presented. The setup dimensions are minimized so to access the inner cavity volume and focus on the surface of equator. Preliminary tests confirmed the system capability to detect and localize with good precision small metal inclusions of few micrograms. The results obtained from the inspection of some 1.3 GHz XFEL series production cavities are also pointed out.

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TUPB088

On Quench Propagation, Quench Detection and Second Sound in SRF Cavities

niobium, SRF, simulation, interface

804

S.R. Markham, R.G. Eichhorn, D.L. Hartill, G.H. Hoffstaetter
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Quench location detection has provided valuable insight in SRF cavity operation since two decades. While in earlier days temperature maps were used the state of the art technique nowadays is detecting the second sound wave, excited by a quench, using oscillating super-leak detector (OSTs). Typically, many OSTs surround the cavity and the quench location is determined by triangulation of the different OST signals. Convenient as the method is there is a mystery: taking the well-known velocity of the second sound wave, the quench seems to come from a place slightly above the cavity’s outer surface. In addition, not all triangulation spheres intersect in one point. We will present a model based on numerical quench propagation simulations that is able to fully explaining this discrepancy.

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TUPB089

High-Precision Measurements of the Quality Factor of Superconducting Cavities at the FREIA Laboratory

coupling, impedance, network, SRF

810

V.A. Goryashko, K.J. Gajewski, L. Hermansson, H. Li, H. Nicander, R.J.M.Y. Ruber, R. Santiago Kern, S. Teerikoski
Uppsala University, Uppsala, Sweden
D.S. Dancila
Uppsala University, Department of Engineering Sciences, Uppsala, Sweden

In this paper we propose a high-precision method of measuring Q0 of SRF cavities. A common way to study the performance of an SRF cavity is to build an oscillator around it that is referred to as a self-exciting loop. In the standard approach, by tuning the loop phase for a maximum field level in the cavity and measuring forward and reflected waves, one finds the cavity coupling. Then, performing a time-decay measurement and finding the total quality factor, one gets Q0. However, this approach suffers from a deficiency originating from a single data-point measurement of the reflection coefficient. In our method by varying the loop phase shift, one obtains amplitudes of the reflection coefficient of the cavity as a function of its phases. The complex reflection coefficient describes a perfect circle in polar coordinates. Fitting the overdetermined set of data to that circle allows more accurate calculation of Q0 via the least-squares procedure. The method has been tested at the FREIA Laboratory on two cavities from IPN Orsay: a single spoke and a prototype ESS double spoke.

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TUPB091

Systematic Uncertainties in RF-Based Measurement of Superconducting Cavity Quality Factors

coupling, resonance, factory, superconducting-cavity

814

W. Schappert, J.P. Holzbauer, Y.M. Pischalnikov, D.A. Sergatskov
Fermilab, Batavia, Illinois, USA

Measurements of cavity quality factor measurements are subject to at least three potentially large sources of systematic error that have not been previously recognized. Imperfect coupler directivity (cross-talk) can lead to large errors in the cavity coupling factor when the cavity coupling factor is significantly different than unity. Energy re-reflected from the circulator can systematically bias the measured cavity decay time which is used to determine the loaded quality factor. Use of the peak probe power or the minimum of the reflected power to determine the cavity resonance frequency rather than the peak of the probe/forward transfer function may lead to errors in the resonance frequency that can also affect quality factors. Each effect is illustrated with measurements in the Fermilab VTS, simulations and analytic calculations. If the magnitude and phase of the cavity RF signals are measured, these effects can be measured and corrected for. If only signal magnitudes are recorded or these effects are not measured, they must be treated as sources of systematic uncertainty.

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TUPB093

Initial Commissioning Experience with the Spallation Neutron Source Vertical Test Area RF System

operation, software, controls, hardware

819

M.T. Crofford, J.A. Ball, M. Doleans, S.-H. Kim, S.W. Lee, J.D. Mammosser, J. Saunders
ORNL, Oak Ridge, Tennessee, USA
T.L. Davidson, S. Whaley
ORNL RAD, Oak Ridge, Tennessee, USA

Funding: SNS is managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. Department of Energy.
The Spallation Neutron Source (SNS) has developed a vertical test area (VTA) for the testing and qualification of superconducting radio frequency cavities. The associated RF System successfully supported the initial commissioning of the VTA system and has been utilized for cavity testing at both 4 and 2 K. As operational experience was gained, improvements to the RF system were implemented to better utilize the dynamic range of the system, and software updates and additions were made to meet the operational needs. The system continues to evolve as we gain better understanding of the testing needs.

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TUPB094

Jefferson Lab Vertical Test Area RF System Improvement

network, controls, software, low-level-rf

823

T. Powers, M.L. Morrone
JLab, Newport News, Virginia, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177 with supplemental funding from the LCLS-II Project U.S. DOE Contract No. DE-AC02-76SF00515.
RF systems for testing critically coupled SRF cavities require the ability to track the cavity frequency excursions while making accurate measurements of the radio frequency (RF) signals associated with the cavity. Two types of systems are being used at Jefferson Lab. The first, the traditional approach, is to use a voltage controlled oscillator configured as a phase locked loop such that it will track the cavity frequency. The more recently developed approach is to use a digital low level RF (LLRF) system in self excited loop (SEL) mode to track the cavity frequency. Using a digital LLRF system in SEL mode has the advantage that it is much easier to lock to the cavity’s resonant frequencies and they tend to have a wider capture range. This paper will report on the system designs used to implement the 12 GeV digital LLRF system in the JLAB vertical test area. Additionally, it will report on the system modifications which are being implemented so that the RF infrastructure in the VTA will be ready to support the LCLS II cryomodule production effort, which is scheduled to begin in calendar year 2016.

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TUPB095

Resonance Control for Narrow-Bandwidth, Superconducting RF Applications

resonance, feedback, SRF, operation

828

W. Schappert, J.P. Holzbauer, Y.M. Pischalnikov
Fermilab, Batavia, Illinois, USA
D. Gonnella
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
M. Liepe
Cornell University, Ithaca, New York, USA

Optimal control techniques have been employed in a variety of applications since they were first developed more than 60 years ago but until now they have been used in few if any accelerator-related applications. The next generation of superconducting accelerators will require both precise control of the gradient and active stabilization of the resonance frequency. Optimal control techniques provide a self-consistent framework within which to construct a combined electro-mechanical controller. Results from recent cold cavity tests at Fermilab are presented.

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TUPB096

Mechanical Damper Study for ISAC-II Quarter Wave Resonators

damping, ISAC, simulation, resonance

832

L. Yang, R.E. Laxdal, V. Zvyagintsev
TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada

ISAC-II superconducting quarter wave resonators are equipped with mechanical dampers to supress mechanical oscillations of the cavity structure. The study has been carried out to optimize the damper efficiency.

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TUPB097

The Study on Microphonics of Low Beta HWR Cavity at IMP

LLRF, cryomodule, SRF, FPGA

837

Z. Gao, W. Chang, Y. He, W.M. Yue, S.H. Zhang, Z.L. Zhu
IMP/CAS, Lanzhou, People's Republic of China
Q. Chen
IHEP, Beijing, People's Republic of China
T. Powers
JLab, Newport News, Virginia, USA

The superconducting linac of China Accelerator-Driven System Injector II will operate at CW-mode. The mechanical vibrations of the superconducting cavity, also known as microphonics, cause shifts in the resonant frequency of the cavity. The microphonics is the main disturbance source of cavity frequency shifts when the cavity running in CW mode. In order to understand the effects, microphonics measurements were performed on the half-wave superconducting cavities when they were operated in the cryostat. And the experimental modal test was also performed to identify noise source and improve the cavity structure optimization. The measurement method and results will be shown and analyzed in this paper.

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TUPB098

Error Analysis on RF Measurement Due to Imperfect RF Components

coupling, SRF, LLRF, radio-frequency

840

G. Wu, S. Aderhold, M. Checchin, M. Martinello, J.P. Ozelis
Fermilab, Batavia, Illinois, USA

Funding: Work supported by FRA under DOE contract DE-AC02-07CH11359
An accurate cavity test involves the accurate power measurement and decay time measurement. The directional coupler in a typical cavity test llrf system usually has low directivity due to broadband requirement and fabrication errors. The imperfection of the directional coupler brings unexpected systematic errors for cavity power measurement in both forward and reflect power. An error analysis will be giving and new specification of directional coupler is proposed.

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TUPB099

Magnetic Foils for SRF Cryomodule

shielding, SRF, cryogenics, niobium

844

G. Wu, S. Aderhold, S.K. Chandrasekaran, A.C. Crawford, A. Grassellino, C.J. Grimm, J.P. Ozelis, D.A. Sergatskov, A. Vostrikov
Fermilab, Batavia, Illinois, USA

Funding: Work supported by FRA under DOE contract DE-AC02-07CH11359
High quality factor niobium cavities require minimal residual magnetic field around the high magnetic field region. A typical global magnetic shield takes more material and provides less effective magnetic screening. On the other hand, local magnetic shield has to introduce complex geometries to cover access ports and instrumentation and thermal straps. Local magnetic source and thermal current will increase residual field seen by SRF cavities regardless the complexity of local magnetic shield. Magnetic foils that is cryogenic compatible provides a great benefit to reduce residual magnetic field. This paper will describe the evaluation of such magnetic foils in both vertical and horizontal test.

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TUPB100

CEA Experience and Effort to Limit Magnetic Flux Trapping in Superconducting Cavities

cryomodule, solenoid, SRF, vacuum

847

J. Plouin, F. Leseigneur
CEA/DSM/IRFU, France
N. Bazin, P. Charon, G. Devanz, H. Dzitko, P. Hardy, J. Neyret, O. Piquet
CEA/IRFU, Gif-sur-Yvette, France

Protecting superconducting cavities from the surrounding static magnetic field is considered as a key point to reach very good cavity performances. This can be achieved by both limiting the causes of magnetic flux around the cavity in the cryomodule, and enclosing cavities and/or cryomodules into magnetic shields. We will present the effort made at CEA into this direction: shield design, shield material characterization, at room and cryogenic temperature, and search and attenuation of the magnetic background present in the cryomodule during the cavities superconducting transition. This last point will be especially studied for the IFMIF project where the cryomodule houses the focusing magnets. Aspects of the cold magnetic shields for ESS will also be discussed.

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TUPB101

Design of the Thermal and Magnetic Shielding for the LHC High Luminosity Crab-Cavity Upgrade

shielding, cryomodule, simulation, operation

852

N. Templeton, T.J. Jones
STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom
K. Artoos, R. Calaga, O. Capatina, T. Capelli, F. Carra, R. Leuxe, C. Zanoni
CERN, Geneva, Switzerland
G. Burt, S.M. Pattalwar
Cockcroft Institute, Warrington, Cheshire, United Kingdom
G. Burt
Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
G. Burt
Lancaster University, Lancaster, United Kingdom
K.B. Marinov, A.J. May, S.M. Pattalwar
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
A. Ratti
LBNL, Berkeley, California, USA

Before the High Luminosity (Hi-Lumi) upgrade of the Large Hadron Collider (LHC), two pairs of superconducting compact Crab Cavities are to be tested within separate cryomodules, on the Super Proton Synchrotron (SPS) at CERN in 2018 prior to Long Shutdown 2. Two novel side-loaded cryomodules, which allow ease of access for assembly, inspection and maintenance, have been developed for the prototype tests. The cryomodule shielding includes a thermal shield and double layer magnetic shield, consisting of a warm-outer shield, and two cold-inner shields (one per cavity). Various constraints and considerations have led to unique cold shielding, mounted inside the cavity helium vessels, resulting in several design challenges. The shielding adopts and utilises the module’s side-loaded configuration, for continuity and accessibility, while satisfying tight spatial constraints and requirements to meet the functional specification. This paper outlines the design, analysis, manufacture and assembly of the Hi-Lumi SPS test cryomodule’s thermal and magnetic shielding, which are critical to achieving the operational stability.

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TUPB102

Validation of Local Magnetic Shielding for FRIB Using a Prototype Cryomodule

solenoid, operation, shielding, cryomodule

857

S.K. Chandrasekaran, K. Saito
FRIB, East Lansing, Michigan, USA

Funding: Work supported by the U.S. Department of Energy Office of Science under Cooperative Agreement DE-SC0000661, and the U.S. National Science Foundation under Grant No. PHY-1102511.
The local magnetic shield design and cryogenic magnetic shielding material for the FRIB QWR cryomodule was validated in a two cavity, one solenoid prototype cryomodule. The magnetic fields were measured inside and outside the magnetic shielding before, during, and after operation of an 8 T superconducting solenoid. The effect of demagnetization cycles of the solenoid was also examined. The magnetic field at the cavity’s high RF magnetic field area, inside the magnetic shield and with the solenoid off, was measured using a single-axis fluxgate to be less than 0.3 μT (3 mG) after cool down of the cryomodule. A 3.07 μT (30.7 mG) residual field was observed at high magnetic field area after conclusion of solenoid operation. This was attributed to the persistent currents circulating in the superconducting solenoid. Demagnetization cycles were therefore determined to be unnecessary for FRIB cryomodules, as long as the solenoid is normal conducting when the cavity is cooled through the superconducting critical temperature.
S.K. Chandrasekaran currently at Fermi National Accelerator Laboratory, Batavia, IL, USA.

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TUPB103

Cryomodule Protection for ARIEL e-Linac

cryomodule, beam-loading, linac, vacuum

861

Z.Y. Yao, R.E. Laxdal, W.R. Rawnsley, V. Zvyagintsev
TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada

The e-Linac cryomodules require high RF power, cryogenics, ultra-high vacuum, and precise mechanical adjustment. They require protection against of failures, like quench in the cavity, bad vacuum or multipacting in power couplers, low liquid helium level or high temperatures. The protection unit should stop RF power in the cryomodule in case of the listed failures. A Interlock Box is developed to implement protection function for the cryomodule. The paper will describe the design of Interlock Box for e-Linac cryomodule protection. As quench protection required, quench evolution analysis with RF transient analysis is investigated. The details of quench detection for e-Linac will also be reported.

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TUPB104

Series Production of BQU at DESY for the EU-XFEL Module Assembly at CEA Saclay

vacuum, acceleration, quadrupole, diagnostics

865

B. van der Horst, M. Helmig, A. Matheisen, S. Saegebarth, M. Schalwat
DESY, Hamburg, Germany

Each of the 10³ XFEL modules foreseen for the EU-XFEL as well as the 3,9 GHZ injector module is equipped with a combination of beam position monitors, superconducting quadrupole and a gate valve connected to the beam position monitor. The subunits are prequalified by the different work package of the EU-XFEL collaboration and handover to the DESY cleanroom. These subunits are assembled in the DESY ISO 4 cleanroom to unit named BQU, quality controlled in respect of cleanliness and handover in status “ready for assembly in ISO 4 cleanroom” for string assembly to the ISO 4 cleanroom located at CEA France. Series production started with production sequences of one unit per week and needed to be accelerated up to five or six units per month (>=1.25 units per week) in beginning of 2015. Analysis of data taken during production and the optimization of work flow for higher production rates are presented.

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TUPB105

String Assembly for the EU-XFEL 3.9 GHz Module at DESY

alignment, vacuum, quadrupole, linac

869

M. Schmökel, R. Bandelmann, A. Daniel, A. Matheisen, P. Schilling, B. van der Horst
DESY, Hamburg, Germany
R. Paparella, P. Pierini, D. Sertore
INFN/LASA, Segrate (MI), Italy

For the injector of the EU- XFEL one so-called 3.9 GHz module is required. This special module houses eight 3.9 GHz s.c. cavities, a beam position monitor and a quadrupole package. The cavities were fabricated and vertically tested as an in-kind contribution to the EU-XFEL by INFN Milano collaborators. The power couplers have been fabricated and conditioned by FNAL. The string assembly took place inside the ISO 4 cleanroom at DESY. A seven meter long alignment and assembly girder for this special string assembly has been designed and fabricated at DESY. The girder facilitates the assembly of the 3.9 GHz resonators with alternating power coupler orientation in ISO 4 cleanrooms. For redundancy and fast action on problems during string assembly, the DESY high pressure rinsing system (HPR) has been modified on the basis of the INFN Milano design for this 3.9 GHz application. The HPR has been qualified by four 3.9 GHz resonators, tested at INFN Milano. The integration of the cavities into Helium vessels, power coupler coupling factor and the power coupler assembly at DESY is qualified by one cavity that has been equipped with Helium tank and a power coupler and tested horizontally.

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TUPB106

First HIE-ISOLDE Cryo-module Assembly at CERN

vacuum, pick-up, insertion, instrumentation

874

M. Therasse, G. Barlow, S. Bizzaglia, J.A. Bousquet, A. Chrul, P. Demarest, J-B. Deschamps, J.A. Ferreira Somoza, J. Gayde, M. Gourragne, A. Harrison, G. Kautzmann, D. Mergelkuhl, V. Parma, M. Struik, W. Venturini Delsolaro, L.R. Williams, P. Zhang
CERN, Geneva, Switzerland
J. Dequaire
Intitek, Lyon, France

The first phase of the HIE-ISOLDE project aims to increase the energy of the existing REX ISOLDE facilities from 3MeV/m to 5MeV/m. It involves the assembly of two superconducting cryo-modules based on quarter wave resonators made by niobium sputtered on copper. The first cryo-module was installed in the linac in May 2015 followed by the commissioning. The first beam is expected for September 2015. In parallel the second cryo-module assembly started. In this paper, we present the different aspects of these two cryo-modules including the assembly facilities and procedures, the quality assurance and the RF parameters (cavity performances, cavity tuning and coupling).

