SRF2015 - List of Keywords (niobium)

Paper	Title	Other Keywords	Page
MOBA03	Sensitivity of Niobium Superconducting RF Cavities to Magnetic Field	cavity, vacuum, impedance, SRF	34
	D. Gonnella, J.J. Kaufman, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	One important characteristic of nitrogen-doped cavities is their very high sensitivity to increased residual surface resistance from trapped ambient magnetic flux. We have performed a systematic study on the losses by trapped flux, and their dependence on the mean-free-path (MFP) of the niobium RF penetration layer. Cavities with a wide range of MFP values were tested in uniform ambient magnetic fields to measure trapped magnetic flux and resulting increase in RF surface resistance. MFP values were determined from surface impedance measurements. It was found that larger mean free paths lead to lower sensitivity to trapped magnetic flux.
	Slides MOBA03 [1.817 MB]
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOBA04	High-Q Operation of SRF Cavities: The Impact of Thermocurrents on the RF Surface Resistance	cavity, simulation, shielding, operation	37
	J.M. Köszegi, J. Knobloch, O. Kugeler HZB, Berlin, Germany
	For CW applications much effort is being expended to minimize the power dissipation (surface resistance) of niobium cavities. Previous studies have shown that residual resistance can be reduced by performing a thermal cycle, a procedure of warming up a cavity after initial cooldown to about 20K and cooling it down again. It was postulated that thermocurrents during cooldown generate additional trapped magnetic flux that impacts the cavity quality factor. Here, we present a more extensive study that includes measurements of two additional passband modes and that confirms the effect. A change in surface resistance of more than a factor seven was observed. In this paper, we also discuss simulations that support the claim. While the layout of the cavity LHe tank system is cylindrically symmetric, we show that the temperature dependence of the material parameters results in a non-symmetric current distribution.
	Slides MOBA04 [2.830 MB]
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOBA06	N Doping: Progress in Development and Understanding	cavity, superconductivity, factory, injection	48
	A. Grassellino Fermilab, Batavia, Illinois, USA
	Significant progress was made recently with N2 doped cavities. This talk will summarize all developments with N-doped Nb cavity work at FNAL in the past two years.
	Slides MOBA06 [7.704 MB]
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOBA08	Niobium Impurity-Doping Studies at Cornell and CM Cool-Down Dynamic Effect on Q0	cavity, cryomodule, SRF, 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]
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB002	Observation of High Field Q-Slope in 3 GHz Nb Cavities	cavity, SRF, radiation, feedback	66
	G.V. Eremeev, F.E. Hannon JLab, Newport News, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. A degradation of the unloaded quality factor is commonly observed above about 100 mT in elliptical niobium cavities. The cause of this degradation has not been fully understood yet, but the empirically found solution of heating to about 100-120 C for 24-48 hrs. eliminates the degradation in electropolished fine grain or large grain niobium cavities. While numerous experiments related to this phenomenon have been done at 1.3 GHz and 1.5 GHz, little data exists at other frequencies, and the frequency dependence of this degradation is not clear. We have measured the unloaded quality factor of 3 GHz fine grain niobium cavities, which were chemically polished as the final treatment before RF tests in a vertical Dewar and observed the characteristic degradation in two cavities. The measurement of the quality factor degradation at different bath temperatures points to a field-dependent rather than a temperature-related effect.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB005	Developing a Setup to Measure Field Dependence of BCS Surface Resistance	cavity, solenoid, radio-frequency, software	77
	J.T. Maniscalco, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: NSF/DOE The temperature-dependent part of the microwave surface resistance of superconducting radio-frequency (SRF) cavities has been shown experimentally to depend on the strength of the applied magnetic surface field. Several theories have recently been proposed to describe this phenomenon. In this paper we present work on the development of a microwave cavity setup for measuring the field-dependence with an applied DC magnetic field.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB006	Hc2 Measurements of Superconductors	SRF, 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.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB010	Field-Dependent Surface Resistance for Superconducting Niobium Accelerating Cavities: The Case of N-Doping	cavity, data-analysis, electron, superconductivity	95
	W. Weingarten Private Address, SERGY, France R.G. Eichhorn Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	The dependence of the Q-value on the RF field (Q-slope) for superconducting RF cavities is actively studied in various accelerator laboratories. Although remedies against this dependence have been found, the physical cause still remains obscure. A rather straightforward two-fluid model description of the Q-slope in the low and high field domains is extended to the case of the recently experimentally identified increase of the Q-value with the RF field obtained by so-called "N-doping”. This paper was initiated when one of the authors (W.W., retiree from CERN) visited Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, NY.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB011	How Uniform Are Cool-Downs?	cavity, interface, simulation, factory	100
	J.A. Robbins, R.G. Eichhorn Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Since the last SRF conference it has become clear that achieving extremely high quality factors of SRF cavities depend on the cool-down scenario. While some findings favor a fast cool-down, others suggest a slow cycle to be advantageous, and many variations to that have been investigated: the role of thermocurrents, amount of ambient magnetic field and flux trapping. This paper will investigate, how uniformly different cool-down procedures are and if they can explain the more efficient magnetic flux expulsion.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB015	Trapped Flux Surface Resistance Analysis for Different Surface Treatments	cavity, resonance, superconductivity, instrumentation	115
	M. Martinello, M. Checchin, A. Grassellino, O.S. Melnychuk, S. Posen, A. Romanenko, D.A. Sergatskov Fermilab, Batavia, Illinois, USA M. Checchin Illinois Institute of Technology, Chicago, Illlinois, USA J. Zasadzinski IIT, Chicago, Illinois, USA
	Funding: Work supported by the US Department of Energy, Office of High Energy Physics The trapped flux surface resistance is one of the main contributions on cavity losses which appears when cavities are cooled in presence of external magnetic field. The study is focused on the understanding of the different parameters which determine the trapped flux surface resistance, and how this change as a function of different surface treatments. The study is performed on 1.3 GHz niobium cavities processed with different surface treatments after the 800 C bake: electro-polishing (EP), 120 C baking, and N-doping varying the time of the Nitrogen exposure. The trapped flux surface resistance normalized for the trapped magnetic flux is then analyzed as a function of the mean free path in order to find the surface treatment which minimized the trapped flux sensitivity.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB018	Introduction of Precisely Controlled Microstructural Defects into SRF Cavity Niobium Sheets and Their Impact on Local Superconducting Properties	cavity, SRF, electron, superconductivity	120
	M. Wang, T.R. Bieler, D. Kang Michigan State University, East Lansing, Michigan, USA C. Compton FRIB, East Lansing, Michigan, USA D.C. Larbalestier, A. Polyanskii, Z-H. Sung ASC, Tallahassee, Florida, USA P.J. Lee NHMFL, Tallahassee, Florida, USA
	Funding: Research supported by DOE/OHEP (contract number DE-FG02-09ER41638 at MSU and DE-SC0009960 at FSU) and the State of Florida. When SRF cavity shapes are formed from Nb sheets, the metallurgical processing introduces microstructural defects such as dislocations and low-angle grain boundaries that can serve as pinning centers for magnetic flux that may degrade cavity performance. Therefore, the relationship between magnetic flux behavior and microstructural defects in carefully strained SRF Nb sheet was investigated. Laue X-ray and EBSD-OIM crystallographic analyses of large grain ingot slices were used to characterize microstructural defects and then predict which grains and sample orientations will produce desired model defects due to tensile deformation. Grain orientations were chosen to favor specific slip systems, which generate dislocations with special angles with respect to the sample surface. Nb bicrystals were also prepared to investigate the effects of grain boundaries on flux pinning. The generated defect structures were confirmed by OIM and TEM. Cryogenic magneto-optical imaging was used to directly observe the penetration of magnetic flux into the deformed Nb. These model samples have deformation that is similar to that expected in typical cavity forming processes.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB020	Mean Free Path Dependence of the Trapped Flux Surface Resistance	electron, SRF, 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.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB024	SRF Cavity Breakdown Calculation Procedure Using FEA-Software	cavity, simulation, cathode, SRF	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.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB027	Modifications of Superconducting Properties of Niobium Caused by Nitrogen Doping of Ultra-High Quality Factor Cavities	SRF, 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.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB030	Measurements of Thermal Impedance on Superconducting Radiofrequency Cavities	cavity, impedance, SRF, 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.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB036	TOF-SIMS Study of Nitrogen Doping Niobium Samples	experiment, cavity, vacuum, ion	169
	Z.Q. Yang, L. Lin, X.Y. Lu, W.W. Tan, D.Y. Yang, J. Zhao PKU, Beijing, People's Republic of China
	Nitrogen doping treatment with the subsequent electropolishing (EP) of the niobium superconducting cavity can significantly increase the cavity’s quality factor up to a factor of 3. The nitrogen doping experiment has been successfully repeated and demonstrated. But the mechanism of the nitrogen doping effect remains unclear. Nitrogen doping study on niobium samples was carried out in Peking University. The niobium samples were manual processed to avoid heat generation. The experiment condition is close to that of the Fermilab. After the nitrogen doping treatment, the samples were mildly electropolished with the thickness of 1.3μm, 1.9μm, 3.3μm, 4.2μm, 5.1μm, 5.9μm and 7.0μm. The time of flight secondary ion mass spectrometry (TOF-SIMS) measurements show that the samples directly after nitrogen doping have a much higher nitrogen concentration in the depth of about 90nm. When the EP removal is larger than 1.3μm, the samples’ impurity elements is remarkably reduced and their distribution is similar to each other. Also the measured results to some extent prove that EP removal can introduce H to the niobium surface.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB039	Analysis of BCS RF Loss Dependence on N-Doping Protocols	cavity, SRF, linac, operation	174
	A.D. Palczewski, P. Dhakal, C.E. Reece JLab, Newport News, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177 with supplemental funding from the LCLS-II Project U.S. DOE Contract No. DE-AC02-76SF00515. We present a study on two parallel-path SRF cavities (one large grain and one fine grain, 1.3 GHz) which seeks to explain the correlation between the amount of nitrogen on the inner surface of a “nitrogen doped” SRF cavity and the change in the temperature dependant (packaged into term BCS) RF losses. For each doping/EP, the cavities were tested at multiple temperatures (2.0 K to 1.5 K in 0.1 K steps) to create a Q0 vs. Eacc vs. T matrix which then could be used to extract temperature dependant and independent components. After each test, the cavities were thermally cycled to 120 K and then re-cooled and retested to assess if evidence of hydrogen migration might appear even at a small level. In addition, TD-5 was also tested at fixed low field (Q0 vs. T) to fit standard BCS theory. In parallel, SIMS data was taken on like-treated samples to correlate the amount of nitrogen within the RF surface to the change in the temperature dependant fitting parameter “A”.** [] H.Tian et al., contributed to SRF2015.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB042	Fundamental Studies on Doped SRF Cavities	cavity, vacuum, simulation, SRF	187
	D. Gonnella, T. Gruber, J.J. Kaufman, P.N. Koufalis, M. Liepe, J.T. Maniscalco, B. Yu Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: NSF Recently, doping with nitrogen has been demonstrated to help SRF cavities reach significantly higher intrinsic quality factors than with standard procedures. However, the quench fields of these cavities have also been shown to be frequently reduced. Here we report on fundamental studies of doped cavities, investigating the source of reduced quench field and exploring alternative dopants. We have focused on studying the quench of nitrogen-doped cavities with temperature mapping and measurements of the flux penetration field using pulsed power to investigate maximum fields in nitrogen doped cavities. We also report on studies of cavities doped with other gases such as helium. These studies have enabled us to shed light on the mechanisms behind the higher Q and lower quench fields that have been observed in cavities doped with impurities.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB045	Study of Slip and Deformation in High Purity Single Crystal Nb for Accelerator Cavities	experiment, SRF, 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.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB047	Secondary Electron Yield of Electron Beam Welded Areas of SRF Cavities	electron, cavity, gun, vacuum	196
	M. Basovic, S. Popović, M. Tomovic, L. Vušković ODU, Norfolk, Virginia, USA F. Čučkov, A. Samolov University of Massachusetts Boston, Boston, Massachusetts, USA
	Secondary Electron Emission (SEE) is a phenomenon that contributes to the total electron activity inside the Superconducting Radiofrequency (SRF) cavities during the accelerator operation. SEE is highly dependent on the state of the surface. During electron beam welding process, significant amount of heat is introduced into the material causing the microstructure change of Niobium (Nb). Currently, all simulation codes for field emission and multipacting are treating the inside of the cavity as a uniform, homogeneous surface. Due to its complex shape and fabricating procedure, and the sensitivity of the SEE on the surface state, it would be interesting to see if the Secondary Electron Yield (SEY) parameters vary in the surface area on and near the equator weld. For that purpose, we have developed experimental setup that can measure accurately the energy distribution of the SEY of coupon-like like samples. To test the influence of the weld area on the SEY of Nb, dedicated samples are made from a welded plate using electron beam welding parameters common for cavity fabrication. SEY data matrix of those samples will be presented.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB049	High Flux Three Dimensional Heat Transport in Superfluid Helium and Its Application to a Trilateration Algorithm for Quench Localization With OSTs	cavity, detector, experiment, software	201
	T. Junginger TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada P. Horn TU Dresden, Dresden, Germany T. Koettig, K.C. Liao, A. Macpherson CERN, Geneva, Switzerland B.J. Peters KIT, Karlsruhe, Germany
