SRF2015 - List of Keywords (SRF)

Paper	Title	Other Keywords	Page
MOAA01	FRIB Project: Moving to Production Phase	cavity, 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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MOAA04	Overview of Recent SRF Developments for ERLs	gun, cavity, 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	cavity, vacuum, niobium, impedance	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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MOBA08	Niobium Impurity-Doping Studies at Cornell and CM Cool-Down Dynamic Effect on Q0	cavity, cryomodule, 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	cavity, 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	cavity, niobium, 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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MOPB006	Hc2 Measurements of Superconductors	niobium, superconducting-RF, radio-frequency, superconductivity	79
	J.T. Maniscalco, D. Gonnella, D.L. Hall, M. Liepe, E.N. Smith Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: NSF/DOE Recently, Cornell has improved a method for extracting the upper critical field Hc2 of a thin-film superconductor using four-point resistivity measurements. In the field of superconducting radio-frequency accelerators (SRF), novel materials and processes such as nitrogen-doped niobium and Nb3Sn may allow for improved SRF performance and cost efficiency over traditional niobium. In this paper we present updated results on Hc2 measurements for Nb3Sn, as well as results for niobium prepared with an 800 C bake. We also extract important material properties from these measurements, such as the Ginzburg Landau parameter, the mean free path, and coherence length, which are critical for determining SRF performance.
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MOPB007	Temperature Excursions in Nb Sheets With Imbedded Delamination Cracks	radiation, cavity, 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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MOPB014	Magnetic Flux Expulsion in Horizontally Cooled Cavities	cavity, interface, 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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MOPB018	Introduction of Precisely Controlled Microstructural Defects into SRF Cavity Niobium Sheets and Their Impact on Local Superconducting Properties	niobium, cavity, 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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MOPB020	Mean Free Path Dependence of the Trapped Flux Surface Resistance	electron, niobium, simulation, superconductivity	129
	M. Checchin, A. Grassellino, M. Martinello, A. Romanenko Fermilab, Batavia, Illinois, USA M. Martinello 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 In this article a calculation of the trapped flux surface resistance is presented. The two main mechanisms considered in such approach are the oscillation of the magnetic flux trapped in the superconductor due to the Lorentz force, and the static resistance associated to the normal conducting vortex core. The model derived shows a good description of the available experimental data, highlighting that the radio frequency vortex dissipation is mostly due to the static part of the surface resistance. We show that the surface resistance for 100% trapped flux normalized to the trapped field (expressed in nOhm/mG) can be approximated to R/B=18.3*(l f)^1/2/(50.1+l) with l the mean free path in nm and f the frequency in GHz.
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MOPB023	Detectors Sensing Second Events Induced by Thermal Quenches of SRF Cavities in He II	cavity, 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	cavity, simulation, cathode, 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, cavity, 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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MOPB030	Measurements of Thermal Impedance on Superconducting Radiofrequency Cavities	cavity, impedance, 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	cavity, cryomodule, 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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MOPB039	Analysis of BCS RF Loss Dependence on N-Doping Protocols	cavity, niobium, 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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MOPB041	Cryomodule Testing of Nitrogen-Doped Cavities	cavity, cryomodule, HOM, 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	cavity, niobium, vacuum, simulation	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, factory, cavity	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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MOPB050	Characterization of SRF Materials at the TRIUMF muSR Facility	TRIUMF, positron, polarization, vacuum	205
	R.E. Laxdal, T.J. Buck, T. Junginger, P. Kolb, Y.Y. Ma, L. Yang, Z.Y. Yao TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada S.H. Abidi University of Toronto, Toronto, Ontario, Canada R. Kiefl UBC & TRIUMF, Vancouver, British Columbia, Canada
	MuSR is a powerful tool to probe local magnetism and hence can be used to diagnose flux penetration in Type-II superconductors. Samples produced at TRIUMF and with collaborators in both coin shaped and ellipsoidal geometries have been characterized by applying either transverse or parallel fields between 0 and 300mT and measuring flux entry as a function of applied field. Samples include Nb treated in standard ways including forming, chemistry, and heat treatments. Further, Nb samples have been doped with Nitrogen and coated with a 2 micron layer of Nb3Sn by collaborators from FNAL and Cornell respectively and measured in three field/geometry configurations. Analysis of the method in particular the effects of geometry and the role of pinning will be presented. Results of the measurements will be presented.
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MOPB051	Muon Spin Rotation on Treated Nb Samples in Parallel Field Geometry	cavity, 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	cavity, 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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MOPB054	An Investigation of Correlations Between Mechanical and Microstructural Properties of High Purity Polycrystalline Niobium	niobium, database, experiment, software	219
	Z. Zhao, 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. An understanding of the relationship between mechanical and functional properties, and processing history is essential in order to manufacture polycrystalline niobium cavities with consistent performance. The crystallographic texture (preferred crystal orientation) and microstructure in polycrystalline sheet varies considerably, so identifying its influence on properties is needed to achieve a better understanding of how to control properties of high purity niobium. Samples extracted from many lots produced by Tokyo Denkai and Ningxia sheet were examined. Through-thickness texture of the undeformed niobium samples was measured using electron backscattered pattern mapping. Texture is identified with pole figures, orientation distribution function, and grain misorientation relationships. Stress-strain tests were done to identify ultimate tensile stress, elongation, 0.2% yield strength, and hardening rate. From tests on many lots, there is no clear trend between the mechanical and material properties in high purity niobium and correlations between various microstructural and mechanical properties show significant scatter and few apparent correlations.
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MOPB055	Characterization of Nitrogen Doping Recipes for the Nb SRF Cavities	niobium, cavity, 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, cavity, niobium, 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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MOPB060	A GPU Based 3D Particle Tracking Code for Multipacting Simulation	GPU, cavity, simulation, gun	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, cavity, cryomodule, 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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MOPB070	Preliminary Conceptual Design of the CEPC SRF System	cavity, HOM, 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	cryomodule, proton, cavity, 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	cavity, niobium, 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	cavity, niobium, 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	cavity, niobium, cathode, radiation	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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MOPB083	Cooling Front Measurement of a 9-Cell Cavity via the Multi-Cell Temperature-Mapping System at Cornell University	cavity, 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	cavity, 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, cavity, experiment, 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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MOPB090	Analysis of Degraded Cavities in Prototype Modules for the European XFEL	cavity, accelerating-gradient, 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	cavity, 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	cavity, cathode, 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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MOPB095	SRF Cavity Processing and Chemical Etching Development for the FRIB Linac	cavity, 