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TUPB107

Development of a Test Bench to Prepare the Assembly of the IFMIF LIPAC Cavity String

solenoid, cryomodule, alignment, SRF

879

N. Bazin, G. Devanz, P. Hardy, C. Servouin
CEA/DSM/IRFU, France
J.K. Chambrillon
CERN, Geneva, Switzerland
H. Dzitko, J. Neyret
CEA/IRFU, Gif-sur-Yvette, France
F. Toral
CIEMAT, Madrid, Spain

The IFMIF LIPAc cryomodule houses eight half-wave resonators and eight solenoids which will be assembled on a support frame in clean room. Due to the short lattice defined by beam dynamics constraints, there is not much room between two elements for the operators’ hands to connect them. In order to test, optimize and validate the clean room assembly procedures and the associated tools, a test bench, consisting of a frame, a little bigger than one eight of the final support has been manufactured. In order to start the tests before the delivery of the actual key components of the cryomodule, a dummy cavity, solenoid and coupler were manufactured and will be used to perform tests outside and inside the clean room to validate the assembly procedure and the tools. The mock-up will then be used to train the operators for the assembly of the whole string.

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TUPB109

Assembly and Cool-Down Tests of STF2 Cryomodule at KEK

HOM, cryomodule, vacuum, network

888

T. Shishido, K. Hara, E. Kako, Y. Kojima, H. Nakai, Y. Yamamoto
KEK, Ibaraki, Japan

As the next step of the quantum beam project, the STF2 project is in progress at KEK. Eight 9-cell SC cavities and one superconducting quardrapole magnet were assembled into the cryomodule called CM1. Four 9-cell SC cavities were assembled into the cryomodule called CM2a. These two cryomodules were connected as one unit, and the examination of completion by a prefectural government was carried out. The target value of beam energy in the STF2 accelerator is 400 MeV with a beam current of 6 mA. The first cool down test for low power level RF measurements was performed in autumn of 2014. In this paper, the assembly procedure of the STF2 cryomodules and the results of the low-power measurement are reported.

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TUPB110

LCLS-II 1.3 GHz Design Integration for Assembly and Cryomodule Assembly Facility Readiness at Fermilab

cryomodule, vacuum, instrumentation, alignment

893

T.T. Arkan, C.M. Ginsburg, Y. He, J.A. Kaluzny, Y.O. Orlov, T.J. Peterson, K. Premo
Fermilab, Batavia, Illinois, USA

Funding: DOE
LCLS-II is a planned upgrade project for the linear coherent light source (LCLS) at Stanford Linear Accelerator Center (SLAC). The LCLS-II linac will consist of thirty-five 1.3 GHz and two 3.9 GHz superconducting RF continuous wave (CW) cryomodules that Fermilab and Jefferson Lab will assemble in collaboration with SLAC. The LCLS-II 1.3 GHz cryomodule design is based on the European XFEL pulsed-mode cryomodule design with modifications needed for CW operation. Both Fermilab and Jefferson Lab will each assemble and test a prototype 1.3 GHz cryomodule to assess the results of the CW modifications. After prototype cryomodule tests, both laboratories will increase cryomodule production rate to meet the challenging LCLS-II project installation schedule requirements of approximately one cryomodule per month per laboratory. This paper presents the 1.3 GHz CW cryomodule design integration for assembly at Fermilab, Fermilab Cryomodule Assembly Facility (CAF) infrastructure modifications for the LCLS-II cryomodules, and readiness for the required assembly throughput.

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TUPB113

JLab Cryomodule Assembly Infrastructure Modifications for LCLS-II

cryomodule, vacuum, cryogenics, controls

898

E. Daly, J. Armstrong, G. Cheng, M.A. Drury, J.F. Fischer, D. Forehand, K. Harding, J. Henry, K. Macha, J.P. Preble, A.V. Reilly, K.M. Wilson
JLab, Newport News, Virginia, USA

Funding: This work was supported by the LCLS-II Project and the U.S. Department of Energy, Contract DE-AC02-76SF00515.
The Thomas Jefferson National Accelerator Facility is currently engaged, along with several other DOE national laboratories, in the Linac Coherent Light Source II project (LCLS II). The SRF Institute at Jefferson Lab will be building 1 prototype and 17 production cryomodules based on the TESLA / ILC / XFEL design. Each cryomodule will contain eight nine cell cavities with coaxial power couplers operating at 1.3 GHz. New and modified infrastructure and assembly tooling is required to construct cryomodules in accordance with LCLS-II requirements. The approach for modifying assembly infrastructure included evaluating the existing assembly infrastructure implemented at laboratories world-wide in support of ILC and XFEL production activities and considered compatibility with existing infrastructure at JLab employed for previous cryomodule production projects. These modifications include capabilities to test cavities, construct cavity strings in a class 10 cleanroom environment, assemble cavity strings into cryostats, and prepare cryomodules for cryogenic performance testing. This paper will give a detailed description of these modifications.

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TUPB114

Transient Study of Beam Loading and Feed-Forward LLRF Control of ARIEL Superconducting RF e-LINAC

controls, linac, beam-loading, feedback

902

E. Thoeng
UBC & TRIUMF, Vancouver, British Columbia, Canada
R.E. Laxdal
TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada

ARIEL e-LINAC is a ½ MW-class SRF accelerator operated at 10 mA of average current. In the initial commissioning, e-LINAC will be tested with increasing duty factors from 0.1% up to CW mode. During the pulsed mode operation, beam loading causes cavity gradient fluctuation and therefore transient behaviour of SRF Cavity gradient needs to be studied in order to determine how the Low-level RF (LLRF) should be implemented. Performance of LLRF control system with and without non-adaptive feed-forward are simulated to determine the resulting beam energy spread and experimental measurements are proposed to measure the increase of beam size due to beam loading.

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TUPB117

Cavities and Cryomodules Managing System at AMTF

cryomodule, cryogenics, status, vacuum

910

M. Wiencek, K. Krzysik, J. Świerbleski
IFJ-PAN, Kraków, Poland
J. Chodak
DESY, Hamburg, Germany

800 SRF cavities and 100 SRF cryomodules are under test in the AMTF Hall at DESY, Hamburg. Testing of such a large volume of components requires a management system which can store the measurement data. In addition the system should simplify tasks which are recurrent. In the case of the system developed at AMTF, communication with external databases has also been developed. An added complication is that not all the test procedures are identical for each component, and therefore the management system keeps track of all work done for each of the individual components. In the case of the vertical acceptance tests for the 800 SRF cavities, the management system provides an interface for specifying a decision of the next step each cavity (e.g. send for module assembly or retreatment). This paper describes the most important parts of this system.

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TUPB118

Improvements of the RF Test Procedures for European XFEL Cryomodule Testing

cryomodule, cryogenics, HOM, LLRF

914

M. Wiencek, K. Kasprzak, D. Konwisorz, S. Myalski, K. Turaj, A. Zwozniak
IFJ-PAN, Kraków, Poland

The testing of the 100 SRF cryomodules for E-XFEL is currently ongoing at the AMTF Hall, located at DESY, Hamburg. Cold tests for the cryomodules have been developed based on TTF (Tesla Test Facility) experience. However, to be able to test the cryomodules with required test rate of one a week, some improvements to the measurements had to be made. The goal of these improvements was to reduce the time needed for testing without losing any of the important data for the cryomodule. Currently, after testing more than 30% of the cryomodules, gathered experience is now allowing us to skip or combine some of the measurements. This paper describes changes in the cold test procedures which have been made since the testing of the first serial cryomodules delivered by IRFU.

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WEA1A02

Surface Resistance Study on Low Frequency (Low Beta) Cavities

niobium, superconductivity, accelerating-gradient, SRF

923

D. Longuevergne, F. Chatelet, G. Michel, G. Olry, F. Rabehasy, L. Renard
IPN, Orsay, France

Additional RF tests and temperature treatments (120°C baking, 100K soaking, …) have been carried out on Spiral2 quarter-wave cavities and ESS double spoke cavities. For each test, residual resistance and BCS resistance have been evaluated by testing the cavities between 4.2K and 1.5K. This talk will summarize the main results and try to highlight the main differences with high frequency cavities.

Slides WEA1A02 [15.993 MB]

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WEA1A04

Commissioning Results of the HZB Quadrupole Resonator

niobium, electron, quadrupole, SRF

930

R. Kleindienst, A. Burrill, S. Keckert, J. Knobloch, O. Kugeler
HZB, Berlin, Germany

Funding: The research leading to these results has received funding from the European Commission under the FP7 Research Infrastructures project EuCARD-2, grant agreement no.312453
Recent cavity results with niobium have demonstrated the necessity of a good understanding of both the BCS and residual resistance. For a complete picture, and comparison with theory, it is essential that one can measure the RF properties as a function of applied magnetic field, temperature, frequency and ambient magnetic field. Standard cavity measurements are limited in their ability to change all parameters freely and in a controlled manner. On the other hand, most sample measurement setups operate at fairly high frequency, where the surface resistance is always BCS dominated. The quadrupole resonator, originally developed at CERN, is ideally suited for RF characterization of samples at frequencies of 400 and 1300 MHz, between which many of today’s SRF cavities operate. We report on a modified version of the QPR with improved RF figures of merit for high-field operation. Experimental challenges in the commissioning run and alternate designs towards a simpler sample change are shown alongside measurement results of a large grain niobium sample.

Slides WEA1A04 [5.611 MB]

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WEA1A05

Nanostructure of the Penetration Depth in Nb Cavities: Debunking the Myths and New Findings

niobium, electron, cryogenics, SRF

937

Y. Trenikhina, A. Romanenko
Fermilab, Batavia, Illinois, USA
J. Kwon, J.-M. Zuo
UIUC, Urbana, USA

Nanoscale defect structure within the magnetic penetration depth of ~100 nm is key to the performance limitations of niobium superconducting radio frequency (SRF) cavities. Using a unique combination of advanced thermometry during cavity RF measurements, and TEM structural and compositional characterization of the samples extracted from cavity walls at both room and cryogenic temperatures, we directly discover the existence of nanoscale hydrides in SRF cavities limited by the high field Q slope, and show the decreased hydride formation after 120C baking. Crucially, in extended studies we demonstrate that adding 800C hydrogen degassing - both with AND without light BCP afterwards - restores the hydride formation to the pre-120C bake level correlating perfectly with the observed high field Q slope behavior. We also show absence of niobium oxides along the grain boundaries and the modifications of the surface oxide upon 120C bake, which contradicts some of the widely used models of niobium surface.

Slides WEA1A05 [31.768 MB]

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WEA2A01

High-Velocity Spoke Cavities

simulation, linac, proton, ion

943

C.S. Hopper
ODU, Norfolk, Virginia, USA
H. Park
JLab, Newport News, Virginia, USA

There are several current and recent projects which explore the feasibility of spoke-loaded cavities operating in the high-velocity region. Spoke cavities have a large number of geometric parameters which often influence multiple rf properties. Fabricating, handling, and processing these cavities presents some unique challenges, not unlike other TEM-class structures. This paper will summarize the current efforts toward the design, fabrication, and testing of spoke cavities with optimum beta greater than 0.8.

Slides WEA2A01 [1.029 MB]

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WEA2A02

High Gradient Testing of the Five-Cell Superconducting RF Module With a PBG Coupler Cell

niobium, dipole, HOM, factory

948

S. Arsenyev
MIT/PSFC, Cambridge, Massachusetts, USA
C.H. Boulware, T.L. Grimm, A. Rogacki
Niowave, Inc., Lansing, Michigan, USA
W.B. Haynes, D.Y. Shchegolkov, E.I. Simakov, T. Tajima
LANL, Los Alamos, New Mexico, USA

Funding: DOE Office of Science/Office of High Energy Physics
Superconducting radio-frequency (SRF) accelerating structures allow high-gradient operation in continuous-wave mode. These machines can be limited by beam-breakup instability at high currents because higher-order modes with very high Q factors are easily excited by the beam. Photonic band gap (PBG) structures provide a way to strongly damp higher-order modes without compromising the performance of the structure in the fundamental mode. We first address the design of the structure and issues that arise from incorporating a complex PBG cell into an SRF module. In particular, the module was tuned to have uneven accelerating gradient profile in order to provide equal peak surface magnetic field in every cell. We then cover the fabrication steps and surface treatment of the five-cell niobium structure and report results of the high gradient tests at temperatures of 4 K and 2 K.

Slides WEA2A02 [7.023 MB]

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WEBA02

RF Measurements for Quality Assurance During SC Cavity Mass Production

HOM, controls, GUI, linac

955

A.A. Sulimov
DESY, Hamburg, Germany

The publication will describe the comprehensive program and results of RF measurements taken during the mass production of superconducting cavities for the European XFEL.

Slides WEBA02 [2.305 MB]

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WEBA03

Production Status of SRF Cavities for the Facility for Rare Isotope Beams (FRIB) Project

vacuum, niobium, linac, controls

961

C. Compton, A. Facco, S.J. Miller, J. Popielarski, L. Popielarski, A.P. Rauch, K. Saito, G.J. Velianoff, E.M. Wellman, K. Witgen, T. Xu
FRIB, East Lansing, Michigan, USA

As the Facility for Rare Isotope Beams (FRIB) project ramps into production, vendor relations, cavity quality, and schedule become critical to success. The driver linac will be constructed of 332 cavities housed in 48 cryomodules and designed with two cavity classes (quarter-wave and half-wave) and four different betas (0.041, 0.085, 0.29, and 0.53). The cavities will be supplied to FRIB from awarded industrial vendors. FRIB’s experience with SRF cavity fabrication will be presented including acceptance inspections, test results, technical issues, and mitigation strategies.

Slides WEBA03 [1.672 MB]

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WEBA04

Performances of Spiral2 Low and High Beta Cryomodules

cryomodule, linac, cryogenics, ion

967

C. Marchand, P. Bosland, G. Devanz, O. Piquet
CEA/IRFU, Gif-sur-Yvette, France
P.-E. Bernaudin, R. Ferdinand
GANIL, Caen, France
Y. Gómez Martínez
LPSC, Grenoble Cedex, France
D. Longuevergne, G. Olry
IPN, Orsay, France

All SPIRAL2 cryomodules (twelve with one quarter wave resonator (QWR) at β=0.07 and seven with two QWRs at β=0.12) have been produced and qualified, and are now in installation phase on the LINAC at GANIL. After a general introduction on the LINAC, we will first remember and compare the different design choices taken for the two families of cryomodules. We will then present a summary of the techniques used for the preparation and integration of the cavities in the cryomodules, and compare the achieved performances with design parameters. At last, we describe the status of the LINAC installation as of end of August 2015.

Slides WEBA04 [4.577 MB]

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WEBA05

Achieving High Peak Fields and Low Residual Resistance in Half-Wave Cavities

niobium, accelerating-gradient, cryomodule, vacuum

973

Z.A. Conway, A. Barcikowski, G.L. Cherry, R.L. Fischer, S.M. Gerbick, C.S. Hopper, M. Kedzie, M.P. Kelly, S.H. Kim, S.W.T. MacDonald, B. Mustapha, P.N. Ostroumov, T. Reid
ANL, Argonne, USA

Funding: Work supported by the U.S. Department of Energy Office of Science, Office of Nuclear Physics contract number DE-AC02-06CH11357, and the Office of High Energy Physics contract number DE-AC02-76CH03000.
We have designed, fabricated and tested two new half-wave resonators following the successful development of a series of niobium superconducting quarter-wave cavities. The half-wave resonators are optimized for β = 0.11 ions, operate at 162.5 MHz and are intended to provide up to 2 MV effective voltage for particles with the optimal velocity. Testing of the first two half-wave resonators is complete with both reaching accelerating voltages greater than 3.5 MV with low-field residual resistances of 1.7 and 2.3 nΩ respectively. The intention of this paper is to provide insight into how Argonne achieves low-residual resistances and high surface fields in low-beta cavities by describing the cavity design, fabrication, processing and testing.

Slides WEBA05 [2.927 MB]

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WEBA07

Beam Commissioning of the 56 MHz QW Cavity in RHIC

HOM, operation, damping, SRF

982

Q. Wu, S.A. Belomestnykh, I. Ben-Zvi, M. Blaskiewicz, T. Hayes, K. Mernick, F. Severino, K.S. Smith, A. Zaltsman
BNL, Upton, Long Island, New York, USA
S.A. Belomestnykh, I. Ben-Zvi
Stony Brook University, Stony Brook, USA

Funding: This work was supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. DOE.
A 56 MHz superconducting RF cavity has been designed, fabricated and installed in the Relativistic Heavy Ion Collider (RHIC). The cavity operates at 4.4 K with a “quiet helium source” to isolate the cavity from environmental acoustic noise. The cavity is a beam driven quarter wave resonator. It is detuned and damped during injection and acceleration cycles and is brought to operation only at store energy. We have observed clear luminosity increase and bunch length reduction in the first operation of the cavity with Au + Au and Au + He3 collisions. The cavity voltage was limited by quenching in the Higher Order Mode coupler. This paper also discusses the cavity beam experiments with no higher order mode coupler in p + p and p + Au RHIC operation.

