IPAC2016 - List of Keywords (niobium)

Paper	Title	Other Keywords	Page
WEPMB009	Status of the Superconducting Cryomodules and Cryogenic System for the Mainz Energy-recovering Superconducting Accelerator MESA	cryomodule, HOM, electron, operation	2134
	T. Stengler, K. Aulenbacher, F. Hug, D. Simon, P. Weber IKP, Mainz, Germany F. Schlander ESS, Lund, Sweden N. Wiehl Johannes Gutenberg University Mainz, Institut of Nuclear Chemistry, Mainz, Germany
	Funding: Work supported by the German Research Foundation (DFG) under the Cluster of Excellence "PRISMA" SRF and the cryogenic system are mandatory for the operation of MESA at the Institut für Kernphysik at Johannes Gutenberg-Universität Mainz. The cryomodule production project is running for one year right now and the recent developments and measurements are presented. Further on the cryogenic concept required for the operation of MESA will be discussed.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMB009
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WEPMB012	Production and Investigation of Superconducting 9-Cell Cavity Made of Large Grain Nb in KEK	cavity, SRF, accelerating-gradient, electron	2141
	T. Dohmae, H. Inoue, K. Umemori, Y. Watanabe, M. Yamanaka KEK, Ibaraki, Japan
	For CW operation of superconducting cavity, reduction of heat load at cavity surface is one of important topics, since generated heat load is much higher than that of pulse wave. Using Large Grain (LG) Nb for superconducting cavity has possibility to reach higher Q0 than using Fine Grain Nb, which reduces heat load to 2K Helium. KEK Cavity Fabrication Facility(CFF) group had successfully produced superconducting 1-cell cavity made of LG Nb in 2013, and reached high Q0 at the vertical test (maximum field of 45 MV/m). Then, KEK CFF group started producing first superconducting 9-cell LG cavity in 2015, which will be completed in the end of December 2015. Whole processes of producing this cavity from sliced Nb are done in KEK. In this report, process flow and strategies of producing 9-cell cavity and results of vertical test will be presented in detail.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMB012
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WEPMB023	Hydroforming SRF Three-cell Cavity from Seamless Niobium Tube	cavity, accelerating-gradient, SRF, superconductivity	2170
	M. Yamanaka, T. Dohmae, H. Inoue, G.-T. Park, K. Umemori KEK, Ibaraki, Japan A. Hocker Fermilab, Batavia, Illinois, USA T. Tajima LANL, Los Alamos, New Mexico, USA
	We are developing the manufacturing method for superconducting radio frequency (SRF) cavities by using a hydroforming instead of using conventional electron beam welding. We expect higher reliability and reduced cost with hydroforming. For successful hydroforming, high-purity seamless niobium tubes with good formability as well as advancing the hydroforming technique are necessary. Using a seamless niobium tube from ATI Wah Chang, we were able to successfully hydroform a 1.3 GHz three-cell TESLA-like cavity and obtained an Eacc of 32 MV/m. A barrel polishing process was omitted after the hydroforming. The vertical test was carried out with very rough inside surface. We got amazing and interesting result.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMB023
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WEPMB029	Research of Nitrogen Doping at IHEP	cavity, vacuum, experiment, electron	2186
	P. Sha Institute of High Energy Physics (IHEP), Chinese Academy of Sciences, Beijing, People's Republic of China J.P. Dai IHEP, Beijing, People's Republic of China F. Jiao PKU, Beijing, People's Republic of China
	Funding: Work funded by National Natural Science Foundation of China, Grant No. 11505197 Recently, nitrogen doping (N-doping) technology has been proved to increase Q0 of superconducting cavity obviously, which lowers the BCS surface resistance. After N-doping, Q0 of 9-cell 1.3 GHz cavity can be increased to 310¹⁰ at Eacc = 16 MV/m, while 1.51010 without N-doping [1]. Since 2013, there have been over 60 cavities nitrogen doped at FNAL, JLAB and Cornell. The Circular Electron Collider (CEPC) has been proposed by IHEP in China, while requests Q0=4e10@Eacc=15.5 MV/m for 650 MHz cavity. It's hard to achieve without N-doping. So research of N-doping was begun in cooperation with Peking University in early 2015. Experiments of niobium samples have showed that nitrogen concentration at niobium surface increased a lot after N-doping. After then, several single-cell 1.3 GHz cavities completed vertical tests, but there're no successful test results of Q0 increasing, yet.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMB029
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WEPMB032	Fabrication and Testing Status of IHEP03	cavity, SRF, superconducting-RF, status	2194
	T.X. Zhao, J. Gao, S. Jin, Z.Q. Li, Y.L. Liu, Z.C. Liu, Y. Wang, J.Y. Zhai, H.J. Zheng IHEP, Beijing, People's Republic of China M. Asano, E. Kako KEK, Ibaraki, Japan H. Yu, H. Yuan BIAM, Beijing, People's Republic of China
	After the successful development of the IHEP01 and IHEP02 1.3GHz 9cell superconducting cavity, we developed a 1.3GHz Tesla-Like 9cell superconducting cavities in collaboration with KEK. The cavity was made by niobium material produced in OTIC, Ningxia, China. After completeing welding, leakage check, BCP, HPR, we sent the cavity to KEK and used the standard procedures of ILC cavity for processing. These include electron polishing, vacuum furnace outgassing, tuning for field flatness and frequency, light EP, baking and vertical test. We target to have a high Q0 cavity for this experiment. In this paper, we will report the experimental status of the IHEP03 cavity.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMB032
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WEPMB034	Analysis of Niobium Quality Control for SRF Cavity	cavity, SRF, controls, radio-frequency	2197
	M.J. Joung IBS, Daejeon, Republic of Korea
	Funding: the Ministry of Science, ICT and Future Planning (MSIP) and the National Research Foundation (NRF) of the Republic of Korea under Contract 2013M7A1A1075764. Clean and smooth surface is important to get low sur-face resistance for superconducting material. SRF (Super-conducting Radio Frequency) cavity made of niobium which is superconducting material and also one of the rare metal. The procedure of niobium quality control was set up to get high performance SRF cavity. The procedure consists of three parts; certificates check, Nb specification verification, and surface inspection and measurements of thickness, roughness, flatness. Three important properties which are RRR value, chemical composition and me-chanical properties were verified to conform Nb specifica-tion. The range of thickness, roughness and flatness for niobium as SRF cavity raw material were obtained by measurement.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMB034
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WEPMB036	High Pressure Rinsing for Niobium Superconducting Cavity	cavity, target, SRF, operation	2202