	Oscillating superleak transducers of second sound can be used to localize quench spots on superconducting cavities by trilateration. However propagation speeds faster than the velocity of second sound are usually observed imped- ing the localization. Dedicated experiments show that the fast propagation cannot be correlated to the dependence of the velocity on the heat flux density, but rather to boiling effects in the vicinity of the hot spot. 17 OSTs were used to detect quenches on a 704MHz one-cell elliptical cavity. Two different algorithms for quench localization have been tested and implemented in a computer program enabling direct crosschecks. The new algorithm gives more consis- tent results for different OST signals analyzed for the same quench spot.
	Poster MOPB049 [0.901 MB]
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB051	Muon Spin Rotation on Treated Nb Samples in Parallel Field Geometry	cavity, SRF, polarization, detector	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]
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB052	Determination of Bulk and Surface Superconducting Properties of N2-Doped Cold Worked, Heat Treated and Electro-polished SRF Grade Niobium	cavity, SRF, superconductivity, 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.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB054	An Investigation of Correlations Between Mechanical and Microstructural Properties of High Purity Polycrystalline Niobium	SRF, 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.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB055	Characterization of Nitrogen Doping Recipes for the Nb SRF Cavities	cavity, SRF, cryogenics, electron	223
	Y. Trenikhina, A. Grassellino, O.S. Melnychuk, A. Romanenko Fermilab, Batavia, Illinois, USA
	For the future development of the nitrogen doping technology, it’s vital to understand the mechanisms behind the performance benefits of N-doped cavities as well as the performance limitations, such as quench field. Following various doping recipes, cavity cutouts and flat niobium samples have been evaluated with XRD, SEM, SIMS and TEM in order to relate structural and compositional changes in the niobium near-surface to SRF performance. Annealing of Nb cavities with nitrogen for various durations and at various temperatures lead to a layer containing inclusions of non-superconducting Nb nitride phases, followed by unreacted Nb with an elevated N-interstitials concentration. We found that EP of the N-treated cavities removes the unwanted niobium nitride phases, confirming that performance benefits are originating from the elevated concentration of N interstitials. The role of low temperature Nb hydride precipitants in the performance limitation of N-doped cavities was evaluated by TEM temperature dependent studies. Finally, extended characterization of the original cavity cutouts from the N-doped RF tested cavity sheds some light on quenching mechanisms.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB057	Crystal Plasticity Modeling of Single Crystal Nb	experiment, cavity, SRF, software	228
	A. Mapar, F. Pourboghrat MSU, East Lansing, Michigan, USA T.R. Bieler, D. Kang Michigan State University, East Lansing, Michigan, USA C. Compton FRIB, East Lansing, Michigan, USA
	Funding: This work was supported by the U.S. Department of Energy, Office of High Energy Physics, through Grant No. DE-FG02-09ER41638. Deformation behavior of niobium (Nb) is not thoroughly studied, although it is widely used in manufacturing superconducting cavities. This deficiency of knowledge limits the predictibality in raw material properties for fine grain sheets, which are less anisotropic and easier to deform uniformly than large grain sheets. Studies on modeling and simulation of deformation of Nb are also limited. Therefore design of a new manufacturing procedure becomes a costly process, because models predicting the deformation of Nb are not accurate. A polycrystal is an aggregate of single crystals. Tensile tests were performed on single crystal with different orientations, to study the deformation behavior of Nb. A number of crystal plasticity models were developed, calibrated and finally used to predict the deformation of single crystal tensile samples. This study compares the predictions of these models. This provides a foundation for physically realistic polycrystal deformation models.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB072	Characterization of Surface Defects on EXFEL Series and ILC-Higrade Cavities	cavity, SRF, laser, radiation	281
	A. Navitski, E. Elsen, V. Myronenko, J. Schaffran, O. Turkot DESY, Hamburg, Germany Y. Tamashevich University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
	Funding: BMBF project 05H12GU9, Alexander von Humboldt Foundation, CRISP (No. 283745) and ”Construction of New Infrastructures-Preparatory Phase” ILC-HiGrade (No. 206711) of the EU 7th FP7/2007-2013 Programme. Inspection of the inner cavity surface by an optical system is an inexpensive and useful means for surface control and identification of critical or suspicious features. Optical inspection of around 100 EXFEL series and ILC-HiGrade cavities has been performed recently using the high-resolution OBACHT system. It is a semi-automated tool based on the Kyoto camera. To gain information about the 3D topography of surface features or defects, a replica technique has been applied additionally. This is a non-destructive surface-study method reaching resolution down to 1 μm by imprinting the details of the surface onto a hardened rubber. The footprint is subsequently investigated with a microscope or profilometer. Based on these studies, several defects on the surface have been found and classified. Most of the cavity failures leading e.g. to field limitations below 20 MV/m have been identified and corresponding feedback given to the production cycle. Typical surface features and defects as well as their influence on the cavity performance will be presented and discussed.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB073	Surface Analyses and Optimization of Centrifugal Barrel Polishing of Nb Cavities	cavity, SRF, laser, embedded	286
	A. Navitski, E. Elsen, B. Foster DESY, Hamburg, Germany B. Foster, A.L. Prudnikava, Y. Tamashevich University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
	Funding: BMBF project 05H12GU9, Alexander von Humboldt Foundation, and CRISP (No. 283745). Centrifugal barrel polishing (CBP) is an acid-free surface-polishing technique based on abrasive media. It considerably reduces the usage of chemicals in the preparation of Nb cavities, typically leaving only a final light electropolishing (EP) and achieves considerably smaller roughness than in chemical treatments alone. CBP addresses in particular the removal of pits, welding spatters, deep scratches, and foreign material inclusions that occasionally occur in the production process. A mirror-smooth surface without chemical contamination is also an important enabling step for thin films. Recent results indicate, however, the need of further optimizations, mainly to reduce the surface damaged layer as well as the pollution by the polishing media. A dedicated study of the CBP process using a “coupon” cavity facilitates better polishing characterisation and optimisation by direct measurements of the roughness, removal rate, and removal profile as well as the amount of contamination left behind and determination of a best combination of the CBP and chemical polishing. Results of the coupon-studies and perspectives of the optimizations will be presented and discussed.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB074	CERN’s Bulk Niobium High Gradient SRF Programme: Developments and Recent Cold Test Results	cavity, cathode, radiation, SRF	291
	A. Macpherson, K.G. Hernández-Chahín, C. Jarrige, P. Maesen, F. Pillon, K.M. Schirm, R. Torres-Sanchez, N. Valverde Alonso CERN, Geneva, Switzerland K.G. Hernández-Chahín DCI-UG, León, Mexico
	Recent results from the bulk niobium high-gradient cavity development program at CERN are presented, with particular focus on test results for the 704 MHz bulk niobium 5-cell elliptical cavity prototypes produced for the Superconducting Proton Linac (SPL) project. Successive cold tests of bare cavities have been used to refine the cavity preparation and testing process, with all steps done in-house at CERN. Current performance results are discussed with reference to observables such as ambient magnetic field, field emission levels, and quenches.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB086	Update and Status of Vertical Test Results of the European XFEL Series Cavities	cavity, status, linac, cryomodule	337
	N. Walker, D. Reschke, J. Schaffran, L. Steder DESY, Hamburg, Germany L. Monaco INFN/LASA, Segrate (MI), Italy M. Wiencek IFJ-PAN, Kraków, Poland
	The series production by two industrial vendors of the 800 1.3-GHz superconducting cavities for the European XFEL has been on-going since the beginning of 2013 and will conclude towards the end of this year. As of publication some 740 cavities (~93%) have been produced at an average rate of 6 cavities per week. As part of the acceptance testing, all cavities have undergone at least one vertical RF test at 2K at the AMTF facility at DESY. The acceptance criterion for module assembly is based on the concept of a “usable gradient”, which is defined as the maximum field taking into account Q0 performance and allowed thresholds for field emission, as well as breakdown limits. Approximate 20% of the cavities have undergone further surface treatment in the DESY infrastructure to improve their usable gradient performance. In this paper we present the performance statistics of the vertical test results, as well as an analysis of the limiting criteria for the usable gradient, and finally the impact of the surface retreatment on both usable gradient and Q0.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB092	Economics of Electropolishing Niobium SRF Cavities in Eco-Friendly Aqueous Electrolytes Without Hydrofluoric Acid	cavity, SRF, 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.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB093	Vertical Electropolishing Studies at Cornell	cavity, cathode, SRF, 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]
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB096	Vertical Electro-Polishing at TRIUMF	cathode, cavity, TRIUMF, operation	378
	J.J. Keir, P.R. Harmer, D. Lang, R.E. Laxdal, T. Shishido, R. Smith TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada T. Shishido KEK, Ibaraki, Japan
	A setup for electropolishing of a superconducting niobium single-cell cavity has been installed at TRIUMF. A vertical method was selected to make the setup compact. To increase removal speed at the equator and remove hydrogen bubbles at the iris surface, 4 cathode paddles were rotated in the cavity cell during electropolishing. We will report on our first electropolishing result.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB100	Cathode Geometry and Flow Dynamics Impact on Vertical Electropolishing of Superconducting Niobium Cavities	cavity, cathode, simulation, operation	385
	L.M.A. Ferreira CERN, Geneva, Switzerland
	CERN has now a fully operating vertical electropolishing installation, which has been used for the processing of 704 MHz high-beta five-cell Superconducting Proton Linac (SPL) niobium cavities. This installation relies only on the electrolyte circulation (HF/H2SO4) for power dissipation, evacuation of gases and homogeneous finishing; thus, parameters like cathode geometry, electrolyte flow and temperature become even more crucial when compared with horizontal electropolishing installations. Based on computational simulations performed with Comsol Multiphysics® and on a methodology developed at CERN, it is possible to assess the impact of the different cathode geometries as well as of the flow on the etching rate distribution. The data obtained with two different cathode geometries are presented: electrolyte velocity distribution, etching rate distribution, average current density and minimum working potential. One geometry was defined through a purely electrochemical approach while the second was defined to minimise the difference between the maximum and the minimum electrolyte speed inside the cavity; in both cases, the influence of the electrolyte flow was taken into account.
	Poster MOPB100 [1.794 MB]
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB101	Electropolishing of Niobium SRF Cavities in Eco-Friendly Aqueous Electrolytes Without Hydrofluoric Acid	cavity, SRF, cathode, target	390
	M.E. Inman, T.D. Hall, S. Lucatero, S.T. Snyder, E.J. Taylor Faraday Technology, Inc., Clayton, Ohio, USA F. Furuta, G.H. Hoffstaetter Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA J.D. Mammosser ORNL, Oak Ridge, Tennessee, USA A.M. Rowe Fermilab, Batavia, Illinois, USA
	Electropolishing of niobium cavities is conventionally conducted in high viscosity electrolytes consisting of concentrated sulfuric and hydrofluoric acids. This use of dangerous and ecologically damaging chemicals requires careful attention to safety protocols to avoid harmful worker exposure and environmental damage. We present an approach for electropolishing of niobium materials based on pulse reverse waveforms, enabling the use of low viscosity aqueous dilute sulfuric acid electrolytes without hydrofluoric acid, or aqueous near-neutral pH salt solutions without any acid. Results will be summarized for both cavity and coupon electropolishing for bulk and final polishing steps. With minimal optimization of pulse reverse waveform parameters we have demonstrated the ability to electropolish single-cell niobium SRF cavities and achieve at least equivalent performance compared to conventionally processed cavities. Cavities are electropolished in a vertical orientation filled with electrolyte and without rotation, offering numerous advantages from an industrial processing perspective. Shielding, external cooling and high surface area cathodes are adaptable to the bipolar EP process. Work supported by DOE Grant Nos. DE-SC0011235 and DE-SC0011342 and DOE Purchase Order No. 594128.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB102	Comments on Electropolishing at Ettore Zanon SpA at the End of EXFEL Production	cavity, controls, cathode, acceleration	394
	M. Rizzi, G. Corniani Ettore Zanon S.p.A., Schio, Italy A. Matheisen DESY, Hamburg, Germany P. Michelato INFN/LASA, Segrate (MI), Italy
	In 2013 a new horizontal Electropolishing facility was developed and implemented by Ettore Zanon SpA (EZ) for the treatment of cavities for the European XFEL series production. More than 300 cavities have been treated. Electropolishing has been used for two applications: bulk removal and recovering of cavities with surface defects. Treatment settings have been analysed and compared with cavities performances to verify possible influences of the various parameters. Main parameters considered are treatment time, voltage and current, that together define average thickness removal. We present here the results of these investigation. The facility and process in use are also presented, together with possible next upgrade of the system, facing the new production of cavities for the LCLSII project.
	Poster MOPB102 [1.535 MB]
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB104	Flux Expulsion Variation in SRF Cavities	cavity, factory, cryogenics, SRF	404
	S. Posen, M. Checchin, A.C. Crawford, A. Grassellino, M. Martinello, O.S. Melnychuk, A. Romanenko, D.A. Sergatskov Fermilab, Batavia, Illinois, USA
	Treating a cavity with nitrogen doping significantly increases Q₀ at medium fields, reducing cryogenic costs for high duty factor linear accelerators such as LCLS II. N-doping also makes cavities more sensitive to increased residual resistance due to trapped magnetic flux, making it critical to either have extremely effective magnetic shielding, or to prevent flux from being trapped in the cavity during cooldown. In this paper, we report on results of a study of flux expulsion. We discuss possible ways in which flux can be pinned in the inner surface, outer surface, or bulk of a cavity, and we present experimental results studying these mechanisms. We show that grain structure appears to play a key role and that a cavity that expelled flux poorly changed to expelling flux well after a high temperature furnace treatment. We further show that after furnace treatment, this cavity exhibited a significant improvement in quality factor when cooled in an external magnetic field. We conclude with implications for SRF accelerators with high Q₀ requirements.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB105	Symmetric Removal of Niobium Superconducting RF Cavity in Vertical Electropolishing	cavity, cathode, experiment, accumulation	409