Slides WEBA07 [2.522 MB]

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THAA01

Recent Developments in Superconducting Deflecting-Mode Cavities

dipole, HOM, simulation, luminosity

987

J.R. Delayen
ODU, Norfolk, Virginia, USA

In the last few years there has been a growing interest in compact superconducting cavities operating in a deflecting mode to be used either in rf separators or crabbing systems. This talk will give an overview of recent progress in global activities towards SRF deflecting mode cavities.

Slides THAA01 [4.729 MB]

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THAA02

SRF Gun Development Overview

gun, cathode, SRF, electron

994

J.K. Sekutowicz
DESY, Hamburg, Germany

The most demanding component of a continuous wave (cw) injector is cw operating RF-gun, delivering highly populated low emittance bunches. RF-guns, both working at room temperature and superconducting, when they generate highly populated low emittance bunches have to be operated at high accelerating gradients to suppress space charge effects diluting emittance. Superconducting RF-guns are technically superior to the normal conducting devices because they dissipate orders of magnitude less power when operating at very high gradients in cw mode. In this contribution progress since 2013 in the R&D programs, designing and operation of the SRF-injectors at KEK, HZB, HZDR, PKU and DESY will be discussed.

Slides THAA02 [6.107 MB]

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THAA03

SRF Gun at BNL: First Beam and Other Commissioning Results

cathode, gun, SRF, electron

1001

W. Xu, Z. Altinbas, S.A. Belomestnykh, I. Ben-Zvi, L. DeSanto, S. Deonarine, D.M. Gassner, R.C. Gupta, H. Hahn, L.R. Hammons, C. Ho, J.P. Jamilkowski, P. K. Kankiya, D. Kayran, R. Kellermann, N. Laloudakis, R.F. Lambiase, C.J. Liaw, V. Litvinenko, G.J. Mahler, L. Masi, G.T. McIntyre, T.A. Miller, D. Phillips, V. Ptitsyn, T. Rao, T. Seda, B. Sheehy, K.S. Smith, A.N. Steszyn, T.N. Tallerico, R. Than, J.E. Tuozzolo, E. Wang, D. Weiss, M. Wilinski, A. Zaltsman, Z. Zhao
BNL, Upton, Long Island, New York, USA
S.A. Belomestnykh, I. Ben-Zvi, V. Litvinenko
Stony Brook University, Stony Brook, USA

The talk shall cover two SRF photoemission electron guns under commissioning at BNL: a 704 MHz elliptical ERL gun and a 112 MHz quarter-wave gun for coherent electron cooling experiment. In particular, the speaker shall report on generating first photoemission beam current from the 704 MHz SRF gun, multipacting issues in the SRF guns, photocathode behavior as well as other commissioning experiences and results.

Slides THAA03 [2.215 MB]

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THAA04

Comparison of Cavity Fabrication and Performances Between Fine Grains, Large Grains and Seamless Cavities

electron, SRF, niobium, vacuum

1006

K. Umemori, H. Inoue, T. Kubo, H. Shimizu, Y. Watanabe, M. Yamanaka
KEK, Ibaraki, Japan
A. Hocker
Fermilab, Batavia, Illinois, USA
T. Tajima
LANL, Los Alamos, New Mexico, USA

In KEK-CFF, L-band SRF cavity fabrication studies have been actively proceeded. Main target of the R&D is investigation of cavity fabrication methods using different Nb materials. In this talk, we report mainly focus on the experiences obtained from single cell cavity fabrications. First, different Nb materials are compared, between fine grain Nb and large grain(LG) Nb from different vendors including low RRR LG Nb, in which, cavities were fabricated by electron beam welding method. Difficulty on LG cavity fabrication come from deformation due to stressed grain boundaries. In addition to nominal electron beam welded cavities, hydro-formed seamless cavities have been fabricated. Relatively large difference of equator and iris ratio cause difficulty on expansion of Nb pipes. Good qualified Nb pipe is essential and control of hydro-forming steps including annealing of materials is also important. In order to evaluate these cavity performances, vertical tests were carried out. Generally, they showed good performances. In this presentation, fabrication processes, technical difficulties, mitigation strategies and vertical test results are presented.

Slides THAA04 [2.810 MB]

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THAA05

First Results of SRF Cavity Fabrication by Electro-Hydraulic Forming at CERN

niobium, simulation, SRF, superconducting-RF

1012

S. Atieh, A. Amorim Carvalho, I. Aviles Santillana, F.F. Bertinelli, R. Calaga, O. Capatina, G. Favre, M. Garlaschè, F. Gerigk, S.A.E. Langeslag, K.M. Schirm, N. Valverde Alonso
CERN, Geneva, Switzerland
D. Alleman, G. Avrillaud, J. Bonafe, E. Mandel, P. Marty, H. Peronnet, R. Plaut
Bmax, Toulouse, France

In the framework of many accelerator projects relying on RF superconducting technology, shape conformity and processing time are key aspects for the optimization of niobium cavity fabrication. An alternative technique to traditional shaping methods, such as deep-drawing and spinning, is Electro-Hydraulic Forming (EHF). In EHF, cavities are obtained through ultra-high-speed deformation of blank sheets, using shockwaves induced in water by a pulsed electrical discharge. With respect to traditional methods, such a highly dynamic process can yield valuable results in terms of effectiveness, repeatability, final shape precision, higher formability and reduced spring-back. In this paper, the first results of EHF on copper prototypes and ongoing developments for niobium for the Superconducting Proton Linac studies at CERN are discussed. The simulations performed in order to master the embedded multi-physics phenomena and to steer process parameters are also presented.

Slides THAA05 [21.123 MB]

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THAA06

Precise Studies on He-Processing and HPR for Recovery From Field Emission by Using X-Ray Mapping System

radiation, cryomodule, operation, linac

1019

H. Sakai, K. Enami, T. Furuya, M. Satoh, K. Shinoe, K. Umemori
KEK, Ibaraki, Japan
M. Sawamura
JAEA, Ibaraki-ken, Japan

We usually met the degradation of superconducting RF cavity on the cryomodule test and beam operation even if the performance of this cavity is good on the vertical test (V.T). Field emission is the most severe problem for this degradation after reassembly work from vertical test. Not only high pressure rinsing (HPR) but also He-processing, which is more suitable method without the reassembly work for recovery, is recommended and tried to recover this degradation. However, we did not investigate the details of how field emission sources were processed and removed after HPR and He-processing. We deeply investigated the processing procedure during He-processing and how many field emission sources removed after HPR by using rotating X-ray mapping system* in V.T .
*H.Sakai et.al., Proc. of IPAC10 p2950-2952.

Slides THAA06 [4.347 MB]

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THBA02

Recent Development in Vertical Electropolishing

cathode, experiment, ion, SRF

1024

V. Chouhan, Y.I. Ida, K.N. Nii, T.Y. Yamaguchi
MGH, Hyogo-ken, Japan
H. Hayano, S. Kato, H. Monjushiro, T. Saeki, M. Sawabe
KEK, Ibaraki, Japan
K. Ishimi
MGI, Chiba, Japan

Horizontal electropolishing (HEP) is being used for final surface treatment of niobium SRF cavities. However a HEP system is equipped with complicated mechanism that makes it expensive and enhances cost of surface treatment of cavities especially when mass production is considered. Vertical electropolishing (VEP) has been introduced by other labs and the research is being carried out to establish the VEP technique. The VEP system requires simple mechanism and has advantages over HEP setup. Positive results have been obtained from the VEPed cavities also as shown by other labs. However further improvement in a VEP setup, cathode and VEP parameters is required. Marui Galvanizing Co., Ltd in collaboration with KEK has been working for development of VEP system, optimization of cathode and VEP parameters to obtain uniform Nb removal with a smooth surface of a cavity. Here we report our recent development of VEP system, unique Ninja cathode and parameter optimization with a 1-cell coupon cavity containing 6 Nb disk coupons at the beam pipes, irises and equator. The coupon surfaces were analyzed to obtain detail of the cavity surface.

Slides THBA02 [5.703 MB]

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THBA04

Overview of Recent HOM Coupler Development

HOM, damping, SRF, operation

1031

B. P. Xiao
BNL, Upton, Long Island, New York, USA

Funding: Work partly supported by Brookhaven Science Associates, LLC under contract No. DE-AC02-98CH10886 with the US DOE， by the US LARP, and by EU FP7 HiLumi LHC - Grant Agreement 284404.
HOM damping is important for SRF applications, especially for high intensity machines. A good HOM damping design will help to reduce power load to the cryogenic system and to reduce the risk of beam breakup. The design of HOM damping, including antenna/loop HOM couplers, beam pipe HOM absorbers and waveguide HOM couplers, is to solve a multi-physics problem that involves RF, thermal, mechanical, and beam-cavity interaction issues. In this talk, the author provides an overview on the latest advances of the HOM couplers for high intensity SRF applications.

Slides THBA04 [2.619 MB]

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THBA05

Higher Order Mode Absorbers for High Current SRF Applications

HOM, higher-order-mode, linac, operation

1036

R.G. Eichhorn, J.V. Conway, T. Gruber, Y. He, G.H. Hoffstaetter, Y. Li, M. Liepe, T.I. O'Connell, P. Quigley, J. Sears, V.D. Shemelin, E.N. Smith, M. Tigner
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Efficient damping of the higher-order modes (HOMs) of the superconducting cavities is essential for any high current operation. The talk will provide an overview on the latest advances of HOM absorber development for high intensity SRF applications. As the ideal absorber does not exist, the different conceptual approaches will be presented and the associated issues are outlined. Design examples from various labs will be given that help explain the issues and resolutions. Some focus will be given to the Cornell HOM beamline absorber that was design for high current, short bunch operation with up to 400 W heating. The design will be reviewed and testing results will be reported.

Slides THBA05 [4.022 MB]

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THBA06

Overview on Magnetic Field Management and Shielding in High Q Modules

cryomodule, cryogenics, shielding, linac

1043

G. Wu
Fermilab, Batavia, Illinois, USA

Funding: Work supported by FRA under DOE contract DE-AC02-07CH11359
Maintaining very high cavity Q0 in linac applications creates new challenges for cryomodule design. Magnetic shielding from both external fields and internal fields is required and its importance to thermal gradients during Tc transition is now emerging. This presentation will describe the design challenges and possible mitigation strategies with examples from various applications or laboratories including FRIB, LCLS-II, PIP-II, Cornell University and KEK.

Slides THBA06 [1.839 MB]

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THPB001

Propagation of the High Frequency Fields in the Chain of the Superconducting Cavities

wakefield, electromagnetic-fields, resonance, accelerating-gradient

1049

A. Novokhatski
SLAC, Menlo Park, California, USA

Funding: Work supported by the Department of Energy. Contract no.DOE-AC03-76SF00515.
Combination with the very high repetion rate requires to use the superconducting cavities to accelerate very short bunches for the FEL operation.. In the cavities these bunches excite very high frequency electromagnetic fields. There are severe concerns, that these fields will remain inside the structure for a long time, bring additional heating or even break up the Cooper pairs. We present results of the simulation of the transient dynamics of wake fields of very short bunches. We show how much of the energy is vanishing through the beam pipes immediately and how much energy is staying in the cavity for a long time.

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THPB002

Second Harmonic Cavity Design for Synchrotron Radiation Energy Compensator in eRHIC Project

HOM, impedance, linac, radiation

1052

C. Xu, S.A. Belomestnykh, I. Ben-Zvi, W. Xu
BNL, Upton, Long Island, New York, USA

Funding: DOE
eRHIC project requires construction of a FFAG ring to accelerate electrons and connect to the existing ion ring of Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory. This new ring will have the same radius as the RHIC ring. Synchrotron radiation lost in the electron ring should be compensated by a CW superconducting radio frequency (SRF) cavity. Here we propose an 845 MHz single cell harmonic cavity. This cavity will experience a high average current (∼0.7 A) passing through it. With this consideration, this cavity design requires optimization to reduce higher order mode power. On the other hand, the cavity will operate at relatively high gradient up to 18 MV/m. Current design requires fundamental couplers to handle 400 kW forward RF power and HOM couplers to extract 2.5 kW HOM power.
This work is supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. DOE.

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THPB003

Calculations for RF Cavities with Dissipative Material

HOM, SRF, dipole, damping

1056

F. Marhauser
JLab, Newport News, Virginia, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177
3D simulations have been performed for a variety of SRF cavities which incorporate Higher Order Mode dampers, either in form of coaxial couplers or waveguide dampers. Instead of utilizing the rather standard approach of matching the output port of the dampers with a broadband coaxial or waveguide port, dissipative materials are modelled for RF field absorption. This for instance not only avoids the otherwise required definition of the number of modes considered for damping, which has an impact on the computational time, but also allows tailoring the load material to conform with experimental data of e.g. non-perfect absorbers. The new calculation scheme is presented. Findings are partially compared with those achieved with the standard waveguide port approach by means of external quality factors. CPU speeds are briefly discussed for both approaches.

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THPB004

HOM Calculations for Different Cavities and Beam Induced HOM Power Analysis of ESS

HOM, sextupole, dipole, quadrupole

1061

H.J. Zheng, J. Gao
IHEP, Beijing, People's Republic of China
J.F. Chen
INFN/LASA, Segrate (MI), Italy
C. Pagani
Università degli Studi di Milano & INFN, Segrate, Italy

For different design of ESS superconducting cavities, the higher order modes (HOM's) of monopoles, dipoles, quadrupoles and sextupoles are found. Their R/Q values are also calculated. Main HOM related issues are the beam instabilities and the HOM induced power especially from TM monopoles. The analysis for the beam induced HOM voltage and power in this paper showed that, if the HOM frequency is a few kHz away from the beam spectrum, it is not a problem. In order to understand the effects of the beam structure, analytic expressions are developed. With these expressions, the induced HOM voltage and power were calculated by assuming external Q for each HOM. Our analysis confirm that, with thebeam structure of ESS and a good cavity design, no special tight tolerances are required for cavity fabrication and no HOM couplers in the cavity beam pipes are planned.

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THPB005

Simulations of 3.9 GHz CW Coupler for LCLS-II Project

simulation, linac, operation, cryomodule

1066

I.V. Gonin, T.N. Khabiboulline, A. Lunin, N. Solyak
Fermilab, Batavia, Illinois, USA

LCLS-II linac is based on XFEL/ILC superconducting technology. TTF-III fundamental power coupler for the 3.9 GHz 9-cell cavities has been modifies to satisfy requirements of LCLS-II, operating in CW regime. In this paper we discuss the results of COMSOL analysis of the possible modification of couplers, working at various operating regimes. We present also the results of mechanical study.

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THPB006

Improvements of Buildcavity Code

HOM, interface, simulation, coupling

1070

J.F. Chen, M. Moretti, C. Pagani, P. Pierini
INFN/LASA, Segrate (MI), Italy
C. Pagani
Università degli Studi di Milano & INFN, Segrate, Italy

Recentely, we improve the BuildCavity code, which is a graphics interface to SUPERFISH for the study of superconducting cavities of elliptical shape. Now it works with latest SUPERFISH 7 and can be installed also on newer Windows system such as Win 7 and 8. Several improvements have been done in the code. As an example, a design of ESS median-beta cavity with BuildCavity will also be presented.

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THPB007

A Study of Resonant Excitation of Longitudinal HOMs in the Cryomodules of LCLS-II

HOM, factory, resonance, impedance

1073

K.L.F. Bane, C. Adolphsen, A. Chao, Z. Li
SLAC, Menlo Park, California, USA

Funding: Work supported by the U.S. Department of Energy under contract DE-AC02-76SF00515
The Linac Coherent Light Source (LCLS) at SLAC, the world's first hard X-ray FEL, is being upgraded to the LCLS-II. The major new feature will be the installation of 35 cryomodules (CMs) of TESLA-type, superconducting accelerating structures. It is envisioned that LCLS-II will eventually be able to deliver 300 pC, 1 kA pulses of beam at a rate of 1 MHz. At a cavity temperature of 2K, any heat generated (even on the level of a few watts) is expensive to remove. In the last linac of LCLS-II, L3–-where the peak current is highest–-the power radiated by the bunch in the CMs is estimated at 14 W (charge 300 pC option, rep rate 1 MHz). But this calculation ignores resonances that can be excited between the bunch frequency and higher order mode (HOM) frequencies in the CMs, which in principle can greatly increase this number. In this report we develop a theory of resonant build up. Then, using 500 numerically obtained modes over the frequency range 3–5 GHz, we estimate the probability of significant resonant build up in L3 of LCLS-II. The effects of small random bunch phase and charge errors will also be addressed.

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THPB008

RF Simulations for an LCLS-II 3rd Harmonic Cavity Cyromodule

HOM, damping, cryomodule, dipole

1078

L. Xiao, C. Adolphsen, Z. Li, T.O. Raubenheimer
SLAC, Menlo Park, California, USA

The FNAL designed 3.9 GHz third harmonic cavity for XFEL will be used in LCLS-II for linearizing the longitudinal beam profile. The 3.9 GHz SRF cavity is scaled down from the 1.3 GHz TESLA cavity shape, but has a disproportionately large beampipe radius for better higher-order mode (HOM) damping. The HOM and fundamental power (FPC) couplers will generate asymmetric field in the beam region, and thereby dilute the beam emittance. Meanwhile, due to the large beampipe, all but a few of the HOMs are above the beampipe cutoff. Thus the HOM damping analyses need to be performed in a full cryomodule, rather than in an individual cavity. The HOM damping in a 4-cavity cryomodule was investigated to determine possible trapped modes using the parallel electromagnetic code suite ACE3P developed at SLAC. The coupler RF kicks induced by the HOM and FPC couplers in the 3.9 GHz cavity were evaluated. A possible cavity-to-cavity arrangement is proposed which could provide effective cancellation of these RF kicks. In this paper we present and discuss the RF simulation results in the 3.9 GHz third harmonic cavity cryomodule.
Work supported by Department of Energy under contract Number DE-AC02-76SF00515.