	Y. Jung, M.J. Joung, M. Lee IBS, Daejeon, Republic of Korea J. Lee, J. Seo Vitzrotech Co., Ltd., Ansan City, Kyunggi-Do, Republic of Korea
	Niobium superconducting cavity is treated with high pressure rinsing to clean the inner surface of the cavity. Either organic or inorganic residues on the inner surface of the cavity can cause serious problems during the cavity operation. A thermal quenching - superconducting material loses its superconductivity - is a typical phenomenon brought out by harmful defects by increasing critical temperature. We have performed high pressure rinsing experiments to check out a prototype HPR machine. HPR experiments were performed with a simplified cavity structure, and analyzed as a function of the pressure, the distance from a nozzle, and the sizes of defects on the niobium surface. In this presentation, we will discuss the performance of the prototype HPR machine.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMB036
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WEPMB056	CVD Deposition of Nb Based Materials for SRF Cavities	SRF, lattice, superconductivity, accelerating-gradient	2241
	P. Pizzol, P. Chalker, T. Heil The University of Liverpool, Liverpool, United Kingdom 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
	Bulk niobium cavities are widely employed in particle accelerators to create high accelerating gradient despite their high material and operation cost. Advancements in technology have taken bulk niobium close to its theoretical operational limits, pushing the research to explore novel materials, such as niobium based alloys. Nitrides of niobium offer such an alternative, exhibiting a higher Tc compared to bulk niobium. Replacing then the niobium with a material with better thermal conductivity, such as copper, coated with thin films of nitrides in a multilayer S-I-S would lead to improved performance at reduced cost. Physical vapour deposition (PVD) is currently used to produce these coatings, but it suffers from lack of conformity. This issue can be resolved by using chemical vapour deposition (CVD), which is able to produce high quality coatings over surfaces with a high aspect ratio. This project explores the use of CVD techniques to deposit NbN thin films starting from their chlorinated precursors. The samples obtained are characterized via SEM, FIB, XRD, and EDX.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMB056
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WEPMB057	First Results of Magnetic Field Penetration Measurements on Multilayer S-I-S Structures	SRF, cavity, target, experiment	2245
	O.B. Malyshev, K.D. Dumbell, L. Gurran, N. Pattalwar, S.M. Pattalwar, R. Valizadeh STFC/DL/ASTeC, Daresbury, 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 O.B. Malyshev, S.M. Pattalwar, R. Valizadeh Cockcroft Institute, Warrington, Cheshire, United Kingdom
	The performance of superconducting RF cavities made of bulk Nb is limited by a breakdown field of Bp=~200 mT, close to the superheating field for Nb. A potentially promising solution to enhance the breakdown field of the SRF cavities beyond the intrinsic limits of Nb is a multilayer coating suggested in [1]. In the simplest case, such a multilayer may be a superconductor-insulator-superconductor (S-I-S) coating, for example, bulk niobium (S) coated with a thin film of insulator (I) followed by a thin layer of another superconductor (S) which could be e.g. dirty niobium [2]. Here we report the first results of our measurements of field penetration in Nb thin films and Nb-AlN-Nb multilayer samples at 4.2 K using the magnetic field penetration facility designed, built and tested in ASTeC.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMB057
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WEPMR002	Ultimate Gradient Limitation in Niobium Superconducting Accelerating Cavities	simulation, factory, SRF, cryogenics	2254
	M. Checchin, A. Grassellino, M. Martinello, S. Posen, A. Romanenko Fermilab, Batavia, Illinois, USA M. Checchin, M. Martinello Illinois Institute of Technology, Chicago, Illlinois, USA J. Zasadzinski IIT, Chicago, Illinois, USA
	Funding: Fermilab is operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy. The present study is addressed to the theoretical description of the ultimate gradient limitation in SRF cavities. Our intent is to exploit experimental data to confirm models which provide feed-backs on how to improve the current state-of-art. New theoretical insight on the cavities limiting factor can be suitable to improve the quench field of N-doped cavities, and therefore to take advantage of high Q0 at high gradients.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMR002
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WEPMR003	Tailoring Surface Impurity Content to Maximize Q-factors of Superconducting Resonators	cavity, superconductivity, simulation, factory	2258
	M. Martinello, M. Checchin, A. Grassellino, O.S. Melnychuk, S. Posen, A. Romanenko, D.A. Sergatskov Fermilab, Batavia, Illinois, USA M. Checchin, M. Martinello Illinois Institute of Technology, Chicago, Illlinois, USA J. Zasadzinski IIT, Chicago, Illinois, USA
	Funding: Fermilab is operated by Fermi Research Alliance, LLC under contract No. DE-AC02-07CH11359 with the United States Department of Energy. Quality factor of superconducting radio-frequency (SRF) cavities is degraded whenever magnetic flux is trapped in the cavity walls during the cooldown. In this contribution we study how the trapped flux sensitivity, defined as the trapped flux surface resistance normalized for the amount of flux trapped, depends on the mean free path. A variety of 1.3 GHz cavities with different surface treatments (EP, 120 C bake and different N-doping) were studied in order to cover the largest range of mean free path nowadays achievable, from few to thousands of nanometers. A bell shaped trend appears for the range of mean free path studied. Over doped cavities falls at the maximum of this curve defining the largest values of sensitivity. In addition, we have also studied the trend of the BCS surface resistance contribution as a function of mean free path, revealing that N-doped cavities follow close to the theoretical minimum of the BCS surface resistance as a function of the mean free path. Adding these results together we unveil that optimal N-doping treatment allows to maximize Q-factor at 2 K and 16 MV/m until the magnetic field fully trapped during the cavity cooldown stays below 10 mG.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMR003
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WEPMR009	Magnetic Flux Expulsion Studies in Niobium SRF Cavities	cavity, cryomodule, background, survey	2277
	S. Posen, M. Checchin, A.C. Crawford, A. Grassellino, M. Martinello, O.S. Melnychuk, A. Romanenko, D.A. Sergatskov, Y. Trenikhina Fermilab, Batavia, Illinois, USA