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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MOPB098	Improvement of Temperature Control During Nb 9-Cell SRF Cavity Vertical Electro-Polishing (VEP) and Progress of VEP Quality	cavity, experiment, cathode, controls	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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MOPB101	Electropolishing of Niobium SRF Cavities in Eco-Friendly Aqueous Electrolytes Without Hydrofluoric Acid	cavity, niobium, 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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MOPB103	Vertical Electro-Polishing at DESY of a 1.3 GHz Gun Cavity for CW Application	cavity, gun, acceleration, injection	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	cavity, niobium, factory, cryogenics	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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MOPB106	Analysis of High Pressure Rinsing Characteristics for SRF Cavities	cavity, target, experiment, 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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MOPB111	Furnace N2 Doping Treatments at Fermilab	vacuum, cavity, 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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MOPB113	Study of the Evolution of Artificial Defects on the Surface of Niobium During Electrochemical and Chemical Polishing	controls, laser, cavity, 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, cavity, vacuum, 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	cavity, vacuum, factory, operation	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	cavity, experiment, hardware, 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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TUAA03	BESSY VSR: A Novel Application of SRF for Synchrotron Light Sources	cavity, damping, 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	cavity, niobium, linac, 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, cavity, 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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TUBA03	On the Understanding of Q-Slope of Niobium Thin Films	ECR, niobium, ion, cavity	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	cavity, simulation, 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	cavity, niobium, vacuum, 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	cavity, 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	cavity, 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	cavity, niobium, 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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TUPB004	Vertical Cavity Test Facility at Fermilab	cavity, controls, instrumentation, experiment	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, cavity, storage-ring, 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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TUPB008	A New Cryogenic Control System for the Vertical Test Area at Jefferson Lab	controls, PLC, cryogenics, operation	549
	G.K. Davis, T. Goodman, P. Kushnick, T. Powers, C.M. Wilson JLab, Newport News, Virginia, USA
	Funding: DOE The Vertical Test Area at Jefferson Lab, consisting of eight vertical dewars, recently received a major upgrade by replacing the original (1995) cryogenic control system. A new, state-of-the-art, distributed control system (DC S) based on Programmable Logic Controllers (PLCs) was installed and commissioned. The new system increases facility throughput, reliability and cryogenic efficiency, while improving safety. The system employs a touchscreen graphical user interface and a highly redundant architecture on an Ethernet backbone.
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TUPB010	Plug Transfer System for GaAs Photocathodes	gun, cathode, operation, vacuum	553
	P. Murcek, A. Arnold, P.N. Lu, J. Teichert, H. Vennekate, R. Xiang HZDR, Dresden, Germany A. Burrill HZB, Berlin, Germany
	The transport and exchange technology of Cs2Te photocathode for the ELBE superconducting rf photoinjector (SRF gun) has been successfully developed and tested at HZDR. The next goal is to realize the transport of GaAs photocathode into SRF gun, which will need a new transfer system with XHV 10^-11 mbar. The key component of the system is the transfer chamber and the load-lock system that will be connected to the SRF-gun. In the carrier four small plugs will be transported, and one of them will be plug on the cathode-body and inserted into the cavity. The new transport chamber allows the transfer and exchange of plugs between HZDR, HZB and other cooperating institutes. In HZDR this transfer system will also provide a direct connection between the SRFGUN and the GaAs preparation chamber in the Elbe-accelerator hall.
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TUPB013	Fermilab Cryomodule Test Stand Design and Plans	cryomodule, cryogenics, controls, cavity	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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TUPB022	Low-Beta SRF Cavity Processing and Testing Facility for the Facility for Rare Isotope Beams at Michigan State University	cavity, 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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TUPB027	Developments on SRF Coatings at CERN	cavity, 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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TUPB029	Material Quality & SRF Performance of Nb Films Grown on Cu via ECR Plasma Energetic Condensation	ECR, ion, plasma, interface	622
	A-M. Valente-Feliciano, G.V. Eremeev, C.E. Reece, J.K. Spradlin JLab, Newport News, Virginia, USA S. Aull CERN, Geneva, Switzerland Th. Proslier ANL, Argonne, Illinois, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. The RF performance of bulk Nb cavities has continuously improved over the years and is approaching the intrinsic limit of the material. Although some margin seems still available with processes such as N surface doping, long term solutions for SRF surfaces efficiency enhancement need to be pursued. Over the years, Nb/Cu technology, despite its shortcomings, has positioned itself as an alternative route for the future of superconducting structures used in accelerators. Significant progress has been made in recent years in the development of energetic deposition techniques such as Electron Cyclotron Resonance (ECR) plasma deposition. Nb films with very high material quality have then been produced by varying the deposition energy alluding to the promise of performing SRF films. This paper presents RF measurements, correlated with surface and material properties, for Nb films showing how, by varying the film growth conditions, the Nb film quality and surface resistance can be altered and how the Q-slope can be eventually overcome.
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TUPB030	Recent Results from the Cornell Sample Host Cavity	cavity, niobium, 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	cavity, cathode, niobium, 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	cavity, 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, cavity, 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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TUPB038	Superconducting Coatings Synthetized by CVD/PECVD for SRF Cavities	niobium, plasma, superconductivity, accelerating-gradient	643
	P. Pizzol, P. Chalker, T. Heil The University of Liverpool, Liverpool, United Kingdom A.N. Hannah, O.B. Malyshev, S.M. Pattalwar, R. Valizadeh STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom G.B.G. Stenning STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom
	Finding a way to overcome the acceleration gradient limits that bulk niobium cavities can provide is a major challenge, fundamental to allow the accelerator science field to progress. In order to overcome the accelerating gradient limits of bulk niobium and reduce manufacturing and operation costs, the idea of using thin layers of niobium deposited on a copper cavity is being explored. This approach has lower material cost with higher availability and more importantly higher thermal conductivity. Physical vapour deposition (PVD) method is currently the preferred method to coat superconducting cavities, but its lack of conformity renders complicated shapes such as crab cavities very difficult to coat. By using chemical vapour deposition (CVD) and plasma enhanced chemical vapour deposition (PECVD) it is possible to deposit thin Nb layers uniformly with density very close to bulk material. This project explores the use of PECVD / CVD techniques to deposit metallic niobium on copper using NbCl5 as precursor and hydrogen as a coreagent. The samples obtained were then characterized via SEM, XRD, and EDX as well as assessing their superconductivity characteristics (RRR and Tc)
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TUPB041	Testing Nb3Sn Coating Using muSR	TRIUMF, niobium, radio-frequency, factory	651
	R.E. Laxdal, T.J. Buck TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada S. Gheidi UBC, Vancouver, B.C., Canada R. Kiefl UBC & TRIUMF, Vancouver, British Columbia, Canada M. Liepe, S. Posen Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	The SRF group at TRIUMF has tested samples relevant for SRF application since 2010 using the TRIUMF μSR facility. In this study collaborators at Cornell coat a Nb coin and a Nb ellipsoid sample with Nb3Sn for characterization using μSR at TRIUMF. Field of first flux entry measurements are performed at M20 on both samples. Measurements include the vortex nucleation field Hnucleate and Tc of both Nb3Sn and Nb. Interestingly the Nb3Sn increases the vortex nucleation field at 2K over standard Nb samples.