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THPB010

INFN Milano - LASA Activities for ESS

vacuum, niobium, linac, cryomodule

1081

P. Michelato, M. Bertucci, A. Bignami, A. Bosotti, J.F. Chen, L. Monaco, M. Moretti, R. Paparella, P. Pierini, D. Sertore
INFN/LASA, Segrate (MI), Italy
C. Pagani
Università degli Studi di Milano & INFN, Segrate, Italy
H.J. Zheng
IHEP, Beijing, People's Republic of China

INFN Milano – LASA is involved in the development and industrialization for the production of 704.4 MHz medium beta (β = 0.67) cavities for the ESS project. In this framework, we are designing a medium beta prototype cavity exploring both Large Grain and Fine Grain Niobium for its production as well as a high beta (β = 0.86) Large Grain cavity. In the meanwhile, an activity is ongoing for upgrading the LASA test facility to be able to test these kind of resonators.

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THPB011

Superconducting Travelling Wave Accelerating Structure Development

accelerating-gradient, status, feedback, operation

1085

R.A. Kostin, P.V. Avrakhov, A.D. Didenko, A. Kanareykin
Euclid TechLabs, LLC, Solon, Ohio, USA
T.N. Khabiboulline, Y.M. Pischalnikov, N. Solyak, V.P. Yakovlev
Fermilab, Batavia, Illinois, USA

Funding: Work supported by US Department of Energy # DE-SC0006300
The 3 cell superconducting TW accelerating structure was developed to experimentally demonstrate and to study tuning issues for a new experimental device - the superconducting traveling wave accelerator (STWA), a technology that may prove of crucial importance to the high energy SRF linacs by raising the effective gradient and therefore reducing the overall cost. Recently, a STWA structure with a feedback waveguide has been suggested. The structure was optimized and has phase advance per cell of 105° which provide 24% higher accelerating gradient than in SW cavities. Also STWA structure has no strong sensitivity of the field flatness and its length may be much longer than SW structure. With this presentation, we discuss the current status of a 3-cell L-band SC traveling wave along with the analysis of its tuning issues. Special attention will be paid to feedback loop operation with the two-coupler feed system. We also report on the development and fabrication of a niobium prototype 3-cell SC traveling wave structure to be tested at 2°K in fall 2015.

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THPB013

A Novel Design and Development of 650 MHz, β=0.61, 5-Cell SRF Cavity for High Intensity Proton Linac

niobium, electron, impedance, HOM

1088

S.S. Som, P. Bhattacharyya, A. Dutta Gupta, S. Ghosh, A. Mandal, S. Seth
VECC, Kolkata, India

Funding: DAE, Govt. of India
DAE laboratories in India are involved in R&D activities on SRF cavity technology for the proposed high intensity proton linacs for ISNS/IADS and also FERMILAB PIP-II program under IIFC. VECC is responsible for design, analysis and development of a 650 MHz, β=0.61, 5-cell elliptical cavity. This paper describes the novel design of the cavity, with different aperture and wall angle, having better field flatness and mechanical stability, reliable surface processing facility and less beam loss. The cavity geometry has been optimized to get acceptable values of field enhancement factors, R/Q, Geometric factor, cell-to-cell coupling etc. The effective impedance of transverse and longitudinal HOMs are low enough to get rid of HOM damper for low beam current. 2-D analysis shows no possibility of multipacting. However, 3-D analysis using CST Particle Studio code confirms its presence and it can be suppressed by introducing a small convexity in the equator region. Two niobium half cells and beam pipes for the single cell cavity have been fabricated. Measurement and RF characterisation of half cells, prototype 1-cell and 5-cell and also 1-cell niobium cavities have been carried out.
email:ssom@vecc.gov.in

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THPB014

Mechanical Optimization of High Beta 650 MHz Cavity for Pulse and CW Operation of PIP-II Project

operation, simulation, resonance, cryomodule

1093

T.N. Khabiboulline, I.V. Gonin, C.J. Grimm, A. Lunin, T.H. Nicol, V.P. Yakovlev
Fermilab, Batavia, Illinois, USA
P. Kumar
RRCAT, Indore (M.P.), India

The proposed design of the 0.8 GeV PIP-II SC Linac employs two families of 650 MHz 5-cell elliptical cavities with 2 different beta. The β=0.61 will cover the 185-500 MeV range and the β=0.92 will cover the 500-800 MeV range. In this paper we will present update of RF and mechanical design of dressed high beta cavity (β=0.92) for pulse regime of operation at 2 mA beam current. In previous CW version of PIP-II project the mechanical design was concentrated on minimization of frequency shift due to helium pressure fluctuation. In current case of pulse regime operation the main goal was Lorentz force detuning minimization. We present the scope of coupled RF-Mechanical issues and their resolution. Also detailed stress analysis of dresses cavity will be presented.

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THPB015

Design of a Medium Beta Half-Wave SC Prototype Cavity at IMP

operation, linac, electromagnetic-fields, accelerating-gradient

1097

A.D. Wu, Y. He, T.C. Jiang, Y.M. Li, F.F. Wang, R.X. Wang, L.J. Wen, W.M. Yue, C. Zhang, S.H. Zhang, S.X. Zhang, H.W. Zhao
IMP/CAS, Lanzhou, People's Republic of China

A superconducting half-wave resonator has been designed with frequency of 325 MHz and beta of 0.51. The geometry parameters and the three shapes of inner conductors (racetrack, ring-shape and elliptical-shape) were studied in details to decrease the peak electromagnetic fields to obtain higher accelerating gradients and minimize the dissipated power on the RF walls. To suppress the operation frequency shift caused by the helium pressure fluctuations and maximize the tuner ranges, the frequency shifts and mechanical characters were simulated in the electric and magnetic areas separately. At the end, the helium vessel was also designed to keep stability as possible. The fabrication and test of the prototype will be complete at the beginning of 2016.

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THPB017

A Higher Harmonic Cavity at 800 MHz for HL-LHC

HOM, polarization, cryomodule, simulation

1100

T. Roggen, P. Baudrenghien, R. Calaga
CERN, Geneva, Switzerland

Funding: Marie Curie action: Grant agreement PCOFUND-GA-2010-267194
A superconducting 800 MHz second harmonic system is proposed for HL-LHC. It serves as a cure for beam instabilities with high beam currents by improving Landau damping and will allow for bunch profile manipulation. This can potentially help to reduce intra-beam-scattering, beam induced heating and e-cloud effects, pile-up density in the detectors and beam losses. An overview of the 800 MHz cavity design and RF power requirements is given. In particular the design parameters of the cavity shape and HOM couplers are described. Some other aspects such as RF power requirements and cryomodule layout are also addressed.

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THPB019

Bead-Pull Measurements of the Main Deflecting Mode of the Double-Quarter-Wave Cavity for the HL-LHC

simulation, luminosity, resonance, factory

1105

M. Navarro-Tapia, R. Calaga
CERN, Geneva, Switzerland

Funding: This research has received funding from the European Commission under the FP7 project HiLumi LHC (Grant agreement no. 284404), and under a Marie Curie action (Grant agreement PCOFUND-GA-2010-267194).
A full-scale model of the double-quarter-wave (DQW) cavity towards the High-Luminosity Large Hadron Collider (HL-LHC) upgrade was built in aluminum to characterize the deflecting mode. Field strength measurements have been carried out for both the transverse and longitudinal electromagnetic fields, by using the bead-pull technique. Perturbation objects of different shapes and material were used to separate the electric and magnetic field components. A reasonably good agreement was found between numerical simulation and measurements, which confirm the reliability and accuracy of the measurements done.

Poster THPB019 [0.237 MB]

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THPB021

Balloon Variant of Single Spoke Resonator

electron, resonance, simulation, superconductivity

1110

Z.Y. Yao, R.E. Laxdal, V. Zvyagintsev
TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada

Spoke resonators have been widely proposed and optimized for various applications. Good performance has been demonstrated by many cavity tests. Accompanying the great progress, the adverse impact of strong multipacting (MP) is also noted by recent test reports, consistent with modern 3D simulations. This paper will discuss MP behaviors in the single spoke resonator. In particular a phenomenological theory is developed to highlight the details of the geometry that affect MP. The analysis leads to an optimized geometry of a single spoke resonator defined here as the ‘balloon geometry’. A 325MHz β=0.3 single spoke resonator based on 'balloon' concept is under development by the RISP-TRIUMF Collaboration. The RF and mechanical design of this cavity will also be reported.

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THPB022

A Preliminary Design of a Superconducting Accelerating Structure for Extremely Low Energy Proton Working in TE210 Mode

proton, simulation, emittance, acceleration

1115

Z.Q. Yang, X.Y. Lu, W.W. Tan, D.Y. Yang, J. Zhao
PKU, Beijing, People's Republic of China

For the application of high intensity continuous wave (CW) proton beam acceleration, a new superconducting accelerating structure for extremely low β proton working in TE210 mode has been proposed at Peking University. The cavity consists of eight electrodes and eight accelerating gaps. The RF frequency is 162.5MHz, and the designed proton input energy is 200keV. A peak field optimization has been performed for the lower surface field. The accelerating gaps are adjusted by phase sweeping based on KONUS beam dynamics. Solenoids are placed outside the cavity to provide transverse focusing. Numerical calculation shows that the transverse defocusing of the KONUS phase is about three times smaller than that of the conventional negative synchronous RF phase. The beam dynamics of a 10mA CW proton beam is simulated by the TraceWin code. The simulation results show that the beam’s size is under effective control. Both the simulation and the numerical calculation show that the cavity has a relatively high effective accelerating gradient of 2.6MV/m. Our results show that this new accelerating structure may be a possible candidate for superconducting operation at such a low energy range.

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THPB023

The Statistics of Industrial XFEL Cavities Fabrication at E.ZANON

target, niobium, controls, accelerating-gradient

1119

A. Gresele, M. Giaretta, A. Visentin
Ettore Zanon S.p.A., Nuclear Division, Schio, Italy
A.A. Sulimov, J.H. Thie
DESY, Hamburg, Germany

Serial production of superconducting cavities for European-XFEL will be completed at E.ZANON by the end of 2015. For that reason we can summarize the results and present the statistics of industrial cavity fabrication. Many parameters have been traced during different steps of cavity production. The most interesting of them, as cavity length, frequency, field flatness and eccentricity, are presented and discussed.

Poster THPB023 [3.227 MB]

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THPB025

Exchange and Repair of Titanium Service Pipes for the EXFEL Series Cavities

alignment, linac, cryomodule, SRF

1122

M. Schalwat, S. Barbanotti, A. Daniel, H. Hintz, K. Jensch, A. Matheisen, S. Saegebarth, P. Schilling
DESY, Hamburg, Germany
A. Schmidt
XFEL. EU, Hamburg, Germany

Longitudinally-welded 72 mm ID service pipes (HSP) made from titanium grade 2 is used by the two suppliers of the helium tanks for the EU-XFEL accelerator. From the perspective of the PED DESY is legally designated as the manufacturer and is responsible for conformity to all relevant codes. During module assemblies at CEA Saclay the orbital welds of the interconnection bellows between cavities showed pores with dimensions outside the specifications set by DESY. These welds needed to be redone which caused a project delay of several months. The X-ray examination of the HSP showed that the pipes already exhibited many out-of- DESY spec pores in the longitudinal welds and were most likely the main cause of the problems in the orbital welds. It was decided to replace the extremities of the service pipes with seamless titanium tubes both on “naked” helium tanks as well as on tanks with cavities already welded in. At DESY more than 750 service pipes were exchanged over a period of 2 years. The qualification of the repair line according to PED regulation and the prove with RF test at 2 K that the repairs do not influence the high performance of the s.c. cavities were done.

Poster THPB025 [0.172 MB]

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THPB026

Update on SRF Cavity Design, Production and Testing for BERLinPro

gun, linac, booster, HOM

1127

A. Neumann, W. Anders, A. Burrill, A. Frahm, H.-W. Glock, J. Knobloch, O. Kugeler
HZB, Berlin, Germany
K. Brackebusch, T. Galek, J. Heller, U. van Rienen
Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
G. Ciovati, W.A. Clemens, C. Dreyfuss, D. Forehand, T. Harris, P. Kneisel, R.B. Overton, L. Turlington
JLab, Newport News, Virginia, USA
E.N. Zaplatin
FZJ, Jülich, Germany

Funding: Work supported by German Bundesministerium für Bildung und Forschung, Land Berlin, and grants of Helmholtz Association.
The BERLinPro Energy Recovery Linac (ERL) is currently being built at Helmholtz-Zentrum Berlin in order to study the accelerator physics of operating a high current, 100 mA, 50 MeV low emittance ERL utilizing all SRF cavity technology. For this machine three different types of SRF cavities are being developed. For the injector section, consisting of an SRF photoinjector and a three two cell booster cavity module, fabrication is completed. The cavities were designed at HZB and manufactured, processed and vertically tested at Jefferson Laboratory. In this paper we will review the design and production process of the two structures and show the latest horizontal acceptance tests at HZB prior to installation into the newly designed cryo-module. For the Linac cavity the latest cavity and module design studies are being shown.

Poster THPB026 [1.535 MB]

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THPB027

Welding a Helium Vessel to a 1.3 GHz 9-Cell Nitrogen Doped Cavity at Fermilab for LCLS-II

alignment, vacuum, operation, pick-up

1132

C.J. Grimm, J.A. Kaluzny, D.J. Watkins
Fermilab, Batavia, Illinois, USA

Fermilab has developed a TIG welding procedure that is used attach a nitrogen doped 1.3 GHz 9-cell niobium (Nb) cavity to a titanium (Ti) helium vessel. These cavities will be used in the two prototype cryomodules for the Linac Coherent Light Source (LCLS-II) upgrade at SLAC National Accelerator Laboratory. Discussion in further detail will include setting up TIG welding parameters and tooling requirements for assembly and alignment of the cavity to the helium vessel. The weld designs and glovebox environment produce the best quality TIG welds that meet ASME Boiler and Pressure Vessel Code. The cavity temperature was monitored to assure the nitrogen doping is preserved, and RF measurements are taken throughout the process to monitor the cavity for excessive cell deformation due to heat loads from welding.

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THPB028

ESS Medium Beta Cavity Prototypes Manufacturing

HOM, linac, coupling, cryomodule

1136

E. Cenni, C. Arcambal
CEA/IRFU, Gif-sur-Yvette, France
P. Bosland, G. Devanz, X. Hanus, P. Hardy, V.M. Hennion, F. Leseigneur, F. Peauger, J. Plouin, D. Roudier
CEA/DSM/IRFU, France
G. Costanza
Lund University, Lund, Sweden
C. Darve
ESS, Lund, Sweden

The ESS elliptical superconducting linac consists of two types of 704.42 MHz cavities, medium and high beta, to accelerate the beam from 216 MeV (spoke cavity linac) up to the full energy at 2 GeV. The last linac optimization, called Optimus+, has been carried out taking into account the limitations of SRF cavity performance (field emission). The medium and high-beta parts of the linac are composed of 36 and 84 elliptical cavities, with geometrical beta values of 0.67 and 0.86 respectively. We describe here the procedures and numerical analysis leading from half-cells to a complete medium cavity assembly, which take into account not only the frequency of the fundamental accelerating mode but also the higher order modes near the machine line. The half cell selection process to form dumb bells will be described, as well as the reshaping and trimming procedure.

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THPB029

MHI's Production Activities of Superconducting Cavity

superconducting-RF, electron, gun, SRF

1141

A. Miyamoto, H. Hara, K. Kanaoka, K. Okihira, K. Sennyu, T. Yanagisawa
MHI, Hiroshima, Japan

Mitsubishi Heavy Industries (MHI) have developed manufacturing process of superconducting cavities for a long time. In this presentation, recent progress will be reported.

