SRF2017 - List of Keywords (SRF)

Paper	Title	Other Keywords	Page
MOYA01	The Superconducting Accelerator for the ESS Project	ion, cavity, cryomodule, linac	24
	F. Schlander, C. Darve, N. Elias, M. Lindroos, C.G. Maiano ESS, Lund, Sweden P. Bosland CEA/IRFU, Gif-sur-Yvette, France M. Ellis STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom P. Michelato INFN/LASA, Segrate (MI), Italy G. Olry IPN, Orsay, France R.J.M.Y. Ruber Uppsala University, Uppsala, Sweden
	The European Spallation Source, ESS, is under construction in Lund since 2014. While the installation of the source and the normal conducting part will start in this autumn, the production and testing of cryomodules and cavities for the superconducting accelerator is in full swing at the partner laboratories. The spoke cavities and cryomodules will be provided by IPN Orsay and the testing of those modules will take place at Uppsala University. Prototyping and assembly of the elliptical cryomodules series is occurring at CEA Saclay, and the modules will be tested at a new test stand at ESS. The fabrication and test of the medium beta cavities is provided by INFN Milan and STFC Daresbury for the high beta cavities respectively. An overview of the current activities and test results will be presented in this talk.
	Slides MOYA01 [26.361 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOYA01
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MOYA02	BESSY VSR: SRF Challenges and Developments for a Variable-pulse Length Next-generation Light Source	ion, cavity, HOM, synchrotron	29
	A.V. Vélez, H.-W. Glock, F. Glöckner, B.D.S. Hall, J. Knobloch, A. Neumann, P. Schnizer, E. Sharples HZB, Berlin, Germany A.V. Tsakanian Helmholtz-Zentrum Berlin für Materialien und Energie GmbH (HZB), Berlin, Germany
	The BESSY VSR project represents an exciting alternative to diffraction limited storage rings in the development of a next generation light source. Such a system should be capable to store "standard" (some 10 ps long) and "short" (ps and sub-ps long) pulses simultaneously in the storage ring opening the door to picosecond dynamic and high-resolution experiments at the same facility. This unique feature can be created by the introduction of the beating effects produced by higher harmonic SRF cavity systems (1.5 GHz & 1.75 GHz). The challenging design specifications as well as the technological demands on the SRF system make BESSY VSR a defiant project where non-standard techniques such as waveguide-damped cavities have been further developed. This talk focuses on the new SRF developments that includes wveguide-damped cavities, high-power couplers and higher-order mode absorbers that must handle nearly 2 kW of HOM power. The cryomodule design and its interaction with the beam will also be discussed. Comment: VSR concept was introduced at SRF15. Much development work has now been done. Here the focus is more one the technology of VSR and the talk could also be listed under "SRF technology R&D"
	Slides MOYA02 [7.961 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOYA02
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MOPB003	A New High Resolution Optical System for Inspection of Gun-and Multi-cell Resonators in ISO-4 Cleanrooms	ion, cavity, gun, MMI	47
	M. Schalwat, R. Bandelmann, A. Daniel, N. Krupka, A. Matheisen, S.T. Sievers DESY, Hamburg, Germany
	Optical inspection of the inner surface of superconducting resonators was established during European XFEL cavity production by usage of the so called OBACHT optical inspection. In addition to the surface inspection by OBACHT a new optical inspection system with integrated high resolution camera is set up at DESY. It allows inspection of multi-cell resonators as well as gun cavity resonators with only single side accessibility to the inner surface. A prototype was commissioned and optical inspections were done with OBACHT and the new system in parallel. Two SRF gun cavities were inspected by this optical system and origin of limitations of the resonators were identified.
	Poster MOPB003 [0.220 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOPB003
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MOPB009	Progress of 650 MHz SRF Cavity for eRHIC SRF Linac	cavity, ion, HOM, linac	64
	W. Xu, I. Ben-Zvi, Y. Gao, D. Holmes, P. Kolb, G.T. McIntyre, C. Pai, R. Porqueddu, K.S. Smith, R. Than, J.E. Tuozzolo, F.J. Willeke, A. Zaltsman BNL, Upton, Long Island, New York, USA I. Ben-Zvi Stony Brook University, Stony Brook, USA
	Funding: This work is supported by LDRD program of Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. DOE. eRHIC ERL SRF requires 160 5-cell 650 MHz SRF cavities. The 650 MHz cavity has been designed and two prototypes have been fabricated, one Cu cavity for HOM study and one Nb cavity for cavity performance study. This paper will describe cavity design and the progress of prototyping.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOPB009
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MOPB012	Status of the IFMIF LIPAc SRF Linac	ion, cavity, cryomodule, operation	74
	N. Bazin, C. Boulch, A. Bruniquel, P. Carbonnier, J.K. Chambrillon, G. Devanz, F. Éozénou, P. Hardy, H. Jenhani, O. Piquet, J. Plouin, A. Riquelme, D. Roudier, C. Servouin CEA/DRF/IRFU, Gif-sur-Yvette, France P. Charon, S. Chel, G. Disset, L. Maurice, J. Relland, B. Renard CEA/IRFU, Gif-sur-Yvette, France P. Contrepois CEA/DSM/IRFU, France D. Regidor, F. Toral CIEMAT, Madrid, Spain
	The IFMIF accelerator aims to provide an accelerator-based D-Li neutron source to produce high intensity high energy neutron flux to test samples as possible candidate materials to a full lifetime of fusion energy reactors. A prototype of the low energy part of the accelerator is under construction at Rokkasho in Japan. It includes one cryomodule containing 8 half-wave resonators (HWR) operating at 175 MHz and eight focusing solenoids. This paper presents the status of the IFMIF SRF Linac.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOPB012
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MOPB013	European XFEL Input Coupler Experiences and Challenges in a Test Field	ion, FEL, GUI, operation	78
	F. Hoffmann, D. Kostin, W.-D. Möller, D. Reschke, M. Wiencek DESY, Hamburg, Germany
	102 European XFEL accelerating modules with 816 superconducting cavities and main input RF power couplers were assembled and then tested at DESY prior to installation in the European XFEL tunnel. In the Accelerating Module Test Facility (AMTF) warm and cold RF tests were done. The test results went directly to the operational setup for the LINAC. Main input couplers did present several problems during the tests, resulting in some minor coupler design changes as well as in a few repair actions. The experience got from the said testing operation is worth to be shared and is presented here together with a discussion.
	Poster MOPB013 [0.648 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOPB013
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MOPB018	Testing of SRF Cavities and Cryomodules for the European Spallation Source	ion, cavity, cryomodule, linac	95
	N. Elias, E. Asensi Conejero, C. Darve, N.F. Hakansson, W. Hees, C.G. Maiano, F. Schlander ESS, Lund, Sweden
	The European Spallation Source (ESS) is currently under construction in Lund, Sweden. The ESS linear accelerator aims to deliver a 62.5 mA , 2.86 ms long proton beam onto a rotating tungsten target, at 14 Hz repetition rate, thus achieving an energy of 2 GeV and 5 MW power. Most of the beam acceleration happens in the superconducting fraction of the linac, which is composed of three sectors of cryomodules named after the cavities housed within. The first sector of the SRF linac is composed of 13 Spoke cryomodules containing 2 double-spoke cavities with a geometric beta of 0.5, the second is composed of 9 medium beta cryomodules each housing four elliptical cavities (β=0.67) and finally 21 high beta cryomodules enclosing four elliptical cavities (β=0.86). ESS has strategically built up a SRF collaboration with other European institutions, these partners will deliver through In-Kind agreements cavities and cryomodules performing within the ESS specification. This article describes the process leading to the acceptance of cavities and cryomodules received from the different partners and the necessary testing required prior to the final installation in the ESS tunnel.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOPB018
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MOPB023	Further Layout Investigations for a Superconducting CW-linac for Heavy Ions at GSI	ion, linac, cavity, heavy-ion	108
	W.A. Barth, K. Aulenbacher, F.D. Dziuba, V. Gettmann, T. Kürzeder, M. Miski-Oglu HIM, Mainz, Germany K. Aulenbacher IKP, Mainz, Germany W.A. Barth, M. Heilmann, S. Yaramyshev GSI, Darmstadt, Germany W.A. Barth, S. Yaramyshev MEPhI, Moscow, Russia M. Basten, H. Podlech, M. Schwarz IAP, Frankfurt am Main, Germany
	Very compact accelerating-focusing structures, as well as short focusing periods, high accelerating gradients and very short drift spaces are strongly required for superconducting (sc) accelerator sections operating at low and medium beam energies. To keep the GSI-Super Heavy Element program competitive on a high level and even beyond, a standalone sc continuous wave Linac in combination with the GSI High Charge State injector, upgraded for cw-operation, is envisaged. The first LINAC section (financed by HIM and GSI) as a demonstration of the capability of 216 MHz multi gap Crossbar H-structures (CH) is still in the beam commissioning phase, while an accelerating gradient of 9.6 MV/m (4 K) at a sufficient quality factor has been already reached. Recently the overall Linac design, based on a standard cryomodule, comprising three CH cavities, a rebuncher section and two 9.3 T-solenoidal lenses, has to be fixed. This paper presents the status of the Linac layout studies as well as the integration in the GSI accelerator facility.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOPB023
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MOPB031	Fabrication and Cold Test Result of FRIB β=0.53 Pre-production Cryomodule	ion, cavity, cryomodule, solenoid	120
	H. Ao, J. Asciutto, B. Bird, N.K. Bultman, E.E. Burkhardt, F. Casagrande, C. Compton, K.D. Davidson, K. Elliott, A. Ganshyn, I. Grender, W. Hartung, L. Hodges, I.M. Malloch, S.J. Miller, D.G. Morris, P.N. Ostroumov, J.T. Popielarski, L. Popielarski, M.A. Reaume, K. Saito, M. Shuptar, S. Stark, J.D. Wenstrom, M. Xu, T. Xu, Z. Zheng FRIB, East Lansing, USA A. Facco INFN/LNL, Legnaro (PD), Italy
	Funding: Work supported by the U.S. Department of Energy Office of Science under Cooperative Agreement DE-SC0000661 The driver linac for the Facility for Rare Isotope Beams (FRIB) comprises four kinds of cavities (β=0.041, 0.085, 0.29, and 0.53) and six types of cryomodules including matching modules. FRIB has completed the fabrication and the cold test of a β=0.53 pre-production cryomodule, which is the first prototype for a half-wave (β=0.29 and 0.53) cavity. This paper describes the fabrication and the cold test result of the β=0.53 pre-production cryomodule including lessons learned.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOPB031
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MOPB035	Cryogenic Probe Station at Old Dominion University Center for Accelerator Science	ion, cavity, cryogenics, niobium	128
	J. Makita, J.R. Delayen, A.V. Gurevich ODU, Norfolk, Virginia, USA G. Ciovati JLab, Newport News, Virginia, USA
	With a growing effort in research and development of an alternative material to bulk Nb for a superconducting radiofrequency (SRF) cavity, it is important to have a cost effective method to benchmark new materials of choice. At Old Dominion University's Center for Accelerator Science, a cryogenic probe station (CPS) will be used to measure the response of superconductor samples under RF fields. The setup consists of a closed-cycle refrigerator for cooling a sample wafer to a cryogenic temperature, a superconducting magnet providing a field parallel to the sample, and DC probes in addition to RF probes. The RF probes will extract a quality factor from a sample patterned in a coplanar waveguide resonator structure on a 2' wafer. From the measured quality factor, the surface resistance and the penetration depth as a function of temperature and magnetic field will be calculated. This paper will discuss the design and measurement procedures of the current CPS setup.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOPB035
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MOPB036	The Study of Deposition Method of Nb3Sn Film on Cu Substrate	ion, niobium, cavity, superconductivity	131
	L. Xiao, X.Y. Lu, W.W. Tan, D. Xie, D.Y. Yang, Y. Yang, Z.Q. Yang, J. Zhao PKU, Beijing, People's Republic of China
	Our work is mainly focused on the fabrication methods of Nb3Sn films on Cu substrates and film's properties. There are diffraction peaks of Nb3Sn in the X-ray diffraction patterns in which without diffraction peaks of copper compounds. Scanning electron microstructures of Nb3Sn film reflect its nice compactness and binding force between film and substrate.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOPB036
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MOPB040	ESS High-beta Cavity Test Preparations at Daresbury Laboratory	ion, cavity, niobium, LLRF	137
	P.A. Smith, L. Bizel-Bizellot, K.D. Dumbell, M. Ellis, P. Goudket, A.J. Moss, E.F. Palade, S.M. Pattalwar, M.D. Pendleton, A.E. Wheelhouse STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
	Science and Technology Facility Council is responsible for supplying, and testing 84 High beta elliptical SRF cavities, as part of the UK In Kind Contribution to the European Spallation Source (ESS). The High-β=0.86, cavities have been designed by CEA- Saclay and are a five cell Niobium cavity operating at 704.42 MHz. They are required to provide an accelerating gradient of 19.9 MV/m at an unloaded Q of 5x10⁹. Preparations are underway to upgrade the cryogenic and RF facilities at Daresbury laboratory prior to the arrival of the first cavities. As part of these arrangements, a niobium coaxial resonator has been manufactured, to validate the test facility. The design considerations, for the coaxial resonator are presented, along with preliminary results. The RF measurement system to perform the cavity conditioning and testing is also presented.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOPB040