	With the recent discovery of nitrogen doping treatment for SRF cavities, ultra-high quality factors at medium accelerating fields are regularly achieved in vertical RF tests. To preserve these quality factors into the cryomodule, it is important to consider background magnetic fields, which can become trapped in the surface of the cavity during cooldown and cause Q₀ degradation. Building on the recent discovery that spatial thermal gradients during cooldown can significantly improve expulsion of magnetic flux, a detailed study was performed of flux expulsion on two cavities with different furnace treatments that are cooled in magnetic fields amplitudes representative of what is expected in a realistic cryomodule. In this contribution, we summarize these cavity results, in order to improve understanding of the impact of flux expulsion on cavity performance.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMR009
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WEPMR016	Vertical Electropolishing Studies at Cornell with KEK and Marui	cathode, cavity, target, SRF	2295
	F. Furuta, G.M. Ge, T. Gruber, J.J. Kaufman, J. Sears Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA V. Chouhan, Y.I. Ida, K.N. Nii, T.Y. Yamaguchi MGH, Hyogo-ken, Japan H. Hayano, S. Kato, T. Saeki KEK, Ibaraki, Japan
	Cornell's SRF group has developed Vertical Electro-Polishing (VEP) and applied on 1.3GHz Niobium SRF cavities as the primary surface treatment. High-Q and high voltage performances of VEP'ed SRF cavities had been successfully demonstrated at Cornell. In 2014, new VEP R&D collaboration has started between Cornell, KEK, and Marui Galvanizing Co. Ltd. (MGI). MGI and KEK has developed their original VEP cathode named 'i-cathode Ninja'® which has four retractable wing-shape parts per cell for single-/9-cell cavities. We will report the results of VEP process using 'i-cathode Ninja'® on single cell cavity at Cornell.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMR016
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WEPMR023	Surface Analysis Studies of Nb3Sn Thin Films	cavity, SRF, radio-frequency, electron	2316
	D.L. Hall, J.J. Kaufman, M. Liepe, J.T. Maniscalco Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	A recent study to optimise the coating of thin-film Nb3Sn cavities has resulted in coating procedures that can fabricate 1.3 GHz cavities capable of reproducibly achieving fields of >16 MV/m with record high Qs >10¹⁰ at 4.2 K. However, the performance of these next generation SRF cavities is as yet well below the theoretical maximum performance expected of Nb3Sn, thus giving ample room for further advancements. Current measurements strongly suggest that the current limits are due to local defects and irregularities in the coated surface. In this paper we analyse, using methods including SEM/EDS, TEM, XRD and EBSD, the surface of both sample coupons and cavity cut-outs, with a view to identifying and understanding the origin of surface non-uniformities that would lead to increased surface resistance and cavity quench.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMR023
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WEPMR024	RF Measurements on High Performance Nb3Sn Cavities	cavity, SRF, radio-frequency, accelerating-gradient	2320
	D.L. Hall, M. Liepe, J.T. Maniscalco Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	A single-cell 1.3 GHz ILC-shape thin-film Nb3Sn-on-Nb cavity recently achieved accelerating gradients of >16 MV/m with a record Q0 of approx. 2·10¹⁰ at 4.2 K, exceeding the power efficiency seen in the current most efficient niobium cavities. A concurrent study of the coating process has resulted in a coating procedure that is capable of replicating this performance in other single-cell cavities. In this paper we demonstrate the RF performance and behaviour of these next generation SRF cavities, with an emphasis on both the impact from both external magnetic fields and the cavity cool down procedure on cavity performance.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMR024
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WEPMR025	Improved N-Doping Protocols for SRF Cavities	simulation, cavity, SRF, radio-frequency	2323
	D. Gonnella, R.G. Eichhorn, F. Furuta, G.M. Ge, T. Gruber, G.H. Hoffstaetter, J.J. Kaufman, P.N. Koufalis, M. Liepe, J.T. Maniscalco Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: NSF, DOE Nitrogen-doping has been shown to consistently produce better quality factors in SRF cavities than is achievable with standard preparation techniques. Unfortunately, nitrogen-doping typically brings with it lower quench fields and higher sensitivities of residual resistance to trapped magnetic flux. Here we present work to understand these effects in hopes of mitigating them while maintaining the high Q desired by future projects. Using a nitrogen diffusion simulation, material parameters of nitrogen-doped cavities can be predicted prior to doping. These simulations results are consistent with SIMS data taken from samples treated with cavities. The nature of doping's effect on quench field has also been studied using CW and pulsed measurements. These results have allowed us to better understand the nature of nitrogen-doping and its effect on cavity performance.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMR025
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WEPMR026	RF Losses from Trapped Flux in SRF Cavities	cavity, vacuum, SRF, site	2327
	D. Gonnella, J.J. Kaufman, P.N. Koufalis, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: NSF Previous measurements at Cornell have shown that the sensitivity of residual resistance to trapped magnetic field in SRF cavities is heavily dependent on the mean free path of the RF penetration layer of the niobium. Here we report on a systematic study of ten cavity preparations with different mean free paths and the effect of these preparations on sensitivity to trapped magnetic flux. In the clean limit, longer mean free path leads to a lower sensitivity to trapped magnetic flux while in the dirty limit the opposite is true, shorter mean free path leads to lower sensitivity. These results are also shown to be in good agreement with theoretical predictions of RF losses due to oscillations of vortex lines.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMR026
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WEPMR027	Dependence of Surface Resistance on N-Doping Level	cavity, SRF, linac, radio-frequency	2331
	D. Gonnella, F. Furuta, G.M. Ge, J.J. Kaufman, P.N. Koufalis, M. Liepe, J.T. Maniscalco Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: NSF, DOE Nitrogen-doping has become a standard tool for reaching high quality factors in SRF cavities in the medium field region at 2 K. This high Q has been shown to be a result of lowering of the temperature dependent BCS resistance. Here we show that this lowering of the BCS resistance is due to interstitial nitrogen in the niobium lowering the mean free path. The BCS resistance extracted from experimental data is shown to be consistent with theoretical predictions from BCS theory; that there is an optimal doping of which the mean free path is lowered to about half the intrinsic coherence length. These results provide insight into understanding the mechanisms behind nitrogen-doping and allow us to more accurately predict doping parameters to reach optimal cavity performance.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMR027