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THPB030

Fabrication and Evaluation of Low RRR Large Grain 1-Cell Cavity

niobium, SRF, electron, accelerating-gradient

1146

H. Shimizu, H. Inoue, E. Kako, T. Saeki, K. Umemori, Y. Watanabe, M. Yamanaka
KEK, Ibaraki, Japan

Successive R&D studies of SRF cavities are ongoing at KEK by using existing facilities of Cavity Fabrication Facility (CFF) and other equipment of Superconducting Test facility (STF). Recently, there are studies on the low RRR of niobium material with high and uniform concentration of tantalum which could be used for the fabrication of high performance SRF cavity, and hence it could reduce the fabrication cost of cavities [1]. In order to confirm the advantage of the material, a large-grain single-cell cavity was fabricated at CFF/KEK with sheets sliced from a low RRR niobium ingot with high and uniform concentration of tantalum. The resistivity measurement of sample from sliced sheet showed the RRR value of 100, whereas it is about 400 for the nominal qualification of fine-grain sheets at KEK. The low RRR large-grain single-cell cavity was already fabricated at CFF/KEK. The quality control of the fabrication processes are well under control. Then several vertical tests of the cavity were done at STF/KEK. In this presentation, the results of the vertical tests are shown. The potential of the low RRR niobium material for SRF cavity are discussed.
*P.Kneisel et al, NIM A774(2015)133

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THPB031

Operation Experience with Half Cell Measurement Machine and Cavity Tuning Machine in 3 Years of European XFEL Cavity Series Production

operation, controls, SRF, HOM

1149

J.H. Thie, A. Gössel, J. Iversen, D. Klinke, C. Müller, A.A. Sulimov, D. Tischhauser
DESY, Hamburg, Germany

For the European XFEL superconducting Cavity series production at both cavity vendors’ four manufacturing machines for production key functions, HAZEMEMA and CTM, are supplied by DESY. Among three years of cavity production in two companies a lot of experience is gathered about influence of surroundings and production quality on cycle times, machine drop outs, general stability time of machines and parts subject to wear. Significant factors on cycle time for tuning operation like temperature stability and drift during tuning and measurements, precision of cell trimming before welding and tuning and generally geometrical factors are shown. RF aspects of tuning and production quality control as additional measurements for TM011-mode to estimate quality of its damping is presented. Performed full Cavity RF measurements exceeds XFEL specifications gives a possibility for additional quality control on welding shrinkage stability and it’s homogeneously distribution. The use of HAZEMEMA and CTM to assess the impact of asymmetric trimming, including calculation of it’s influence on the higher-order modes, is shown.

Poster THPB031 [0.201 MB]

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THPB032

Release Processes and Documentation Methods During Series Treatment of SRF Cavities for the European XFEL by Using an Engineering Data Management System

data-management, SRF, linac, database

1154

J. Iversen, J.A. Dammann, A. Matheisen, N. Steinhau-Kühl
DESY, Hamburg, Germany

For the European XFEL more than 800 superconducting cavities need to be treated. At least 65 quality documents per cavity have to be emitted and transferred to DESY by the vendor; two acceptance levels must be passed successfully to release a cavity for transportation to DESY. All quality documents, non-conformity reports and acceptance levels are automatically processed by using DESY’s Engineering Data Management System (EDMS). We summarize documentation methods, document transfer procedures, review and release processes; we describe the exchange of process information between customer and vendor; and report about experiences.

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THPB033

Frequency Measurement and Tuning of a 9-Cell Superconducting Cavity Developed with UK Industry

simulation, superconducting-RF, niobium, electron

1158

L.S. Cowie, P. Goudket, A.R. Goulden, P.A. McIntosh, A.E. Wheelhouse
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
J.R. Everard, N. Shakespeare
Shakespeare Engineering, South Woodham Ferrers, Essex, United Kingdom
B. Lamb, S. Postlethwaite, N. Templeton
STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom

As part of an STFC Innovations Partnership Scheme (IPS) grant, in support of enabling UK industry to address the large potential market for superconducting RF structures, Daresbury Laboratory and Shakespeare Engineering Ltd are collaborating to produce a 1.3 GHz 9 cell niobium cavity. This paper describes the procedures to ensure the cavity reaches the required frequency and field flatness. The frequency of each half-cell was measured using a custom measurement apparatus. Combined mechanical and RF simulations were used to compensate for cavity deformation during measurement. Results of Coordinate Measurement Machine measurements of one half-cell are presented. The same procedure will be used to trim the cells at the dumbbell stage, and the full 9-cell cavity will be tuned once welded.

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THPB035

Fabrication of the 3.9 GHz SRF Structures for the European XFEL

controls, operation, linac, status

1162

P. Pierini, M. Bertucci, A. Bosotti, J.F. Chen, P. Michelato, L. Monaco, M. Moretti, R. Paparella, D. Sertore
INFN/LASA, Segrate (MI), Italy
A. Gresele
Ettore Zanon S.p.A., Nuclear Division, Schio, Italy
C.G. Maiano, P. Pierini, E. Vogel
DESY, Hamburg, Germany
C. Pagani
Università degli Studi di Milano & INFN, Segrate, Italy
M. Rizzi
Ettore Zanon S.p.A., Schio, Italy

One batch of 10 cavities has been completed and eight structures have been installed in the 3.9 GHz cryomodule for the European XFEL Injector operation. A second batch of 10 RF structures for a spare injector module is under fabrication. The fabrication has been performed according to the European Pressure Vessel regulations, as needed for the EXFEL operation. This paper describes the fabrication, quality control/assurance procedures and frequency preparation steps in order to achieve cavities at the correct frequency and length within the specifications.

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THPB038

XFEL Database Structure & Loading System

database, interface, linac, status

1166

S. Yasar, P.D. Gall, V. Gubarev
DESY, Hamburg, Germany

XFEL database was designed to store cavity production, preparation, and test data for the whole LINAC on the very detailed level: from half cells up to module tests. To load this amount of data (more than 140 files per cavity) in automatic regime the special Data Loading System was developed.

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THPB039

XFEL Database User Interface

database, GUI, controls, interface

1168

S. Yasar, P.D. Gall, V. Gubarev, D. Reschke, A.A. Sulimov, J.H. Thie
DESY, Hamburg, Germany

The XFEL database plays an important role for an effective part of the quality control system for the whole cavity production and preparation process for the European XFEL on a very detailed level. Database has the Graphical User Interface based on the web-technologies, and it can be accessed via low level Oracle SQL.

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THPB040

Hydroforming of Large Grain Niobium Tube

niobium, experiment, vacuum, electron

1171

A. Mapar, F. Pourboghrat
MSU, East Lansing, Michigan, USA
T.R. Bieler
Michigan State University, East Lansing, Michigan, USA
C. Compton
FRIB, East Lansing, Michigan, USA
J.E. Murphy
University of Nevada, Reno, Reno, Nevada, USA

Funding: This work was supported by the U.S. Department of Energy, Office of High Energy Physics, through Grant No. DE-FG02-09ER41638.
Currently most of Niobium (Nb) cavities are manufactured from fine grain Nb sheets. As-cast ingots go through a series of steps including forging, milling, rolling, and intermediate annealing, before they are deep-drawn into a half-cell shape and subsequently electron beam welded to make a full cavity. Tube hydroforming, a manufacturing technique where a tube is deformed using a pressurized fluid, is an alternative to the current costly manufacturing process. A whole cavity can be made from a tube using tube hydroforming. This study focuses on deformation of large grain Nb tubes during hydroforming. The crystal orientation of the grains is recorded. The tube is marked with a square-circle-grid which is used to measure the strain after deformation. The deformation of the tube is going to be modeled with crystal plasticity finite element and compared with experiments. This paper only covers the characterization of the tube and the hydroforming process.

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THPB041

Hydroforming SRF Cavities from Seamless Niobium Tubes

niobium, SRF, accelerating-gradient, superconductivity

1176

M. Yamanaka, H. Inoue, H. Shimizu, K. Umemori
KEK, Ibaraki, Japan
A. Hocker
Fermilab, Batavia, Illinois, USA
T. Tajima
LANL, Los Alamos, New Mexico, USA

The authors are developing the manufacturing method for super conducting radio frequency (SRF) cavities by using a hydroforming instead of an electron beam welding, which is the major manufacturing method. We expect a cost reduction by hiring the hydroforming. To realize this development, getting a high-purity seamless niobium tube with good forming ability and an advancement of hydroforming technique are necessary. We got the seamless niobium tube made by ATI Wah Chang with the cooperation of Fermilab, and succeeded to manufacture the 1-cell cavity by hydroforming. The accelerating gradient attained to 36 MV/m, and we confirmed it was available to use as the SRF cavity.

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THPB042

Advance Additive Manufacturing Method for SRF Cavities of Various Geometries

niobium, SRF, electron, vacuum

1181

P. Frigola, R.B. Agustsson, L. Faillace, A.Y. Murokh
RadiaBeam, Santa Monica, California, USA
G. Ciovati, W.A. Clemens, P. Dhakal, F. Marhauser, R.A. Rimmer, J.K. Spradlin, R.S. Williams
JLab, Newport News, Virginia, USA
J. Mireles, P.A. Morton, R.B. Wicker
University of Texas El Paso, W.M. Keck Center for 3D Innovation, El Paso, Texas, USA

An alternative fabrication method for superconducting radio frequency (SRF) cavities is presented. The novel fabrication method, based on 3D printing (or additive manufacturing, AM) technology capable of producing net-shape functional metallic parts of virtually any geometry, promises to greatly expand possibilities for advance cavity and end-group component designs. A description of the AM method and conceptual cavity designs are presented along with material analysis and RF measurement results of additively manufactured niobium samples.

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THPB043

Alternative Fabrication Methods for the ARIEL e-Linac SRF Separator Cavity

niobium, SRF, linac, induction

1185

D.W. Storey
Victoria University, Victoria, B.C., Canada
R.E. Laxdal, N. Muller
TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada

The ARIEL e-Linac RF deflecting cavity is a 650 MHz superconducting deflecting mode cavity that will allow simultaneous beam delivery to both the Rare Isotope Beam program and an Energy Recovery Linac. The cavity will be operated at 4 K and with deflecting voltages of up 0.6 MV, resulting in a dissipated RF power of less than 1 W. Due to the modest performance requirements, alternative methods are being employed for the fabrication of this cavity. These include fabricating the entire cavity from reactor grade Niobium and welding the cavity using tungsten inert gas (TIG) welding in a high purity Argon environment. A post purification heat treatment will be performed in an RF induction oven to increase the cavity performance.

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THPB044

A Superconducting RF Deflecting Cavity for the ARIEL e-Linac Separator

HOM, linac, electron, impedance

1187

D.W. Storey
Victoria University, Victoria, B.C., Canada
R.E. Laxdal, L. Merminga, B.S. Waraich, Z.Y. Yao, V. Zvyagintsev
TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada

A 650 MHz SRF deflecting mode cavity has been designed for the ARIEL e-Linac to separate interleaved beams heading towards either Rare Ion Beam production or a recirculation loop for energy recovery, allowing the e-Linac to provide beam delivery to multiple users simultaneously. The cavity geometry has been optimized for the ARIEL specifications, resulting in a very compact cavity with high shunt impedance and low dissipated power. Analyses have been performed on the susceptibility to multipacting, input coupling considering beam loading and microphonics, and extensive studies into the damping of transverse and longitudinal higher order modes. The pressure sensitivity, frequency tuning, and thermal behaviour have also been studied using ANSYS. The cavity design resulting from these considerations will be discussed here.

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THPB045

Progress in IFMIF Half Wave Resonators Manufacturing and Test Preparation

simulation, cryomodule, vacuum, controls

1191

G. Devanz, N. Bazin, G. Disset, P. Hardy, O. Piquet, J. Plouin
CEA/DSM/IRFU, France
H. Dzitko, H. Jenhani, J. Neyret, N. Sellami
CEA/IRFU, Gif-sur-Yvette, France

The IFMIF accelerator aims to provide an accelerator-based D-Li neutron source to produce high intensity high energy neutron flux to test samples as possible candidate materials to a full lifetime of fusion energy reactors. The first phase of the project aims at validating the technical options for the construction of an accelerator prototype, called LIPAc (Linear IFMIF Prototype Accelerator). A cryomodule hosting 8 Half Wave Resonators (HWR) at 175 MHz will provide the acceleration from 5 to 9 MeV. We report on the progress of the HWR manufacturing. A pre-series cavity will be used to assess and optimize the tuning procedure of the HWR, as well as the processing steps and related tooling. A new horizontal test cryostat (SATHORI) is also being set up at Saclay in the existing SRF test area. The SATHORI is dedicated to the IFMIF HWR performance check, fully equipped with its power coupler and cold tuning system. A 30kW-RF power will be available for these tests.

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THPB046

Design and Development of Superconducting Spoke Cavity for Compact Photon Source

laser, photon, simulation, scattering

1196

M. Sawamura
Japan Atomic Energy Agency (JAEA), Gamma-ray Non-Destructive Assay Research Group, Tokai-mura, Ibaraki-ken, Japan
E. Cenni
CEA/IRFU, Gif-sur-Yvette, France
R. Hajima
JAEA, Ibaraki-ken, Japan
H. Hokonohara, Y. Iwashita, H. Tongu
Kyoto ICR, Uji, Kyoto, Japan
T. Kubo, T. Saeki
KEK, Ibaraki, Japan

Funding: This study is supported by Photon and Quantum Basic Research Coordinated Development Program of MEXT, Japan.
The spoke cavity is expected to have advantages for compact ERL accelerator for X-ray source based on laser Compton scattering. We have been developing the spoke cavity under a research program of MEXT, Japan to establish the fabrication process. Since our designed shape of the spoke cavity is complicated due to increase the RF properties, we have been designing the mold including the process of press work and the support parts for vacuum tolerance with the mechanical simulation. In this paper we present status of the spoke cavity fabrication.

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THPB047

Analysis of a 750 MHz SRF Dipole Cavity

dipole, simulation, cryogenics, cathode

1200

A. Castilla, J.R. Delayen
ODU, Norfolk, Virginia, USA
A. Castilla, J.R. Delayen
JLab, Newport News, Virginia, USA
A. Castilla
DCI-UG, León, Mexico

Funding: Authored by Jefferson Science Associates, LLC under U. S. DOE Contract No. DE-AC05-06OR23177.
There is a growing interest in using rf transverse deflecting structures for a plethora of applications in the current and future high performance colliders. In this paper, we present the results of a proof of principle superconducting rf dipole, designed as a prototype for a 750 MHz crabbing corrector for the Medium Energy Electron-Ion Collider (MEIC), which has been successfully tested at 4.2 K and 2 K at the Jefferson Lab’s Vertical Testing Area (VTA). The analysis of its rf performance during cryogenic testing, along with Helium pressure sensitivity, Lorentz detuning, surface resistance, and multipacting processing analysis are presented in this work. Detailed calculations of losses at the port flanges are included for completeness of the cavity’s cryogenic performance studies.

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THPB048

Design of a Compact Superconducting Crab-Cavity for LHC Using Nb-on-Cu-Coating Technique

cathode, impedance, HOM, SRF

1205

A. Grudiev, S. Atieh, R. Calaga, S. Calatroni, O. Capatina, F. Carra, G. Favre, L.M.A. Ferreira, J.-F. Poncet, T. Richard, A. Sublet, C. Zanoni
CERN, Geneva, Switzerland

The design of a compact superconducting crab-cavity for LHC using Nb-on-Cu-coating technique is presented. The cavity shape is based on the ridged waveguide resonator with wide open apertures to provide access to the inner surface of the cavity for coating. It also provides natural damping for HOMs and rather low longitudinal and transverse impedances. The results of the cavity shape optimization taking into account RF performance, coating, and thermo-mechanical considerations as well as the design and fabrication plans of the first prototype for coating and cold tests are presented.

Poster THPB048 [0.534 MB]

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THPB050

Performance Evaluation of HL-LHC Crab Cavity Prototypes in a CERN Vertical Test Cryostat

SRF, monitoring, HOM, electron

1210

K.G. Hernández-Chahín
DCI-UG, León, Mexico
G. Burt
Cockcroft Institute, Warrington, Cheshire, United Kingdom
C. Christophe, A. Macpherson, M. Navarro-Tapia, R. Torres-Sanchez
CERN, Geneva, Switzerland
S.U. De Silva
ODU, Norfolk, Virginia, USA
A.R.J. Tutte
Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
S. Verdú-Andrés
BNL, Upton, Long Island, New York, USA

Funding: My work is supported by the Mexican CONACYT(Consejo Nacional de Ciencia y Tecnologia) program through the Mexican national scholarship (Becas Nacionales y Becas Mixtas).
Three proof-of-principle compact crab cavity designs have been fabricated in bulk niobium and cold tested at their home labs, as a first validation step towards the High Luminosity LHC project. As a cross check, all three bare cavities have been retested at CERN, in order to cross check their performance, and cross-calibrate the CERN SRF cold test facilities. While achievable transverse deflecting voltage is the key performance indicator, secondary performance aspects derived from multiple cavity monitoring systems are also discussed. Temperature mapping profiles, quench detection, material properties, and trapped magnetic flux effects have been assessed, and the influence on performance discussed. The significant effort invested in developing expertise in preparation and testing of these crab cavities has already been fruitful for all partners, and more is to come within this ongoing program.

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THPB051

Lorentz Detuning for a Double-Quarter Wave Cavity

simulation, radiation, vacuum, electromagnetic-fields

1215

S. Verdú-Andrés, S.A. Belomestnykh, Q. Wu, B. P. Xiao
BNL, Upton, Long Island, New York, USA
S.A. Belomestnykh
Stony Brook University, Stony Brook, USA
J. Wang
CST of America, Wellesley Hills, Massachusetts, USA

Funding: Work supported by US DOE via BSA LLC contract No.DE-AC02-98CH10886 and US LARP program and by EU FP7 HiLumi LHC grant No.284404. Used NERSC resources by US DOE contract No.DE-AC02-05CH11231.
The Lorentz detuning is the resonant frequency change in an RF cavity due to the radiation pressure on the cavity walls. We present benchmarking studies of Lorentz detuning calculations for a Double-Quarter Wave Crab Cavity (DQWCC) using the codes ACE3P. The results are compared with the Lorentz detuning measurements performed during the cold tests of the Proof-of-Principle DQWCC at BNL.