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MOPB041	Status of the SOLEIL Superconducting RF System	ion, cavity, operation, GUI	141
	M. Diop, J.P. Baete, R.C. Cuoq, H.D. Dias, J.L. Labelle, L.R. Lopes, M. Louvet, P. Marchand, C.M. Monnot, S. Petit, F. Ribeiro, T. Ruan, R. Sreedharan, K.T. Tavakoli SOLEIL, Gif-sur-Yvette, France
	The 352 MHz SOLEIL SRF systems consist in two cryomodules, each containing a pair of SC Nb/Cu cavities, cooled with LHe at 4K from a single 350 W cryogenic plant. In order to store 500 mA, a power of 575 kW and an accelerating voltage of 3-4 MV are required. The RF power is provided by 4 SSPA's delivering up to 180 kW each. The original cavity input power couplers, which are LEP-type antennas designed to handle up to 200 kW, are being replaced by upgraded versions, able to operate at 300 kW CW. This will open the possibility to operate at full beam current with only one active cryomodule. The SRF system operational experience over the past ten years as well as the different upgrades will be reported here.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOPB041
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MOPB046	LCLS-II Cryomodule Production at JLab	ion, cryomodule, cavity, vacuum	163
	R.A. Legg, G. Cheng, E. Daly, G.K. Davis, M.A. Drury, J.F. Fischer, T. Hiatt, N.A. Huque, L.K. King, J.P. Preble, A.V. Reilly, M. Stirbet, K.M. Wilson JLab, Newport News, Virginia, USA
	Funding: This work was supported by the LCLS-II Project and the U.S. Department of Energy, Contract DE-AC02-76SF00515. The LCLS-II cryomodule construction program leverages the mature XFEL cryomodule design to produce technologically sophisticated cryomodules with a minimum of R&D according to an accelerated manufacturing schedule. Jlab, as one of the partner labs, is producing 18 cryomodules for LCLS-II. To meet the quality and schedule demands of LCLS-II, many upgrades to the JLAB cryomodule assembly infrastructure and techniques have been made. JLab has installed a new cleanroom for string assembly and instituted new protocols to minimize particulate transfer into the cavities during the cryomodule construction process. JLab has also instituted a set of magnetic hygiene protocols to be used during the assembly process to minimize magnetic field impingement on the finished cavity structure. The goal has been to have gradients, both maximum and field emission onset, that do not degrade between the cavity vertical test and final cryomodule qualification, while maximizing the Q0 of each finished cavity. Results from the prototype cryomodule assembly are presented.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOPB046
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MOPB050	Cavity Processing and Testing Activities at Jefferson Lab for LCLS-II Production	cavity, ion, FEL, cryomodule	173
	L. Zhao, G.K. Davis, J. Follkie, D. Forehand, K. Macha, A.D. Palczewski, A.V. Reilly JLab, Newport News, Virginia, USA
	Funding: Work supported by Jefferson Science Associates, LLC under U.S. DOE Contracts DE-AC05-06OR23177 and DE-AC02-76SF00515 for the LCLS-II Project. Cryomodule production for LCLS-II is well underway at Jefferson Lab. This paper explains the process flow for production cavities, from being received at the Test Lab to being assembled onto cavity strings. Taking our facility and infrastructure into consideration, process optimization and process control are implemented to ensure high quality products.
	Poster MOPB050 [2.338 MB]
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MOPB063	Fundamental Studies for the STF-type Power Coupler for ILC	ion, vacuum, FEL, cavity	194
	Y. Yamamoto, E. Kako, T. Matsumoto, S. Michizono, A. Yamamoto KEK, Ibaraki, Japan M. Irikura, M. Ishibashi, H. Yasutake Toshiba Electron Tubes & Devices Co., Ltd (TETD), Tochigi, Japan
	From the view point of mass-production for the power coupler in ILC, the fundamental studies for the STF-type power coupler are under progress by the collaboration between KEK and TETD. At present, there are various rinsing procedures for power coupler in the world-wide laboratories. In this R&D, the main topic is to investigate the various rinsing effects in the copper plating and the ceramic through the high power test. In this paper, the first results will be presented.
	Poster MOPB063 [2.237 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOPB063
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MOPB065	Development of Hybrid Superconducting Photocathodes on Niobium Using High QE Coatings	ion, cathode, electron, site	205
	M. Warren, A.R. Denchfield, N. Samuelson, J. Zasadzinski IIT, Chicago, Illinois, USA W. Gai, J.H. Shao, E.E. Wisniewski ANL, Argonne, Illinois, USA L.K. Spentzouris, Z.M. Yusof Illinois Institute of Technology, Chicago, Illinois, USA
	High power, low emittance electron beams require superconducting RF photoinjectors, typically made of pure Nb, and a superconducting photocathode is desired. However, superconductivity and high photocathode quantum efficiency (QE) are not compatible, e.g. QE for pure Nb is only 10^-5 at 260 nm wavelength. Here is presented the current status of the development of hybrid superconducting photocathodes by the deposition of thin films of a high QE metal or semiconductor on Nb. Nb plugs coated with 10-100 nm of Mg have been tested for adhesion and dark current under RF fields as high as 60MV/m. QE measurements show significant enhancements over Nb. In another test, ultra thin films of the high QE material Cs2Te deposited on Nb are reported. Using the standard deposition procedure, QE ~12% is found for films ~ 200Å. As the thickness is reduced QE maintains a high value ~ 6% for films as thin as 2.0 nm. These results are quite promising for future superconducting photocathodes.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOPB065
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MOPB086	First Results of the IFMIF/EVEDA-SaTHoRI Tests	ion, cavity, controls, cryomodule	262
	O. Piquet, N. Bazin, P. Carbonnier, J.K. Chambrillon, M. Desmons, G. Devanz, H. Jenhani, C. Servouin CEA/DRF/IRFU, Gif-sur-Yvette, France P. Cara Fusion for Energy, Garching, Germany J.F. Denis, L. Maurice, J. Relland CEA/IRFU, Gif-sur-Yvette, France F. Éozénou, P. Hardy, E. Jacques, Y. Lussignol, P. Sahuquet CEA/DSM/IRFU, France D. Gex, A. Jokinen, G. Phillips F4E, Germany I. Moya, P. Méndez CIEMAT, Madrid, Spain
	The SaTHoRI test stand (Satellite de Tests Horizontal des Résonateurs IFMIF) aims to characterize a jacketed and fully dressed cavity with its coupler and tuner. A dedicated test cryostat has been manufactured and is connected to an existing horizontal test cryostat which provides the cryogenic coolant. A RF source ' provided by the IFMIF collaboration, one of the four RF sources which will be used for the cryomodule at Rokkasho ' has been installed and commissioned at CEA. This paper describes the test stand and presents the first results.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOPB086
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MOPB087	Frequency Tuner Development and Testing at Cornell for the RAON Half-wave-resonator	ion, cavity, cryogenics, cryomodule	266
	M. Ge, F. Furuta, J.E. Gillette, T. Gruber, S.W. Hartman, M. Liepe, T.I. O'Connell, P.J. Pamel, P. Quigley, J. Sears, V. Veshcherevich Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA B.H. Choi, J. Joo, J.W. Kim, W.K. Kim, J. Lee, I. Shin IBS, Daejeon, Republic of Korea
	The half-wave-resonators (HWRs) for the RAON project require a slow frequency tuner that can provide >80 kHz tuning range. Cornell University is currently in the process of designing, prototyping, and testing this HWR tuner. In this paper, we present the optimized tuner design, prototype fabrication, test insert preparation, and cryogenic test results. The performance of the tuner is analysed in detail.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOPB087
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MOPB104	Development of a Novel Supporting System for High Luminosity LHC SRF Crab Cavities	ion, cavity, cryomodule, interface	304
	T.J. Jones STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom K. Artoos, R. Calaga, O. Capatina, T. Capelli, M. Sosin, J.S. Swieszek, C. Zanoni CERN, Geneva, Switzerland G. Burt Cockcroft Institute, Lancaster University, Lancaster, United Kingdom T.J. Jones Lancaster University, Lancaster, United Kingdom
	Compact SRF Crab Cavities are integral to the HL-LHC upgrade. This paper details the design of support structures within the SPS (Super Proton Synchrotron) Crab Cavity Cryomodule. For ease of alignment each cavity is supported with the mechanical tuner and RF Fundamental Power Coupler (FPC) via a common support plate. To reduce heat leak and remove bellows in the FPC it was determined that this would be the fixed support for the cavity (V. Parma, 2013). In addition, novel flexural blades were designed to give increased stiffness yet allow for thermal contraction of the cavity towards the fixed point of the FPC. This approach was superior when compared via simulation to several alternative techniques. A detailed simulation model was used for optimisation of directional stiffness, identification of vibration modes and minimising thermal stresses. A transmission matrix was developed in MS Excel to assess modal deflection for given ground vibration conditions. The spreadsheet gives an instantaneous yet comparable result to time consuming random vibration FE Analyses. The final engineering design of the supporting system is now complete and will also be described in this paper. References V. Parma, R. B. (2013). Status of the Superconducting Proton Linac (SPL) Cryomodule. SRF2013.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOPB104
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MOPB110	Results of Accelerated Life Testing of LCLS-II Cavity Tuner Motor	ion, cavity, cryomodule, operation	323
	N.A. Huque, E. Daly JLab, Newport News, Virginia, USA Y.M. Pischalnikov Fermilab, Batavia, Illinois, USA
	An Accelerated Life Test (ALT) of the Phytron stepper motor used in the LCLS-II cavity tuner has been conducted at JLab. Since the motor will reside inside the cryomodule, any failure would lead to a very costly and arduous repair. As such, the motor was tested for the equivalent of 30 lifetimes before being approved for use in the production cryomodules. The 9-cell LCLS-II cavity is simulated by disc springs with an equivalent spring constant. Plots of the motor position vs. tuner position ' measured via an installed linear variable differential transformer (LVDT) ' are used to measure motor motion. The titanium spindle was inspected for loss of lubrication. The motor passed the ALT, and is set to be installed in the LCLS-II cryomodules.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOPB110
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TUXAA01	CEPC SRF System Design and Challenges	ion, cavity, HOM, cryomodule	332
	J.Y. Zhai, Y.L. Chi, J. Dai, J. Gao, R. Ge, D.J. Gong, R. Han, T.M. Huang, S. Jin, Z.Q. Li, B. Liu, Z.C. Liu, Q. Ma, F. Meng, Z.H. Mi, G. Pei, Q. Qin, P. Sha, Q.Y. Wang, T.X. Zhao, H.J. Zheng IHEP, Beijing, People's Republic of China C. Pagani Università degli Studi di Milano & INFN, Segrate, Italy
	Funding: Work supported by National Key Programme for S&T Research and Development of China (Grant NO.: 2016YFA0400400) CEPC is a 100 km circular electron positron collider operating at 90-240 GeV center-of-mass energy of Z, W and Higgs bosons. CEPC and its successor SPPC, a 100 TeV center-of-mass super proton-proton collider, will ensure the elementary particle physics a vibrant field for decades to come. The conceptual design report (CDR) of CEPC will be completed in the end of 2017 as an important step to move the project forward. In this contribution, CEPC SRF system CDR design and challenges will be introduced, including the system layout and parameter choices, configuration at different operation energies, transient beam loading and its compensation, cavity fundamental mode (FM) and higher order mode (HOM) induced coupled bunch instabilities (CBI) and the beam feedback requirement, etc. The SRF technology R&D plan and progress as well as the SRF infrastructure and industrialization plan are discussed at last.
	Slides TUXAA01 [9.124 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUXAA01
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TUXAA03	Progress of FRIB SRF Production	ion, cavity, cryomodule, linac	345
	T. Xu, H. Ao, B. Bird, N.K. Bultman, F. Casagrande, C. Compton, K.D. Davidson, K. Elliott, A. Facco, V. Ganni, A. Ganshyn, W. Hartung, M. Ikegami, P. Knudsen, S.M. Lidia, E.S. Metzgar, S.J. Miller, D.G. Morris, P.N. Ostroumov, J.T. Popielarski, L. Popielarski, M.A. Reaume, K. Saito, S. Shanab, M. Shuptar, S. Stark, D.R. Victory, J. Wei, J.D. Wenstrom, M. Xu, Y. Xu, Y. Yamazaki FRIB, East Lansing, Michigan, USA A. Facco INFN/LNL, Legnaro (PD), Italy K. Hosoyama KEK, Ibaraki, Japan M.P. Kelly ANL, Argonne, Illinois, USA R.E. Laxdal TRIUMF, Vancouver, Canada M. Wiseman JLab, Newport News, Virginia, USA
	Funding: Work supported by the U.S. Department of Energy Office of Science under Cooperative Agreement DE-SC0000661 The Facility for Rare Isotope Beams (FRIB), under construction at Michigan State University, will utilize a driver linac to accelerate stable ion beams from protons to uranium up to energies of >200 MeV per nucleon with a beam power of up to 400 kW. The FRIB linac consists of 46 cryomodules containing a total of 324 superconducting radio-frequency (SRF) resonators and 69 superconducting solenoids. The design of all six type cryomodules has been completed. The critical SRF components are tested as subsystem and validated in the pre-production cryomodules. The mass production of SRF cryomodules is underway. Here we report on the progress of the technical construction of FRIB superconducting linac.