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TUPB044	High Quality Factor Studies in SRF Nb3Sn Cavities	cavity, niobium, 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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TUPB046	Structure and Composition of Nb3Sn Diffusion Coated Films on Nb	ion, niobium, electron, cavity	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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TUPB047	Next Generation of SRF-Guns: Low Secondary Electron Yield Based on a Thin Film Approach	electron, target, gun, cathode	673
	C. Schlemper, X. Jiang, M. Vogel University Siegen, Siegen, Germany
	Multipacting is a common issue in the context of cathode units of superconducting radiofrequency photoinjectors (SRF-guns) utilized in linear accelerators under resonant conditions. In this study, Titanium Nitride (TiN) and Carbon thin films have been prepared by DC and RF magnetron sputtering in a Nitrogen and Argon plasma discharge, respectively. Films featuring a thickness of about 600 nm were produced under various deposition conditions on substrates such as Copper, Molybdenum, and Silicon. Materials characterization was carried out utilizing SEM, Raman and FTIR spectroscopy, XRD and AFM. In order to evaluate the SEY a new device is introduced, which is capable of quasi in-situ measurements. The latter is realized by connecting the coating-, the SEY- and a contamination chamber into one setup allowing sample transfer under UHV conditions. Even after an exposure to air carbon shows SEY values down to 0.69. This value, however, turns out to be quite sensitive with respect to the actual surface morphology. Clean TiN surfaces, on the other hand, displayed a SEY value as low as 1.4. In this case the SEY value is strongly affected by potential surface contamination.
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TUPB048	Fermilab Nb3Sn R&D Program	niobium, cavity, 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	cavity, niobium, electron, 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, vacuum, cavity	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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TUPB051	Development of Nb3Sn Coatings by Magnetron Sputtering for SRF Cavities	vacuum, radio-frequency, target, quadrupole	691
	G.J. Rosaz, S. Calatroni, F.M. Leaux, F. Motschmann, Z. Mydlarz, M. Taborelli, W. Vollenberg CERN, Geneva, Switzerland
	Funding: The work is part of EuCARD-2, partly funded by the European Commission, GA 312453 Cost and energy savings are an integral requirement in the design of future particle accelerators. Very low losses SRF accelerating systems, together with high-efficiency cryogenics systems, have the potential of low running costs. The association to the capital cost reduction allowed by thin films coated copper cavities may represent the best overall cost-performance compromise. This strategy has been applied for instance in LEP, the LHC and HIE-ISOLDE with the niobium thin films technology. New materials must be considered to improve the quality factor of the cavities, such as Nb3Sn, which could also ideally operate at higher temperature thus allowing further energy savings. The study considers the possibility to coat a copper resonator with an Nb3Sn layer by means of magnetron sputtering using an alloyed target. We present the impact of the process parameters on the as-deposited layer stoichiometry. The latter is in good agreement with previous results reported in the literature and can be tuned by acting on the coating pressure. The effect of post-coating annealing temperature on the morphology, crystallinity and superconducting properties of the film was also investigated.
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TUPB053	Research on MgB2 at LANL for the Application to SRF Structures	vacuum, superconductivity, status, electron	700
	T. Tajima, L. Civale, R.K. Schulze LANL, Los Alamos, New Mexico, USA
	Funding: U.S. Department of Energy (DOE) Office of Science Office of Nuclear Physics Early Career Research Program This paper is focused on the development of MgB2 coating technique at LANL. Using boron film samples obtained at a large furnace system, we succeeded in obtaining superconducting MgB2 films (Tc of up to 37 K so far) by reacting them with Mg vapor. The major improvements were 1) confinement of the Mg vapor in a hot zone to mitigate the insufficient Mg pressure due to condensation on low temperature surfaces of the connected vacuum pipes and 2) reduction of cooldown time, i.e., ~13 minutes instead of ~1 day with the large system to prevent MgB2 from decomposing.
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TUPB056	Characterization of Nb3Sn Coated Nb Samples	electron, cavity, 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, superconductivity, operation, cavity	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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TUPB059	A Facility for Magnetic Field Penetration Measurements on Multilayer S-I-S Structures	experiment, niobium, superconducting-magnet, data-acquisition	716
	O.B. Malyshev, K.D. Dumbell, L. Gurran, N. Pattalwar, S.M. Pattalwar, R. Valizadeh STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom K.D. Dumbell, S.M. Pattalwar, R. Valizadeh Cockcroft Institute, Warrington, Cheshire, United Kingdom A.V. Gurevich ODU, Norfolk, Virginia, USA L. Gurran Lancaster University, Lancaster, United Kingdom L. Gurran Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
	Funding: STFC and US Department of Energy under contract No. DE-SC0010081. Superconducting RF cavities made of bulk Nb has reached a breakdown field of about 200 mT which is close to the superheating field for Nb. As it was theoretically shown* a multilayer coating can be used to enhance the breakdown field of SRF cavities. The simple example is a superconductor-insulator-superconductor (S-I-S), for example bulk niobium (S) coated with a thin film of insulator (I) followed by a thin layer of a superconductor (S) which could be a dirty niobium*. To verify such an enhancement in a presence of a DC magnetic field at 4.2 K a simple experimental facility was designed, built and tested in ASTeC. The details of experimental setup and results of the measurements will be shown at the conference. A. Gurevich, APL 88, 012511 (2006) **A. Gurevich, AIP Advances, 5, 017112 (2015)
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TUPB060	Measurements of RF Properties of Thin Film Nb3Sn Superconducting Multilayers Using a Calorimetric Technique	cavity, 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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TUPB065	Cryogenic RF Characterization of Superconducting Materials at SLAC With Hemispherical Cavities	cavity, niobium, 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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TUPB067	Design and First Measurements of an Alternative Calorimetry Chamber for the HZB Quadrupole Resonator	niobium, quadrupole, simulation, operation	739
	S. Keckert, R. Kleindienst, J. Knobloch, O. Kugeler HZB, Berlin, Germany
	Funding: The work is part of EuCARD-2, partly funded by the European Commission, GA 312453. The systematic research on superconducting thin films requires dedicated testing equipment. The Quadrupole Resonator (QPR) is a specialized tool to characterize the superconducting properties of circular samples. A calorimetric measurement of the RF surface losses allows the surface resistance to be measured with sub nano-ohm resolution. This measurement can be performed over a wide temperature and magnetic field range, at frequencies of 433, 866 and 1300 MHz. The system at Helmholtz-Zentrum Berlin (HZB) is based on a resonator built at CERN and has been optimized to lower peak electric fields and an improved resolution. An alternative calorimetry chamber has been designed in order to provide flat samples for coating and to ease changing of samples. Furthermore it enables exchangeability of samples between the QPRs at HZB and CERN. With this poster the design and first measurements of the new calorimetry chamber is presented.
	Poster TUPB067 [1.776 MB]
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TUPB078	Developments on a Cold Bead-Pull Test Stand for SRF Cavities	cavity, HOM, 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	cavity, detector, simulation, 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	cavity, diagnostics, monitoring, 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	cavity, 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	cavity, niobium, background, radio-frequency	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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TUPB085	Characterization of Optical Surface Properties of 1.3 GHz SRF Cavities for the European XFEL	cavity, background, electron, niobium	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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TUPB088	On Quench Propagation, Quench Detection and Second Sound in SRF Cavities	niobium, cavity, 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	cavity, coupling, impedance, network	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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MOAA01