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WEPMR028	Studies on the Field Dependence of the BCS Surface Resistance	cavity, SRF, experiment, radio-frequency	2335
	J.T. Maniscalco, D. Gonnella, G.H. Hoffstaetter, P.N. Koufalis, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Experiments have shown that the temperature-dependent portion of the RF surface resistance of SRF materials also exhibits a dependence on the magnitude of the surface field, manifested as a "Q-slope" or "anti-Q-slope" in the medium field region. Recent theoretical work proposes an explanation of the anti-Q-slope in dirty-limit superconductors. In this report, we compare theoretical predictions with the results of systematic experimental studies on the RF field dependence of the surface resistance using 1.3 GHz niobium SRF cavities with a wide range of mean free paths. We find very good agreement between theory and experiment in the dirty limit, with some divergence as the cavities approach the clean limit.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMR028
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WEPMR029	New Material Studies in the Cornell Sample Host Cavity	cavity, SRF, superconducting-RF, vacuum	2338
	J.T. Maniscalco, D.L. Hall, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA O.B. Malyshev, R. Valizadeh, S. Wilde STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom S. Wilde Loughborough University, Loughborough, Leicestershire, United Kingdom
	Cornell has developed a TE mode sample host microwave cavity in order to study large, flat samples of novel SRF materials. In recent calibration tests, the cavity was shown to reach peak magnetic fields on the sample plate of >100 mT and a quality factor Q₀ greater than 10¹⁰, making it a powerful system to study the performance of superconductors at high RF fields with nOhms sensitivity. In this report we present results of measurements of two samples of thin-film Nb deposited on Cu using HiPIMS at 500 C and at 800 C.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMR029
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WEPMR030	Pulsed Field Limits in SRF Cavities	cavity, SRF, klystron, factory	2341
	J.T. Maniscalco, D. Gonnella, D.L. Hall, P.N. Koufalis, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	High-power pulsed (HPP) measurements of SRF cavities offer several different avenues of experimentation from standard continuous wave (CW) measurements by probing higher fields and reducing thermal effects. In this paper we report upon recent measurements of N-doped Nb and Nb3Sn cavities, investigating the limitations of the superheating field, flux entry field, and other maximum fields. We also investigate the potential of these materials for operation in a pulsed accelerator, which would partially or fully mitigate the effects of defects (i.e. thermal quenches).
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMR030
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WEPMR033	Observation of Stable Low Surface Resistance in Large-Grain Niobium SRF Cavities	cavity, SRF, vacuum, site	2344
	R.L. Geng JLab, Newport News, Virginia, USA S.C. Huang IMP/CAS, Lanzhou, People's Republic of China
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. Low surface resistance, or high unloaded quality factor (Q0), superconducting radio frequency (SRF) cavities are being pursued actively nowadays as their application in large-scale CW SRF accelerators can save capital and operational cost in cryogenics. There are different options in realization of such cavities. One of them is the large-grain (LG) niobium cavity. In this contribution, we present new experimental results in evaluation of LG niobium cavities cooled down in the presence of an external magnetic field. High Q0 values are achieved even with an ambient magnetic field of up to 100 mG. More over, it is observed that these high Q0 values are super-robust against repeated quench, literally not affected at all after the cavity being deliberately quenched for hundreds of times in the presence of an ambient magnetic field of up to 200 mG.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMR033
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THOBB02	Impurity Doping of Superconducting Radio Frequency Cavities	cavity, vacuum, SRF, radio-frequency	3195
	P.N. Koufalis, F. Furuta, G.M. Ge, D. Gonnella, J.J. Kaufman, M. Liepe, J.T. Maniscalco Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: NSF PHYS-1416318 Impurity doping of bulk-niobium superconducting radio frequency (SRF) cavities is a relatively new field of study and the underlying physics is not yet fully understood. Previous studies have shown an increase in the intrinsic quality factor and the corresponding decrease of the temperature-dependent component of the surface resistance of nitrogen-doped cavities with increasing accelerating field.* Here we investigate the effects of alternative inert dopants on the surface resistance and thus the intrinsic quality factor of SRF cavities in pursuit of the optimal dopant and doping level. A. Grassellino et al., Nitrogen and Argon Doping of Niobium for Superconducting Radio Frequency Cavities. Supercond. Sci. Technol., 26(102001), 2013
	Slides THOBB02 [4.048 MB]
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-THOBB02
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THPMY024	Upgrade of a UHV Furnace for 1700 C Heat Treatment and Processing of Niobium Samples	vacuum, power-supply, radiation, radio-frequency	3709
	J. Conrad, L. Alff, R. Grewe, T. Kürzeder, M. Major, N. Pietralla TU Darmstadt, Darmstadt, Germany F. Hug IKP, Mainz, Germany S.T. Sievers MIT, Marburg, Germany
	Funding: Supported by the German Federal Ministry for Education and Research (BMBF) under Grant No. 05H15RDRBA In 2005 a high temperature vacuum furnace was put into operation at the Institute for Nuclear Physics at the Technische Universität Darmstadt. It has been designed for firing pure Niobium at temperatures of up to 1870 C. Until now several Nb cavities have been heat treated at 850 C with a proven record of success. The current focus of research in improving the superconductive characteristics of accelerator cavities is on new materials such as Nb3Sn or NbN or on the doping of Nb surfaces with nitrogen, so called N2-Doping. The surface preparations generally take place at temperatures of not more than 1000 C. To study phenomena that occur at higher temperatures, like the formation of delta-phase NbN at 1300 to 1700 C, it is planned to refurbish the UHV furnace and use it for corresponding studies. We will report on the design of a new annealing pot and a sample holder and give a review on our first experiences with the upgraded furnace.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-THPMY024
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Status of the Superconducting Cryomodules and Cryogenic System for the Mainz Energy-recovering Superconducting Accelerator MESA