	Slides TUXAA03 [4.006 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUXAA03
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TUYAA01	The Importance of the Electron Mean Free Path for Superconducting RF Cavities	cavity, ion, niobium, electron	359
	J.T. Maniscalco, P.N. Koufalis, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Theoretical results offer a potential explanation for the anti-Q-slope, the phenomenon of decreasing microwave surface resistance with increasing radiofrequency electromagnetic field strength. This effect has been observed in niobium doped with impurities, chiefly nitrogen, and has been put to use in the Linac Coherent Light Source II (LCLS-II) accelerator currently under construction. Our work, presented here, finds a strong link between the electron mean free path, the main measure of impurity doping, to the overheating of quasiparticles in the RF penetration layer. This is an important effect that adjusts the magnitude of the theoretical anti-Q-slope by providing a mechanism to counteract it and introduce a surface resistance that increases with field strength. We discuss our findings in a study of niobium cavities doped at high temperature (800-990 °C) as well as new analysis of low-temperature-doped cavities.
	Slides TUYAA01 [6.988 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUYAA01
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TUYBA01	Progress on Characterization and Optimization of Multilayers	ion, cavity, site, niobium	368
	C.Z. Antoine CEA/DSM/IRFU, France M. Aburas, A. Four CEA/DRF/IRFU, Gif-sur-Yvette, France H. Hayano, S. Kato, T. Kubo, T. Saeki KEK, Ibaraki, Japan Y. Iwashita Kyoto ICR, Uji, Kyoto, Japan
	Multilayers MgO/NbN/MgO/Nb with several thicknesses are being tested by local magnetometry, Scanning tunneling and various standard structural techniques experiment providing usefull information to compare experiments and recent theoretical advances proposed by A. Gurevich or T. Kubo.
	Slides TUYBA01 [5.819 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUYBA01
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TUPB002	Novel HOM Damper Design for High Current SRF Cavities	HOM, ion, GUI, cavity	385
	W. Xu, I. Ben-Zvi, M. Blaskiewicz, Y. Gao, D. Holmes, P. Kolb, G.T. McIntyre, R. Porqueddu, K.S. Smith, R. Than, F.J. Willeke, B. P. Xiao, T. Xin, C. Xu, A. Zaltsman BNL, Upton, Long Island, New York, USA I. Ben-Zvi Stony Brook University, Stony Brook, USA Y. Gao PKU, Beijing, People's Republic of China
	Funding: This work is supported by LDRD program of Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. DOE. ERL-Ring eRHIC aims to build a new high current (50 mA), multi-pass (6 passes) ERL to provide 3-18 GeV electron beams to collide with proton beams from existing RHIC. One critical challenge for eRHIC is to damp HOMs. The average HOM power is up to 8 kW per cavity, and it will get worse when the electron beam spectrum overlaps with cavity HOM spectrum. A novel HOM damping scheme by employing ridge waveguides has been worked out at BNL, which is able to well damp both longitudinal and transversal modes. This paper will describe the design of the HOM damping scheme, including RF design, HOM damping results, progress of prototyping.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB002
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TUPB005	Developed Spoke Cavity Module for Main Linac of China ADS HOM Simulations and Damping Scheme for CEPC Cavities	cavity, ion, linac, niobium	393
	Z.Q. Li, J.S. Cao, Y.L. Chi, F.S. He, S.P. Li, H.Y. Lin, Q. Ma, Z.H. Mi, W.M. Pan, P. Sha, B. Xu, J.Y. Zhai, X.Y. Zhang IHEP, Beijing, People's Republic of China
	During past five year, two kind of spoke of Beta equal 0.21 and 0.40 were developed at IHEP CAS, the spoke cavity of beta 0.21 was adopted to accelerate proton from 10 to 32MeV, and 32 to 160MeV for beta 0.40 spoke cavity. Up to now, two kind of naked spoke cavities have been test in vertical, also the module of beta 0.21 spoke cavity, which equipped the liquid helium jacket, magnetic shield layer and frequency tuner has been fulfilled and test, the performance of all of components reach the design requirements.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB005
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TUPB008	Performance of SRF Half-wave-resonators Tested at Cornell for the RAON Project	cavity, ion, radiation, multipactoring	396
	M. Ge, F. Furuta, J.E. Gillette, T. Gruber, S.W. Hartman, M. Liepe, T.I. O'Connell, P.J. Pamel, J. Sears, V. Veshcherevich Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA B.H. Choi, J. Joo, J.W. Kim, W.K. Kim, J. Lee, I. Shin IBS, Daejeon, Republic of Korea
	Two prototype half-wave-resonators (HWR; 162.5MHz and β=0.12) for the RAON project were tested at Cornell University. In this paper, we report and analyse detailed results from vertical tests, including tests of the HWRs without and with helium tank. Surface preparation at Research Instruments is discussed, as well as the development of new HWR preparation and test infrastructure at Cornell.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB008
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TUPB009	High-frequency SRF Cavities	cavity, ion, cryogenics, ECR	400
	T.E. Oseroff, D.L. Hall, M. Liepe, J.T. Maniscalco Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Historically, the frequency of SRF cavities has been limited by cryogenic power dissipation increasing rapidly with frequency, due to the BCS surface resistance having a quadratic dependence on frequency. Now, new SRF surfaces using doped niobium and compound superconductors like Nb3Sn can drastically reduce the BCS part of the surface resistance. The temperature independent part of the surface resistance (residual resistance) can therefore become dominant, and has its own, different frequency dependence. We have developed a model to analyze cryogenic cooling power requirements for SRF cavities as function of operating frequency, temperature, and trapped flux to evaluate the impact of the novel low-loss SRF surfaces on the questions of optimal operating frequency and frequency limit. We show that high-frequency SRF cavities now become a realistic option for future SRF driven accelerators. As the transverse cavity size decreases inversely with respect to its resonant frequency, such high-frequency SRF cavities could greatly reduce cost.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB009
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TUPB020	Microphonics Passive Damping	ion, cavity, simulation, operation	423
	E.N. Zaplatin FZJ, Jülich, Germany A. Kanareykin Euclid TechLabs, LLC, Solon, Ohio, USA V.P. Yakovlev Fermilab, Batavia, Illinois, USA
	Different types of external loads on the resonator walls predetermine the main working conditions of the SRF cavities. The most important of them are very high electromagnetic fields that result in strong Lorentz forces and the pressure on cavity walls from the helium tank that also deforms the cavity shape. For pulsed operation, the Lorentz forces usually play the decisive role for the cavity design. For CW operation, the liquid helium vessel pressure instability even for 2K operations is the source of large microphonics. All deformations resulting from any type of external loads on cavity walls lead to shifts in the working RF frequency in the range of hundreds of kHz. Taking into account high Q-factor of SC cavities such a large frequency shift takes the cavity out of operation. Here we present and discuss the achievements and problems of microphonics passive damping in different type SRF cavities.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB020
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TUPB021	First Considerations on HZB High Frequency Elliptical Resonator Stiffening	ion, cavity, simulation, cryomodule	428
	E.N. Zaplatin FZJ, Jülich, Germany H.-W. Glock, J. Knobloch, A. Neumann, A.V. Vélez HZB, Berlin, Germany
	There are two projects that currently are under development and construction at HZB which utilize high frequency elliptical resonators ' Energy Recovery Linac Prototype (BERLinPro, 7-cell, 1300 MHz, β=1) and BESSY Variable pulse-length Storage Ring (VSR, 5-cell, 1500/1750 MHz, β=1). A critical issue of both projects is small effective beam loading in cavities operating at high CW fields (Eacc of 20 MV/m) with a narrow band width. This necessitates precise tuning and therefore good compensation of microphonics and coupled Lorentz-force detuning driven instabilities. Here we present a conceptual study of an integrated SRF resonator and helium vessel structure design to ensure a reduced resonance frequency dependence on pressure and Lorentz forces to minimize their impact on the accelerating field profile.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB021
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TUPB023	Further Tests on the SC 325 MHz CH-cavity and Power Coupler Test Setup	ion, cavity, linac, pick-up	437
	M. Busch, M. Basten, H. Podlech, U. Ratzinger, M. Schwarz IAP, Frankfurt am Main, Germany W.A. Barth MEPhI, Moscow, Russia W.A. Barth GSI, Darmstadt, Germany W.A. Barth, F.D. Dziuba, V. Gettmann HIM, Mainz, Germany
	Funding: Work supported by BMBF contr. No. 05P15RFRBA The 325MHz CH-cavity which has been developed and successfully vertically tested at the Institute for Applied Physics, Frankfurt, has has been welded to the helium vessel at the frontal joints of the cavity and further vertical and horizontal tests are in preparation. Finally a beam test with a 11.4 AMeV, 10 mA ion beam at GSI, Darmstadt is projected. Furthermore a newly developed, dedicated test stand for the 217 MHz power couplers has been set up for the cavities of the sc cw-LINAC project at GSI.
	Poster TUPB023 [2.579 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB023
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TUPB028	Improvement of Magnetic Condition for KEK-STF Vertical Test Facility Toward High-Q Study	ion, cavity, solenoid, controls	444
	K. Umemori, T. Dohmae, E. Kako, T. Konomi, T. Kubo, M. Masuzawa, G.-T. Park, A. Terashima, K. Tsuchiya, R. Ueki KEK, Ibaraki, Japan T. Okada Sokendai, Ibaraki, Japan
	Improvement of unloaded Q-values of SRF cavities are important to reduce surface loss of cavity and heat loads of He refrigerators. R&D activities have been developed worldwide. We also started work toward high-Q, but soon realized that magnetic condition of KEK-STF vertical test facility was not good enough to carry out high-Q measurements. First, magnetized components were searched. Shafts to move variable coupler were found to be most magnetized one and exceed more than 1 Gauss. Magnetized components were exchanged to non-magnetized one. In order to further reduce remnant magnetic field, a solenoid coil was prepared and used to cancel it. To suppress flux trapping, a heater was located around an upper beampipe of cavity and made thermal gradient. Owing to these efforts, Q-value of more than 1x10¹¹ can be measured with a condition of residual resistance of ~3 nΩ. Clear flux expulsion signal can be also observed. In this presentation, we report about efforts to reduce ambient magnetic field and to realize high-Q measurements. Results of vertical tests, including flux expulsion measurements, are also presented.
	Poster TUPB028 [1.961 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB028
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TUPB032	Study on 650MHz 5-cell Prototype Cavities at IHEP	ion, cavity, HOM, simulation	448
	S. Jin, J. Gao, D.J. Gong, Z.C. Liu, P. Sha, J.Y. Zhai, T.X. Zhao, H.J. Zheng IHEP, Beijing, People's Republic of China
	CEPC Pre CDR pointed that the 650 MHz 5-cell SRF cavity could be a candidate for the main ring of the single-ring pretzel scheme at the Higgs energy in 2015. Then EM design of 5-cell cavities were published later. So, the study on the fabrication of a 5-cell prototype cavity with waveguide HOM couplers were carried on at IHEP. In the paper, we will mainly report the mechanical design and fabrication progress of the 5-cell prototype. Besides, fabrication of a bare 2-cell prototype cavity was also carried on according to the further study after Pre-CDR. Challenges and possible solutions for the prototypes development will also be discussed.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB032
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TUPB034	The 166.6 MHz Proof-of-principle SRF Cavity for HEPS-TF	cavity, ion, HOM, storage-ring	454
	P. Zhang, J. Dai, H.X. Hao, T.M. Huang, Z.Q. Li, H.Y. Lin, Q. Ma, F. Meng, Z.H. Mi, W.M. Pan, Y. Sun, G.W. Wang, Q.Y. Wang, X.Y. Zhang IHEP, Beijing, People's Republic of China
	Funding: This work has been supported by HEPS-TF project and also partly supported by Pioneer "Hundred Talents Program" of Chinese Academy of Sciences. The 166.6 MHz superconducting RF cavities have been proposed for the High Energy Photon Source (HEPS), a 6 GeV kilometer-scale light source. The cavity is of quarter-wave type made of bulk niobium with β =1. Each cavity will be operated at 4 K providing 1.2 MV accelerating voltage and 145 kW of power to the electron beam. During the HEPS - Test Facility (HEPS-TF) phase, a proof-of-principle cavity of 166.6 MHz has been designed in IHEP and manufactured in Beijing. The subsequent BCP was conducted in Ningxia, while HPR, cleanroom assembly and 120 degree baking was done in IHEP. The cavity was finally vertical tested at both 4K and 2K in IHEP. The cavity Q0 at nominal gradient at 4 K was measured to be 2.4·10⁹ with Epeak of 42 MV/m and Bpeak of 65 mT. The maximum Epeak and Bpeak reached 86MV/m and 131 mT respectively at both 4 K and 2 K, and the corresponding Q0 was measured to be 5.10⁸ (4 K) and 3.3·10⁹ (2 K). The residual surface resistance was measured to be 2.3 nOhm.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB034