	V. Chouhan, Y.I. Ida, K.N. Nii, T.Y. Yamaguchi MGH, Hyogo-ken, Japan H. Hayano, S. Kato, H. Monjushiro, T. Saeki, M. Sawabe KEK, Ibaraki, Japan K. Ishimi MGI, Chiba, Japan
	Vertical electropolishing (VEP) leads several advantages over horizontal EP in respect of easy operation and mechanism of an EP system resulting in lower cost. However, till yet VEP always resulted inhomogeneous removal of a niobium (Nb) cavity along its length and bubble traces especially on the top iris of a vertically set cavity. In this work we performed lab EP and VEP experiments in order to study and solve these two problems. A coupon cavity which contains 6 disk type Nb coupons positioned at beam pipes, irises and equator was vertically electropolished to optimize VEP parameters so as to get almost uniform removal of Nb and a smooth surface of the cavity without bubble traces. Our patented unique i-Ninja cathode having 4 wings was used with an optimized rotation speed to get homogeneous removal of Nb. The homogeneous removal and the surface without bubble traces might be result of a uniform thickness of a viscous layer on the surface of the cavity cell and no accumulation of hydrogen bubbles on the top iris surface. The surfaces of the coupons were studied in detail with surface analytical tools.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB106	Analysis of High Pressure Rinsing Characteristics for SRF Cavities	cavity, target, experiment, SRF	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.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB110	The Transfer of Improved Cavity Processing Protocols to Industry for LCLS-II: N-Doping and Electropolishing	cavity, cathode, controls, superconductivity	418
	C.E. Reece, F. Marhauser, A.D. Palczewski JLab, Newport News, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177 with supplemental funding from the LCLS-II Project U.S. DOE Contract No. DE-AC02-76SF00515. Based on the R&D efforts of colleagues at FNAL, Cornell, and JLab, the LCLS-II project adopted a modification to the rather standard niobium SRF cavity surface processing protocol that incorporates a high temperature diffusion doping with nitrogen gas. This change was motivated by the resulting higher Q0 and the prospect of significantly lower cryogenic heat load for LCLS-II. JLab is responsible for managing the cavity procurement for the LCLS-II project. The first phase of the procurement action is to transfer the nitrogen-doping protocol to the industrial vendors. We also seek to exploit improvements in understanding of the niobium electropolishing process as part of the production processing of the TESLA-style LCLS-II cavities. We report on the technology transfer activities and progress toward the envisaged performance demonstration of vendor-processed cavities.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUAA04	Rapid Growth of SRF in India	cavity, linac, SRF, electron	467
	D. Kanjilal IUAC, New Delhi, India
	Funding: Funding received from Ministry of Higher Education through University Grants Commission of India and from Department of Atomic Energy are gratefully acknowledged. The talk shall summarize the recent advances in the SRF program in various research centres in India. The SRF related activities at Inter-University Accelerator Centre (IUAC) at Delhi , Raja Ramanna Centre for Advanced Technology (RRCAT) at Indore, Bhabha Atomic Research Centre (BARC) and Tata Institute of Fundamental Research (TIFR) both at Mumbai, and Variable Energy Cyclotron Centre (VECC) at Kolkata shall be addressed. In particular indigenous niobium resonator fabrication and test facilities of IUAC operational for more than a decade which have been used extensively for development, fabrication and utilization of various types of resonators will be discussed. The results from the commissioning of the full three linac modules having eight niobium quarter wave resonators in each module of the heavy ion linac at IUAC for regular scheduled experiments will be presented. The technology and infrastructure developments at RRCAT, BARC, TIFR and VECC for fabrication, processing and tests of future cavities will be discussed.
	Slides TUAA04 [5.918 MB]
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUBA02	Thermal Contact Resistance at the Nb-Cu Interface	cavity, interface, feedback, superconductivity	488
	V. Palmieri INFN/LNL, Legnaro (PD), Italy R. Vaglio UniNa, Napoli, Italy
	Funding: Work performed thanks to the financement in Italy by the INFN 5th group for Accelerator and Applied Physics Niobium thin film sputtered copper cavities are strongly limited for the application in high field accelerators by the unsolved “Q-slope” problem. In the present paper, we examine the different contributions of the niobium film, the copper substrate, the Helium-Copper interface and the Niobium-Copper Interface, proposing the hypothesis that main cause of losses is due to an enhanced thermal boundary resistance RNb/Cu at the Nb/Cu interface, due to poor thermal contact between film and substrate. So, starting from different Q vs Eacc experimental curves from different sources, and using a typical “inverse problem” method, we deduced the corresponding distribution functions generating those curves. Assuming that only a small fraction of the film over the cavity surface is in poor thermal contact with the substrate (or even partially detached), due to bad adhesion problems, we propose as a possible solution of the problem, the possibility to use higher temperatures of deposition and the adoption at the interface of a buffer layer of a material that alloys both with Copper and with Niobium.
	Slides TUBA02 [18.852 MB]
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUBA03	On the Understanding of Q-Slope of Niobium Thin Films	ECR, ion, SRF, 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]
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUBA04	Nb3Sn Cavities: Material Characterization and Coating Process Optimization	cavity, simulation, SRF, 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]
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUBA05	Progress With Multi-Cell Nb3Sn Cavity Development Linked With Sample Materials Characterization	cavity, vacuum, SRF, factory	505
	G.V. Eremeev, M.J. Kelley, C.E. Reece JLab, Newport News, Virginia, USA M.J. Kelley, U. Pudasaini The College of William and Mary, Williamsburg, Virginia, USA J. Tuggle Virginia Polytechnic Institute and State University, Blacksburg, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. Exploiting both the new Nb3Sn coating system and the materials characterization tools nearby, we report our progress in low-loss Nb3Sn films development. Nb3Sn films a few micrometers thick were grown on Nb coupons as well as single- and multi-cell cavities by the Sn-diffusion technique. Films structure and composition were investigated on coated samples and cavity cutouts with characterization tools including SEM/EDS/EBSD, AFM, XPS, SIMS towards correlating film growth and RF loss to material properties and deposition parameters. Cavity coating efforts focused on establishing techniques for coating progressively more complicated RF structures, and understanding limiting mechanisms in coated cavities. Nb3Sn coated 1.5 GHz 1-cell and 1.3 GHz 2-cell cavities have shown quality factors of 10¹⁰ at 4.3 K, with several cavities reaching above Eacc = 10 MV/m. The dominant limiting mechanisms were low field quenches and quality factor degradation above 8 MV/m. The surface data indicates a near-stoichiometric Nb3Sn consistent with the transition temperature and gap measurements. The Nb3Sn layer is covered with Nb2O5 and SnO2 native oxides and has little memory of the pre-coating surface.
	Slides TUBA05 [2.418 MB]
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB001	Progress on Superconducting RF Cavity Development With UK Industry	cavity, SRF, superconducting-RF, accelerating-gradient	521
	A.E. Wheelhouse, R.K. Buckley, L.S. Cowie, P. Goudket, A.R. Goulden, P.A. McIntosh STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom J.R. Everard, N. Shakespeare Shakespeare Engineering, South Woodham Ferrers, Essex, United Kingdom
	As part of a STFC Industrial Programme Support (IPS) Scheme grant, Daresbury Laboratory and Shakespeare Engineering Ltd have been developing the capability to fabricate, process, and test a 9-cell, 1.3 GHz superconducting RF cavity. The objective of the programme of work is to achieve an accelerating gradient of greater than 20 MV/m at an unloaded quality factor of 1.0 x 10¹⁰ or better. Processes such as the high pressure rinsing and the buffer chemical polishing are being developed at Daresbury Laboratory and the manufacturing of the cavity half cells and beampipes are being optimised by Shakespeare Engineering to enable this target to be achieved. These are discussed in this paper.
	Poster TUPB001 [2.155 MB]
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB030	Recent Results from the Cornell Sample Host Cavity	cavity, SRF, radio-frequency, superconducting-RF	626
	J.T. Maniscalco, B. Clasby, T. Gruber, D.L. Hall, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: DOE/NSF Many novel materials are under investigation for the future of superconducting radio-frequency accelerators (SRF). In particular, thin-film materials such as Nb3Sn, NbN, SIS multilayers, and also thin-film niobium on copper, may offer improvements in cost efficiency and RF performance over the standard niobium cavities. To avoid the difficulties of depositing thin films on full cavities, Cornell has developed a TE-mode sample host cavity which allows for RF measurements of large, flat samples at fields up to and over 100 mT. We present recent performance results from the cavity, reaching record high fields and quality factor using a niobium calibration plate. We also discuss plans for future collaborations.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB032	Energetic Condensation Growth of Nb on Cu SRF Cavities	cavity, cathode, SRF, plasma	629
	K.M. Velas, S.F. Chapman, I. Irfan, M. Krishnan AASC, San Leandro, California, USA
	Funding: This research is supported by the US DOE via and SBIR grant: DE-SC0011371 Alameda Applied Sciences Corporation (AASC) grows Nb thin films via Coaxial Energetic Deposition (CED) from a cathodic arc plasma. The plasma from the cathode consists exclusively of 60-120eV Nb ions (Nb+ and Nb2+) that penetrate a few monolayers into the substrate and enable sufficient surface mobility to ensure that the lowest energy state (crystalline structure with minimal defects) is accessible to the film. AASC is coating 1.3 GHz SRF cavities using a graded anode to ensure uniform film thickness in the beam tube and elliptical regions. Copper cavities are centrifugal barrel polished and electropolished (done for us by the Fermilab Technical Division, Superconducting RF Development Department and by Thomas Jefferson National Accelerator Facility (JLAB)) before coating, to ensure good adhesion and improved film quality. The Nb coated copper cavities will undergo RF tests at JLAB and at Fermilab to measure Qo vs. E.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB037	Superconducting NbN-Based Multilayer and NbTiN Thin Films for the Enhancement of SRF Accelerator Cavities	target, lattice, cavity, SRF	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]
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB038	Superconducting Coatings Synthetized by CVD/PECVD for SRF Cavities	SRF, 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)
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB041	Testing Nb3Sn Coating Using muSR	TRIUMF, SRF, 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.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB042	Low Energy Muon Spin Rotation and Point Contact Tunneling Applied to Niobium Films for SRF Cavities	cavity, experiment, scattering, data-analysis	656
	T. Junginger TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada S. Calatroni, G. Terenziani CERN, Geneva, Switzerland T. Prokscha, Z. Salman, A. Suter PSI, Villigen PSI, Switzerland Th. Proslier ANL, Argonne, Illinois, USA G. Terenziani Sheffield University, Sheffield, United Kingdom J. Zasadzinski IIT, Chicago, Illinois, USA
	Muon spin rotation (muSR) and point contact tunneling (PCT) are used since several years for bulk niobium studies. Here we present studies on niobium thin film samples of different deposition techniques (diode, magnetron and HIPIMS) and compare the results with RF measurements and bulk niobium results. It is consistently found from muSR and RF measurements that HIPIMS can be used to produce thin films of high RRR. Hints for magnetism are especially found on the HIPIMS samples. These could possibly contribute to the field dependent losses of superconducting cavities, which are strongly pronounced on niobium on copper cavities.
	Poster TUPB042 [0.932 MB]
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB044	High Quality Factor Studies in SRF Nb3Sn Cavities	cavity, SRF, radio-frequency, accelerating-gradient	661
	D.L. Hall, B. Clasby, H. Conklin, R.G. Eichhorn, T. Gruber, G.H. Hoffstaetter, J.J. Kaufman, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: Work supported by DOE grant DE-SC0008431 and NSF grant PHY-141638 A significant advantage of Nb3Sn coated on niobium over conventional bulk niobium is the substantial reduction in the BCS losses at equal temperatures of the former relative to the latter. The quality factor of a 1.3 GHz Nb3Sn cavity is thus almost entirely dictated by the residual resistance at temperatures at and below 4.2 K, which, if minimised, offers the ability to operate the cavity in liquid helium at atmospheric pressure with quality factors exceeding 4·10¹⁰. In this paper we look at the impact of the cooldown procedure – which is intrinsically linked to the effect of spatial and temporal gradients – and the impact of external ambient magnetic fields on the performance of a Nb3Sn cavity.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB045	Surface Analysis and Material Property Studies of Nb3Sn on Niobium for Use in SRF Cavities	cavity, radio-frequency, klystron, electron	665
	D.L. Hall, H. Conklin, T. Gruber, J.J. Kaufman, M. Liepe, J.T. Maniscalco, B. Yu Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA Th. Proslier ANL, Argonne, Illinois, USA
	Funding: Work supported by DOE grant DE-SC0008431 and NSF grant PHY-141638. Use of CCMR via NSF MRSEC program (DMR-1120296) Studies of superconducting Nb3Sn cavities and samples at Cornell University and Argonne National Lab have shown that current state-of-the-art Nb3Sn cavities are limited by material properties and imperfections. In particular, the presence of regions within the Nb3Sn layer that are deficient in tin are suspected to be the cause of the lower than expected peak accelerating gradient. In this paper we present results from a material study of the Nb3Sn layer fabricated using the vapour deposition method, with data collected using AFM, SEM, TEM, EDX, and XRD methods as well as with pulsed RF testing.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB046	Structure and Composition of Nb3Sn Diffusion Coated Films on Nb	ion, electron, SRF, 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.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB048	Fermilab Nb3Sn R&D Program	cavity, SRF, cryogenics, accelerating-gradient	678
	S. Posen, M. Merio, A. Romanenko, Y. Trenikhina Fermilab, Batavia, Illinois, USA
	A substantial program has been initiated at FNAL for R&D on Nb3Sn coated cavities. Since early 2015, design, fabrication, and commissioning has been ongoing on a coating chamber, designed for deposition via vapor diffusion. The volume of the chamber will be large enough to accommodate not just R&D cavities, but full production-style cavities such as TeSLA 9-cells. In this contribution, we overview the development of the chamber and we introduce the R&D program planned for the coming years. We discuss research paths that may yield increased maximum fields and reduced residual resistances as well as new applications that could be explored with larger coated cavities.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB049	Cutout Study of a Nb3Sn Cavity	cavity, electron, SRF, accelerating-gradient	681