cryomodule, HOM, electron, operation

2134

T. Stengler, K. Aulenbacher, F. Hug, D. Simon, P. Weber
IKP, Mainz, Germany
F. Schlander
ESS, Lund, Sweden
N. Wiehl
Johannes Gutenberg University Mainz, Institut of Nuclear Chemistry, Mainz, Germany

Funding: Work supported by the German Research Foundation (DFG) under the Cluster of Excellence "PRISMA"
SRF and the cryogenic system are mandatory for the operation of MESA at the Institut für Kernphysik at Johannes Gutenberg-Universität Mainz. The cryomodule production project is running for one year right now and the recent developments and measurements are presented. Further on the cryogenic concept required for the operation of MESA will be discussed.

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WEPMB012

Production and Investigation of Superconducting 9-Cell Cavity Made of Large Grain Nb in KEK

cavity, SRF, accelerating-gradient, electron

2141

T. Dohmae, H. Inoue, K. Umemori, Y. Watanabe, M. Yamanaka
KEK, Ibaraki, Japan

For CW operation of superconducting cavity, reduction of heat load at cavity surface is one of important topics, since generated heat load is much higher than that of pulse wave. Using Large Grain (LG) Nb for superconducting cavity has possibility to reach higher Q0 than using Fine Grain Nb, which reduces heat load to 2K Helium. KEK Cavity Fabrication Facility(CFF) group had successfully produced superconducting 1-cell cavity made of LG Nb in 2013, and reached high Q0 at the vertical test (maximum field of 45 MV/m). Then, KEK CFF group started producing first superconducting 9-cell LG cavity in 2015, which will be completed in the end of December 2015. Whole processes of producing this cavity from sliced Nb are done in KEK. In this report, process flow and strategies of producing 9-cell cavity and results of vertical test will be presented in detail.

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WEPMB023

Hydroforming SRF Three-cell Cavity from Seamless Niobium Tube

cavity, accelerating-gradient, SRF, superconductivity

2170

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

We are developing the manufacturing method for superconducting radio frequency (SRF) cavities by using a hydroforming instead of using conventional electron beam welding. We expect higher reliability and reduced cost with hydroforming. For successful hydroforming, high-purity seamless niobium tubes with good formability as well as advancing the hydroforming technique are necessary. Using a seamless niobium tube from ATI Wah Chang, we were able to successfully hydroform a 1.3 GHz three-cell TESLA-like cavity and obtained an Eacc of 32 MV/m. A barrel polishing process was omitted after the hydroforming. The vertical test was carried out with very rough inside surface. We got amazing and interesting result.

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WEPMB029

Research of Nitrogen Doping at IHEP

cavity, vacuum, experiment, electron

2186

P. Sha
Institute of High Energy Physics (IHEP), Chinese Academy of Sciences, Beijing, People's Republic of China
J.P. Dai
IHEP, Beijing, People's Republic of China
F. Jiao
PKU, Beijing, People's Republic of China

Funding: Work funded by National Natural Science Foundation of China, Grant No. 11505197
Recently, nitrogen doping (N-doping) technology has been proved to increase Q0 of superconducting cavity obviously, which lowers the BCS surface resistance. After N-doping, Q0 of 9-cell 1.3 GHz cavity can be increased to 3*10¹⁰ at Eacc = 16 MV/m, while 1.5*1010 without N-doping [1]. Since 2013, there have been over 60 cavities nitrogen doped at FNAL, JLAB and Cornell. The Circular Electron Collider (CEPC) has been proposed by IHEP in China, while requests Q0=4e10@Eacc=15.5 MV/m for 650 MHz cavity. It's hard to achieve without N-doping. So research of N-doping was begun in cooperation with Peking University in early 2015. Experiments of niobium samples have showed that nitrogen concentration at niobium surface increased a lot after N-doping. After then, several single-cell 1.3 GHz cavities completed vertical tests, but there're no successful test results of Q0 increasing, yet.

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WEPMB032

Fabrication and Testing Status of IHEP03

cavity, SRF, superconducting-RF, status

2194

T.X. Zhao, J. Gao, S. Jin, Z.Q. Li, Y.L. Liu, Z.C. Liu, Y. Wang, J.Y. Zhai, H.J. Zheng
IHEP, Beijing, People's Republic of China
M. Asano, E. Kako
KEK, Ibaraki, Japan
H. Yu, H. Yuan
BIAM, Beijing, People's Republic of China

After the successful development of the IHEP01 and IHEP02 1.3GHz 9cell superconducting cavity, we developed a 1.3GHz Tesla-Like 9cell superconducting cavities in collaboration with KEK. The cavity was made by niobium material produced in OTIC, Ningxia, China. After completeing welding, leakage check, BCP, HPR, we sent the cavity to KEK and used the standard procedures of ILC cavity for processing. These include electron polishing, vacuum furnace outgassing, tuning for field flatness and frequency, light EP, baking and vertical test. We target to have a high Q0 cavity for this experiment. In this paper, we will report the experimental status of the IHEP03 cavity.