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TUPB035	Frequency Pre-tuning of the 166.6 MHz Proof-of-principle SRF Cavity for HEPS-TF	cavity, ion, simulation, target	459
	P. Zhang, H.X. Hao, Z.Q. Li, X.Y. Zhang IHEP, Beijing, People's Republic of China
	Funding: This work has been supported by HEPS-TF project and also partly supported by Pioneer 'Hundred Talents Program' of Chinese Academy of Sciences. A 166.6 MHz proof-of-principle SRF cavity has been designed for the High Energy Photon Source - Test Facility (HEPS) at IHEP in Beijing. The cavity is a β=1 quarter-wave resonator made of bulk niobium operating at 4 K. A pre-tuning scheme was made to accommodate the cavity frequency shift mainly due to mechanical tolerances during cavity production, the subsequent surface treatment and cooldown process. To this end, the length of the cavity outer conductor was chosen as a free parameter for the pre-tuning. The cavity frequency was carefully monitored during the production, post-processing steps and vertical test. The measurement results agree well with our calculations. It is worth noticing that the pre-tuning method only involves one-time measurement of the cavity resonant frequency and its outer conductor length.
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TUPB036	R&D of CEPC Cavity	cavity, ion, cryomodule, experiment	463
	P. Sha Institute of High Energy Physics (IHEP), Chinese Academy of Sciences, Beijing, People's Republic of China B. Liu, Z.H. Mi, J.Y. Zhai, X.Y. Zhang, H.J. Zheng IHEP, Beijing, People's Republic of China
	Funding: This study was supported by National Key Programme for S&T Research and Development (Grant NO.: 2016YFA0400400) and National Natural Science Foundation of China (Grant NO.: 11505197) CEPC will use 650 MHz cavities for the collider (Main Ring) and 1.3 GHz cavities for the Booster. Each booster cryomodule contains eight 1.3 GHz 9-cell cavities, which is similar as LCLS-II. Each collider cryomodule contains six 650 MHz 2-cell cavities, which is totally new. So our R&D of CEPC cavity mainly focuses on the 650 MHz 2-cell cavity. A cryomodule which consists of two 650 MHz 2-cell cavities has began in early 2017. In this thesis, the RF and mechanical design is displayed with Helium Vessel. Besides, multipacting is analyzed. In order to achieve high Q, N-doping is also studied.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB036
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TUPB037	A 166.6 MHz Proof-of-principle SRF Cavity for HEPS-TF: Mechanical Design and Fabrication	ion, cavity, storage-ring, superconducting-RF	466
	X.Y. Zhang Institute of High Energy Physics (IHEP), Chinese Academy of Sciences, Beijing, People's Republic of China H.X. Hao, Z.Q. Li, H.Y. Lin, Y. Sun, P. Zhang IHEP, Beijing, People's Republic of China
	166.6 MHz superconducting RF cavities operating at 4.2 K have been proposed by IHEP for the High Energy Photon Source - Test Facility (HEPS-TF). The cavity is a quarter wave resonator with beam going through the cavity inner conductor. The cavity and its stiffness were designed and optimized to meet pressure safety requirement and to reduce frequency sensitivity due to helium pressure fluctuations. Tuning sensitivity, Lorentz force detuning and microphonics were also simulated. Most calculations have been validated by experiments. This paper reports the mechanical design and fabrication details of the first proof-of-principle cavity.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB037
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TUPB038	Mechanical Design of a 650 MHz Superconducting RF Cavity for CEPC	ion, cavity, collider, positron	471
	X.Y. Zhang Institute of High Energy Physics (IHEP), Chinese Academy of Sciences, Beijing, People's Republic of China F.S. He, Q. Ma, Z.H. Mi, P. Sha, J.Y. Zhai IHEP, Beijing, People's Republic of China
	Funding: This study was supported by National Key Programme for S&T Research and Development (Grant NO.: 2016YFA0400400) The 650 MHz superconducting RF cavities have been proposed by IHEP for the Circular Electron-Positron Collider (CEPC). The major components are a 2-cell elliptical cavity, end groups, stiffness and helium vessel, which have been optimized to meet the design requirement. The minimization of the Lorentz force detuning and the sensitivity of resonance frequency to Helium pressure variations was the main goal of the optimization. Also detailed stress analysis, tuning and microphonics performance of dresses cavity will be presented in this paper.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB038
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TUPB039	Electropolishing of Niobium from Deep Eutectic Solvents Based on Choline Chloride	ion, ECR, cavity, niobium	475
	Q.W. Chu, H. Guo, Y. He, L. Li, P.R. Xiong, Z.M. You, S.H. Zhang IMP/CAS, Lanzhou, People's Republic of China
	Niobium (Nb) was successfully electropolished from a green ionic liquid, choline chloride/urea deep eutectic solvent (DES). This paper was to investigate the influence of various electropolishing parameters, including electropolishing time, temperature and voltage, on the electropolishing rate, surface roughness, glossiness and microstructure of Nb. The result showed that the electropolishing parameters had a significant impact on the performance of Nb. Based on surface analysis by scanning electron microscope (SEM) and atomic force microscope (AFM), smooth Nb can be achieved under properly controlled conditions.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB039
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TUPB049	Design Study on the Superconducting HWR for Secondary Particle Generation at KOMAC	ion, cavity, proton, linac	499
	H.S. Kim KAERI, Daejon, Republic of Korea Y.-S. Cho, J.J. Dang, H.S. Jeong, H.-J. Kwon, S. Lee Korea Atomic Energy Research Institute (KAERI), Gyeongbuk, Republic of Korea
	Funding: This work has been supported through KOMAC (Korea of Multi-purpose Accelerator Complex) operation fund of KAERI by MSIP (Ministry of Science, ICT and Future Planning). A 100-MeV proton linac has been operated since 2013 at KOMAC (Korea Multi-purpose Accelerator Complex) and provides the accelerated proton beam to various users from the research institutes, universities and industries. To expand the utilization fields of the accelerator, we have a plan to develop a secondary particle utilization facility including a pulsed neutron source and radio-isotope beam based on the 100-MeV linac. According to the preliminary analysis, the neutron yields can be increased by about 2.5 times if the incident proton beam energy increases from 100 MeV to 160 MeV. Therefore, we carried out design study on the SRF linac based on half-wave resonator to increase the proton beam energy. Baseline design parameters include 350 MHz operating frequency, 2 K operation temperature, and peak electric field and magnetic field less than 35 MV/m and 70 mT, respectively. The available space at existing accelerator tunnel was also taken into consideration. Details on the design study on the SRF linac based on HWR cavity for the secondary particle utilization facility at KOMAC will be given in this presentation.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB049
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TUPB055	Nb3Sn Thin Film Deposition On Copper By DC Magnetron Sputtering	ion, target, cavity, niobium	512
	W.W. Tan, B.T. Li, X.Y. Lu, L. Xiao, D. Xie, D.Y. Yang, Y. Yang, Z.Q. Yang, J. Zhao PKU, Beijing, People's Republic of China
	Nb3Sn for SRF cavities has been coated on copper samples by DC magnetron Sputtering. Pure Nb target and pure Sn target were installed separately in the magnetron sputtering device. Nb3Sn precursor was coated on copper in the Ar atmosphere of 0.5 Pa. The Nb3Sn precursor was annealed in the vacuum furnace whose pressure is 10^-4 Pa. The XRD results demonstrate the exist of Nb3Sn crystal, and MPMS results show superconductivity of Nb3Sn. The highest critical temperature obtained is 15K.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB055
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TUPB060	Innovative Cryogenic Test Facility for Testing SRF Cavity Series Production	ion, cavity, operation, cryogenics	520
	L. Bizel-Bizellot, M. Ellis, S.M. Pattalwar, M.D. Pendleton, P.A. Smith, A.E. Wheelhouse STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
	Testing SRF cavities in a vertical cryostat is the first step in qualifying the performance of SRF cavities before being integrated into a cryomodule. The European Spallation Source (ESS) requires 84 high-beta 5 cells, 704 MHz cavities which will be manufactured and qualified for their RF performance in a vertical cryostat at Science and Technology Facility Council (STFC) Daresbury Laboratory (United-kingdom). Taking a conventional approach each vertical test would require a large cryostat demanding more than 7000 litres of liquid helium per test for testing 3 cavities simultaneously. In order to reduce the overall operating cost, we plan to develop an alternative method to divide the liquid helium consumption by 5 by filling liquid helium only in each individual helium vessels enclosing each cavity placed horizontally in the cryostat. Therefore the test is performed in more realistic conditions such as in a cryomodule and reduces the operating time. This also reduces the mass flow-rate to be handled by a factor 10, leading to 2 g/s, thus reducing the size of the associated components such as the 2 K pumps, the safety device, the valves and transfer lines.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB060
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TUPB065	Design of Multi-frequency Coaxial Test Resonators	ion, cavity, niobium, operation	531
	Z.Y. Yao, T. Junginger, R.E. Laxdal, B. Matheson, B.S. Waraich, V. Zvyagintsev TRIUMF, Vancouver, Canada
	A significant issue in low beta resonators is medium field Q-slope (MFQS) at 4K. To study the MFQS and the field dependence of surface resistance in low beta resonators, a quarter-wave resonator (QWR) and a half-wave resonator (HWR) were designed to be tested at integer harmonic frequencies of 200MHz, and up to 1.2GHz. A series of chemistry and heat treatments will be applied to these cavities so that a systemic study on the surface resistance of the coaxial resonators associating with post-processing, RF field, and frequency can be done. The detail design of these cavities and the status of cavity fabrication will be reported in this paper.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB065
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TUPB066	RF Results of Nb Coated SRF Accelerator Cavities via HiPIMS	ion, cavity, lattice, site	535
	M.C. Burton, M. Beebe, R.A. Lukaszew The College of William and Mary, Williamsburg, Virginia, USA A.D. Palczewski, H.L. Phillips, C.E. Reece JLab, Newport News, Virginia, USA
	Funding: Jefferson Lab Bulk Nb SRF cavities are the preferred method for acceleration of charged particles. However, bulk Nb cavities suffer from variable RF performance, high cost and impose material & design restrictions on other components of a particle accelerator. Since SRF is a shallow surface phenomena, a proposed solution is to deposit a Nb thin film on the interior of a cavity made of an alternative material such as Cu. While this approach has been attempted in the past, new energetic condensation techniques, such as High Power Impulse Magnetron Sputtering (HiPIMS), offer the opportunity to create Nb films with improved properties compared to traditional methods. To test HiPIMS, a study was performed in which Nb films were deposited on samples in multiple 'series' where only one parameter (Ion Fraction, Condensation Energy'etc.) is varied. Sample properties were then characterized using: XRD, AFM, SEM'etc., and correlations made between deposition parameters and film properties. Nb films were then deposited on 1.3GHz Cu cavities at select parameter sets and RF tested. Here we present the results from the Nb film studies and correlate the sample properties to RF results of Nb/Cu cavities.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB066
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TUPB067	Insights into Formation of Nb3Sn Film During the Vapor Diffusion Process	ion, niobium, experiment, cavity	539
	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 M.J. Kelley, J. Tuggle Virginia Polytechnic Institute and State University, Blacksburg, USA
	Funding: Supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC05-06OR23177 and Office of High Energy Physics under grant DE-SC-0014475. The potential of Nb3Sn for SRF cavities is widely recognized and renewed R&D efforts continue to bring new insights about material structure and its properties. We have systematically coated niobium with Nb3Sn using "vapor diffusion" under varying coating conditions to elucidate the reaction of tin with niobium at the temperatures of interest. The analysis of the coated samples is revealing new understanding about the two-stage nucleation/deposition ("vapor diffusion") process that allows us to form a hypothesis regarding Nb3Sn formation mechanism. The essential aspect of nucleation is the deposition of a high coverage, nanoscale thin tin film with particle assemblage by decomposition of tin chloride on the niobium surface at temperatures sufficient for reduction of the thick niobium oxide film, usually at about 500°C. The deposition is followed by the reaction of tin from tin vapor with the niobium surface to form Nb3Sn at about 1200°C, where the surface and grain boundaries start to play key role in the formation process initiation and progression. These findings improve understanding of the Nb3Sn growth in the typical vapor diffusion process used for accelerator cavity coatings.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB067
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TUPB069	Rigorous Data Processing and Automatic Documentation of SRF Cold Tests	ion, LabView, software, cavity	543