	S. Posen, O.S. Melnychuk, A. Romanenko, D.A. Sergatskov, Y. Trenikhina Fermilab, Batavia, Illinois, USA D.L. Hall, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	The first 1.3 GHz single cell Nb₃Sn cavity coated at Cornell was shown in RF measurements at Cornell and FNAL to have poor RF performance. Though subsequent cavities showed much higher quality factors, this cavity exhibited Q₀ on the order of 10⁹ caused by strong heating concentrated in one of the half cells. This paper presents an investigation into the source of this excess heating, for the purpose of process improvement, so that similar degradation can be avoided in future coatings. Through the use of temperature mapping both at Cornell and at FNAL, locations with high and low surface resistance were located, cut out from the cavity, and studied with microscopic tools. We present the RF measurements and temperature maps as well as the microscopic analyses, then conclude with plans for continued studies.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB050	Secondary Electron Yield of SRF Materials	electron, SRF, 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.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB054	Local Composition and Topography of Nb3Sn Diffusion Coatings on Niobium	cavity, electron, site, accelerating-gradient	703
	U. Pudasaini, M.J. Kelley The College of William and Mary, Williamsburg, Virginia, USA G.V. Eremeev, M.J. Kelley, C.E. Reece JLab, Newport News, Virginia, USA
	Funding: Co-authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. College of William & Mary supported by U.S. DOE Office of High Energy Physics under grant DE-SC-0014475. The potential for energy savings and for increased gradient continues to bring attention to Nb3Sn-coated niobium as a future SRF cavity technology. We prepared these materials by vapor diffusion coating on polycrystalline and single crystal niobium. The effect of changing substrate preparation, coating parameters and post-treatment were examined by AFM and SEM/EDS. The AFM data were analyzed in terms of power spectral density (PSD). We found little effect of pre-coating topography on the result. The PSD’s show some surprising kinship to those obtained from BCP-treated surfaces. SEM/EDS revealed no composition non-uniformities at the micron scale.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB056	Characterization of Nb3Sn Coated Nb Samples	SRF, electron, cavity, ion	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.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB059	A Facility for Magnetic Field Penetration Measurements on Multilayer S-I-S Structures	experiment, SRF, 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)
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB063	A Multi-Sample Residual Resistivity Ratio System for High Quality Superconductor Measurements	ECR, cavity, feedback, electron	726
	J.K. Spradlin, C.E. Reece, A-M. Valente-Feliciano JLab, Newport News, Virginia, USA
	Funding: This work is supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC05-06OR2317. For developing accelerator cavity materials, superconducting transition temperature (T_C), transition width (ΔTC), and residual resistivity ratio (RRR), are useful parameters to correlate with SRF performance and fabrication processes of bulk, thin film, and novel materials. The RRR gauges the purity and structure of the superconductor based on the temperature dependence of electron scattering in the normal conducting state. Combining a four point probe delta pulse setup with a switch allows multiplexing of the electrical measurements to 32 samples per cooldown cycle. The samples are measured inside of an isothermal setup in a liquid helium (LHe) dewar. The isothermal setup is required for a quasistatic warmup of the samples through TC. This contribution details the current setup for collecting RRR and TC data, the current standard of throughput, measurement quality of the setup, and the improvements underway to increase the system’s resolution and ease of use.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB064	Superconducting Thin Film Test Cavity Commissioning	cavity, vacuum, cryogenics, resonance	731
	P. Goudket, K.D. Dumbell, L. Gurran, O.B. Malyshev, N. Pattalwar, S.M. Pattalwar, R. Valizadeh STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom G. Burt, L. Gurran Cockcroft Institute, Lancaster University, Lancaster, United Kingdom G. Burt, L. Gurran Lancaster University, Lancaster, United Kingdom P. Goudket, O.B. Malyshev, S.M. Pattalwar, R. Valizadeh Cockcroft Institute, Warrington, Cheshire, United Kingdom T.J. Jones, E.S. Jordan STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom
	A radiofrequency (RF) cavity and cryostat dedicated to the measurement of superconducting coatings at GHz frequencies was designed to evaluate surface resistive losses on a flat sample. The test cavity consists of two parts: a cylindrical half-cell made of bulk niobium (Nb) and a flat Nb disc. The two parts can be thermally and electrically isolated via a vacuum gap, whereas the electromagnetic fields are constrained through the use of RF chokes. Both parts are conduction cooled hence the cavity halves are suspended in vacuum during operation. The flat disc can be replaced with a sample, such as a Cu disc coated with a film of niobium or any other superconducting material. The RF test provides simple cavity Q-factor measurements as well as calorimetric measurements of the losses on the sample. The advantage of this method is the combination of a compact cavity with a simple planar sample. The paper describes the RF, mechanical and cryogenic design, and initial commissioning of the system with notes on how any issues arising are to be addressed.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB065	Cryogenic RF Characterization of Superconducting Materials at SLAC With Hemispherical Cavities	cavity, SRF, factory, cryogenics	735
	P.B. Welander, M.A. Franzi, S.G. Tantawi SLAC, Menlo Park, California, USA
	For the characterization of SRF materials, we have commissioned a second-generation, X-band cavity cryostat that can rapidly analyze thin-film coatings or bulk samples. The system operates at 11.4 GHz, at temperatures down to 4 K, and utilizes two interchangeable hemispherical cavities (one Cu, one Nb) that can accommodate 51 mm-diameter samples on the flat side. The cavities are designed to operate with a TE032-like mode where the magnetic field is strongest on the sample surface. As a result, the sample accounts for 33% of the overall cavity loss, despite comprising less than 8% of the total surface area. For low-power testing we utilize a programmable network analyzer, while for high-power testing we connect the cavity to a 50 MW XL-4 klystron. With the Nb cavity we can measure surface resistances down to 0.7 microhm, while with the Cu cavity we can measure quenching fields up to 360 mT. X-band operation permits a compact cavity and cryostat design with a reasonable sample size, while the closed-cycle pulse-tube cryorefrigerator allows for rapid sample cycling. We will discuss cryostat design, cavity modeling, measurement limits, and recent sample testing results.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB067	Design and First Measurements of an Alternative Calorimetry Chamber for the HZB Quadrupole Resonator	quadrupole, SRF, 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]
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB073	Cold Tests of SSR1 Resonators Manufactured by IUAC for the Fermilab PIP-II Project	cavity, electron, proton, radio-frequency	750
	L. Ristori, A. Grassellino, O.S. Melnychuk, D.A. Sergatskov, A.I. Sukhanov Fermilab, Batavia, Illinois, USA K.K. Mistri, P.N. Potukuchi, A. Rai, J. Sacharias, S.S.K. Sonti IUAC, New Delhi, India
	In the framework of the Indian Institutions and Fermilab Collaboration (IIFC) within the PIP-II project, two Superconducting Single Spoke Resonators were manufactured at the Inter-University Accelerator Centre (IUAC) in New Delhi and tested at Fermilab. The resonators were subject to the routine series of inspections and later processed chemically by means of Buffered Chemical Polishing, heat-treated at 600 C and cold-tested at Fermilab in the Vertical Test Stand. In this paper we present the findings of the inspections and the results of the cold-tests.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB074	High-Vacuum Simulations and Measurements on the SSR1 Cryomodule Beam-Line	vacuum, cavity, cryomodule, simulation	754
	D. Passarelli, T.H. Nicol, M. Parise, L. Ristori Fermilab, Batavia, Illinois, USA
	Funding: Work supported by Fermi Research Alliance, LLC under Contract No. DEAC02- 07CH11359 with the United States Department of Energy In order to guarantee an effective cool-down process for the SSR1 cryomodule, a high-vacuum level must be achieved at room temperature in the beam-line before introducing gaseous and liquid helium. The SSR1 cavities in the beamline have a small beam aperture compared to the size of their internal volume. To avoid unnecessary complications for the vacuum piping of the cryomodule cold-mass, a pilot study was conducted on the string prior to processing and qualification of the components to investigate the vacuum level achievable by pumping only through the beam-line. To estimate the pressure distribution inside the cavity string we used a mathematical model implemented in a test-particle Monte-Carlo simulator for ultra-high-vacuum systems.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB076	The Multipacting Study of Niobium Sputtered High-Beta Quarter-Wave Resonators for HIE-ISOLDE	cavity, electron, simulation, pick-up	760
	P. Zhang, W. Venturini Delsolaro CERN, Geneva, Switzerland
	Funding: This work has been supported partly by a Marie Curie Early Initial Training Network Fellowship of the European Community’s 7th Programme under contract number PITN-GA-2010-264330-CATHI. Superconducting quarter-Wave Resonators (QWRs) will be used in the superconducting linac upgrade in the frame of HIE-ISOLDE project at CERN. The cavities are made of bulk copper with thin niobium film coated. They will be operated at 101.28 MHz at 4.5 K providing 6 MV/m accelerating gradient with 10 W power dissipation. Multipacting (MP) has been studied for the high-beta (β=10.9%) QWRs and two MP barriers have been found: Eacc at around 0.05MV/m and 1.5MV/m. We have used both CST Microwave Studio & Particle Studio and the parallel codes Omega3P & Track3P developed at SLAC. The results from the two codes are consistent and are in good agreement with cavity vertical cold test results. Both MP barriers can be processed by RF during the cavity cold test.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB077	The Influence of Cooldown Conditions at Transition Temperature on the Quality Factor of Niobium Sputtered Quarter-Wave Resonators for HIE-ISOLDE	cavity, accelerating-gradient, linac, cathode	765
	P. Zhang, G.J. Rosaz, A. Sublet, M. Therasse, W. Venturini Delsolaro CERN, Geneva, Switzerland
	Funding: This work has been supported partly by a Marie Curie Early Initial Training Network Fellowship of the European Community’s 7th Programme under contract number PITN-GA-2010-264330-CATHI. Superconducting quarter-wave resonators (QWRs) are to be used in the ongoing linac upgrade of the ISOLDE facility at CERN. The cavities are made of niobium sputtered on copper substrates. They will be operated at 101.28 MHz at 4.5 K providing 6 MV/m accelerating gradient with 10 W power dissipation. In recent measurements, we found the thermal gradient along the cavity during the niobium superconducting transition has an impact on the cavity quality factor. On the other hand, the speed of the cooling down through the superconducting transition turned out to have no influence on the cavity Q-factor.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB080	Diagnostic Developments at CERN’s SRF Testing Facility	cavity, diagnostics, monitoring, SRF	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.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB082	Automatic Surface Defect Detection and Sizing for Superconducting Radio Frequency Cavity Using Haar Cascades	cavity, background, radio-frequency, SRF	788
	G.V. Eremeev JLab, Newport News, Virginia, USA D.C. Iriks Santa Rosa Junior College, Santa Rosa, USA
	Serious albeit tiny surface defects can remain on the surface of superconducting radio frequency (SRF) cavities after polishing and cleaning. These defects reduce the efficiency of cavities and often limit the maximum attainable fields. We applied a Haar cascade artificial vision technique for automated identification, counting, and sizing of defects induced on niobium surface by Nb-H precipitates formed at cryogenic temperatures. The defects were counted and sized by a computer program and also counted and measured manually to estimate detection rate and accuracy of sizing. The overall detection rate was 53%, and the overall false positive rate was 29%. The technique that was used to automatically size the features was found to oversize the features, but oversize them consistently, resulting in a size histogram that represents the defect size distribution on the sample. After scaling the histogram data, the average defect area was found to be 90 square micrometers with the standard deviation of 70 square micrometers.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB085	Characterization of Optical Surface Properties of 1.3 GHz SRF Cavities for the European XFEL	cavity, background, electron, SRF	795
	M. Wenskat, L. Steder DESY, Hamburg, Germany
	The optical inspection of the inner surface of superconducting rf cavities is a well-established tool at many laboratories. Its purpose is to recognise and understand field limitations and to allow optical quality assurance during cavity production. Within the ILC-HiGrade programme at DESY, as part of the XFEL cavity production, an automated image processing and analysis algorithm has been developed that recognises structural boundaries. The count of features, the length of boundaries and their orientation can be used for characterisation. Appreciable differences are observed depending on the fabrication process at the vendor and the chemical treatment applied. The potential of this framework for automated quality assurance as an integral part of large-scale cavity production will be outlined. In addition, correlations between geometrical surface properties and the maximal accelerating field of twenty cavities have been found. These observations coincide with quench localisation by second sound of two cavities. The distribution of the limiting cell is vendor dependent, indicating weaknesses in the fabrication procedure.
	Poster TUPB085 [2.272 MB]
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB087	Development of an X-Ray Fluorescence Probe for Inner Cavity Inspection	cavity, detector, radiation, background	799
	M. Bertucci, P. Michelato, L. Monaco, M. Moretti, C. Pagani INFN/LASA, Segrate (MI), Italy A. Navitski DESY, Hamburg, Germany
	The development of an x-ray fluorescence probe for detection of foreign material inclusions of the inner surface of 1.3 GHz tesla-type Niobium cavities is here presented. The setup dimensions are minimized so to access the inner cavity volume and focus on the surface of equator. Preliminary tests confirmed the system capability to detect and localize with good precision small metal inclusions of few micrograms. The results obtained from the inspection of some 1.3 GHz XFEL series production cavities are also pointed out.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB088	On Quench Propagation, Quench Detection and Second Sound in SRF Cavities	cavity, SRF, simulation, interface	804
	S.R. Markham, R.G. Eichhorn, D.L. Hartill, G.H. Hoffstaetter Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Quench location detection has provided valuable insight in SRF cavity operation since two decades. While in earlier days temperature maps were used the state of the art technique nowadays is detecting the second sound wave, excited by a quench, using oscillating super-leak detector (OSTs). Typically, many OSTs surround the cavity and the quench location is determined by triangulation of the different OST signals. Convenient as the method is there is a mystery: taking the well-known velocity of the second sound wave, the quench seems to come from a place slightly above the cavity’s outer surface. In addition, not all triangulation spheres intersect in one point. We will present a model based on numerical quench propagation simulations that is able to fully explaining this discrepancy.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB099	Magnetic Foils for SRF Cryomodule	cavity, shielding, SRF, cryogenics	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.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