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THPB052

Thermal Losses in Couplers and Ports of a SPS Double-Quarter Wave Crab Cavity

HOM, pick-up, simulation, niobium

1219

S. Verdú-Andrés, S.A. Belomestnykh, Q. Wu, B. P. Xiao
BNL, Upton, Long Island, New York, USA
S.A. Belomestnykh
Stony Brook University, Stony Brook, USA
G. Burt
Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
G. Burt
Lancaster University, Lancaster, United Kingdom
R. Calaga, O. Capatina, F. Carra, C. Zanoni
CERN, Geneva, Switzerland
F. Carra
Politecnico di Torino, Torino, Italy
T.J. Jones
STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom
Z. Li
SLAC, Menlo Park, California, USA

Funding: Supported by US DOE via US LARP, through BSA LLC under contract No. DE-AC02-98CH10886 and using NERSC resources under contract No. DE-AC02-05CH11231. Also supported by EU FP7 HiLumi LHC No.284404.
The Double-Quarter Wave Crab Cavity for beam tests at SPS will be equipped with a Fundamental Power Coupler (FPC), three HOM filters and one pickup. FPC and HOM couplers are located in high magnetic field region and have a hook shape. The FPC will be made in copper while HOM and pickup are in niobium. This paper explains the material choice for the FPC, HOM and pickup couplers given the calculated power dissipation for fundamental and selected high order modes. It also describes the envisaged cooling system and corresponding thermal distribution for each coupler.

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THPB053

Electromagnetic Design of 400 MHz RF-Dipole Crabbing Cavity for LHC High Luminosity Upgrade

HOM, dipole, luminosity, impedance

1222

S.U. De Silva, J.R. Delayen, H. Park
ODU, Norfolk, Virginia, USA
Z. Li
SLAC, Menlo Park, California, USA

The beam crabbing proposed for the LHC High Luminosity Upgrade requires two crabbing systems operating in both horizontal and vertical planes. In addition, the crabbing cavity design needs to meet strict dimensional constraints and functional specifications of the cavities. This paper presents the detailed electromagnetic design including em properties, multipole analysis, multipacting levels of the 400 MHz rf-dipole crabbing cavity.

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THPB055

RF Performance Results of the 2nd ELBE SRF Gun

gun, SRF, electron, cathode

1227

A. Arnold, M. Freitag, P.N. Lu, P. Murcek, J. Teichert, H. Vennekate, R. Xiang
HZDR, Dresden, Germany
G. Ciovati, P. Kneisel, M. Stirbet, L. Turlington
JLab, Newport News, Virginia, USA

As in 2007 the first 3.5 cell superconducting radio frequency (SRF) gun was taken into operation at Helmholtz-Zentrum Dresden-Rossendorf, it turned out that the specified performance to realize an electron energy of 9.4 MeV has not been achieved. Instead, the resonator of the gun was limited by field emission to about one third of this value and the measured beam parameters remained significantly below its expectations. However, to demonstrate the full potential of this electron source for the ELBE linear accelerator, a second and slightly modified SRF gun was developed and built in collaboration with Thomas Jefferson National Accelerator Facility. We will report on commissioning of this new SRF gun and present a full set of RF performance results. Additionally, investigations are shown that try to explain a particle contamination that happened recently during our first cathode transfer.

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THPB056

SRF Gun Cavity R&D at DESY

SRF, gun, cathode, operation

1231

D. Kostin, C. Albrecht, A. Brinkmann, Th. Buettner, J. Eschke, T. Feldmann, A. Gössel, D. Klinke, A. Matheisen, W.-D. Möller, D. Reschke, M. Schmökel, J.K. Sekutowicz, W. Singer, X. Singer, N. Steinhau-Kühl, J. Ziegler, B. van der Horst
DESY, Hamburg, Germany
M. Barlak, J.A. Lorkiewicz, R. Nietubyć
NCBJ, Świerk/Otwock, Poland

SRF Gun Cavity is an ongoing accelerator R&D project at DESY, being developed since several years. Currently several SRF Gun cavity prototypes were simulated, built and tested in our Lab and elsewhere. Lately the 1.6 cells Pb thin film cathode niobium cavity was tested in a vertical cryostat with a different cathode plug configurations. Cathode plug design was improved, as well as SRF Gun Cavity cleaning procedures. Results of the last cavity performance tests are presented and discussed.

Poster THPB056 [1.257 MB]

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THPB059

Design, Fabrication and Performance of SRF-Gun Cavity

gun, SRF, cathode, target

1243

T. Konomi, E. Kako, Y. Kobayashi, K. Umemori, S. Yamaguchi
KEK, Ibaraki, Japan
R. Matsuda
Mitsubishi Heavy Industries Ltd. (MHI), Takasago, Japan
T. Yanagisawa
MHI, Hiroshima, Japan

The development of superconducting RF gun has been started at KEK. The performance targets are that average current is 100 mA, normalized emittance is less than 1 μm.rad, beam energy is 2 MeV and energy spread is less than 0.1 %. The SRF gun consists of 1.3 GHz and 1.5 cell elliptical cavity and backward illuminated photocathode. The cavity shape was designed by using SUPERFISH and GPT. The cavity has been fabricated by Japanese industry. Accelerating field tuning and vertical test without cathode plug was done. The surface peak electric field reached 66 MV/m, and this meet the target value 42 MV/m sufficiently. For next vertical test, cathode rod without photocathode is in preparation. In the workshop, the SRF-Gun concepts and vertical test results will be reported.

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THPB060

Development of SRF Cavity Tuners for CERN

cryomodule, vacuum, operation, SRF

1247

K. Artoos, R. Calaga, O. Capatina, T. Capelli, F. Carra, L. Dassa, N. Kuder, R. Leuxe, P. Minginette, W. Venturini Delsolaro, G. Villiger, C. Zanoni, P. Zhang
CERN, Geneva, Switzerland
G. Burt
Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
J.R. Delayen, H. Park
ODU, Norfolk, Virginia, USA
T.J. Jones, N. Templeton
STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom
S. Verdú-Andrés, B. P. Xiao
BNL, Upton, Long Island, New York, USA

Superconducting RF cavity developments are currently on-going for new accelerator projects at CERN such as HIE ISOLDE and HL-LHC. Mechanical RF tuning systems are required to compensate cavity frequency shifts of the cavities due to temperature, mechanical, pressure and RF effects on the cavity geometry. A rich history and experience is available for such mechanical tuners developed for existing RF cavities. Design constraints in the context of HIE ISOLDE and HL-LHC such as required resolution, space limitation, reliability and maintainability have led to new concepts in the tuning mechanisms. This paper will discuss such new approaches, their performances and planned developments.

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THPB061

Performance of the Tuner Mechanism for SSR1 Resonators During Fully Integrated Tests at Fermilab

controls, niobium, resonance, linac

1252

D. Passarelli, J.P. Holzbauer, L. Ristori
Fermilab, Batavia, Illinois, USA

In the framework of the Proton Improvement Plan-II (PIPII) at Fermilab, a cavity tuner was developed to control the frequency of 325 MHz spoke resonators (SSR1). The behavior of the tuner mechanism and compliance with technical specifications were investigated through a campaign of experimental tests in operating conditions in the spoke test cryostat (STC) and at room temperature. Figures of merit for the tuner such as tuning range, stiffness, components hysteresis and overall performance were measured and are reported in this paper.

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THPB062

Accelerated Life Testing of LCLS-II Cavity Tuner Motor

cryomodule, acceleration, operation, SRF

1257

N.A. Huque, M.E. Abdelwhab, E. Daly
JLab, Newport News, Virginia, USA
Y.M. Pischalnikov
Fermilab, Batavia, Illinois, USA

An Accelerated Life Test (ALT) of the Phytron stepper motor used in the LCLS-II cavity tuner is being carried out at JLab. Since the motor will reside inside the cryomodule, any failure would lead to a very costly and arduous repair. As such, the motor will be tested for the equivalent of five lifetimes before being approved for use in the production cryomodules. The 9-cell LCLS-II cavity will be simulated by disc springs with an equivalent spring constant. Hysteresis plots of the motor position vs. tuner position – measured via an installed linear variable differential transformer (LVDT) – will be used to determine any drift from the required performance. The titanium spindle will also be inspected for loss of lubrication. This paper outlines the ALT plan and latest results.

Poster THPB062 [2.794 MB]

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THPB063

BNL 56 MHz HOM Damper Fabrication at JLab

HOM, niobium, feedback, SRF

1262

N.A. Huque, W.A. Clemens, E. Daly
JLab, Newport News, Virginia, USA
S. Bellavia, G.T. McIntyre, S.K. Seberg, Q. Wu
BNL, Upton, Long Island, New York, USA

The Higher-Order Mode (HOM) Dampers for the Relativistic Heavy-Ion Collider’s (RHIC) 56 MHz cavity at Brookhaven National Laboratory (BNL) are currently being fabricated at JLab. The coaxial damper is primarily constructed with high RRR niobium, with a combination of niobium and sapphire rings as the filter assembly. Several design changes have been made with respect to the performance of a prototype damper – also fabricated at JLab – which was found to quench at low power. The production dampers are being tuned and tested in the JLab vertical test area (VTA) prior to delivery. Two HOM dampers will be delivered to BNL; they are to be used in the RHIC in November, 2015. This paper outlines the challenges faced in the fabrication and tuning process.

Poster THPB063 [2.315 MB]

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THPB065

Reliability of the LCLS II SRF Cavity Tuner

radiation, vacuum, SRF, operation

1267

Y.M. Pischalnikov, B. Hartman, J.P. Holzbauer, W. Schappert, S.J. Smith, J.C. Yun
Fermilab, Batavia, Illinois, USA

The SRF cavity tuner for LCLS II must work reliably for more than 20 years in a cryomodule environment. Tuner’s active components- electromechanical actuator and piezo-actuators must work reliably in an insulating vacuum environment at low temperature for the lifetime of the machine. Summary of the accelerated lifetime tests (ALT) of the electromechanical and piezo actuators inside cold/ insulated vacuum environment and irradiation hardness test (dose level up to 5*10⁸ Rad) of tuner components are presented. Methodology to design and build reliable SRF cavity tuner, based on “lessons learned” approach, are discussed.

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THPB066

RF Analysis of Equator Welding Stability for the European XFEL Cavities

controls, linac, HOM, factory

1272

A.A. Sulimov
DESY, Hamburg, Germany

In order to guaranty a sufficient High Order Modes (HOM) damping in the European XFEL cavities, a detailed analysis of the mechanical cavity production was performed. The mechanical measurements are precise enough to control the shape of cavity parts, but cannot be used for a welded cavity. To estimate the shape deformation during equator welding, the eigenfrequencies of cavity cells are compared with frequencies of cavity parts. This simple RF analysis can indicate irregularity of 9 equator welds and was used in addition to control of mean values for longitudinal and transverse deformations.

Poster THPB066 [0.148 MB]

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THPB067

HOM Coupler Notch Filter Tuning for the European XFEL Cavities

HOM, controls, resonance, database

1274

A.A. Sulimov
DESY, Hamburg, Germany

The notch filter (NF) tuning prevents the extraction of fundamental mode (1.3 GHz) RF power through Higher Order Modes (HOM) couplers. The procedure of NF tuning was optimized at the beginning of serial European XFEL cavities production. It allows keeping the filter more stable against temperature and pressure changes during cavity cool down. Some statistics of NF condition during cavities and modules cold tests is presented.

Poster THPB067 [0.404 MB]

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THPB068

Practical Aspects of HOM Suppression Improvement for TM011

HOM, damping, simulation, dipole

1277

A.A. Sulimov, A. Ermakov, J.H. Thie
DESY, Hamburg, Germany
A. Gresele
Ettore Zanon S.p.A., Nuclear Division, Schio, Italy

Some Higher Order Modes (HOM) pass bands were controlled during cryo-tests at DESY for the European XFEL cavities. The second monopole mode (TM011) showed most instabilities and suppression degradation. The authors will explain this phenomenon on the example of cavity CAV00553 and present the practical method of TM011 damping improvement.

Poster THPB068 [0.182 MB]

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THPB069

Engineering Design and Prototype Fabrication of HOM Couplers for HL-LHC Crab Cavities

HOM, niobium, luminosity, SRF

1279

C. Zanoni, S. Atieh, I. Aviles Santillana, R. Calaga, O. Capatina, T. Capelli, F. Carra, P. Freijedo Menendez, M. Garlaschè, J.-M. Geisser, R. Leuxe, L. Marques Antunes Ferreira, E. Rigutto
CERN, Geneva, Switzerland
S.A. Belomestnykh, S. Verdú-Andrés, Q. Wu, B. P. Xiao
BNL, Upton, Long Island, New York, USA
G. Burt
Lancaster University, Lancaster, United Kingdom
S.U. De Silva, J.R. Delayen, R.G. Olave, H. Park
ODU, Norfolk, Virginia, USA
T.J. Jones, N. Templeton
STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom
Z. Li
SLAC, Menlo Park, California, USA
A.J. May, S.M. Pattalwar
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
T.H. Nicol
Fermilab, Batavia, Illinois, USA
A. Ratti
LBNL, Berkeley, California, USA

The High-Luminosity upgrade for the LHC relies on a set of RF Crab Cavities for reaching its goals. Two parallel concepts, the Double Quarter Wave (DQW) and the RF Dipole (RFD), are going through a comprehensive design process along with preparation of fabrication in view of extensive tests with beam in SPS. High Order Modes (HOM) couplers are critical in providing damping in RF cavities for operation in accelerators. HOM prototyping and fabrication have recently started at CERN. In this paper, an overview of the final shape is provided along with an insight in the mechanical and thermal analyses performed to validate the design of these critical components. Emphasis is also given to test campaigns, material selection, prototyping and initial fabrication that are aimed at fulfilling the highly demanding tolerances of the couplers.

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THPB070

Design of Dressed Crab Cavities for the HL-LHC Upgrade

niobium, cryomodule, SRF, operation

1284

C. Zanoni, K. Artoos, S. Atieh, I. Aviles Santillana, J.P. Brachet, R. Calaga, O. Capatina, T. Capelli, F. Carra, L. Dassa, G. Favre, P. Freijedo Menendez, M. Garlaschè, M. Guinchard, N. Kuder, S.A.E. Langeslag, R. Leuxe, L. Prever-Loiri, G. Vandoni
CERN, Geneva, Switzerland
S.A. Belomestnykh, I. Ben-Zvi, S. Verdú-Andrés, Q. Wu, B. P. Xiao
BNL, Upton, Long Island, New York, USA
I. Ben-Zvi
Stony Brook University, Stony Brook, USA
G. Burt
Lancaster University, Lancaster, United Kingdom
S.U. De Silva, R.G. Olave, H. Park
ODU, Norfolk, Virginia, USA
J.R. Delayen
JLab, Newport News, Virginia, USA
T.J. Jones, N. Templeton
STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom
Z. Li
SLAC, Menlo Park, California, USA
K.B. Marinov, A.J. May, S.M. Pattalwar
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
T.H. Nicol
Fermilab, Batavia, Illinois, USA
A. Ratti
LBNL, Berkeley, California, USA

The HL-LHC upgrade relies on a set of RF crab cavities for reaching its goals. Two parallel concepts, the Double Quarter Wave (DQW) and the RF Dipole (RFD), are going through a comprehensive design process along with preparation of fabrication in view of extensive tests with beam in SPS. High Order Modes (HOM) couplers are critical in providing damping in RF cavities for operation in accelerators. HOM prototyping and fabrication have recently started at CERN. In this paper, an overview of the final geometry is provided along with an insight in the mechanical and thermal analyses performed to validate the design of this critical component. Emphasis is also given to material selection, prototyping, initial fabrication and test campaigns that are aimed at fulfilling the highly demanding tolerances of the couplers.

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THPB071

Developments of SiC Damper for SuperKEKB Superconducting Cavity

HOM, operation, factory, higher-order-mode

1289

M. Nishiwaki, K. Akai, T. Furuya, A. Kabe, S. Mitsunobu, Y. Morita
KEK, Ibaraki, Japan

Upgrade works for SuperKEKB is in the final stage and the commissioning operation will start in this JFY. Eight superconducting accelerating cavities were operated for more than ten years at KEKB electron ring and are to be used at SuperKEKB. The cavity operation at those high current accelerators requires sufficient absorption of the beam-induced HOM power. In KEKB, the absorbed HOM power of 16 kW in two ferrite dampers attached to each cavity was achieved at the beam current of 1.4 A. On the other hand, the expected HOM power at SuperKEKB is calculated to be 37 kW in the beam current of 2.6 A. To cope with the HOM power issue, we developed additional HOM dampers made of SiC to be installed to the downstream of the cavity module. From precise calculations, it was found that the additional dampers reduce the HOM power loads of the ferrite dampers more effectively than the large beam pipe model of cavity module, which is another option to reduce the HOM loads. New SiC dampers were fabricated and high power-tested. Those SiC dampers successfully absorbed the expected HOM power. In this report, we will describe the results of calculations and high-power RF tests of new SiC dampers.