	K.G. Hernández-Chahín Universidad de Guanajuato, División de Ciencias e Ingenierías, León, Mexico S. Aull, P.F. Fernández López, K.G. Hernández-Chahín, N. Schwerg, N. Stapley CERN, Geneva, Switzerland
	Performance curves for SRF cavities are derived from primary quantities which are processed by software. Commonly, the mathematical implementation of this analysis is hidden in software such as Excel or LabVIEW, making it difficult to verify or to trace, while text-based programming like Python and MATLAB require some programming skills for review and use. As part of an initiative to consolidate and standardise SRF data analysis tools, we present a Python program converting a module containing the collection of all commonly used functions into a \LaTeX (PDF) document carrying all features of the implementation and allowing for a review by SRF experts, not programmers. The resulting document is the reference for non-experts, beginners and test stand operators. The module is imported in any subsequent processing and analysis steps like the symbolic analysis of the measurement uncertainties or the study of sensitivities. As an additional layer of protection the functions can be further wrapped including assertions, type and sanity checks. This process maximises function reuse, reduces the risk of human errors and guarantees automatically validated and documented cold test results.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB069
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TUPB072	Investigation of BCP Parameters for Mastery of SRF Cavity Treatment	ion, cavity, niobium, experiment	558
	F. Éozénou CEA/DSM/IRFU, France E. Cenni, G. Devanz, T. Percerou, Th. Proslier, C. Servouin CEA/DRF/IRFU, Gif-sur-Yvette, France M.L.L. Nghiem UPMC, Paris, France
	Mastery of Standard Buffered Chemical Polishing (with mixture of hydrofluoric, nitric and phosphoric acids) is of paramount importance for the treatment of SRF resonators with complex geometry has IFMIF half-wave resonators, in order to control accurately their frequency evolution. Furthermore, strong and unexpected asymmetry in removals has recently been observed after BCP treatment of ESS-medium beta resonators. The goal of this study is to investigate accurately influence of parameters such as surface geometry and orientation, acid temperature, agitation and their coupling on the removal rate. We will also focus on the influence of by-products such has NOx on kinetics. The mixture used is HF(40%)- HNO3(65%)-H3PO4(85%) with ratio 1-1-2.4.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB072
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TUPB073	Vertical Electro-polishing Collaboration Between Cornell, KEK, and Marui Galvanizing Co. Ltd	cathode, cavity, ion, linac	563
	F. Furuta, M. Ge, T. Gruber, J.J. Kaufman, M. Liepe, 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, KEK, and Marui Galvanizing Co. Ltd (MGI) have collaborated since 2014 on Vertical Electro-Polishing (VEP) R&D as a part of a US/Japan Program for Cooperation in High Energy Physics. We have focused on an improvement of removal uniformity during the VEP process. MGI and KEK have developed their original VEP cathode named i-cathode Ninja®, which has four retractable wing-shape parts per cell. Cornell processed one single cell cavity with VEP using this cathode and performed a vertical test. KEK also provided one 9-cell cavity to Cornell. Cornell then performed surface treatments including Cornell VEP and RF test on this 9-cell cavity. The progress by the VEP collaboration and RF test results are presented in this paper.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB073
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TUPB074	RF Performance of Multi-cell Scale Niobium SRF Cavities Prepared with HF Free Bipolar Electro-polishing at Faraday Technology	cavity, ion, niobium, MMI	567
	F. Furuta, M. Ge, T. Gruber, J.J. Kaufman, M. Liepe, J. Sears Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA T.D. Hall, M.E. Inman, R. Radhakrishnan, S.T. Snyder, E.J. Taylor Faraday Technology, Inc., Clayton, Ohio, USA
	Cornell's SRF group and Faraday Technology, Inc. have been collaborating on two phase-II SBIR projects. One of them is the development and commissioning of a 9-cell scale HF free Bipolar Electro-Polishing (BEP) system. Faraday Technology had completed the proof of principle on BEP with single cell scale prior to the work reported here, and has now developed a new 9-cell scale BEP system. Cornell has fabricated three single cell cavities and has assembled them together as a 9-cell scale test string. The 9-cell scale test string has received BEP at Faraday Technology and RF testing has been performed on the three single cell cavities one-by-one at Cornell. Here we give a status update on the new 9-cell scale BEP system commissioning and on results from RF tests of the BEP cavities.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB074
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TUPB075	Vertical Electro Polishing of Superconducting Single-and Multi Cell Gun Resonators	gun, cavity, ion, cathode	571
	N. Steinhau-Kühl, R. Bandelmann, A. Matheisen, S. Saegebarth, M. Schmökel DESY, Hamburg, Germany A. Arnold HZDR, Dresden, Germany
	At DESY activities on surface treatment of superconducting RF gun cavity resonators at 1.3 GHz are ongoing. Due to the small opening on the endplate for insertion of cathodes, no reasonable acid flow can be realized with the existing set up for horizontal electro polishing. To benefit from electro polishing of Niobium surfaces, an adapter to the existing horizontal electro polishing bench at DESY was set up and is in operation now. Vertical EP was applied on 1.3 GHz SRF gun resonators with 1.6 and 3.5 cell geometry. Work flow, process conditions as well as test results of gun cavities treated so far at DESY are described.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB075
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TUPB082	Setup of a Spatially Resolving Vector Magnetometry System for the Investigation of Flux Trapping in Superconducting Cavities	ion, cavity, niobium, superconducting-cavity	580
	B. Schmitz, K. Alomari, J. Knobloch, O. Kugeler, J.M. Köszegi, Y. Tamashevich HZB, Berlin, Germany
	Flux trapping is the major contribution to the residual resistance of superconducting cavities. In order to gain a better understanding of the mechanisms involved and aiming at an eventual minimization of trapped flux, a measurement setup based on AMR sensors was devised that allows for monitoring the magnetic field vector at various positions near the cavity surface. First results of the efforts are presented.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB082
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TUPB083	Post Processing of a 166.6 MHz HEPS-TF Cavity at Institute of High Energy Physics	cavity, ion, photon, target	583
	J. Dai, Z.Q. Li, P. Zhang IHEP, Beijing, People's Republic of China
	Funding: Work supported by High Energy Photon Source Test Facility (HEPS-TF) project A 166.667 MHz Proof-of-Principle (PoP) superconducting RF cavity has been fabricated by IHEP for the High Energy Photon Source Test Facility (HEPS-TF) [1]. After a series of post-processing including chemical etching (BCP), high temperature heat treatment, High Pressure water Rinsing (HPR) and 120°C baking, the cavity was cold RF tested and reached E_peak=86.5 MV/m and B_peak=132.1 mT with Q₀=5.1×〖10〗⁸ at 4.2K. The cavity was RF tested again at 2K, and reached E_peak=85.5 MV/m and B_peak=131.1 mT with Q₀=3.3×〖10〗⁹. daijin@ihep.ac.cn
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB083
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TUPB084	EP System Development at IHEP	cavity, ion, controls, cathode	586
	S. Jin, J. Dai, J. Gao, D.J. Gong, F.S. He, Z.Q. Li, Z.C. Liu, P. Sha, J.Y. Zhai, P. Zhang, T.X. Zhao IHEP, Beijing, People's Republic of China
	Electropolishing (EP) System is a critical facility for SRF cavity treatment, especially for high performance cavities which are necessary for several great projects like LCLS-II, CEPC, Shanghai XFEL, and so on. So, an EP system was under development at IHEP. At this stage, we would like a horizontal EP facility. Main purpose is for elliptical SRF Nb cavities like 500MHz single cell cavities. Besides, it should be compatible for other frequency cavities, such as 650MHz and 1.3GHz cavities. In this paper, we will mainly report the preliminary design for the EP system. Several key points in the design will be also discussed.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB084
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TUPB085	Quench Detection on Superconducting Cavity by Second Sound	ion, cavity, detector, site	589
	Z.C. Liu, J. Gao, F.S. He, H.Y. Lin, P. Zhang IHEP, Beijing, People's Republic of China
	High gradient is very important for superconducting cavity, however it may be limited by quench on the cavity high field region. Quench can be caused by various reasons. To locate the position is the key to reveal the mysteries of quench. OST sensor was widely used to locate the quench position. Now we are developing the quench position detection system by RTD sensors such as Cernox. In this paper, we will show the design of the second sound system and testing results on the QWR cavity.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB085
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TUPB086	Study on Local Chemical Treatment for Recovery From Surface Oxidation by HPR Process on SRF Cavities	cavity, ion, experiment, niobium	592
	H. Guo, Y. He, Y.M. Li, T. Tan, A.D. Wu, P.R. Xiong, Z.M. You, W.M. Yue, S.H. Zhang IMP/CAS, Lanzhou, People's Republic of China
	High pressure rinsing (HPR) with ultra-pure water (UPW) is the last step which is commonly used for SRF cavities cleaning. The serious surface damage will be caused due to the failure of the distance control between the jet and cavity surface or the breakdown of the jet rotation. The surface of taper HWR cavities which are used for CIADS project was damaged in HPR process. Two methods were used for surface recovery and the result will be presented in this paper.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB086
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TUPB090	Investigation of High Temperature Baking of Jacketed Quarter Wave Resonators	ion, cavity, linac, niobium	598
	A. Rai, D. Kanjilal, K.K. Mistri, P. Patra, P.N. Potukuchi, S.K. Sonti IUAC, New Delhi, India
	The Superconducting booster Linac at IUAC has been delivering accelerated beams for scheduled experiments since 2013. It has three accelerating modules with 8 Quarter Wave Resonators (QWR)in each. The QWRs for the first module were built at Argonne National Laboratory while those for the second and third modules have been built in-house. During the electropolishing of one of the indigenously built resonators (QWR # I03) the RF surface got spoiled due to a wrong acid mixture that was being used for etching. In subsequent cold tests of the cavity, its performance was poor (2.6 MV/m @ 4W). There was evidence of Q disease also, as the performance deteriorated further (~20%) when the cavity was held at 100-120K for ~8 hours .In an attempt to recover the cavity it was baked at 650 °C for 10 hours along with its stainless steel jacket. A series of tests were conducted thereafter wherein, a substantial improvement (factor of two) in the performance was observed. Encouraged with the results another QWR designed for a lower beta (β=0.05) was also heat treated identically. This paper presents the different treatments followed to enhance the cavity performance vis-à-vis the test results.
	Poster TUPB090 [1.240 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB090
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TUPB095	Modeling the Hydroforming of a Large Grain Niobium Tube With Crystal Plasticity	ion, cavity, niobium, experiment	616
	A. Mapar MSU, East Lansing, Michigan, USA T.R. Bieler Michigan State University, East Lansing, Michigan, USA J.E. Murphy University of Nevada, Reno, Reno, Nevada, USA F. Pourboghrat Ohio State University, Columbus, Ohio, USA
	Current SRF cavities are made from fine grained polycrystalline niobium half-cells welded together. Hot spots are commonly found in the heat-affected zone, making seamless hydroformed cavities attractive. Large grain cavities usually perform as well as fine grain cavities, often having a higher Q, presumably due to fewer grain boundaries. Large grain Nb forms non-uniformly, which introduces problems in manufacturing. A model that could realistically predict the deformation response of large grain Nb could facilitate the design of large grain hydroformed tubes. To this end, a crystal plasticity model was developed and calibrated with tensile stress-strain data of Nb single crystals. A seamless large grain tube was made from rolling a fine grain sheet into a tube, welded, and heat treated to grow large grains. The heat treatment resulted in a large grain tube with a single grain orientation in the center. The tube was hydroformed until it cracked. The hydroforming process was simulated with the crystal plasticity model, which was able to predict the deformed shape of the tube, the location of the crack and other localized areas with heterogeneous strain.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB095
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TUPB096	SRF Cavity Assembly in Clean Room with Horizontal Laminar Flow	ion, cavity, GUI, cryomodule	620
	A. Miyamoto, H. Hara, K. Sennyu, T. Yanagisawa MHI-MS, Kobe, Japan
	Mitsubishi Heavy Industries Mechatronics Systems(MHI-MS) has developed manufacturing process of superconducting cavitis for a long time. In this presentation, recent progress will be reported.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB096
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TUPB097	R&D of Electro-polishing (EP) Process with HF-free Neutral Electrolyte by Bipolar-pulse (BP) Method	ion, experiment, cavity, cathode	623