WEA1A02	Surface Resistance Study on Low Frequency (Low Beta) Cavities	cavity, superconductivity, accelerating-gradient, SRF	923
	D. Longuevergne, F. Chatelet, G. Michel, G. Olry, F. Rabehasy, L. Renard IPN, Orsay, France
	Additional RF tests and temperature treatments (120°C baking, 100K soaking, …) have been carried out on Spiral2 quarter-wave cavities and ESS double spoke cavities. For each test, residual resistance and BCS resistance have been evaluated by testing the cavities between 4.2K and 1.5K. This talk will summarize the main results and try to highlight the main differences with high frequency cavities.
	Slides WEA1A02 [15.993 MB]
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

WEA1A04	Commissioning Results of the HZB Quadrupole Resonator	cavity, electron, quadrupole, SRF	930
	R. Kleindienst, A. Burrill, S. Keckert, J. Knobloch, O. Kugeler HZB, Berlin, Germany
	Funding: The research leading to these results has received funding from the European Commission under the FP7 Research Infrastructures project EuCARD-2, grant agreement no.312453 Recent cavity results with niobium have demonstrated the necessity of a good understanding of both the BCS and residual resistance. For a complete picture, and comparison with theory, it is essential that one can measure the RF properties as a function of applied magnetic field, temperature, frequency and ambient magnetic field. Standard cavity measurements are limited in their ability to change all parameters freely and in a controlled manner. On the other hand, most sample measurement setups operate at fairly high frequency, where the surface resistance is always BCS dominated. The quadrupole resonator, originally developed at CERN, is ideally suited for RF characterization of samples at frequencies of 400 and 1300 MHz, between which many of today’s SRF cavities operate. We report on a modified version of the QPR with improved RF figures of merit for high-field operation. Experimental challenges in the commissioning run and alternate designs towards a simpler sample change are shown alongside measurement results of a large grain niobium sample.
	Slides WEA1A04 [5.611 MB]
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