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WEPMB034

Analysis of Niobium Quality Control for SRF Cavity

cavity, SRF, controls, radio-frequency

2197

M.J. Joung
IBS, Daejeon, Republic of Korea

Funding: the Ministry of Science, ICT and Future Planning (MSIP) and the National Research Foundation (NRF) of the Republic of Korea under Contract 2013M7A1A1075764.
Clean and smooth surface is important to get low sur-face resistance for superconducting material. SRF (Super-conducting Radio Frequency) cavity made of niobium which is superconducting material and also one of the rare metal. The procedure of niobium quality control was set up to get high performance SRF cavity. The procedure consists of three parts; certificates check, Nb specification verification, and surface inspection and measurements of thickness, roughness, flatness. Three important properties which are RRR value, chemical composition and me-chanical properties were verified to conform Nb specifica-tion. The range of thickness, roughness and flatness for niobium as SRF cavity raw material were obtained by measurement.

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WEPMB036

High Pressure Rinsing for Niobium Superconducting Cavity

cavity, target, SRF, operation

2202

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

Niobium superconducting cavity is treated with high pressure rinsing to clean the inner surface of the cavity. Either organic or inorganic residues on the inner surface of the cavity can cause serious problems during the cavity operation. A thermal quenching - superconducting material loses its superconductivity - is a typical phenomenon brought out by harmful defects by increasing critical temperature. We have performed high pressure rinsing experiments to check out a prototype HPR machine. HPR experiments were performed with a simplified cavity structure, and analyzed as a function of the pressure, the distance from a nozzle, and the sizes of defects on the niobium surface. In this presentation, we will discuss the performance of the prototype HPR machine.

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WEPMB056

CVD Deposition of Nb Based Materials for SRF Cavities

SRF, lattice, superconductivity, accelerating-gradient

2241

P. Pizzol, P. Chalker, T. Heil
The University of Liverpool, Liverpool, United Kingdom
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

Bulk niobium cavities are widely employed in particle accelerators to create high accelerating gradient despite their high material and operation cost. Advancements in technology have taken bulk niobium close to its theoretical operational limits, pushing the research to explore novel materials, such as niobium based alloys. Nitrides of niobium offer such an alternative, exhibiting a higher Tc compared to bulk niobium. Replacing then the niobium with a material with better thermal conductivity, such as copper, coated with thin films of nitrides in a multilayer S-I-S would lead to improved performance at reduced cost. Physical vapour deposition (PVD) is currently used to produce these coatings, but it suffers from lack of conformity. This issue can be resolved by using chemical vapour deposition (CVD), which is able to produce high quality coatings over surfaces with a high aspect ratio. This project explores the use of CVD techniques to deposit NbN thin films starting from their chlorinated precursors. The samples obtained are characterized via SEM, FIB, XRD, and EDX.

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WEPMB057

First Results of Magnetic Field Penetration Measurements on Multilayer S-I-S Structures

SRF, cavity, target, experiment

2245

O.B. Malyshev, K.D. Dumbell, L. Gurran, N. Pattalwar, S.M. Pattalwar, R. Valizadeh
STFC/DL/ASTeC, Daresbury, 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
O.B. Malyshev, S.M. Pattalwar, R. Valizadeh
Cockcroft Institute, Warrington, Cheshire, United Kingdom

The performance of superconducting RF cavities made of bulk Nb is limited by a breakdown field of Bp=~200 mT, close to the superheating field for Nb. A potentially promising solution to enhance the breakdown field of the SRF cavities beyond the intrinsic limits of Nb is a multilayer coating suggested in [1]. In the simplest case, such a multilayer may be a superconductor-insulator-superconductor (S-I-S) coating, for example, bulk niobium (S) coated with a thin film of insulator (I) followed by a thin layer of another superconductor (S) which could be e.g. dirty niobium [2]. Here we report the first results of our measurements of field penetration in Nb thin films and Nb-AlN-Nb multilayer samples at 4.2 K using the magnetic field penetration facility designed, built and tested in ASTeC.

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WEPMR002

Ultimate Gradient Limitation in Niobium Superconducting Accelerating Cavities

simulation, factory, SRF, cryogenics

2254

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

Funding: Fermilab is operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy.
The present study is addressed to the theoretical description of the ultimate gradient limitation in SRF cavities. Our intent is to exploit experimental data to confirm models which provide feed-backs on how to improve the current state-of-art. New theoretical insight on the cavities limiting factor can be suitable to improve the quench field of N-doped cavities, and therefore to take advantage of high Q0 at high gradients.

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WEPMR003

Tailoring Surface Impurity Content to Maximize Q-factors of Superconducting Resonators

cavity, superconductivity, simulation, factory

2258

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

Funding: Fermilab is operated by Fermi Research Alliance, LLC under contract No. DE-AC02-07CH11359 with the United States Department of Energy.
Quality factor of superconducting radio-frequency (SRF) cavities is degraded whenever magnetic flux is trapped in the cavity walls during the cooldown. In this contribution we study how the trapped flux sensitivity, defined as the trapped flux surface resistance normalized for the amount of flux trapped, depends on the mean free path. A variety of 1.3 GHz cavities with different surface treatments (EP, 120 C bake and different N-doping) were studied in order to cover the largest range of mean free path nowadays achievable, from few to thousands of nanometers. A bell shaped trend appears for the range of mean free path studied. Over doped cavities falls at the maximum of this curve defining the largest values of sensitivity. In addition, we have also studied the trend of the BCS surface resistance contribution as a function of mean free path, revealing that N-doped cavities follow close to the theoretical minimum of the BCS surface resistance as a function of the mean free path. Adding these results together we unveil that optimal N-doping treatment allows to maximize Q-factor at 2 K and 16 MV/m until the magnetic field fully trapped during the cavity cooldown stays below 10 mG.