FRIB Project: Moving to Production Phase

cavity, 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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MOAA04

Overview of Recent SRF Developments for ERLs

gun, cavity, 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

cavity, vacuum, niobium, impedance

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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MOBA08

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

cavity, cryomodule, 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

cavity, 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

cavity, niobium, 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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MOPB006

Hc2 Measurements of Superconductors

niobium, superconducting-RF, radio-frequency, superconductivity

79

J.T. Maniscalco, D. Gonnella, D.L. Hall, M. Liepe, E.N. Smith
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: NSF/DOE
Recently, Cornell has improved a method for extracting the upper critical field Hc2 of a thin-film superconductor using four-point resistivity measurements. In the field of superconducting radio-frequency accelerators (SRF), novel materials and processes such as nitrogen-doped niobium and Nb3Sn may allow for improved SRF performance and cost efficiency over traditional niobium. In this paper we present updated results on Hc2 measurements for Nb3Sn, as well as results for niobium prepared with an 800 C bake. We also extract important material properties from these measurements, such as the Ginzburg Landau parameter, the mean free path, and coherence length, which are critical for determining SRF performance.

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MOPB007

Temperature Excursions in Nb Sheets With Imbedded Delamination Cracks

radiation, cavity, 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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MOPB014

Magnetic Flux Expulsion in Horizontally Cooled Cavities

cavity, interface, 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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MOPB018

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

niobium, cavity, 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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MOPB020

Mean Free Path Dependence of the Trapped Flux Surface Resistance

electron, niobium, simulation, superconductivity

129

M. Checchin, A. Grassellino, M. Martinello, A. Romanenko
Fermilab, Batavia, Illinois, USA
M. Martinello
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
In this article a calculation of the trapped flux surface resistance is presented. The two main mechanisms considered in such approach are the oscillation of the magnetic flux trapped in the superconductor due to the Lorentz force, and the static resistance associated to the normal conducting vortex core. The model derived shows a good description of the available experimental data, highlighting that the radio frequency vortex dissipation is mostly due to the static part of the surface resistance. We show that the surface resistance for 100% trapped flux normalized to the trapped field (expressed in nOhm/mG) can be approximated to R/B=18.3*(l f)^1/2/(50.1+l) with l the mean free path in nm and f the frequency in GHz.

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MOPB023

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

cavity, 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

cavity, simulation, cathode, 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, cavity, 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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MOPB030

Measurements of Thermal Impedance on Superconducting Radiofrequency Cavities

cavity, impedance, 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

cavity, cryomodule, 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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MOPB039

Analysis of BCS RF Loss Dependence on N-Doping Protocols

cavity, niobium, 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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MOPB041

Cryomodule Testing of Nitrogen-Doped Cavities

cavity, cryomodule, HOM, 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

cavity, niobium, vacuum, simulation

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, factory, cavity

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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MOPB050

Characterization of SRF Materials at the TRIUMF muSR Facility

TRIUMF, positron, polarization, vacuum

205

R.E. Laxdal, T.J. Buck, T. Junginger, P. Kolb, Y.Y. Ma, L. Yang, Z.Y. Yao
TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada
S.H. Abidi
University of Toronto, Toronto, Ontario, Canada
R. Kiefl
UBC & TRIUMF, Vancouver, British Columbia, Canada

MuSR is a powerful tool to probe local magnetism and hence can be used to diagnose flux penetration in Type-II superconductors. Samples produced at TRIUMF and with collaborators in both coin shaped and ellipsoidal geometries have been characterized by applying either transverse or parallel fields between 0 and 300mT and measuring flux entry as a function of applied field. Samples include Nb treated in standard ways including forming, chemistry, and heat treatments. Further, Nb samples have been doped with Nitrogen and coated with a 2 micron layer of Nb3Sn by collaborators from FNAL and Cornell respectively and measured in three field/geometry configurations. Analysis of the method in particular the effects of geometry and the role of pinning will be presented. Results of the measurements will be presented.