	J. Taguchi, Y. Mochida, T. Nakajima Nomura Plating Co, Ltd., Osaka, Japan H. Hayano, T. Saeki KEK, Ibaraki, Japan S. Kakudo, M. Kunieda The University of Tokyo, Tokyo, Japan
	Currently the Electro-Polishing (EP) process of Superconducting Radio-Frequency (SRF) accelerating cavity is performed with the electrolyte that is the mixture of hydrofluoric and sulfuric acids. However, the electrolyte is very dangerous and the environmental load in the disposal process of electrolyte is very heavy. This is the reason why the high cost is necessary in the safe design of facility and the safe operation of process in the conventional EP method. In such situation, considering the reduction of cost and environmental load in the EP process, we performed the R&D of novel EP process with HF-free neutral electrolyte by Bipolar-Pulse (BP) method. In this presentation, we will report the removal rate, surface roughness and the results of surface analysis for the Nb-coupon samples that were processed by the BP-EP with HF-free neutral electrolyte.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB097
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TUPB098	The Effect of Process Parameters on the Surface Properties of Niobium During Plasma Etching	ion, plasma, cavity, experiment	628
	J.J. Peshl, S. Popović, L. Vušković ODU, Norfolk, Virginia, USA J. Upadhyay LANL, Los Alamos, New Mexico, USA A-M. Valente-Feliciano JLab, Newport News, Virginia, USA
	Funding: This work is supported by the Department of Energy, Grant DE-SC0014397. We have shown that plasma etching using an electronegative Ar/Cl2 discharge can effectively remove surface oxide layers on Nb samples as well as bulk Nb from single cell SRF cavities. With accelerating fields on the order of wet etching processes and a decrease in field emission the use of plasma assisted etching for bulk Nb processing is a worthwhile endeavor. We are presenting the surface properties of plasma etched Nb. Cavity grade Nb coupons were made by water jet cutting, and then polished to achieve surface roughness equivalent to electropolishing (<1 micron). The coupons were plasma etched while process parameters (rf power, gas pressure, temperature and DC bias voltage) are varied. These samples are placed on the inner surface of the cylindrical cavity to be etched. The experimental setup is similar to the single cell cavity plasma etching setup. Each sample is weighed and scanned before and after plasma processing with an AFM, SEM, and digital optical microscope that provide both atomic composition and surface roughness profiles. Comparing the scans allows us to make conclusions about the effect of each parameter on the surface roughness. J. Upadhyay et. al. 'Cryogenic rf test of the first plasma etched SRF cavity,' arXiv: 1605.06494 [physics.acc-ph] (2016).*
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB098
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TUPB100	Determining BCP Etch Rate and Uniformity in High Luminosity LHC Crab Cavities	ion, cavity, experiment, simulation	635
	T.J. Jones STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom G. Burt Cockcroft Institute, Lancaster University, Lancaster, United Kingdom R. Calaga, O. Capatina, L.M.A. Ferreira, R. Leuxe CERN, Geneva, Switzerland T.J. Jones, J.A. Mitchell Lancaster University, Lancaster, United Kingdom S.M. Pattalwar STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom S. Verdú-Andrés, B. P. Xiao BNL, Upton, Long Island, New York, USA
	The compact SRF Crab Cavities required for HL-LHC have complex geometries making prediction of average and local BCP etch rates a difficult task. This paper describes a series of experiments and simulations used to determine the etch uniformity and rate within these structures. An initial experiment was conducted to determine the correlation between etch rate and flow rate in a Nb tube. These results were then incorporated into Computational Fluid Dynamics simulations of acid flow in the Double Quarter Wave (DQW) cavity to predict etch rates across the surface and allow optimisation of the BCP setup. There were several important findings from the work; one of which is that the flow rate in the relatively large body of the cavity is predominantly driven by natural convection due to the exothermic reaction. During BCP processing of the DQW cavity a significant difference in etching was observed between upper and lower horizontal surfaces which was mitigated by etching in several orientations. Two DQW cavities manufactured by CERN have received a heavy BCP of 200μm followed by 2 light BCPs of 30μm each with subsequent vertical cold tests showing performance exceeding specification.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB100
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TUPB104	First Full Cryogenic Test of the SRF Thin Film Test Cavity	ion, cavity, cryogenics, niobium	644
	R. Valizadeh, L. Bizel-Bizellot, P. Goudket, L. Gurran, O.B. Malyshev, N. Pattalwar, S.M. Pattalwar STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom G. Burt, L. Gurran Lancaster University, Lancaster, United Kingdom G. Burt, P. Goudket, O.B. Malyshev, S.M. Pattalwar, R. Valizadeh Cockcroft Institute, Warrington, Cheshire, United Kingdom L. Gurran Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
	A test cavity that uses RF chokes, rather than a physical seal, to contain the field is a promising method of SRF sample testing, especially in thin films research where the rate of sample production far outstrips that of full SRF characterisation. Having the sample and cavity physically separate reduces the complexity involved in changing samples - major causes of low throughput rate and high running costs for other test cavities - and also allows direct measurement of the RF power dissipated in the sample via power calorimetry. Choked test cavities operating at 7.8 GHz with three RF chokes have been designed and tested at Daresbury Laboratory. As part of the commissioning of this system, we performed the first full SRF test with a bulk Nb sample and we verified that the system would perform as required for future superconducting thin film sample tests.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB104
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TUPB106	Standardized Beamline Particulate Characterization Analysis: Initial Application to CEBAF and LCLS-II Cryomodule Components	ion, cavity, cryomodule, linac	647
	C.E. Reece, J.K. Spradlin, O. Trofimova, A-M. Valente-Feliciano JLab, Newport News, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177 Despite continuously evolving efforts to minimize particulates in operational SRF accelerator systems, the presence of electron field emission from contaminating particulates on SRF surfaces with high surface electric fields remains a challenge. Jefferson Lab has recently initiated a standardized particulate sampling and characterization practice in order to gain more systematic knowledge of the particulates actually present. It is expected that patterns that emerge from such sampling will strengthen source attribution and guide improvement efforts. Initial samples were gathered from a cryomodule and adjoining warm girders removed from the CEBAF tunnel for reprocessing. The collection and analysis techniques were also used to characterize particulates on the inside of LCLS-II string components. Samples are transferred to clean industry-standard forensic GSR carbon tape spindles and examined via automated cleanroom SEM scanning for particle localization and sizing. The particulates are subsequently analyzed with EDS for elemental composition. A catalogue of particle types is being accumulated. The methods used and results obtained from these initial applications will be presented.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB106
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TUPB108	Genesis of Topography in Buffered Chemical Polishing of Niobium for Application to Superconducting Radiofrequency Accelerator Cavities	ion, niobium, cavity, electron	651
	L. Zhao, C.E. Reece JLab, Newport News, Virginia, USA M.J. Kelley The College of William and Mary, Williamsburg, Virginia, USA
	Funding: Supported by Office of High Energy Physics, U.S. Department of Energy, Grant SC0007907 to the College of William & Mary and by U.S. DOE Contract No. DE-AC05-06OR23177 to Jefferson Science Associates Topography arising from the final etch step in preparing niobium superconducting radiofrequency (SRF) accelerator cavities is understood to significantly impact cavity performance at high field levels. This study investigated the effect of process temperature and time on the etch rate and topography arising from the widely-used buffered chemical polishing (BCP). This study aims to understand more thoroughly the genesis of topography in BCP of polycrystalline niobium, with the ultimate aim of finding a path to surface smoothness comparable to that obtained by electropolishing (EP). It was found that the etch process is controlled by the surface reaction; and that the etch rate varies with crystallographic orientation. The familiar micron-scale roughening necessarily results. Gas evolution has an impact, but is secondary. The major outcome is that surface smoothness comparable to EP appears to be inherently unachievable for polycrystalline niobium using BCP, setting an upper limit to the gradient for which it is useful.
	Poster TUPB108 [3.782 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB108
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TUPB112	First Test of Electropolishing System at IMPCAS	ion, cavity, cathode, controls	660
	L. Li, Q.W. Chu, H. Guo, Y. He, P.R. Xiong, Z.Q. Yang, Z.M. You, B. Zhang, S.H. Zhang, X. Zhu IMP/CAS, Lanzhou, People's Republic of China
	The first SRF cavity electropolishing system of China has been built by IMPCAS. We used two type of cathodes in different process parameters to test the typical Voltage-Current Density curves of 1.3GHz one-cell SRF cavity.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB112
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WEXA01	High Performance Nb3Sn Cavities	ion, cavity, niobium, site	667
	D.L. Hall, M. Liepe, R.D. Porter Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA T. Arias, P. Cueva, D. Liarte, D.A. Muller, J.P. Sethna, N. Sitaraman Cornell University, Ithaca, New York, USA
	In recent years, 1.3 GHz single-cell cavities coated with Nb3Sn at Cornell University have repeatedly demonstrated quality factors of >10¹⁰ at 4.2 K and >15 MV/m. Ongoing research is currently focussed on the impact of intrinsic and extrinsic factors that limit the quality factor and quench field in these cavities. New single-cell cavities have been commissioned to enable further exploration of the coating parameter space. Experimental studies on both cavities and sample coupons have been supplemented by theoretical work done on layer growth, trapped vortex motion and flux entry. In this paper, we provide a comprehensive overview of the latest developments on Nb3Sn cavities, including work conducted in collaboration with the new NSF Centre for Bright Beams, with a brief summary on work being done in the field at large.
	Slides WEXA01 [10.681 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-WEXA01
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WEXA03	High-performance Thin-film Niobium Produced via Chemical Vapor Deposition (CVD)	niobium, ion, cavity, electron	674
	R.D. Porter, D.L. Hall, M. Liepe, J.T. Maniscalco Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA V.M. Arrieta, S.R. McNeal, W.E. Williams Ultramet, Pacoima, California, USA
	Bulk niobium cavities have been the standard for superconducting particle accelerators for many years. However, the cost of high RRR niobium start materials makes them expensive. The use of Chemical Vapor Deposition (CVD) processing technologies to produce thin Nb films on low-cost substrates (e.g. copper) offers a method to significantly reduce the cost of accelerator cavity fabrication while increasing cavity performance capabilities. Recent optimization of CVD niobium processes for high RRR Nb films has led to RF performance approaching that of bulk Nb. In collaboration with Ultramet, Cornell continues to explore the potential of CVD techniques. This paper presents results from a detailed study of CVD thin film Nb materials produced by Ultramet on 5-inch diameter copper and molybdenum substrates, including RF performance results with T-mapping and detailed surface analysis of performance limiting regions. Our work shows that CVD-based cavity fabrication methods are a promising alternative to sheet-formed bulk cavities, and to other thin Nb film techniques, warranting further development. Additional results from the field will be discussed.
	Slides WEXA03 [1.503 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-WEXA03
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WEYA05	Progress Toward 2 K High Performance Half-wave Resonators and Cryomodule	ion, cavity, cryomodule, cryogenics	692
	Z.A. Conway, B.M. Guilfoyle, M. Kedzie, M.P. Kelly, T. Reid ANL, Argonne, Illinois, USA H. Guo IMP/CAS, Lanzhou, People's Republic of China
	Funding: This material is based upon work supported by the U.S. DOE, Office of Science's Office of Nuclear Physics and Office of High Energy Physics, contract numbers DE-AC02-06CH11357 and DE-AC02-76CH03000. Argonne National Laboratory is implementing a novel 2.0 K superconducting cavity cryomodule operating at 162.5 MHz. This cryomodule is designed for the acceleration of 2 mA H-/proton beams from 2.1 to 10.3 MeV as part of the Fermilab Proton Improvement Project-II (PIP-II). The 2.0 K cryomodule is comprised of 8 half-wave cavities operated in the continuous wave mode with 8 superconducting magnets, one in front of each cavity. In this paper we will review recent cavity results which demonstrate continuous-wave operated cavities with low-field residual resistances of 2.5 nΩ which achieve peak surface fields up to 134 MV/m and 144 mT, electric and magnetic respectively, with field emission onset fields greater than 70 MV/m in the production cavities following the prototyping effort.