WEA1A05	Nanostructure of the Penetration Depth in Nb Cavities: Debunking the Myths and New Findings	cavity, electron, cryogenics, SRF	937
	Y. Trenikhina, A. Romanenko Fermilab, Batavia, Illinois, USA J. Kwon, J.-M. Zuo UIUC, Urbana, USA
	Nanoscale defect structure within the magnetic penetration depth of ~100 nm is key to the performance limitations of niobium superconducting radio frequency (SRF) cavities. Using a unique combination of advanced thermometry during cavity RF measurements, and TEM structural and compositional characterization of the samples extracted from cavity walls at both room and cryogenic temperatures, we directly discover the existence of nanoscale hydrides in SRF cavities limited by the high field Q slope, and show the decreased hydride formation after 120C baking. Crucially, in extended studies we demonstrate that adding 800C hydrogen degassing - both with AND without light BCP afterwards - restores the hydride formation to the pre-120C bake level correlating perfectly with the observed high field Q slope behavior. We also show absence of niobium oxides along the grain boundaries and the modifications of the surface oxide upon 120C bake, which contradicts some of the widely used models of niobium surface.
	Slides WEA1A05 [31.768 MB]
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

WEA2A02	High Gradient Testing of the Five-Cell Superconducting RF Module With a PBG Coupler Cell	cavity, dipole, HOM, factory	948
	S. Arsenyev MIT/PSFC, Cambridge, Massachusetts, USA C.H. Boulware, T.L. Grimm, A. Rogacki Niowave, Inc., Lansing, Michigan, USA W.B. Haynes, D.Y. Shchegolkov, E.I. Simakov, T. Tajima LANL, Los Alamos, New Mexico, USA
	Funding: DOE Office of Science/Office of High Energy Physics Superconducting radio-frequency (SRF) accelerating structures allow high-gradient operation in continuous-wave mode. These machines can be limited by beam-breakup instability at high currents because higher-order modes with very high Q factors are easily excited by the beam. Photonic band gap (PBG) structures provide a way to strongly damp higher-order modes without compromising the performance of the structure in the fundamental mode. We first address the design of the structure and issues that arise from incorporating a complex PBG cell into an SRF module. In particular, the module was tuned to have uneven accelerating gradient profile in order to provide equal peak surface magnetic field in every cell. We then cover the fabrication steps and surface treatment of the five-cell niobium structure and report results of the high gradient tests at temperatures of 4 K and 2 K.
	Slides WEA2A02 [7.023 MB]
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

WEBA03	Production Status of SRF Cavities for the Facility for Rare Isotope Beams (FRIB) Project	cavity, vacuum, linac, controls	961
	C. Compton, A. Facco, S.J. Miller, J. Popielarski, L. Popielarski, A.P. Rauch, K. Saito, G.J. Velianoff, E.M. Wellman, K. Witgen, T. Xu FRIB, East Lansing, Michigan, USA
	As the Facility for Rare Isotope Beams (FRIB) project ramps into production, vendor relations, cavity quality, and schedule become critical to success. The driver linac will be constructed of 332 cavities housed in 48 cryomodules and designed with two cavity classes (quarter-wave and half-wave) and four different betas (0.041, 0.085, 0.29, and 0.53). The cavities will be supplied to FRIB from awarded industrial vendors. FRIB’s experience with SRF cavity fabrication will be presented including acceptance inspections, test results, technical issues, and mitigation strategies.
	Slides WEBA03 [1.672 MB]
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

WEBA05	Achieving High Peak Fields and Low Residual Resistance in Half-Wave Cavities	cavity, accelerating-gradient, cryomodule, vacuum	973
	Z.A. Conway, A. Barcikowski, G.L. Cherry, R.L. Fischer, S.M. Gerbick, C.S. Hopper, M. Kedzie, M.P. Kelly, S.H. Kim, S.W.T. MacDonald, B. Mustapha, P.N. Ostroumov, T. Reid ANL, Argonne, USA
	Funding: Work supported by the U.S. Department of Energy Office of Science, Office of Nuclear Physics contract number DE-AC02-06CH11357, and the Office of High Energy Physics contract number DE-AC02-76CH03000. We have designed, fabricated and tested two new half-wave resonators following the successful development of a series of niobium superconducting quarter-wave cavities. The half-wave resonators are optimized for β = 0.11 ions, operate at 162.5 MHz and are intended to provide up to 2 MV effective voltage for particles with the optimal velocity. Testing of the first two half-wave resonators is complete with both reaching accelerating voltages greater than 3.5 MV with low-field residual resistances of 1.7 and 2.3 nΩ respectively. The intention of this paper is to provide insight into how Argonne achieves low-residual resistances and high surface fields in low-beta cavities by describing the cavity design, fabrication, processing and testing.
	Slides WEBA05 [2.927 MB]
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

THAA04	Comparison of Cavity Fabrication and Performances Between Fine Grains, Large Grains and Seamless Cavities	cavity, electron, SRF, 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]
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

THAA05	First Results of SRF Cavity Fabrication by Electro-Hydraulic Forming at CERN	simulation, SRF, 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]
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

THPB010	INFN Milano - LASA Activities for ESS	cavity, vacuum, linac, cryomodule	1081
	P. Michelato, M. Bertucci, A. Bignami, A. Bosotti, J.F. Chen, L. Monaco, M. Moretti, R. Paparella, P. Pierini, D. Sertore INFN/LASA, Segrate (MI), Italy C. Pagani Università degli Studi di Milano & INFN, Segrate, Italy H.J. Zheng IHEP, Beijing, People's Republic of China
	INFN Milano – LASA is involved in the development and industrialization for the production of 704.4 MHz medium beta (β = 0.67) cavities for the ESS project. In this framework, we are designing a medium beta prototype cavity exploring both Large Grain and Fine Grain Niobium for its production as well as a high beta (β = 0.86) Large Grain cavity. In the meanwhile, an activity is ongoing for upgrading the LASA test facility to be able to test these kind of resonators.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

THPB013	A Novel Design and Development of 650 MHz, β=0.61, 5-Cell SRF Cavity for High Intensity Proton Linac	cavity, electron, impedance, HOM	1088
	S.S. Som, P. Bhattacharyya, A. Dutta Gupta, S. Ghosh, A. Mandal, S. Seth VECC, Kolkata, India
	Funding: DAE, Govt. of India DAE laboratories in India are involved in R&D activities on SRF cavity technology for the proposed high intensity proton linacs for ISNS/IADS and also FERMILAB PIP-II program under IIFC. VECC is responsible for design, analysis and development of a 650 MHz, β=0.61, 5-cell elliptical cavity. This paper describes the novel design of the cavity, with different aperture and wall angle, having better field flatness and mechanical stability, reliable surface processing facility and less beam loss. The cavity geometry has been optimized to get acceptable values of field enhancement factors, R/Q, Geometric factor, cell-to-cell coupling etc. The effective impedance of transverse and longitudinal HOMs are low enough to get rid of HOM damper for low beam current. 2-D analysis shows no possibility of multipacting. However, 3-D analysis using CST Particle Studio code confirms its presence and it can be suppressed by introducing a small convexity in the equator region. Two niobium half cells and beam pipes for the single cell cavity have been fabricated. Measurement and RF characterisation of half cells, prototype 1-cell and 5-cell and also 1-cell niobium cavities have been carried out. email:ssom@vecc.gov.in
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