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MOPB051

Muon Spin Rotation on Treated Nb Samples in Parallel Field Geometry

cavity, 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

cavity, 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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MOPB054

An Investigation of Correlations Between Mechanical and Microstructural Properties of High Purity Polycrystalline Niobium

niobium, database, experiment, software

219

Z. Zhao, 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.
An understanding of the relationship between mechanical and functional properties, and processing history is essential in order to manufacture polycrystalline niobium cavities with consistent performance. The crystallographic texture (preferred crystal orientation) and microstructure in polycrystalline sheet varies considerably, so identifying its influence on properties is needed to achieve a better understanding of how to control properties of high purity niobium. Samples extracted from many lots produced by Tokyo Denkai and Ningxia sheet were examined. Through-thickness texture of the undeformed niobium samples was measured using electron backscattered pattern mapping. Texture is identified with pole figures, orientation distribution function, and grain misorientation relationships. Stress-strain tests were done to identify ultimate tensile stress, elongation, 0.2% yield strength, and hardening rate. From tests on many lots, there is no clear trend between the mechanical and material properties in high purity niobium and correlations between various microstructural and mechanical properties show significant scatter and few apparent correlations.

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MOPB055

Characterization of Nitrogen Doping Recipes for the Nb SRF Cavities

niobium, cavity, 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, cavity, niobium, 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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MOPB060

A GPU Based 3D Particle Tracking Code for Multipacting Simulation

GPU, cavity, simulation, gun

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, cavity, cryomodule, 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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MOPB070

Preliminary Conceptual Design of the CEPC SRF System

cavity, HOM, 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

cryomodule, proton, cavity, 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

cavity, niobium, 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

cavity, niobium, 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

cavity, niobium, cathode, radiation

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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MOPB083

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

cavity, 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

cavity, 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, cavity, experiment, 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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MOPB090

Analysis of Degraded Cavities in Prototype Modules for the European XFEL

cavity, accelerating-gradient, 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

cavity, 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

cavity, cathode, 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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MOPB095

SRF Cavity Processing and Chemical Etching Development for the FRIB Linac

cavity, 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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MOPB098

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

cavity, experiment, cathode, controls

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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MOPB101

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

cavity, niobium, 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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MOPB103

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

cavity, gun, acceleration, injection

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

cavity, niobium, factory, cryogenics

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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MOPB106

Analysis of High Pressure Rinsing Characteristics for SRF Cavities

cavity, target, experiment, 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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MOPB111

Furnace N2 Doping Treatments at Fermilab

vacuum, cavity, 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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MOPB113

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

controls, laser, cavity, 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, cavity, vacuum, 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

cavity, vacuum, factory, operation

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

cavity, experiment, hardware, 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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TUAA03

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

cavity, damping, 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

cavity, niobium, linac, 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, cavity, 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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TUBA03

On the Understanding of Q-Slope of Niobium Thin Films

ECR, niobium, ion, cavity

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

cavity, simulation, 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

cavity, niobium, vacuum, 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

cavity, 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

cavity, 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

cavity, niobium, 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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TUPB004

Vertical Cavity Test Facility at Fermilab

cavity, controls, instrumentation, experiment

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, cavity, storage-ring, 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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TUPB008

A New Cryogenic Control System for the Vertical Test Area at Jefferson Lab

controls, PLC, cryogenics, operation

549

G.K. Davis, T. Goodman, P. Kushnick, T. Powers, C.M. Wilson
JLab, Newport News, Virginia, USA

Funding: DOE
The Vertical Test Area at Jefferson Lab, consisting of eight vertical dewars, recently received a major upgrade by replacing the original (1995) cryogenic control system. A new, state-of-the-art, distributed control system (DC S) based on Programmable Logic Controllers (PLCs) was installed and commissioned. The new system increases facility throughput, reliability and cryogenic efficiency, while improving safety. The system employs a touchscreen graphical user interface and a highly redundant architecture on an Ethernet backbone.

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TUPB010

Plug Transfer System for GaAs Photocathodes

gun, cathode, operation, vacuum

553

P. Murcek, A. Arnold, P.N. Lu, J. Teichert, H. Vennekate, R. Xiang
HZDR, Dresden, Germany
A. Burrill
HZB, Berlin, Germany

The transport and exchange technology of Cs2Te photocathode for the ELBE superconducting rf photoinjector (SRF gun) has been successfully developed and tested at HZDR. The next goal is to realize the transport of GaAs photocathode into SRF gun, which will need a new transfer system with XHV 10^-11 mbar. The key component of the system is the transfer chamber and the load-lock system that will be connected to the SRF-gun. In the carrier four small plugs will be transported, and one of them will be plug on the cathode-body and inserted into the cavity. The new transport chamber allows the transfer and exchange of plugs between HZDR, HZB and other cooperating institutes. In HZDR this transfer system will also provide a direct connection between the SRFGUN and the GaAs preparation chamber in the Elbe-accelerator hall.

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TUPB013

Fermilab Cryomodule Test Stand Design and Plans

cryomodule, cryogenics, controls, cavity

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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TUPB022

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

cavity, 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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TUPB027

Developments on SRF Coatings at CERN

cavity, 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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TUPB029

Material Quality & SRF Performance of Nb Films Grown on Cu via ECR Plasma Energetic Condensation

ECR, ion, plasma, interface

622

A-M. Valente-Feliciano, G.V. Eremeev, C.E. Reece, J.K. Spradlin
JLab, Newport News, Virginia, USA
S. Aull
CERN, Geneva, Switzerland
Th. Proslier
ANL, Argonne, Illinois, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
The RF performance of bulk Nb cavities has continuously improved over the years and is approaching the intrinsic limit of the material. Although some margin seems still available with processes such as N surface doping, long term solutions for SRF surfaces efficiency enhancement need to be pursued. Over the years, Nb/Cu technology, despite its shortcomings, has positioned itself as an alternative route for the future of superconducting structures used in accelerators. Significant progress has been made in recent years in the development of energetic deposition techniques such as Electron Cyclotron Resonance (ECR) plasma deposition. Nb films with very high material quality have then been produced by varying the deposition energy alluding to the promise of performing SRF films. This paper presents RF measurements, correlated with surface and material properties, for Nb films showing how, by varying the film growth conditions, the Nb film quality and surface resistance can be altered and how the Q-slope can be eventually overcome.