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THPB072

Higher Order Mode Damping in a Higher Harmonic Cavity for the Advanced Photon Source Upgrade

HOM, impedance, dipole, simulation

1293

S.H. Kim, J. Carwardine, Z.A. Conway, G. Decker, M.P. Kelly, B. Mustapha, P.N. Ostroumov, G.J. Waldschmidt
ANL, Argonne, Illinois, USA

Funding: Results in this report are derived from work performed at Argonne National Laboratory. Argonne is operated by UChicago Argonne, LLC, for the U.S. Department of Energy under contract DE-AC02-06CH11357.
A superconducting higher-harmonic cavity (HHC) is under development for the Advanced Photon Source Upgrade based on a Multi-Bend Achromat lattice. This cavity will be used to improve the Touschek lifetime and the single bunch current limit by lengthening the beam. A single-cell 1.4 GHz (the 4th harmonic of the main RF) cavity is designed based on the TESLA shape. Two adjustable fundamental mode power couplers are included. The harmonic cavity voltage of 0.84 MV will be driven by the 200 mA beam with a bunch length of >50 ps RMS. Higher-order modes (HOM) must be extracted and damped. This will be done with two silicon carbide beamline HOM absorbers to minimize heating of RF structures such as the superconducting cavity and/or couplers and suppress possible beam instabilities. The HHC system is designed such that 1) most monopole and dipole HOMs are extracted along the beam pipes and damped in the ‘beamline’ silicon carbide absorbers and 2) a few HOMs, resulting from introduction of the couplers, are extracted through the coupler and dissipated in a room temperature water-cooled load. We will present time and frequency domain simulation results and discuss damping of HOMs.

Poster THPB072 [2.187 MB]

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THPB074

High Current eRHIC Cavity Design and HOM Damping Scheme

HOM, damping, linac, impedance

1297

W. Xu, S.A. Belomestnykh, I. Ben-Zvi, H. Hahn
BNL, Upton, Long Island, New York, USA

Funding: This work is supported by LDRD program of Brookhaven Science Associates.
A 422 MHz cavity was designed for high current FFAG lattice ERLs for high luminosity eRHIC. The cavity was optimized to be able to propagate all the HOMs out of the cavity for high BBU threshold current and low HOM power (loss factor). Coupling the full spectrum (up to 30 GHz) HOMs out of the cavity and delivering the HOM power (up to 8 kW) out of the cryomodule is a challenge. A damping scheme with 6 coaxial line HOM couplers for low frequency HOMs and 3 waveguide HOM dampers for high frequency (so that the waveguide is small) is proposed to damp the full spectrum and high power HOMs. This paper will present the cavity design and HOM damping scheme.

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THPB077

Modified TTF3 Couplers for LCLS-II

operation, vacuum, simulation, linac

1306

C. Adolphsen, K. Fant, Z. Li, C.D. Nantista, G. Stupakov, J. Tice, F.Y. Wang, L. Xiao
SLAC, Menlo Park, California, USA
I.V. Gonin, K. Premo, N. Solyak
Fermilab, Batavia, Illinois, USA

The LCLS-II 4 GeV SC electron linac will use 280 TESLA cavities and TTF3 couplers, modified for CW operation with input power up to about 7 kW. The coupler modifications include shortening the antenna to achieve higher Qext and thickening the copper plating on the warm section inner conductor to lower the peak temperature. Another change is the use a waveguide transition box that is machined out of a solid piece of aluminum, significantly reducing its cost and improving its fit to the warm coupler window section. This paper describes the changes, simulations of the coupler operation (heat loads and temperatures), rf processing results and CW tests with LCLS-II dressed cavities.

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THPB078

Status of the Power Couplers for the ESS Elliptical Cavity Prototypes

cryomodule, vacuum, status, simulation

1309

C. Arcambal
CEA/IRFU, Gif-sur-Yvette, France
P. Bosland, M. Desmons, G. Devanz, G. Ferrand, A. Hamdi, P. Hardy, H. Jenhani, F. Leseigneur, C. Marchand, F. Peauger, O. Piquet, D. Roudier, C. Servouin
CEA/DSM/IRFU, France
C. Darve
ESS, Lund, Sweden

In the frame of the European Spallation Source (ESS) project, a linear accelerator composed of a superconducting section is being developed. This accelerator owns two kinds of cavities called “medium beta cavity” (β=0.67) and “high beta cavity” (β= 0.86). These cavities are equipped with RF power couplers whose main characteristics are: fundamental frequency: 704.42MHz, peak RF power: 1.1MW, repetition rate: 14Hz, RF pulse width>3.1ms. These couplers are common to the two cavities. The CEA Saclay is responsible for the design, the manufacture, the preparation and the conditioning of the couplers used for the Elliptical Cavities Cryomodule Technological Demonstrators (ECCTD). This work is performed in collaboration with ESS and the IPNO. This paper describes the coupler architecture, its different components, the main characteristics and the specific features of its elements (RF performance, dissipated power, cooling, coupler box test for the conditioning). The status of the manufacture of each coupler part is also presented.

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THPB081

FPC and HOM Coupler Test Boxes for HL-LHC Crab Cavities

HOM, dipole, coupling, operation

1321

A.R.J. Tutte, G. Burt
Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
R. Calaga, A. Macpherson, E. Montesinos
CERN, Geneva, Switzerland
S.U. De Silva
ODU, Norfolk, Virginia, USA
Z. Li
SLAC, Menlo Park, California, USA
B. P. Xiao
BNL, Upton, Long Island, New York, USA

The LHC luminosity upgrade will involve the installation of thirty-two 400 MHz SRF crab cavities. The cavities have two variants known as the RF dipole and double quarter-wave crab cavities. Each cavity has a fundamental power coupler (FPC) at 400 MHz and two or three HOM couplers. Before integration onto the cavities it is necessary to condition the FPC, and to measure the transmission on the HOM couplers at low power to ensure the operate as designed, each requiring a special test box. The FPC test box should provide a high transmission between two couplers without creating high surface fields. The low power HOM test boxes should be terminated to a load such that the natural stop and pass-bands of the couplers are preserved allowing the reflection to me measured and compared to simulations. In addition, due to the possibility of high HOM power in the LHC crab cavities, the concept of creating a broadband high power HOM coupler test box in order to condition and test the couplers at high power has been investigated. The Rf design of all test boxes is presented and discussed.

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THPB082

Design of QWR Power Coupler for the Rare Isotope Science Project in Korea

simulation, pick-up, diagnostics, cryomodule

1326

I. Shin, M.O. Hyun
IBS, Daejeon, Republic of Korea
E. Kako
KEK, Ibaraki, Japan
C.K. Sung
Korea University Sejong Campus, Sejong, Republic of Korea

A power coupler has been designed for the Rare Isotope Science Project (RISP) in Korea. The power couplers will provide 4 kW RF power to 81.25 MHz superconducting quarter wave resonators with β=0.047. The coupler is a coaxial capacitive type with an impedance of 50 ohms using a disc type ceramic window. Design studies of the coupler are presented.

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THPB084

Design of Input Coupler for RIKEN Superconducting Quarter-Wavelength Resonator

radiation, cryomodule, Windows, ion

1335

K. Ozeki, O. Kamigaito, H. Okuno, N. Sakamoto, K. Suda, Y. Watanabe, K. Yamada
RIKEN Nishina Center, Wako, Japan
E. Kako, H. Nakai, K. Umemori
KEK, Ibaraki, Japan
K. Okihira, K. Sennyu, T. Yanagisawa
MHI, Hiroshima, Japan

In RIKEN Nishina Center, for the purpose of development of elemental technology for the superconducting linear accelerator, the designing and construction of accelerator system based on superconducting quarter-wavelength resonator are carried out. The basic designs of the input coupler are as follows: The resonance frequency of the cavity is 75.5 MHz and assumed beam loading is about 1 kW. Double vacuum windows, which are disk-type, are adopted. A thermal anchor of 40 K is installed near the cold-window. The optimum positions of the cold-window and the thermal anchor depending on the effective RRR of copper-plate are being studied. In this contribution, the details of these designs will be reported. This work was funded by ImPACT Program of Council for Science, Technology and Innovation (Cabinet Office, Government of Japan).

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THPB087

Design and Simulation of High Power Input Coupler for C-ADS Linac 5-Cell Elliptical Cavities

simulation, electron, RF-structure, impedance

1343

K.X. Gu
Institute of High Energy Physics (IHEP), Chinese Academy of Sciences, Beijing, People's Republic of China
X. Chen, T.M. Huang, Q. Ma, W.M. Pan
IHEP, Beijing, People's Republic of China

Two 650 MHz elliptical cavity sections (elliptical 063, elliptical 082) are chosen to accelerate medium energy protons for China Accelerator Driven sub-critical System (C-ADS) linac. For each 5-cell cavity, RF power up to 150 kW in CW mode is required to be fed by a fundamental power coupler (FPC). A coaxial type coupler is designed to meet the power and RF coupling requirements. This paper presents the RF design, thermal analysis and multipacting simulations of the coupler for C-ADS 5-cell elliptical cavities.

Poster THPB087 [0.593 MB]

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THPB088

20 kW CW Power Couplers for the APS-U Harmonic Cavity

Windows, operation, storage-ring, electron

1346

M.P. Kelly, A. Barcikowski, Z.A. Conway, D. Horan, M. Kedzie, S.H. Kim, P.N. Ostroumov
ANL, Argonne, Illinois, USA
S.V. Kutsaev
RadiaBeam, Santa Monica, California, USA
J. Rathke
AES, Medford, New York, USA

Funding: This work supported by the U.S. DOE, Office of Nuclear Physics, Contract No. DE-AC02-06CH11357. This research used resources of ANL’s ATLAS facility, which is a DOE Office of Science User Facility.
A pair of 20 kW CW adjustable RF power couplers optimized for 1.4 GHz have been designed and are being built as part of the APS-U bunch lengthening system. The system uses one superconducting RF cavity to be installed into the APS Upgrade electron storage ring and will provide a tremendous practical benefit to the majority of users by increasing the beam lifetime by 2-3 times. The 80 mm diameter, 50 Ω coaxial couplers include 4 cm (~20 dB) of adjustability. This allows optimization of bunch lengthening for a range of storage ring beam currents and fill patterns while, simultaneously, maintaining the required 0.84 MV harmonic cavity voltage. To provide bunch lengthening, the cavity/coupler system must extract RF power (up to 32 kW) from the beam. Each coupler will transmit roughly half of the total extracted power to external water-cooled loads. The design extends upon on a well-tested ANL two RF window concept, using a pair of simple rugged 80 mm diameter alumina disks. A new feature is the ‘hourglass-shaped’ inner conductor chosen to maximize transmission at 1.4 GHz. Results of electromagnetic and thermal simulations, as well as, prototyping and initial RF testing are presented.

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THPB089

HOM Coupler Performance in CW Regime in Horizontal and Vertical Tests

HOM, operation, coupling, higher-order-mode

1349

N. Solyak, M.H. Awida, A. Grassellino, C.J. Grimm, A. Hocker, J.P. Holzbauer, T.N. Khabiboulline, O.S. Melnychuk, A.M. Rowe, D.A. Sergatskov, N. Solyak
Fermilab, Batavia, Illinois, USA
J.K. Sekutowicz
DESY, Hamburg, Germany

Power dissipation in HOM coupler antenna can limit cavity gradient in cw operation. XFEL design of HOM coupler, feedthrough and thermal connection to 2K pipe was accepted for LCLS-II cavity based on simulation results. Recently a series of vertical and horizontal tests was done to prove design for cw operation. In vertical test was found no effect of HOM coupler heating on high-Q cavity performance. In horizontal cryostat HOM coupler was tested up-to 23MV/m in continuous wave mode. Result proves that XFEL HOM coupler meets LCLS-II specifications.

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THPB091

Mechanical Design of a High Power Coupler for the PIP-II 325 MHz SSR1 RF Cavity

vacuum, status, cryomodule, instrumentation

1354

O.V. Pronitchev, S. Kazakov
Fermilab, Batavia, Illinois, USA

The Project X Injector Experiment (PXIE) at Fermilab will include one cryomodule with eight 325 MHz single spoke superconductive cavities (SSR1). Each cavity requires approximately 2 kW CW RF power for 1 mA beam current operation. A future upgrade will require up to 8 kW RF power per cavity. Fermilab has designed and procured ten production couplers for the SSR1 type cavities. Status of the 325 MHz main coupler development for PXIE SSR1 cryomodule is reported.

Poster THPB091 [1.821 MB]

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THPB092

Mechanical Design of a High Power Coupler for the PIP-II 162.5 MHz RF Quadrupole

rfq, vacuum, ion, ion-source

1357

O.V. Pronitchev, S. Kazakov
Fermilab, Batavia, Illinois, USA

PXIE is a prototype front end system for the proposed PIP-II accelerator upgrade at Fermilab. An integral component of the front end is a 162.5 MHz, normal conducting, continuous wave (CW), radiofrequency quadrupole (RFQ) cavity. Two identical couplers will deliver approximately 100 kW total CW RF power to the RFQ. Fermilab has designed and procured main couplers for the CW RFQ accelerating cavity. The mechanical design of the coupler, along with production status, is presented below.

Poster THPB092 [0.476 MB]

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THPB093

A 1.3 GHz Waveguide to Coax Coupler for Superconducting Cavities With a Minimum Kick

emittance, niobium, electron, dipole

1360

J.A. Robbins, C. Egerer, R.G. Eichhorn, V. Veshcherevich
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Transversal forces as a result of asymmetric field generated by the fundamental power couplers have become a concern for low emittance beam in future accelerators. In pushing for smallest emittances, Cornell has finished a physics design for a symmetric coupler for superconducting accelerating cavities. This coupler consists of a rectangular waveguide that transforms into a coaxial line inside the beam pipe, eventually feeding the cavity. We will report on the RF design yielding to the extremely low transversal kick. In addition, heating, heat transfer and thermal stability of this coupler has been evaluated.

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THPB097

New Possible Configuration of 3.9 GHz Coupler

Windows, multipactoring, simulation, electron

1373

S. Kazakov
Fermilab, Batavia, Illinois, USA

The LCLS-II superconducting accelerator supposedly will use 3.9 GHz (3-d harmonic) superconductive cavities. A new possible configuration of 3.9 GHz main coupler is presented in the papar. This configuration contains two coaxial ceramic windows, a cold and a warm one. Inner conductors of windows are connected through the capacitive gap and have no mechanical no thermal contacts. It allows to avoid using bellows and thus avoid the problem of heating and cooling. The windows have shields protecting shields against the electron, and this prevents the window ceramics from charging. Results of computer simulation of the new coupler are posted.

Poster THPB097 [1.036 MB]

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THPB098

Testing of 325 MHz Couplers at Test Stand in Resonance Mode

resonance, multipactoring, rf-amplifier, monitoring

1376

S. Kazakov, B.M. Hanna, O.V. Pronitchev
Fermilab, Batavia, Illinois, USA

The linear accelerator for the PIP-II program utilizes two types of 325 MHz Single Spoke resonator cavities: SSR-I and SSR-II. Operating power of SSR-II is about 17 kW and requires input couplers which can reliably work at power levels > 20 kW with full reflection at any reflected phase. Currently only one 10 kW RF amp is available for coupler testing. To increase testing power, a special resonance configuration were used. This configuration allows us to raise RF power approximately 3 times. The testing scheme and results are discussed in the paper.

Poster THPB098 [1.600 MB]

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THPB100

Nb Coatings on Bellows Used in SRF Accelerators

SRF, ion, impedance, plasma

1379

S.F. Chapman, I. Irfan, M. Krishnan, K.M. Velas
AASC, San Leandro, California, USA

Funding: This research is supported by the US DOE via SBIR grant: DE-SC0007678
Alameda Applied Sciences Corporation (AASC) is developing bellows with the strength and flexibility of stainless steel and the low surface impedance of a superconductor. Such unique bellows would enable alignment of SRF cavity sections with greatly reduced RF losses. To that end, we grow Nb thin films via Coaxial Energetic Deposition (CED) from a cathodic arc plasma. Films of Nb were grown on stainless steel bellows, with and without an intermediate layer of Cu deposited via the same technique, to produce a working bellows with a well adhered superconducting inner layer. The Nb coated bellows have undergone tests conducted by our collaborators to evaluate their RF performance.

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THPB101

High Power Input Couplers for C-ADS

cryomodule, linac, vacuum, proton

1383

T.M. Huang, X. Chen, H.Y. Lin, Q. Ma, F. Meng, W.M. Pan, G.W. Wang, X.Y. Zhang
IHEP, Beijing, People's Republic of China
K.X. Gu
Institute of High Energy Physics (IHEP), Chinese Academy of Sciences, Beijing, People's Republic of China

High power input couplers are key components of the superconducting system for China Accelerator Driven sub-critical System (C-ADS) project. For the first phase, C-ADS includes four types of superconducting cavities (SCCs) of two frequencies, 162.5 MHz HWR SCC and 325 MHz Spoke SCC up to the energy of 25 MeV. All input couplers for the SCCs are developed in IHEP. This paper will describe the development status of the high power input couplers for C-ADS.