THPB023	The Statistics of Industrial XFEL Cavities Fabrication at E.ZANON	cavity, target, controls, accelerating-gradient	1119
	A. Gresele, M. Giaretta, A. Visentin Ettore Zanon S.p.A., Nuclear Division, Schio, Italy A.A. Sulimov, J.H. Thie DESY, Hamburg, Germany
	Serial production of superconducting cavities for European-XFEL will be completed at E.ZANON by the end of 2015. For that reason we can summarize the results and present the statistics of industrial cavity fabrication. Many parameters have been traced during different steps of cavity production. The most interesting of them, as cavity length, frequency, field flatness and eccentricity, are presented and discussed.
	Poster THPB023 [3.227 MB]
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

THPB030	Fabrication and Evaluation of Low RRR Large Grain 1-Cell Cavity	cavity, SRF, electron, accelerating-gradient	1146
	H. Shimizu, H. Inoue, E. Kako, T. Saeki, K. Umemori, Y. Watanabe, M. Yamanaka KEK, Ibaraki, Japan
	Successive R&D studies of SRF cavities are ongoing at KEK by using existing facilities of Cavity Fabrication Facility (CFF) and other equipment of Superconducting Test facility (STF). Recently, there are studies on the low RRR of niobium material with high and uniform concentration of tantalum which could be used for the fabrication of high performance SRF cavity, and hence it could reduce the fabrication cost of cavities [1]. In order to confirm the advantage of the material, a large-grain single-cell cavity was fabricated at CFF/KEK with sheets sliced from a low RRR niobium ingot with high and uniform concentration of tantalum. The resistivity measurement of sample from sliced sheet showed the RRR value of 100, whereas it is about 400 for the nominal qualification of fine-grain sheets at KEK. The low RRR large-grain single-cell cavity was already fabricated at CFF/KEK. The quality control of the fabrication processes are well under control. Then several vertical tests of the cavity were done at STF/KEK. In this presentation, the results of the vertical tests are shown. The potential of the low RRR niobium material for SRF cavity are discussed. *P.Kneisel et al, NIM A774(2015)133
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

THPB033	Frequency Measurement and Tuning of a 9-Cell Superconducting Cavity Developed with UK Industry	cavity, simulation, superconducting-RF, electron	1158
	L.S. Cowie, P. Goudket, A.R. Goulden, P.A. McIntosh, A.E. Wheelhouse STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom J.R. Everard, N. Shakespeare Shakespeare Engineering, South Woodham Ferrers, Essex, United Kingdom B. Lamb, S. Postlethwaite, N. Templeton STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom
	As part of an STFC Innovations Partnership Scheme (IPS) grant, in support of enabling UK industry to address the large potential market for superconducting RF structures, Daresbury Laboratory and Shakespeare Engineering Ltd are collaborating to produce a 1.3 GHz 9 cell niobium cavity. This paper describes the procedures to ensure the cavity reaches the required frequency and field flatness. The frequency of each half-cell was measured using a custom measurement apparatus. Combined mechanical and RF simulations were used to compensate for cavity deformation during measurement. Results of Coordinate Measurement Machine measurements of one half-cell are presented. The same procedure will be used to trim the cells at the dumbbell stage, and the full 9-cell cavity will be tuned once welded.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

THPB040	Hydroforming of Large Grain Niobium Tube	cavity, experiment, vacuum, electron	1171
	A. Mapar, F. Pourboghrat MSU, East Lansing, Michigan, USA T.R. Bieler Michigan State University, East Lansing, Michigan, USA C. Compton FRIB, East Lansing, Michigan, USA J.E. Murphy University of Nevada, Reno, Reno, Nevada, USA
	Funding: This work was supported by the U.S. Department of Energy, Office of High Energy Physics, through Grant No. DE-FG02-09ER41638. Currently most of Niobium (Nb) cavities are manufactured from fine grain Nb sheets. As-cast ingots go through a series of steps including forging, milling, rolling, and intermediate annealing, before they are deep-drawn into a half-cell shape and subsequently electron beam welded to make a full cavity. Tube hydroforming, a manufacturing technique where a tube is deformed using a pressurized fluid, is an alternative to the current costly manufacturing process. A whole cavity can be made from a tube using tube hydroforming. This study focuses on deformation of large grain Nb tubes during hydroforming. The crystal orientation of the grains is recorded. The tube is marked with a square-circle-grid which is used to measure the strain after deformation. The deformation of the tube is going to be modeled with crystal plasticity finite element and compared with experiments. This paper only covers the characterization of the tube and the hydroforming process.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

THPB041	Hydroforming SRF Cavities from Seamless Niobium Tubes	cavity, SRF, accelerating-gradient, superconductivity	1176
	M. Yamanaka, H. Inoue, H. Shimizu, K. Umemori KEK, Ibaraki, Japan A. Hocker Fermilab, Batavia, Illinois, USA T. Tajima LANL, Los Alamos, New Mexico, USA
	The authors are developing the manufacturing method for super conducting radio frequency (SRF) cavities by using a hydroforming instead of an electron beam welding, which is the major manufacturing method. We expect a cost reduction by hiring the hydroforming. To realize this development, getting a high-purity seamless niobium tube with good forming ability and an advancement of hydroforming technique are necessary. We got the seamless niobium tube made by ATI Wah Chang with the cooperation of Fermilab, and succeeded to manufacture the 1-cell cavity by hydroforming. The accelerating gradient attained to 36 MV/m, and we confirmed it was available to use as the SRF cavity.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

THPB042	Advance Additive Manufacturing Method for SRF Cavities of Various Geometries	cavity, SRF, electron, vacuum	1181
	P. Frigola, R.B. Agustsson, L. Faillace, A.Y. Murokh RadiaBeam, Santa Monica, California, USA G. Ciovati, W.A. Clemens, P. Dhakal, F. Marhauser, R.A. Rimmer, J.K. Spradlin, R.S. Williams JLab, Newport News, Virginia, USA J. Mireles, P.A. Morton, R.B. Wicker University of Texas El Paso, W.M. Keck Center for 3D Innovation, El Paso, Texas, USA
	An alternative fabrication method for superconducting radio frequency (SRF) cavities is presented. The novel fabrication method, based on 3D printing (or additive manufacturing, AM) technology capable of producing net-shape functional metallic parts of virtually any geometry, promises to greatly expand possibilities for advance cavity and end-group component designs. A description of the AM method and conceptual cavity designs are presented along with material analysis and RF measurement results of additively manufactured niobium samples.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

THPB043	Alternative Fabrication Methods for the ARIEL e-Linac SRF Separator Cavity	cavity, SRF, linac, induction	1185
	D.W. Storey Victoria University, Victoria, B.C., Canada R.E. Laxdal, N. Muller TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada
	The ARIEL e-Linac RF deflecting cavity is a 650 MHz superconducting deflecting mode cavity that will allow simultaneous beam delivery to both the Rare Isotope Beam program and an Energy Recovery Linac. The cavity will be operated at 4 K and with deflecting voltages of up 0.6 MV, resulting in a dissipated RF power of less than 1 W. Due to the modest performance requirements, alternative methods are being employed for the fabrication of this cavity. These include fabricating the entire cavity from reactor grade Niobium and welding the cavity using tungsten inert gas (TIG) welding in a high purity Argon environment. A post purification heat treatment will be performed in an RF induction oven to increase the cavity performance.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

THPB052	Thermal Losses in Couplers and Ports of a SPS Double-Quarter Wave Crab Cavity	HOM, cavity, pick-up, simulation	1219
	S. Verdú-Andrés, S.A. Belomestnykh, Q. Wu, B. P. Xiao BNL, Upton, Long Island, New York, USA S.A. Belomestnykh Stony Brook University, Stony Brook, USA G. Burt Cockcroft Institute, Lancaster University, Lancaster, United Kingdom G. Burt Lancaster University, Lancaster, United Kingdom R. Calaga, O. Capatina, F. Carra, C. Zanoni CERN, Geneva, Switzerland F. Carra Politecnico di Torino, Torino, Italy T.J. Jones STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom Z. Li SLAC, Menlo Park, California, USA
	Funding: Supported by US DOE via US LARP, through BSA LLC under contract No. DE-AC02-98CH10886 and using NERSC resources under contract No. DE-AC02-05CH11231. Also supported by EU FP7 HiLumi LHC No.284404. The Double-Quarter Wave Crab Cavity for beam tests at SPS will be equipped with a Fundamental Power Coupler (FPC), three HOM filters and one pickup. FPC and HOM couplers are located in high magnetic field region and have a hook shape. The FPC will be made in copper while HOM and pickup are in niobium. This paper explains the material choice for the FPC, HOM and pickup couplers given the calculated power dissipation for fundamental and selected high order modes. It also describes the envisaged cooling system and corresponding thermal distribution for each coupler.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

THPB061	Performance of the Tuner Mechanism for SSR1 Resonators During Fully Integrated Tests at Fermilab	cavity, controls, resonance, linac	1252
	D. Passarelli, J.P. Holzbauer, L. Ristori Fermilab, Batavia, Illinois, USA
	In the framework of the Proton Improvement Plan-II (PIPII) at Fermilab, a cavity tuner was developed to control the frequency of 325 MHz spoke resonators (SSR1). The behavior of the tuner mechanism and compliance with technical specifications were investigated through a campaign of experimental tests in operating conditions in the spoke test cryostat (STC) and at room temperature. Figures of merit for the tuner such as tuning range, stiffness, components hysteresis and overall performance were measured and are reported in this paper.
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

THPB063	BNL 56 MHz HOM Damper Fabrication at JLab	HOM, cavity, feedback, SRF	1262
	N.A. Huque, W.A. Clemens, E. Daly JLab, Newport News, Virginia, USA S. Bellavia, G.T. McIntyre, S.K. Seberg, Q. Wu BNL, Upton, Long Island, New York, USA

Paper

Title

Other Keywords

Page

MOBA03

Sensitivity of Niobium Superconducting RF Cavities to Magnetic Field

cavity, vacuum, impedance, SRF

34

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

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

Slides MOBA03 [1.817 MB]

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOBA04

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

cavity, simulation, shielding, operation

37

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

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

Slides MOBA04 [2.830 MB]

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOBA06

N Doping: Progress in Development and Understanding

cavity, superconductivity, factory, injection

48

A. Grassellino
Fermilab, Batavia, Illinois, USA

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

Slides MOBA06 [7.704 MB]

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOBA08

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

cavity, cryomodule, SRF, 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]

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB002

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

cavity, SRF, radiation, feedback

66

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB005

Developing a Setup to Measure Field Dependence of BCS Surface Resistance

cavity, solenoid, radio-frequency, software

77

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB006

Hc2 Measurements of Superconductors

SRF, 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.