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TUPB030

Recent Results from the Cornell Sample Host Cavity

cavity, niobium, 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

cavity, cathode, niobium, 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

cavity, 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, cavity, 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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TUPB038

Superconducting Coatings Synthetized by CVD/PECVD for SRF Cavities

niobium, plasma, superconductivity, accelerating-gradient

643

P. Pizzol, P. Chalker, T. Heil
The University of Liverpool, Liverpool, United Kingdom
A.N. Hannah, O.B. Malyshev, S.M. Pattalwar, R. Valizadeh
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
G.B.G. Stenning
STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom

Finding a way to overcome the acceleration gradient limits that bulk niobium cavities can provide is a major challenge, fundamental to allow the accelerator science field to progress. In order to overcome the accelerating gradient limits of bulk niobium and reduce manufacturing and operation costs, the idea of using thin layers of niobium deposited on a copper cavity is being explored. This approach has lower material cost with higher availability and more importantly higher thermal conductivity. Physical vapour deposition (PVD) method is currently the preferred method to coat superconducting cavities, but its lack of conformity renders complicated shapes such as crab cavities very difficult to coat. By using chemical vapour deposition (CVD) and plasma enhanced chemical vapour deposition (PECVD) it is possible to deposit thin Nb layers uniformly with density very close to bulk material. This project explores the use of PECVD / CVD techniques to deposit metallic niobium on copper using NbCl5 as precursor and hydrogen as a coreagent. The samples obtained were then characterized via SEM, XRD, and EDX as well as assessing their superconductivity characteristics (RRR and Tc)

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TUPB041

Testing Nb3Sn Coating Using muSR

TRIUMF, niobium, radio-frequency, factory

651

R.E. Laxdal, T.J. Buck
TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada
S. Gheidi
UBC, Vancouver, B.C., Canada
R. Kiefl
UBC & TRIUMF, Vancouver, British Columbia, Canada
M. Liepe, S. Posen
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

The SRF group at TRIUMF has tested samples relevant for SRF application since 2010 using the TRIUMF μSR facility. In this study collaborators at Cornell coat a Nb coin and a Nb ellipsoid sample with Nb3Sn for characterization using μSR at TRIUMF. Field of first flux entry measurements are performed at M20 on both samples. Measurements include the vortex nucleation field Hnucleate and Tc of both Nb3Sn and Nb. Interestingly the Nb3Sn increases the vortex nucleation field at 2K over standard Nb samples.

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TUPB044

High Quality Factor Studies in SRF Nb3Sn Cavities

cavity, niobium, 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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TUPB046

Structure and Composition of Nb3Sn Diffusion Coated Films on Nb

ion, niobium, electron, cavity

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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TUPB047

Next Generation of SRF-Guns: Low Secondary Electron Yield Based on a Thin Film Approach

electron, target, gun, cathode

673

C. Schlemper, X. Jiang, M. Vogel
University Siegen, Siegen, Germany

Multipacting is a common issue in the context of cathode units of superconducting radiofrequency photoinjectors (SRF-guns) utilized in linear accelerators under resonant conditions. In this study, Titanium Nitride (TiN) and Carbon thin films have been prepared by DC and RF magnetron sputtering in a Nitrogen and Argon plasma discharge, respectively. Films featuring a thickness of about 600 nm were produced under various deposition conditions on substrates such as Copper, Molybdenum, and Silicon. Materials characterization was carried out utilizing SEM, Raman and FTIR spectroscopy, XRD and AFM. In order to evaluate the SEY a new device is introduced, which is capable of quasi in-situ measurements. The latter is realized by connecting the coating-, the SEY- and a contamination chamber into one setup allowing sample transfer under UHV conditions. Even after an exposure to air carbon shows SEY values down to 0.69. This value, however, turns out to be quite sensitive with respect to the actual surface morphology. Clean TiN surfaces, on the other hand, displayed a SEY value as low as 1.4. In this case the SEY value is strongly affected by potential surface contamination.

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TUPB048

Fermilab Nb3Sn R&D Program

niobium, cavity, 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

cavity, niobium, electron, 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, vacuum, cavity

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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TUPB051

Development of Nb3Sn Coatings by Magnetron Sputtering for SRF Cavities

vacuum, radio-frequency, target, quadrupole

691

G.J. Rosaz, S. Calatroni, F.M. Leaux, F. Motschmann, Z. Mydlarz, M. Taborelli, W. Vollenberg
CERN, Geneva, Switzerland

Funding: The work is part of EuCARD-2, partly funded by the European Commission, GA 312453
Cost and energy savings are an integral requirement in the design of future particle accelerators. Very low losses SRF accelerating systems, together with high-efficiency cryogenics systems, have the potential of low running costs. The association to the capital cost reduction allowed by thin films coated copper cavities may represent the best overall cost-performance compromise. This strategy has been applied for instance in LEP, the LHC and HIE-ISOLDE with the niobium thin films technology. New materials must be considered to improve the quality factor of the cavities, such as Nb3Sn, which could also ideally operate at higher temperature thus allowing further energy savings. The study considers the possibility to coat a copper resonator with an Nb3Sn layer by means of magnetron sputtering using an alloyed target. We present the impact of the process parameters on the as-deposited layer stoichiometry. The latter is in good agreement with previous results reported in the literature and can be tuned by acting on the coating pressure. The effect of post-coating annealing temperature on the morphology, crystallinity and superconducting properties of the film was also investigated.

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TUPB053

Research on MgB2 at LANL for the Application to SRF Structures

vacuum, superconductivity, status, electron

700

T. Tajima, L. Civale, R.K. Schulze
LANL, Los Alamos, New Mexico, USA

Funding: U.S. Department of Energy (DOE) Office of Science Office of Nuclear Physics Early Career Research Program
This paper is focused on the development of MgB2 coating technique at LANL. Using boron film samples obtained at a large furnace system, we succeeded in obtaining superconducting MgB2 films (Tc of up to 37 K so far) by reacting them with Mg vapor. The major improvements were 1) confinement of the Mg vapor in a hot zone to mitigate the insufficient Mg pressure due to condensation on low temperature surfaces of the connected vacuum pipes and 2) reduction of cooldown time, i.e., ~13 minutes instead of ~1 day with the large system to prevent MgB2 from decomposing.