Poster THPB101 [0.430 MB]

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THPB103

High Power Coupler Test for ARIEL SC Cavities

vacuum, TRIUMF, linac, cryomodule

1390

Y. Ma, P.R. Harmer, D. Lang, R.E. Laxdal, B.S. Waraich, V. Zvyagintsev
TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada

TRIUMF ARIEL[1](The Advanced Rare Isotope Laboratory) project employs five 1.3 GHz 9-cell superconducting elliptical cavities[2] for acceleration of 10 mA electron beam up to energy of 50 MeV. 100 kW CW RF power will be delivered into each cavity by means of pair of Power Couplers: 50 kW per each coupler. Before installing the power couplers with the cavities, they have to be assembled on Power Coupler Test Stand(PCTS) and conditioned with a 30 kW IOT. Six couplers have been conditioned at room temperature and four of them have been installed to the cavities and tested during beam commissioning. Test results of the power couplers will be described and discussed in this paper.
#mayanyun@triumf.ca

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THPB104

Higher Order Modes Simulation and Measurements for 2400 MHz Cavity

HOM, damping, simulation, higher-order-mode

1394

Ya.V. Shashkov, D.S. Bazyl, R.V. Donetskiy, M.V. Lalayan, N.P. Sobenin
MEPhI, Moscow, Russia
R. Calaga
CERN, Geneva, Switzerland
A.A. Zavadtsev
Nano, Moscow, Russia
M. Zobov
INFN/LNF, Frascati (Roma), Italy

Funding: *Work supported by Ministry of Education and Science grant 3.245.2014/r and the EU FP7 HiLumi LHC – Grant Agreement 284404
In the frameworks of the High Luminosity LHC upgrade program an application of additional harmonic cavities operating at multiples of the main RF system frequency of 400 MHz is currently under discussion. The 800 MHz superconducting cavities with grooved beam pipes were suggested for implementation. A scaled aluminum prototype with a frequency of the operational mode of 2400 MHz was manufactured for testing the results of simulations. The load reflection coefficient measurements were performed as well as the Qload measurements for cavities with the load. Here we discuss the prototype design and report the obtained measurement results.
Higher order modes, superconducting cavities, srf

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THPB105

Demonstration of Coaxial Coupling Scheme at 26 MV/m for 1.3 GHz Tesla-Type SRF Cavities

coupling, niobium, SRF, HOM

1397

Y. Xie, A. Kanareykin
Euclid TechLabs, LLC, Solon, Ohio, USA
T.N. Khabiboulline, A. Lunin, V. Poloubotko, A.M. Rowe, N. Solyak, V.P. Yakovlev
Fermilab, Batavia, Illinois, USA
J. Rathke
AES, Medford, New York, USA

Superconducting ILC-type cavities have an rf input coupler that is welded on. A detachable input coupler will reduce conditioning time (can be conditioned separately), reduce cost and improve reliability. The problem with placing an extra flange in the superconducting cavity is about creating a possible quench spot at the seal place. Euclid Techlabs LLC has developed a coaxial coupler which has an on the surface with zero magnetic field (hence zero surface current). By placing a flange in that area we are able to avoid disturbing surface currents that typically lead to a quench. The coupler is optimized to preserve the axial symmetry of the cavity and rf field. The surface treatments and rf test of the proto- type coupler with a 1.3 GHz ILC-type single-cell cavity at Fermilab will be reported and discussed.

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THPB110

Procurements for LCLS-II Cryomodules at JLab

HOM, cryomodule, vacuum, operation

1405

E. Daly, G. Cheng, G.K. Davis, T. Hiatt, N.A. Huque, F. Marhauser, H. Park, J.P. Preble, K.M. Wilson
JLab, Newport News, Virginia, USA

Funding: This work was supported by the LCLS-II Project and the U.S. Department of Energy, Contract DE-AC02-76SF00515.
The Thomas Jefferson National Accelerator Facility is currently engaged, along with several other DOE national laboratories, in the Linac Coherent Light Source II project (LCLS II). The SRF Institute at Jefferson Lab will be building 1 prototype and 17 production cryomodules based on the TESLA / ILC / XFEL design. Each cryomodule will contain eight nine cell cavities with coaxial power couplers operating at 1.3 GHz. Procurement of components for cryomodule construction has been divided amongst partner laboratories in a collaborative manner. JLab has primary responsibility for six procurements include the dressed cavities, cold gate valves, higher-order-mode (HOM) and field probe feedthroughs, beamline bellows cartridges, cavity tuner assemblies and HOM absorbers. For procurements led by partner laboratories, JLab collaborates and provides technical input on specifications, requirements and assembly considerations. This paper will give a detailed description of plans and status for JLab procurements.

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THPB115

TRIUMF's Injector and Accelerator Cryomodules

cryomodule, TRIUMF, alignment, linac

1409

N. Muller, P.R. Harmer, J.J. Keir, D. Kishi, P. Kolb, A. Koveshnikov, C. Laforge, D. Lang, R.E. Laxdal, Y. Ma, A.K. Mitra, R.R. Nagimov, R. Smith, B.S. Waraich, L. Yang, Z.Y. Yao, V. Zvyagintsev
TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada

TRIUMF's ARIEL project includes a 50 MeV-10mA electron linear accelerator (e-Linac) using 1.3 GHz superconducting technology. The accelerator consists of three cryomodules; an injector cryomodule with one cavity and two accelerating cryomodules with two cavities each. One injector and one accelerator have been assembled and commissioned at TRIUMF with a second injector cryomodule being assembled for VECC in Kolkata. Both Injector and Accelerator cryomodules utilize a top-loaded cold mass design contained in a box-type cryomodule; design and early test results of both cryomodules are presented.

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THPB119

LCLS-II 1.3 GHz Cryomodule Design – Modified TESLA-Style Cryomodule for CW Operation

cryomodule, vacuum, cryogenics, operation

1417

T.J. Peterson, T.T. Arkan, C.M. Ginsburg, Y. He, J.A. Kaluzny, M.W. McGee, Y.O. Orlov
Fermilab, Batavia, Illinois, USA

Funding: Work supported, in part, by the US DOE and the LCLS-II Project.
We will present the design of the 1.3 GHz cryomodule for the Linear Coherent Light Source upgrade (LCLS-II) at SLAC. Fermilab is responsible for the design of this cryomodule, a modified TESLA-style cryomodule to accommodate continuous wave (CW) mode operation and LCLS-II beam parameters, consisting of eight 1.3 GHz superconducting RF cavities, a corrector magnet package, and instrumentation. Thirty-five of these cryomodules, approximately half built at Fermilab and half at Jefferson Lab, will become the main accelerating elements of the 4 GeV linac. The modifications and special features of the cryomodule include: thermal and cryogenic design to handle high heat loads in CW operation, magnetic shielding and cool-down configurations to enable high quality factor (Q0) performance of the cavities, liquid helium management to address the different liquid levels in the 2-phase pipe with 0.5% SLAC tunnel longitudinal slope, support structure design to meet California seismic design requirements, and with the overall design consistent with space constrains in the existing SLAC tunnel. The prototype cryomodule assembly will begin in August 2015 and is to be completed in early 2016.

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THPB120

Status of LCLS-II QA Systems Collaboration for Cyromodule Construction at TJNAF and FNAL

cryomodule, controls, database, status

1422

E.A. McEwen, V. Bookwalter, J. Leung
JLab, Newport News, Virgina, USA
J.N. Blowers, J.B. Szal
Fermilab, Batavia, Illinois, USA

At the Thomas Jefferson National Accelerator Facility (JLab), we are supporting the LCLS-II Project at SLAC. The plan is to build thirty-five 1.3 GHz continuous wave cryomodules, production to be split between JLab and FNAL (Fermilab). This has required a close collaboration between the partner labs, including enhancing our existing quality systems to include this collaboration. This over view describes the current status of the Quality System development as of August 2015, when the partner labs start the assembly of the prototype cryomodules.

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FRAA01

Overview of Recent Tuner Development on Elliptical and Low-Beta Cavities

linac, cryomodule, controls, operation

1425

R. Paparella
INFN/LASA, Segrate (MI), Italy

The talk will provide an overview on the latest advances of tuner development for SRF applications. Issues and present approaches on how to resolve them will be emphasized for both TM and TEM cavities and examples from various labs and projects (XFEL, LCLS-II, ESS, SPL, ARIEL, SPIRAL2, FRIB, ANL, IFMIF) will be given in order to better explain issues and solutions. Details on author’s contributions to European-XFEL tuner activity for 1.3 GHz and 3.9 GHz cavities will be also shown.

Slides FRAA01 [3.421 MB]

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FRAA03

High Gradient Performance in Fermilab ILC Cryomodule

cryomodule, vacuum, operation, detector

1432

E.R. Harms, C.M. Baffes, K. Carlson, B.E. Chase, D.J. Crawford, E. Cullerton, D.R. Edstrom, A. Hocker, A.L. Klebaner, M.J. Kucera, J.R. Leibfritz, J.N. Makara, D. McDowell, O.A. Nezhevenko, D.J. Nicklaus, Y.M. Pischalnikov, P.S. Prieto, J. Reid, W. Schappert, W.M. Soyars, P. Varghese, A. Warner
Fermilab, Batavia, Illinois, USA

Funding: Operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy.
Fermilab has assembled an ILC like cryomodule using U.S. processed high gradient cavities and achieved an average gradient of 31.5 MV/m for the entire cryomodule. Test results and challenges along the way will be discussed.

Slides FRAA03 [5.878 MB]

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FRAA04

Performance of the Cornell ERL Main Linac Prototype Cryomodule

HOM, linac, cryomodule, operation

1437

F. Furuta, B. Clasby, R.G. Eichhorn, B. Elmore, G.M. Ge, D. Gonnella, D.L. Hall, G.H. Hoffstaetter, R.P.K. Kaplan, J.J. Kaufman, M. Liepe, T.I. O'Connell, S. Posen, P. Quigley, D.M. Sabol, J. Sears, E.N. Smith, V. Veshcherevich
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Cornell has designed, fabricated, and tested (by the time of the conference) a high current (100 mA) CW SRF prototype cryomodule for the Cornell ERL. This talk will report on the design and performance of this very high Q0 CW cryomodule including design issues and mitigation strategies.

Slides FRAA04 [4.614 MB]

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FRAA05

A 1.3 GHz Cryomodule with 2x9-Cell Cavity for SETF at Peking University

SRF, cryomodule, operation, experiment

1443

F. Zhu, J.E. Chen, L.W. Feng, Y. Gao, J.K. Hao, S. Huang, L. Lin, K.X. Liu, S.W. Quan, F. Wang, X.D. Wen, D.H. Zhuang
PKU, Beijing, People's Republic of China

Funding: Work supported by National Basic Research Project (No. 2011CB808304 and 2011CB808302）and NDRC project.
The straight beam line of SETF at Peking University is under construction, which consists of a DC-SRF photoinjector and a superconducting linac with two 9-cell cavities. Stable operation of the DC-SRF photoinjector has been realized and the design, manufacture and assembly of the cryomodule with two 9-cell cavities have been completed. Improved capacitive coupling RF power coupler and fast tuner with piezo are adopted

Slides FRAA05 [3.709 MB]

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FRBA01

Technical and Logistical Challenges for IFMIF-LIPAC Cryomodule Construction

cryomodule, vacuum, cryogenics, solenoid

1453

H. Dzitko, N. Bazin, A. Bruniquel, P. Charon, S. Chel, G. Devanz, G. Disset, P. Gastinel, P. Hardy, J. Neyret, J. Relland, B. Renard, N. Sellami, M.R. Vallcorba-Carbonell
CEA/IRFU, Gif-sur-Yvette, France
N. Berton, P. Contrepois, V.M. Hennion, H. Jenhani, O. Piquet
CEA/DSM/IRFU, France
D. Gex, G. Phillips
F4E, Germany
A. Kasughai
Japan Atomic Energy Agency (JAEA), International Fusion Energy Research Center (IFERC), Rokkasho, Kamikita, Aomori, Japan
J. Knaster
IFMIF/EVEDA, Rokkasho, Japan
D. Regidor, F. Toral
CIEMAT, Madrid, Spain

This paper provides an overview of the final design and fabrication status of the IFMIF cryomodule, including the design issues, and deals with the strategies implemented in order to mitigate the main technical and logistical risks identified. The seismic constraints as well as licensing requirements, transportation issue and assembly process are also addressed. The IFMIF cryomodule presented here will be part of the LIPAc project (Linear IFMIF Prototype Accelerator). It is a full scale prototype of one of the IFMIF accelerators, from the injector to the first cryomodule, aiming at validating the technical options for the future accelerator-based D-Li neutron source to produce high intensity high energy neutron flux for testing of candidate materials for use in fusion energy reactors. The cryomodule contains all the equipment to transport and accelerate a 125 mA deuteron beam from an input energy of 5 MeV up to 9 MeV. It consists of a horizontal cryostat of about 6 m long, 3 m high and 2 m wide, which includes 8 superconducting HWRs for beam acceleration working at 175 MHz and at 4.5 K, 8 power couplers to provide RF power to cavities, and 8 Solenoid Packages as focusing elements.

Slides FRBA01 [9.263 MB]

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FRBA02

Crab Cavity and Cryomodule Development for HL-LHC

HOM, cryomodule, shielding, operation

1460

F. Carra, A. Amorim Carvalho, K. Artoos, S. Atieh, I. Aviles Santillana, A.B. Boucherie, J.P. Brachet, K. Brodzinski, R. Calaga, O. Capatina, T. Capelli, L. Dassa, T. Dijoud, H.M. Durand, G. Favre, L.M.A. Ferreira, P. Freijedo Menendez, M. Garlaschè, M. Guinchard, N. Kuder, S.A.E. Langeslag, R. Leuxe, A. Macpherson, P. Minginette, E. Montesinos, F. Motschmann, C. Parente, L. Prever-Loiri, D. Pugnat, E. Rigutto, V. Rude, M. Sosin, G. Vandoni, G. Villiger, C. Zanoni
CERN, Geneva, Switzerland
S.A. Belomestnykh, S. Verdú-Andrés, Q. Wu, B. P. Xiao
BNL, Upton, Long Island, New York, USA
G. Burt
Lancaster University, Lancaster, United Kingdom
S.U. De Silva, J.R. Delayen, R.G. Olave, R.G. Olave, H. Park
ODU, Norfolk, Virginia, USA
T.J. Jones, N. Templeton
STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom
Z. Li
SLAC, Menlo Park, California, USA
K.B. Marinov, S.M. Pattalwar
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
T.H. Nicol
Fermilab, Batavia, Illinois, USA
A. Ratti
LBNL, Berkeley, California, USA

The HL-LHC project aims at increasing the LHC luminosity by a factor 10 beyond the design value. The installation of a set of RF Crab Cavities to increase bunch crossing angle is one of the key upgrades of the program. Two concepts, Double Quarter Wave (DQW) and RF Dipole (RFD) have been proposed and are being produced in parallel for test in the SPS beam before the next long shutdown of CERN accelerator’s complex. In the retained concept, two cavities are hosted in one single cryomodule, providing thermal insulation and interfacing with RF coupling, tuning, cryogenics and beam vacuum. This paper overviews the main design choices for the cryomodule and its different components, which have the goal of optimizing the structural, thermal and electro-magnetic behavior of the system, while respecting the existing constraints in terms of integration in the accelerator environment. Prototyping and testing of the most critical components, manufacturing, preparation and installation strategies are also described.

Slides FRBA02 [4.678 MB]

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FRBA03

SRF, Compact Accelerators for Industry & Society

SRF, electron, cathode, gun

1467

R.D. Kephart, B.E. Chase, I.V. Gonin, A. Grassellino, S. Kazakov, T.N. Khabiboulline, S. Nagaitsev, R.J. Pasquinelli, S. Posen, O.V. Pronitchev, A. Romanenko, V.P. Yakovlev
Fermilab, Batavia, Illinois, USA
S. Biedron, S.V. Milton, N. Sipahi
CSU, Fort Collins, Colorado, USA
S. Chattopadhyay
Northern Illinois Univerity, Dekalb, Illinois, USA
P. Piot
Northern Illinois University, DeKalb, Illinois, USA

Accelerators developed for Science now are used broadly for industrial, medical, and security applications. Over 30,000 accelerators touch over $500B/yr in products producing a major impact on our economy, health, and well being. Industrial accelerators must be cost effective, simple, versatile, efficient, and robust. Many industrial applications require high average beam power. Exploiting recent advances in Superconducting Radio Frequency (SRF) cavities and RF power sources as well as innovative solutions for the SRF gun and cathode system, a collaboration of Fermilab-CSU-NIU has developed a design for a compact SRF high-average power electron linac. Capable of 5-50 kW average power and continuous wave operation this accelerator will produce electron beam energies up to 10 MeV and small and light enough to mount on mobile platforms, such accelerators will enable new in-situ environmental remediation methods and new applications involving in-situ crosslinking of materials. More importantly, we believe this accelerator will be the first of a new class of simple, turn-key SRF accelerators that will find broad application in industry, medicine, security, and science.

Slides FRBA03 [2.342 MB]

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FRBA04

SRF for Future Circular Colliders

radiation, HOM, proton, collider

1474

R. Calaga, O. Brunner, A.C. Butterworth, E. Jensen
CERN, Geneva, Switzerland

The future circular colliders (FCC) will require superconducting RF systems for the proton-proton, electron-positron and lepton-hadron modes of the collider operation. The SCRF systems will accelerate the protons beams to 50 TeV and the lepton beams from 45.5 to 175 GeV in a staged approach with a possible 60 GeV energy recovery linac for the lepton-hadron to option as an intermediate step. The expected stored beam currents in some modes exceed 1 A with very short bunch lengths. A first conceptual design of the FCC RF system is proposed along with highlights of specfic R&D topics to reach the design performance. Challenges related to RF structure design, intensity limitations due to beam loading, RF powering and higher order modes are addressed. Synergies between the different collider modes and the present LHC are identified.

Slides FRBA04 [2.699 MB]

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