	Slides WEYA05 [1.967 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-WEYA05
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THXA04	Fabrication, Treatment and Test of Large Grain Cavities	cavity, ion, superconducting-cavity, FEL	700
	J.K. Hao, J.E. Chen, L.W. Feng, L. Lin, K.X. Liu, S.W. Quan, F. Wang, H.M. Xie, F. Zhu PKU, Beijing, People's Republic of China
	Development of SRF technology has been included in the project of Soft X-ray FEL (SXFEL) for a hard X-ray FEL plan in China which would be operated in CW mode. Six 9-cell TESLA type cavities as well as several single-cell cavities made of Ningxia large grain niobium material have been fabricated by Peking University for achieving high gradient and high intrinsic quality factor Q0. The measurements of gradient and Q0 have been carried out with a new vertical test system at PKU. The process of fabrication, surface treatment and test results of these large grain cavities will be presented.
	Slides THXA04 [7.911 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-THXA04
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THXA08	Review of Heat Treatments for Low Beta Cavities : What's So Different from Elliptical Cavities	ion, cavity, niobium, accelerating-gradient	708
	D. Longuevergne IPN, Orsay, France
	Heat treatments done for low beta (low frequency) cavities are usually, due to the lack of feedback, inspired from elliptical (high frequency) cavity results. Is that still relevant now that experimental data are available thanks to the florishing business of low beta structures (Spiral2, ESS, FRIB, C-ADS, MYRRHA, PROJECTX, …). These 2 families are moreover not usually operating in the same resistance regime (BCS and residual). The paper will review procedures applied and results obtained on different type of cavities (Quarter-Wave resonator, Half-Wave resonator and Spoke) and different temperature treatments (low temperature baking, hydrogen degassing, nitrogen doping, …) and compare these to elliptical cavities.
	Slides THXA08 [5.567 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-THXA08
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THYA01	Performance Testing of FRIB Early Series Cryomodules	ion, cavity, cryomodule, linac	715
	J.T. Popielarski, C. Compton, A. Ganshyn, W. Hartung, D. Luo, S.J. Miller, D.G. Morris, P.N. Ostroumov, L. Popielarski, K. Saito, S. Shanab, S. Stark, T. Xu, S. Zhao, Z. Zheng FRIB, East Lansing, USA
	Funding: U.S. Department of Energy Office of Science under Cooperative Agreement DE SC0000661. Construction of a new accelerator for nuclear physics research, the Facility for Rare Isotope Beams (FRIB), is underway at Michigan State University (MSU). The FRIB linac will use superconducting resonators at an operating temperature of 2 K to accelerate ions to 200 MeV per nucleon. The linac requires 10⁶ quarter wave resonators (80.5 MHz, β = 0.043 and 0.086) and 248 half wave resonators (322 MHz, β = 0.29 and 0.54), all made from sheet Nb. Production resonators being delivered to MSU by cavity vendors. At MSU, the resonators are etched, rinsed, and tested in MSU's certification test facility. Certification testing is done before the installation of the high-power input coupler and the tuner. After certification, the resonators are tested in the cryomodule before installation into the FRIB tunnel. The cryomodule test goals are to verify integrated operation of the resonators, RF couplers, tuners, RF controls, and superconducting solenoids. To date, 10 cryomodules out of 48 have been fabricated, and 8 of the cryomodules have been certified. Cryomodule test results are presented in this paper.
	Slides THYA01 [31.165 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-THYA01
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THPB003	An Innovative Design of a Flexible Temperature-mapping System	cavity, ion, electron, superconducting-cavity	746
	M. Ge, F. Furuta, M. Liepe, P.J. Pamel Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	A temperature-mapping (T-Map) system is an essential tool for fundamental SRF research as it provides spatial information of RF power dissipation and so allows localizing hot-spots on a cavity surface at cryogenic temperatures. However, the temperature sensors are mounted on rigid boards in most current systems, so each can only work for one specific cavity size and shape. In this paper, we proposed a flexible design, which allows this temperature mapping system to work for different cavity shapes.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-THPB003
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THPB005	Design Updates on Cavity to Measure Suppression of Microwave Surface Resistance by DC Magnetic Fields	ion, cavity, niobium, experiment	754
	J.T. Maniscalco, M. Liepe, R.D. Porter Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Our research has shown good agreement between experimental measurements of the anti-Q-slope in niobium SRF cavities and predictions from a recent theoretical model of the suppression of the microwave surface resistance with applied RF field. To confirm that this mechanism is indeed what causes the anti-Q-slope in impurity-doped niobium, it will be necessary to measure the theory's prediction that the same effect may be achieved by applying a constant (i.e. DC) magnetic field parallel to the RF surface. This will also allow for systematic studies of the proposed fundamental effect of the anti-Q-slope and of the behavior of the anti-Q-slope for many surface preparations and alternative materials, since it provides a cleaner measurement by eliminating the counteracting quasiparticle overheating and the complexifying oscillation of the screening currents. In this report we give an update on work at Cornell to design and build a coaxial cavity to measure this effect.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-THPB005
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THPB007	Nitrogen Infusion R&D on Single Cell Cavities at DESY	ion, cavity, niobium, injection	759
	M. Wenskat, D. Reschke, J. Schaffran DESY, Hamburg, Germany A.L. Prudnikava University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
	A first series of single cell cavities underwent the "Nitrogen Infusion" treatment at DESY. Samples, which were in the furnace together with the cavities, underwent a series of SEM/EDX measurements and showed some unexpected structures. In parallel, the cavity performance deteriorated after the treatment. The furnace pressure and temperature and the residual gases during the treatment were analyzed and the possible cause for the deterioration has been found. Steps to prevent this deterioration in following treatments are discussed and first results are shown.
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THPB018	Towards the Perfect Meissner State: A Magneto-Optical Study on Competing Pinning Centers in Niobium	ion, niobium, cavity, background	766
	J.M. Köszegi, J. Knobloch, O. Kugeler HZB, Berlin, Germany
	Over the past years trapped magnetic flux has emerged as a main limiting factor of high quality factors in SRF cavities. Several studies investigated how the ambient magnetic field can be minimized or how the flux expulsion during the phase transition can be improved. We now present a study that targets the pinning centers which allow for the flux to remain inside the superconductor in the first place. Using magneto-optical imaging we were able to not only measure the amount of trapped flux but in addition we managed to image its distribution with a resolution below 10μm and correlate it with electron backscatter diffraction maps. As a result we found that the grain boundaries did not play a major role as pinning centers nor did the crystal orientation influence the amount of trapped flux signifi-cantly. Niobium hydrides which formed during the cool down to cryogenic temperatures however were found to enhance trapping.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-THPB018
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THPB021	Trial of Nitrogen Infusion and Nitrogen Doping by Using J-PARC Furnace	ion, cavity, niobium, controls	775
	T. Konomi, T. Dohmae, Y. Hori, E. Kako, T. Kubo, G.-T. Park, H. Sakai, K. Umemori KEK, Ibaraki, Japan J. Kamiya, K. Takeishi JAEA/J-PARC, Tokai-mura, Japan T. Nagata ULVAC, Inc., Tsukuba, Japan
	KEK has been carrying out SRF cavity developments toward higher Q-values and higher accelerating gradients. In the past nitrogen-doping was tested using the KEK furnaces, but it did not succeed. This time nitrogen infusion and nitrogen doping are tested using the J-PARC's furnace, which has an oil-free pumping system and is mainly pumped by a 10000 L/s cryopump and three 3000 L/s turbo pumps. Nitrogen pressure is controlled by a variable leak valve and an additional turbo pump. To avoid performance degradation during heat treatment, flanges of cavities are covered by Nb caps and foils. Nitrogen infusion at 120 degrees was applied to a single cell cavity and cavity performance was measured by vertical tests after HPR and assembly. Nitrogen doping at 800 degrees is also applied to another single cell cavity. After applying EP and HPR, vertical tests were carried out. Nb samples were also installed into the furnace during heat treatment. Surfaces are analyzed by SIMS and XPS. In this presentation, we report procedure of nitrogen infusion and doping, vertical test results and results of surface analysis.
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THPB024	Investigation on Depth Profiling of Niobium Surface Composition and Work Function of SRF Cavities	ion, niobium, cavity, electron	779
	A.D. Wu, L. Chen, Q.W. Chu, H. Guo, Y. He, Y.M. Li, F. Pan, L. Yang, S.H. Zhang, H.W. Zhao IMP/CAS, Lanzhou, People's Republic of China
	The niobium samples were prepared by different surface treatments that commonly applied for the superconducting RF cavities preparation, as the following of electrochemical polishing, the buffered chemical polishing and high temperature annealing. In order to understand the property of niobium surface, especially the relationship between the composition and the work function value, the X-ray and ultraviolet photoelectron spectra depth profiling has been studied. The intensity photoelectrons signals of O1s, C1s and the Nb3d were identified for composition of the niobium oxide and the hydrocarbon contamination. And the work function of sample surface was measured via the means of the ultraviolet photoelectron spectra band width. To make a depth profiling, the sputtering of Argon ions was used to remove surface material gradually under by control the sputtering times. The results shown that the value of work function strongly depends on the chemical composition.
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THPB026	Investigation of the Effect of Strategically Selected Grain Boundaries on Superconducting Properties of SRF Cavity Niobium	ion, niobium, cavity, cryogenics	787
	M. Wang, T.R. Bieler Michigan State University, East Lansing, Michigan, USA S. Balachandran, P.J. Lee NHMFL, Tallahassee, Florida, USA S. Chetri, A. Polyanskii ASC, Tallahassee, Florida, USA C. Compton FRIB, East Lansing, Michigan, USA
	Funding: Research supported by DOE/OHEP contracts DE-SC0009962, DE-SC0009960, NSF-DMR-1157490, and the State of Florida. High purity Nb is commonly used for fabricating SRF cavities due to its high critical temperature and its formability. However, microstructural defects such as dislocations and grain boundaries in niobium can serve as favorable sites for pinning centers of magnetic flux that can degrade SRF cavity performance. In this study, two bi-crystal niobium samples extracted from strategically selected grain boundaries were investigated for the effect of grain misorientation on magnetic flux behavior. Laue X-ray and EBSD-OIM crystallographic analyses were used to characterize grain orientations and orientation gradients. Cryogenic Magneto-Optical Imaging (MOI) was used to directly observe magnetic flux penetration at about 5-8 K. Flux penetration was observed along one of the grain boundaries, as well as along a low angle boundary that was not detected prior to MOI imaging. Hydride scars on the sample surface after MOI were examined using atomic force microscopy (AFM) analysis. The relationships between dislocation content, cryo-cooling, flux penetration and grain boundaries are examined.
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THPB027	Characterization of Microstructural Defects in SRF Cavity Niobium using Electron Channeling Contrast Imaging	ion, cavity, niobium, electron	792
	M. Wang, T.R. Bieler, D. Kang Michigan State University, East Lansing, Michigan, USA C. Compton FRIB, East Lansing, Michigan, USA
	Funding: Research supported by DOE/OHEP contract DE-SC0009962 Although the quality factor of niobium cavities has improved, performance variability arises from microstructural defects such as dislocations and grain boundaries that can trap magnetic flux, block heat transfer, and perturb superconducting currents. Microstructural defect evolution is compared in four samples extracted from a 2.8 mm thick large-grain niobium slice, with tensile axes chosen to generate desired dislocation structures during deformation. The four samples are 1) as-extracted, 2) extracted and annealed, 3) extracted and then deformed to 40% strain, and 4) extracted, annealed at 800 °C 2 hours, and deformed to 40% strain. Electron Channeling Contrast Imaging (ECCI) was performed on all samples to characterize initial dislocation density, dislocation structure evolution due to annealing and deformation, and related to the mechanical behavior observed in stress-strain curves. The orientation evolution and geometrically necessary dislocation (GND) density were characterized with electron backscattered diffraction (EBSD) maps. Fundamental understanding of dislocation evolution in niobium is necessary to develop models for computational cavity design.
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Paper