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TUPB056

Characterization of Nb3Sn Coated Nb Samples

electron, cavity, 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, superconductivity, operation, cavity

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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TUPB059

A Facility for Magnetic Field Penetration Measurements on Multilayer S-I-S Structures

experiment, niobium, superconducting-magnet, data-acquisition

716

O.B. Malyshev, K.D. Dumbell, L. Gurran, N. Pattalwar, S.M. Pattalwar, R. Valizadeh
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
K.D. Dumbell, S.M. Pattalwar, R. Valizadeh
Cockcroft Institute, Warrington, Cheshire, United Kingdom
A.V. Gurevich
ODU, Norfolk, Virginia, USA
L. Gurran
Lancaster University, Lancaster, United Kingdom
L. Gurran
Cockcroft Institute, Lancaster University, Lancaster, United Kingdom

Funding: STFC and US Department of Energy under contract No. DE-SC0010081.
Superconducting RF cavities made of bulk Nb has reached a breakdown field of about 200 mT which is close to the superheating field for Nb. As it was theoretically shown* a multilayer coating can be used to enhance the breakdown field of SRF cavities. The simple example is a superconductor-insulator-superconductor (S-I-S), for example bulk niobium (S) coated with a thin film of insulator (I) followed by a thin layer of a superconductor (S) which could be a dirty niobium**. To verify such an enhancement in a presence of a DC magnetic field at 4.2 K a simple experimental facility was designed, built and tested in ASTeC. The details of experimental setup and results of the measurements will be shown at the conference.
*A. Gurevich, APL 88, 012511 (2006)
**A. Gurevich, AIP Advances, 5, 017112 (2015)

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TUPB060

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

cavity, 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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TUPB065

Cryogenic RF Characterization of Superconducting Materials at SLAC With Hemispherical Cavities

cavity, niobium, 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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TUPB067

Design and First Measurements of an Alternative Calorimetry Chamber for the HZB Quadrupole Resonator

niobium, quadrupole, simulation, operation

739

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

Funding: The work is part of EuCARD-2, partly funded by the European Commission, GA 312453.
The systematic research on superconducting thin films requires dedicated testing equipment. The Quadrupole Resonator (QPR) is a specialized tool to characterize the superconducting properties of circular samples. A calorimetric measurement of the RF surface losses allows the surface resistance to be measured with sub nano-ohm resolution. This measurement can be performed over a wide temperature and magnetic field range, at frequencies of 433, 866 and 1300 MHz. The system at Helmholtz-Zentrum Berlin (HZB) is based on a resonator built at CERN and has been optimized to lower peak electric fields and an improved resolution. An alternative calorimetry chamber has been designed in order to provide flat samples for coating and to ease changing of samples. Furthermore it enables exchangeability of samples between the QPRs at HZB and CERN. With this poster the design and first measurements of the new calorimetry chamber is presented.

Poster TUPB067 [1.776 MB]

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TUPB078

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

cavity, HOM, 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

cavity, detector, simulation, 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

cavity, diagnostics, monitoring, 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

cavity, 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

cavity, niobium, background, radio-frequency

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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TUPB085

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

cavity, background, electron, niobium

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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TUPB088

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

niobium, cavity, 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

cavity, coupling, impedance, network

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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TUPB095

Resonance Control for Narrow-Bandwidth, Superconducting RF Applications

cavity, resonance, feedback, 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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TUPB097

The Study on Microphonics of Low Beta HWR Cavity at IMP

cavity, LLRF, cryomodule, 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

cavity, coupling, 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

cavity, shielding, 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, cavity, solenoid, 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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TUPB107

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

cavity, solenoid, cryomodule, alignment

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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TUPB120

The Cryogenic Infrastructure for SRF Testing at TRIUMF

cryogenics, cryomodule, ISAC, TRIUMF

919

R.R. Nagimov, P.R. Harmer, D. Kishi, A. Koveshnikov, R.E. Laxdal, H. Liu, N. Muller
TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada

Funding: Canada Foundation for Innovation, British Columbia Knowledge Development Fund, and National Research Council Canada.
At the moment TRIUMF operates one superconductive radio-frequency (SRF) accelerator and is building the second one. The superconducting heavy ion linear accelerator of the Isotope Separation and Acceleration (ISAC) facility utilizes medium beta quarter wave cavities cooled down to 4 K. The Advanced Rare IsotopE Laboratory (ARIEL) is a major expansion of the ISAC facility. ARIEL SRF electron linear accelerator (e-linac) operates nine-cell TESLA type cavities at 2 K. Both accelerators have dedicated cryogenic systems including liquid helium plants and distribution systems. In addition to accelerator cryogenic support, ISAC cryoplant provides liquid helium for the SRF testing facility at both 4 K and 2 K temperatures. TRIUMF’s SRF development involves both SRF testing facility and accelerators cryogenic support systems. This paper presents the details of the SRF testing cryogenic systems as well as recent commissioning results of the new e-linac cryogenic system.

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WEA1A02

Surface Resistance Study on Low Frequency (Low Beta) Cavities

cavity, niobium, superconductivity, accelerating-gradient

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, cavity, electron, quadrupole

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, cavity, electron, cryogenics

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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WEBA07

Beam Commissioning of the 56 MHz QW Cavity in RHIC

cavity, HOM, operation, damping

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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THAA02

SRF Gun Development Overview

gun, cathode, cavity, 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, cavity, 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

cavity, electron, 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, cavity, 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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THBA02

Recent Development in Vertical Electropolishing

cavity, cathode, experiment, ion

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, cavity, damping, 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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THPB003

Calculations for RF Cavities with Dissipative Material

HOM, cavity, 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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THPB025

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

cavity, alignment, linac, cryomodule

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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THPB029

MHI's Production Activities of Superconducting Cavity

cavity, superconducting-RF, electron, gun

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

cavity, niobium, 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

cavity, operation, controls, 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

cavity, data-management, 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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THPB041

Hydroforming SRF Cavities from Seamless Niobium Tubes

cavity, niobium, 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, cavity, 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

cavity, niobium, 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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THPB048

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

cavity, cathode, impedance, HOM

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

cavity, 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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THPB055

RF Performance Results of the 2nd ELBE SRF Gun

gun, cavity, 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

cavity, 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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THPB057

ELBE SRF Gun II - Emittance Compensation Schemes

cathode, emittance, gun, focusing

1235

H. Vennekate, A. Arnold, D. Janssen, P.N. Lu, P. Murcek, J. Teichert, R. Xiang
HZDR, Dresden, Germany
P. Kneisel
JLab, Newport News, Virginia, USA

In May 2014 the first SRF photo injector at HZDR has been replaced by a new gun, featuring a new resonator and cryostat. The intention for this upgrade has been to reach for higher beam energies, bunch charges and therefore an increased average beam current, which is to be injected into the superconducting, CW ELBE accelerator, where it can be used for multiple purposes, such as THz generation or Compton backscattering. Because of the increased bunch charge of this injector compared to its predecessor, it demands upgrades of the existing and/or novel approaches to alleviate the transverse emittance growth. One of these methods is the integration of a superconducting solenoid into the cryostat. Another method, the so called RF focusing, is realized by displacing the photo cathode's tip and retracting it from the last cell of the resonator. In this case, part of the accelerating field is sacrificed for a better focus of the electron bunch right at the start of its generation. Besides particle tracking simulations, a recent study, investigating on the exact position of the cathode tip with respect to the cell's back plane after tuning and cool down, has been performed.