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WEPMR009

Magnetic Flux Expulsion Studies in Niobium SRF Cavities

cavity, cryomodule, background, survey

2277

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

With the recent discovery of nitrogen doping treatment for SRF cavities, ultra-high quality factors at medium accelerating fields are regularly achieved in vertical RF tests. To preserve these quality factors into the cryomodule, it is important to consider background magnetic fields, which can become trapped in the surface of the cavity during cooldown and cause Q₀ degradation. Building on the recent discovery that spatial thermal gradients during cooldown can significantly improve expulsion of magnetic flux, a detailed study was performed of flux expulsion on two cavities with different furnace treatments that are cooled in magnetic fields amplitudes representative of what is expected in a realistic cryomodule. In this contribution, we summarize these cavity results, in order to improve understanding of the impact of flux expulsion on cavity performance.

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WEPMR016

Vertical Electropolishing Studies at Cornell with KEK and Marui

cathode, cavity, target, SRF

2295

F. Furuta, G.M. Ge, T. Gruber, J.J. Kaufman, J. Sears
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
V. Chouhan, Y.I. Ida, K.N. Nii, T.Y. Yamaguchi
MGH, Hyogo-ken, Japan
H. Hayano, S. Kato, T. Saeki
KEK, Ibaraki, Japan

Cornell's SRF group has developed Vertical Electro-Polishing (VEP) and applied on 1.3GHz Niobium SRF cavities as the primary surface treatment. High-Q and high voltage performances of VEP'ed SRF cavities had been successfully demonstrated at Cornell. In 2014, new VEP R&D collaboration has started between Cornell, KEK, and Marui Galvanizing Co. Ltd. (MGI). MGI and KEK has developed their original VEP cathode named 'i-cathode Ninja'® which has four retractable wing-shape parts per cell for single-/9-cell cavities. We will report the results of VEP process using 'i-cathode Ninja'® on single cell cavity at Cornell.

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WEPMR023

Surface Analysis Studies of Nb3Sn Thin Films

cavity, SRF, radio-frequency, electron

2316

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

A recent study to optimise the coating of thin-film Nb3Sn cavities has resulted in coating procedures that can fabricate 1.3 GHz cavities capable of reproducibly achieving fields of >16 MV/m with record high Qs >10¹⁰ at 4.2 K. However, the performance of these next generation SRF cavities is as yet well below the theoretical maximum performance expected of Nb3Sn, thus giving ample room for further advancements. Current measurements strongly suggest that the current limits are due to local defects and irregularities in the coated surface. In this paper we analyse, using methods including SEM/EDS, TEM, XRD and EBSD, the surface of both sample coupons and cavity cut-outs, with a view to identifying and understanding the origin of surface non-uniformities that would lead to increased surface resistance and cavity quench.

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WEPMR024

RF Measurements on High Performance Nb3Sn Cavities

cavity, SRF, radio-frequency, accelerating-gradient

2320

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

A single-cell 1.3 GHz ILC-shape thin-film Nb3Sn-on-Nb cavity recently achieved accelerating gradients of >16 MV/m with a record Q0 of approx. 2·10¹⁰ at 4.2 K, exceeding the power efficiency seen in the current most efficient niobium cavities. A concurrent study of the coating process has resulted in a coating procedure that is capable of replicating this performance in other single-cell cavities. In this paper we demonstrate the RF performance and behaviour of these next generation SRF cavities, with an emphasis on both the impact from both external magnetic fields and the cavity cool down procedure on cavity performance.

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WEPMR025

Improved N-Doping Protocols for SRF Cavities

simulation, cavity, SRF, radio-frequency

2323

D. Gonnella, R.G. Eichhorn, F. Furuta, G.M. Ge, T. Gruber, G.H. Hoffstaetter, J.J. Kaufman, P.N. Koufalis, M. Liepe, J.T. Maniscalco
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: NSF, DOE
Nitrogen-doping has been shown to consistently produce better quality factors in SRF cavities than is achievable with standard preparation techniques. Unfortunately, nitrogen-doping typically brings with it lower quench fields and higher sensitivities of residual resistance to trapped magnetic flux. Here we present work to understand these effects in hopes of mitigating them while maintaining the high Q desired by future projects. Using a nitrogen diffusion simulation, material parameters of nitrogen-doped cavities can be predicted prior to doping. These simulations results are consistent with SIMS data taken from samples treated with cavities. The nature of doping's effect on quench field has also been studied using CW and pulsed measurements. These results have allowed us to better understand the nature of nitrogen-doping and its effect on cavity performance.

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WEPMR026

RF Losses from Trapped Flux in SRF Cavities

cavity, vacuum, SRF, site

2327

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

Funding: NSF
Previous measurements at Cornell have shown that the sensitivity of residual resistance to trapped magnetic field in SRF cavities is heavily dependent on the mean free path of the RF penetration layer of the niobium. Here we report on a systematic study of ten cavity preparations with different mean free paths and the effect of these preparations on sensitivity to trapped magnetic flux. In the clean limit, longer mean free path leads to a lower sensitivity to trapped magnetic flux while in the dirty limit the opposite is true, shorter mean free path leads to lower sensitivity. These results are also shown to be in good agreement with theoretical predictions of RF losses due to oscillations of vortex lines.