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB010

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

cavity, data-analysis, electron, superconductivity

95

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB011

How Uniform Are Cool-Downs?

cavity, interface, simulation, factory

100

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB015

Trapped Flux Surface Resistance Analysis for Different Surface Treatments

cavity, resonance, superconductivity, instrumentation

115

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB018

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

cavity, SRF, electron, superconductivity

120

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB020

Mean Free Path Dependence of the Trapped Flux Surface Resistance

electron, SRF, 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.

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB024

SRF Cavity Breakdown Calculation Procedure Using FEA-Software

cavity, simulation, cathode, SRF

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.

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB027

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

SRF, 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.

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB030

Measurements of Thermal Impedance on Superconducting Radiofrequency Cavities

cavity, impedance, SRF, 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.

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB036

TOF-SIMS Study of Nitrogen Doping Niobium Samples

experiment, cavity, vacuum, ion

169

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB039

Analysis of BCS RF Loss Dependence on N-Doping Protocols

cavity, SRF, linac, operation

174

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB042

Fundamental Studies on Doped SRF Cavities

cavity, vacuum, simulation, SRF

187

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB045

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

experiment, SRF, 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.

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB047

Secondary Electron Yield of Electron Beam Welded Areas of SRF Cavities

electron, cavity, gun, vacuum

196

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB049

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

cavity, detector, experiment, software

201

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

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

Poster MOPB049 [0.901 MB]

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB051

Muon Spin Rotation on Treated Nb Samples in Parallel Field Geometry

cavity, SRF, polarization, detector

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]

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB052

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

cavity, SRF, superconductivity, 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.

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB054

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

SRF, 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.

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB055

Characterization of Nitrogen Doping Recipes for the Nb SRF Cavities

cavity, SRF, cryogenics, electron

223

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB057

Crystal Plasticity Modeling of Single Crystal Nb

experiment, cavity, SRF, software

228

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB072

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

cavity, SRF, laser, radiation

281

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB073

Surface Analyses and Optimization of Centrifugal Barrel Polishing of Nb Cavities

cavity, SRF, laser, embedded

286

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB074

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

cavity, cathode, radiation, SRF

291

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB086

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

cavity, status, linac, cryomodule

337

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB092

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

cavity, SRF, 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.

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB093

Vertical Electropolishing Studies at Cornell

cavity, cathode, SRF, 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]

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB096

Vertical Electro-Polishing at TRIUMF

cathode, cavity, TRIUMF, operation

378

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB100

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

cavity, cathode, simulation, operation

385

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

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

Poster MOPB100 [1.794 MB]

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB101

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

cavity, SRF, cathode, target

390

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB102

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

cavity, controls, cathode, acceleration

394

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

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

Poster MOPB102 [1.535 MB]

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB104

Flux Expulsion Variation in SRF Cavities

cavity, factory, cryogenics, SRF

404

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB105

Symmetric Removal of Niobium Superconducting RF Cavity in Vertical Electropolishing

cavity, cathode, experiment, accumulation

409

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB106

Analysis of High Pressure Rinsing Characteristics for SRF Cavities

cavity, target, experiment, SRF

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.

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB110

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

cavity, cathode, controls, superconductivity

418

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUAA04

Rapid Growth of SRF in India

cavity, linac, SRF, electron

467

D. Kanjilal
IUAC, New Delhi, India

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

Slides TUAA04 [5.918 MB]

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUBA02

Thermal Contact Resistance at the Nb-Cu Interface

cavity, interface, feedback, superconductivity

488

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

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

Slides TUBA02 [18.852 MB]

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUBA03

On the Understanding of Q-Slope of Niobium Thin Films

ECR, ion, SRF, 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]

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUBA04

Nb3Sn Cavities: Material Characterization and Coating Process Optimization

cavity, simulation, SRF, 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]

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUBA05

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

cavity, vacuum, SRF, factory

505

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

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

Slides TUBA05 [2.418 MB]

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB001

Progress on Superconducting RF Cavity Development With UK Industry

cavity, SRF, superconducting-RF, accelerating-gradient

521

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

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

Poster TUPB001 [2.155 MB]

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB030

Recent Results from the Cornell Sample Host Cavity

cavity, SRF, radio-frequency, superconducting-RF

626

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB032

Energetic Condensation Growth of Nb on Cu SRF Cavities

cavity, cathode, SRF, plasma

629

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB037

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

target, lattice, cavity, SRF

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]

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB038

Superconducting Coatings Synthetized by CVD/PECVD for SRF Cavities

SRF, 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)

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB041

Testing Nb3Sn Coating Using muSR

TRIUMF, SRF, 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.

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB042

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

cavity, experiment, scattering, data-analysis

656

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

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

Poster TUPB042 [0.932 MB]

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB044

High Quality Factor Studies in SRF Nb3Sn Cavities

cavity, SRF, radio-frequency, accelerating-gradient

661

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB045

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

cavity, radio-frequency, klystron, electron

665

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB046

Structure and Composition of Nb3Sn Diffusion Coated Films on Nb

ion, electron, SRF, 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.

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB048

Fermilab Nb3Sn R&D Program

cavity, SRF, cryogenics, accelerating-gradient

678

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB049

Cutout Study of a Nb3Sn Cavity

cavity, electron, SRF, accelerating-gradient

681

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB050

Secondary Electron Yield of SRF Materials

electron, SRF, 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.

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB054

Local Composition and Topography of Nb3Sn Diffusion Coatings on Niobium

cavity, electron, site, accelerating-gradient

703

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB056

Characterization of Nb3Sn Coated Nb Samples

SRF, electron, cavity, ion

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.

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB059

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

experiment, SRF, 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)

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB063

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

ECR, cavity, feedback, electron

726

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB064

Superconducting Thin Film Test Cavity Commissioning

cavity, vacuum, cryogenics, resonance

731

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB065

Cryogenic RF Characterization of Superconducting Materials at SLAC With Hemispherical Cavities

cavity, SRF, factory, cryogenics

735

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB067

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

quadrupole, SRF, 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]

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB073

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

cavity, electron, proton, radio-frequency

750

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB074

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

vacuum, cavity, cryomodule, simulation

754

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB076

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

cavity, electron, simulation, pick-up

760

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB077

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

cavity, accelerating-gradient, linac, cathode

765

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB080

Diagnostic Developments at CERN’s SRF Testing Facility

cavity, diagnostics, monitoring, SRF

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.

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB082

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

cavity, background, radio-frequency, SRF

788

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB085

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

cavity, background, electron, SRF

795

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

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

Poster TUPB085 [2.272 MB]

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB087

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

cavity, detector, radiation, background

799

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB088

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

cavity, SRF, simulation, interface

804

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

TUPB099

Magnetic Foils for SRF Cryomodule

cavity, shielding, SRF, cryogenics

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.

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

WEA1A02

Surface Resistance Study on Low Frequency (Low Beta) Cavities

cavity, superconductivity, accelerating-gradient, SRF

923

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

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

Slides WEA1A02 [15.993 MB]

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

WEA1A04

Commissioning Results of the HZB Quadrupole Resonator

cavity, electron, quadrupole, SRF

930

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

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

Slides WEA1A04 [5.611 MB]

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

WEA1A05

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

cavity, electron, cryogenics, SRF

937

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

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

Slides WEA1A05 [31.768 MB]

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

WEA2A02

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

cavity, dipole, HOM, factory

948

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

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

Slides WEA2A02 [7.023 MB]

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

WEBA03

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

cavity, vacuum, linac, controls

961

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

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

Slides WEBA03 [1.672 MB]

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

WEBA05

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

cavity, accelerating-gradient, cryomodule, vacuum

973

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

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

Slides WEBA05 [2.927 MB]

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

THAA04

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

cavity, electron, SRF, 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]

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

THAA05

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

simulation, SRF, 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]

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

THPB010

INFN Milano - LASA Activities for ESS

cavity, vacuum, linac, cryomodule

1081

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

THPB013

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

cavity, electron, impedance, HOM

1088

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

THPB023

The Statistics of Industrial XFEL Cavities Fabrication at E.ZANON

cavity, target, controls, accelerating-gradient

1119

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

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

Poster THPB023 [3.227 MB]

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

THPB030

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

cavity, SRF, electron, accelerating-gradient

1146

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

THPB033

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

cavity, simulation, superconducting-RF, electron

1158

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

THPB040

Hydroforming of Large Grain Niobium Tube

cavity, experiment, vacuum, electron

1171

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

THPB041

Hydroforming SRF Cavities from Seamless Niobium Tubes

cavity, SRF, accelerating-gradient, superconductivity

1176

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

THPB042

Advance Additive Manufacturing Method for SRF Cavities of Various Geometries

cavity, SRF, electron, vacuum

1181

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

THPB043

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

cavity, SRF, linac, induction

1185

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

THPB052

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

HOM, cavity, pick-up, simulation

1219

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

THPB061

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

cavity, controls, resonance, linac

1252

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

THPB063

BNL 56 MHz HOM Damper Fabrication at JLab

HOM, cavity, feedback, SRF

1262

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

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

Poster THPB063 [2.315 MB]

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

THPB069

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

HOM, cavity, luminosity, SRF

1279

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

THPB070

Design of Dressed Crab Cavities for the HL-LHC Upgrade

cavity, cryomodule, SRF, operation

1284

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

THPB093

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

cavity, emittance, electron, dipole

1360

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

THPB105

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

cavity, coupling, SRF, HOM

1397

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

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

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

THPB116

Modified ELBE Type Cryomodules for the Mainz Energy-Recovering Superconducting Accelerator MESA

cryomodule, HOM, operation, electron

1413

T. Stengler, K. Aulenbacher, R.G. Heine, F. Schlander, D. Simon
IKP, Mainz, Germany
M. Pekeler, D. Trompetter
RI Research Instruments GmbH, Bergisch Gladbach, Germany

At the Institut für Kernphysik of Johannes Gutenberg-Universität Mainz, the new multiturn energy recovery linac MESA is under construction. Two modified ELBE-type cryomodules with two 9-cell TESLA/XFEL cavities each will provide an energy gain of 50 MeV per turn. Those are currently in the production process at RI Research Instruments GmbH, Bergisch Gladbach, Germany. Modifications for the tuner and the HOM damper are under development. In addition, a 4K/2K Joule Thomson expansion stage will also be integrated into the cryomodule. The current status of the development of the cryomodules and their modifications will be discussed.

Poster THPB116 [1.472 MB]

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)