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THPB058

Commissioning of the 112 MHz SRF Gun

gun, cathode, electron, laser

1240

S.A. Belomestnykh, I. Ben-Zvi, J.C. Brutus, T. Hayes, V. Litvinenko, K. Mernick, G. Narayan, P. Orfin, I. Pinayev, T. Rao, F. Severino, J. Skaritka, K.S. Smith, R. Than, J.E. Tuozzolo, E. Wang, Q. Wu, B. P. Xiao, A. Zaltsman
BNL, Upton, Long Island, New York, USA
S.A. Belomestnykh, I. Ben-Zvi, V. Litvinenko, T. Xin
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.
A 112 MHz superconducting RF photoemission gun was designed, fabricated and installed in RHIC for the Coherent electron Cooling Proof-of-Principle (CeC PoP) experiment at BNL. The gun was commissioned first without beam. This was followed by generating the first photoemission beam from a multi-alkali cathode. The paper presents the commissioning results.

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THPB059

Design, Fabrication and Performance of SRF-Gun Cavity

cavity, gun, 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

cavity, cryomodule, vacuum, operation

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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THPB062

Accelerated Life Testing of LCLS-II Cavity Tuner Motor

cavity, cryomodule, acceleration, operation

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, cavity, feedback

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, operation, cavity

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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THPB069

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

HOM, niobium, cavity, luminosity

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

cavity, niobium, cryomodule, 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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THPB079

Improved Capacitive Coupling Type RF Power Couplers for a Cryomodule With Two 9-Cell Cavities

coupling, impedance, cryomodule, simulation

1313

D.H. Zhuang, P.L. Fan, L.W. Feng, L. Lin, K.X. Liu, S.W. Quan, F. Wang, Z.L. Wang
PKU, Beijing, People's Republic of China

Funding: Work supported by Major State Basic Research Development Program of China(Grant No. 2011CB808302 and 2011CB808304)
A capacitive coupling RF power coupler was used for the DC-SRF photoinjector at Peking University. Recently, improved capacitive coupling power couplers, which will be used for a new cryomodule with two 9-cell cavities have been designed and fabricated. The main modifications include enlarging the supporting rods of inner conductors in order to increase heat conduction, moving the bellows from the quarter-wave transformer to the 50 Ω coaxial line to avoid the mismatch during Qext adjusting. Two modified power coupler have already finished RF conditioning up to 10kW, TW, duty factor 30%. In this paper, detailed design based on multi-physics analysis and the conditioning of this improved capacitive coupling RF Power coupler will be presented.

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THPB083

Energetic Copper Coating on Stainless Steel Power Couplers for SRF Application

cathode, plasma, laser, ion

1330

I. Irfan, S.F. Chapman, M. Krishnan, K.M. Velas
AASC, San Leandro, California, USA
W. Kaabi
LAL, Orsay, France

Funding: This research is supported by the US DOE via and SBIR grant: DE-SC0009581
Delivering RF power from the outside (at room temperature) to the inside of SRF cavities (at ~4 K temperature), requires a power coupler to be thermally isolating, while still electrically conducting on the inside. Stainless steel parts that are coated on the insides with a few skin depths of copper can meet these conflicting requirements. The challenge has been the adhesion strength of copper coating on stainless steel coupler parts when using electroplating methods. These methods also require a nickel flash layer that is magnetic and can therefore pose problems. Alameda Applied Sciences Corporation (AASC) uses Coaxial Energetic Deposition (CED) from a cathodic arc plasma to grow copper films directly on stainless steel coupler parts with no Ni layer and no electrochemistry. The vacuum arc plasma consists of ~100 eV Cu ions that penetrate a few monolayers into the stainless steel substrate to promote growth of highly adhesive films with crystalline structure. Adhesion strength and coating quality of copper coatings on complex stainless steel tubes, bellows, mock coupler parts and an actual Tesla Test Facility (TTF) type coupler part, are discussed.
* Adhesion and Cu quality testing were done for us by the Fermilab Technical Division, Superconducting RF Development Department

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THPB095

Automatic RF Conditioning Test Bench of Fundamental Power Couplers for the European XFEL Accelerator

vacuum, controls, interface, data-acquisition

1367

S. Sierra, C. Lievin, P. Rouillon
TED, Velizy, France
H. Guler, W. Kaabi, A. Verguet
LAL, Orsay, France

In order to perform the RF conditioning of the fundamental coupler for the XFEL accelerator, Thales and LAL developed together a test bench being able to make the automatic RF conditioning. The capability of this test bench is of 4 pairs of coupler at the same time with automatic sequences of increasing the RF power. The test bench is composed of the overall RF station providing up to 5 MW peak power at 1.3 GHz. The waveguide distribution allows 4 individual RF lines for conditionning,and the automatic sequence applied to the couplers in respect with all signals monitored and controlled during the RF process. The paper will also provide some examples of such process.

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THPB096

Lesson Learned on the Manufacturing of Fundamental Power Couplers for the European XFEL Accelerator

controls, status, FEL, cryomodule

1370

S. Sierra, G. Garcin, C. Lievin, G. Vignette
TED, Velizy, France
M. Knaak, M. Pekeler
RI Research Instruments GmbH, Bergisch Gladbach, Germany

In this paper we described lesson learned during the production of Fundamental Power Couplerfor the European XFEL accelerator and different steps necessaries for obtaining a rate of 8 couplers a week. From the manufacturing of individual components up to the RF conditioning. This paper also propose some possible ways to be optimized for a future mass production of such components. With comparison of processes and adaptation which could benefit to an increase rate or a more secure program. Some of them which could be studies from the coupler definition to the manufacturing process in order to obtain a stable and possible increased rate or lower cost of production by decreasing the risks on programs. This analysis is based on a current production of more than 500 couplers

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THPB100

Nb Coatings on Bellows Used in SRF Accelerators

cavity, 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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THPB105

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

cavity, coupling, niobium, 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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FRAA05

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

cavity, 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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FRBA03

SRF, Compact Accelerators for Industry & Society

cavity, 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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