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WEPMR027

Dependence of Surface Resistance on N-Doping Level

cavity, SRF, linac, radio-frequency

2331

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

Funding: NSF, DOE
Nitrogen-doping has become a standard tool for reaching high quality factors in SRF cavities in the medium field region at 2 K. This high Q has been shown to be a result of lowering of the temperature dependent BCS resistance. Here we show that this lowering of the BCS resistance is due to interstitial nitrogen in the niobium lowering the mean free path. The BCS resistance extracted from experimental data is shown to be consistent with theoretical predictions from BCS theory; that there is an optimal doping of which the mean free path is lowered to about half the intrinsic coherence length. These results provide insight into understanding the mechanisms behind nitrogen-doping and allow us to more accurately predict doping parameters to reach optimal cavity performance.

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WEPMR028

Studies on the Field Dependence of the BCS Surface Resistance

cavity, SRF, experiment, radio-frequency

2335

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

Experiments have shown that the temperature-dependent portion of the RF surface resistance of SRF materials also exhibits a dependence on the magnitude of the surface field, manifested as a "Q-slope" or "anti-Q-slope" in the medium field region. Recent theoretical work proposes an explanation of the anti-Q-slope in dirty-limit superconductors. In this report, we compare theoretical predictions with the results of systematic experimental studies on the RF field dependence of the surface resistance using 1.3 GHz niobium SRF cavities with a wide range of mean free paths. We find very good agreement between theory and experiment in the dirty limit, with some divergence as the cavities approach the clean limit.

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WEPMR029

New Material Studies in the Cornell Sample Host Cavity

cavity, SRF, superconducting-RF, vacuum

2338

J.T. Maniscalco, D.L. Hall, M. Liepe
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
O.B. Malyshev, R. Valizadeh, S. Wilde
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
S. Wilde
Loughborough University, Loughborough, Leicestershire, United Kingdom

Cornell has developed a TE mode sample host microwave cavity in order to study large, flat samples of novel SRF materials. In recent calibration tests, the cavity was shown to reach peak magnetic fields on the sample plate of >100 mT and a quality factor Q₀ greater than 10¹⁰, making it a powerful system to study the performance of superconductors at high RF fields with nOhms sensitivity. In this report we present results of measurements of two samples of thin-film Nb deposited on Cu using HiPIMS at 500 C and at 800 C.

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WEPMR030

Pulsed Field Limits in SRF Cavities

cavity, SRF, klystron, factory

2341

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

High-power pulsed (HPP) measurements of SRF cavities offer several different avenues of experimentation from standard continuous wave (CW) measurements by probing higher fields and reducing thermal effects. In this paper we report upon recent measurements of N-doped Nb and Nb3Sn cavities, investigating the limitations of the superheating field, flux entry field, and other maximum fields. We also investigate the potential of these materials for operation in a pulsed accelerator, which would partially or fully mitigate the effects of defects (i.e. thermal quenches).

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WEPMR033

Observation of Stable Low Surface Resistance in Large-Grain Niobium SRF Cavities

cavity, SRF, vacuum, site

2344

R.L. Geng
JLab, Newport News, Virginia, USA
S.C. Huang
IMP/CAS, Lanzhou, People's Republic of China

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
Low surface resistance, or high unloaded quality factor (Q0), superconducting radio frequency (SRF) cavities are being pursued actively nowadays as their application in large-scale CW SRF accelerators can save capital and operational cost in cryogenics. There are different options in realization of such cavities. One of them is the large-grain (LG) niobium cavity. In this contribution, we present new experimental results in evaluation of LG niobium cavities cooled down in the presence of an external magnetic field. High Q0 values are achieved even with an ambient magnetic field of up to 100 mG. More over, it is observed that these high Q0 values are super-robust against repeated quench, literally not affected at all after the cavity being deliberately quenched for hundreds of times in the presence of an ambient magnetic field of up to 200 mG.

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reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMR033

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THOBB02

Impurity Doping of Superconducting Radio Frequency Cavities

cavity, vacuum, SRF, radio-frequency

3195

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

Funding: NSF PHYS-1416318
Impurity doping of bulk-niobium superconducting radio frequency (SRF) cavities is a relatively new field of study and the underlying physics is not yet fully understood. Previous studies have shown an increase in the intrinsic quality factor and the corresponding decrease of the temperature-dependent component of the surface resistance of nitrogen-doped cavities with increasing accelerating field.* Here we investigate the effects of alternative inert dopants on the surface resistance and thus the intrinsic quality factor of SRF cavities in pursuit of the optimal dopant and doping level.
A. Grassellino et al., Nitrogen and Argon Doping of Niobium for Superconducting Radio Frequency Cavities. Supercond. Sci. Technol., 26(102001), 2013

Slides THOBB02 [4.048 MB]

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reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-THOBB02

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THPMY024

Upgrade of a UHV Furnace for 1700 C Heat Treatment and Processing of Niobium Samples

vacuum, power-supply, radiation, radio-frequency

3709

J. Conrad, L. Alff, R. Grewe, T. Kürzeder, M. Major, N. Pietralla
TU Darmstadt, Darmstadt, Germany
F. Hug
IKP, Mainz, Germany
S.T. Sievers
MIT, Marburg, Germany

Funding: Supported by the German Federal Ministry for Education and Research (BMBF) under Grant No. 05H15RDRBA
In 2005 a high temperature vacuum furnace was put into operation at the Institute for Nuclear Physics at the Technische Universität Darmstadt. It has been designed for firing pure Niobium at temperatures of up to 1870 C. Until now several Nb cavities have been heat treated at 850 C with a proven record of success. The current focus of research in improving the superconductive characteristics of accelerator cavities is on new materials such as Nb3Sn or NbN or on the doping of Nb surfaces with nitrogen, so called N2-Doping. The surface preparations generally take place at temperatures of not more than 1000 C. To study phenomena that occur at higher temperatures, like the formation of delta-phase NbN at 1300 to 1700 C, it is planned to refurbish the UHV furnace and use it for corresponding studies. We will report on the design of a new annealing pot and a sample holder and give a review on our first experiences with the upgraded furnace.

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reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-THPMY024

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