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MOYA01

The Superconducting Accelerator for the ESS Project

ion, cavity, cryomodule, linac

24

F. Schlander, C. Darve, N. Elias, M. Lindroos, C.G. Maiano
ESS, Lund, Sweden
P. Bosland
CEA/IRFU, Gif-sur-Yvette, France
M. Ellis
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
P. Michelato
INFN/LASA, Segrate (MI), Italy
G. Olry
IPN, Orsay, France
R.J.M.Y. Ruber
Uppsala University, Uppsala, Sweden

The European Spallation Source, ESS, is under construction in Lund since 2014. While the installation of the source and the normal conducting part will start in this autumn, the production and testing of cryomodules and cavities for the superconducting accelerator is in full swing at the partner laboratories. The spoke cavities and cryomodules will be provided by IPN Orsay and the testing of those modules will take place at Uppsala University. Prototyping and assembly of the elliptical cryomodules series is occurring at CEA Saclay, and the modules will be tested at a new test stand at ESS. The fabrication and test of the medium beta cavities is provided by INFN Milan and STFC Daresbury for the high beta cavities respectively. An overview of the current activities and test results will be presented in this talk.

Slides MOYA01 [26.361 MB]

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MOYA02

BESSY VSR: SRF Challenges and Developments for a Variable-pulse Length Next-generation Light Source

ion, cavity, HOM, synchrotron

29

A.V. Vélez, H.-W. Glock, F. Glöckner, B.D.S. Hall, J. Knobloch, A. Neumann, P. Schnizer, E. Sharples
HZB, Berlin, Germany
A.V. Tsakanian
Helmholtz-Zentrum Berlin für Materialien und Energie GmbH (HZB), Berlin, Germany

The BESSY VSR project represents an exciting alternative to diffraction limited storage rings in the development of a next generation light source. Such a system should be capable to store "standard" (some 10 ps long) and "short" (ps and sub-ps long) pulses simultaneously in the storage ring opening the door to picosecond dynamic and high-resolution experiments at the same facility. This unique feature can be created by the introduction of the beating effects produced by higher harmonic SRF cavity systems (1.5 GHz & 1.75 GHz). The challenging design specifications as well as the technological demands on the SRF system make BESSY VSR a defiant project where non-standard techniques such as waveguide-damped cavities have been further developed. This talk focuses on the new SRF developments that includes wveguide-damped cavities, high-power couplers and higher-order mode absorbers that must handle nearly 2 kW of HOM power. The cryomodule design and its interaction with the beam will also be discussed.
Comment: VSR concept was introduced at SRF15. Much development work has now been done. Here the focus is more one the technology of VSR and the talk could also be listed under "SRF technology R&D"

Slides MOYA02 [7.961 MB]

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MOPB003

A New High Resolution Optical System for Inspection of Gun-and Multi-cell Resonators in ISO-4 Cleanrooms

ion, cavity, gun, MMI

47

M. Schalwat, R. Bandelmann, A. Daniel, N. Krupka, A. Matheisen, S.T. Sievers
DESY, Hamburg, Germany

Optical inspection of the inner surface of superconducting resonators was established during European XFEL cavity production by usage of the so called OBACHT optical inspection. In addition to the surface inspection by OBACHT a new optical inspection system with integrated high resolution camera is set up at DESY. It allows inspection of multi-cell resonators as well as gun cavity resonators with only single side accessibility to the inner surface. A prototype was commissioned and optical inspections were done with OBACHT and the new system in parallel. Two SRF gun cavities were inspected by this optical system and origin of limitations of the resonators were identified.

Poster MOPB003 [0.220 MB]

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MOPB009

Progress of 650 MHz SRF Cavity for eRHIC SRF Linac

cavity, ion, HOM, linac

64

W. Xu, I. Ben-Zvi, Y. Gao, D. Holmes, P. Kolb, G.T. McIntyre, C. Pai, R. Porqueddu, K.S. Smith, R. Than, J.E. Tuozzolo, F.J. Willeke, A. Zaltsman
BNL, Upton, Long Island, New York, USA
I. Ben-Zvi
Stony Brook University, Stony Brook, USA

Funding: This work is supported by LDRD program of Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. DOE.
eRHIC ERL SRF requires 160 5-cell 650 MHz SRF cavities. The 650 MHz cavity has been designed and two prototypes have been fabricated, one Cu cavity for HOM study and one Nb cavity for cavity performance study. This paper will describe cavity design and the progress of prototyping.

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MOPB012

Status of the IFMIF LIPAc SRF Linac

ion, cavity, cryomodule, operation

74

N. Bazin, C. Boulch, A. Bruniquel, P. Carbonnier, J.K. Chambrillon, G. Devanz, F. Éozénou, P. Hardy, H. Jenhani, O. Piquet, J. Plouin, A. Riquelme, D. Roudier, C. Servouin
CEA/DRF/IRFU, Gif-sur-Yvette, France
P. Charon, S. Chel, G. Disset, L. Maurice, J. Relland, B. Renard
CEA/IRFU, Gif-sur-Yvette, France
P. Contrepois
CEA/DSM/IRFU, France
D. Regidor, F. Toral
CIEMAT, Madrid, Spain

The IFMIF accelerator aims to provide an accelerator-based D-Li neutron source to produce high intensity high energy neutron flux to test samples as possible candidate materials to a full lifetime of fusion energy reactors. A prototype of the low energy part of the accelerator is under construction at Rokkasho in Japan. It includes one cryomodule containing 8 half-wave resonators (HWR) operating at 175 MHz and eight focusing solenoids. This paper presents the status of the IFMIF SRF Linac.

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MOPB013

European XFEL Input Coupler Experiences and Challenges in a Test Field

ion, FEL, GUI, operation

78

F. Hoffmann, D. Kostin, W.-D. Möller, D. Reschke, M. Wiencek
DESY, Hamburg, Germany

102 European XFEL accelerating modules with 816 superconducting cavities and main input RF power couplers were assembled and then tested at DESY prior to installation in the European XFEL tunnel. In the Accelerating Module Test Facility (AMTF) warm and cold RF tests were done. The test results went directly to the operational setup for the LINAC. Main input couplers did present several problems during the tests, resulting in some minor coupler design changes as well as in a few repair actions. The experience got from the said testing operation is worth to be shared and is presented here together with a discussion.

Poster MOPB013 [0.648 MB]

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MOPB018

Testing of SRF Cavities and Cryomodules for the European Spallation Source

ion, cavity, cryomodule, linac

95

N. Elias, E. Asensi Conejero, C. Darve, N.F. Hakansson, W. Hees, C.G. Maiano, F. Schlander
ESS, Lund, Sweden

The European Spallation Source (ESS) is currently under construction in Lund, Sweden. The ESS linear accelerator aims to deliver a 62.5 mA , 2.86 ms long proton beam onto a rotating tungsten target, at 14 Hz repetition rate, thus achieving an energy of 2 GeV and 5 MW power. Most of the beam acceleration happens in the superconducting fraction of the linac, which is composed of three sectors of cryomodules named after the cavities housed within. The first sector of the SRF linac is composed of 13 Spoke cryomodules containing 2 double-spoke cavities with a geometric beta of 0.5, the second is composed of 9 medium beta cryomodules each housing four elliptical cavities (β=0.67) and finally 21 high beta cryomodules enclosing four elliptical cavities (β=0.86). ESS has strategically built up a SRF collaboration with other European institutions, these partners will deliver through In-Kind agreements cavities and cryomodules performing within the ESS specification. This article describes the process leading to the acceptance of cavities and cryomodules received from the different partners and the necessary testing required prior to the final installation in the ESS tunnel.

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MOPB023

Further Layout Investigations for a Superconducting CW-linac for Heavy Ions at GSI

ion, linac, cavity, heavy-ion

108

W.A. Barth, K. Aulenbacher, F.D. Dziuba, V. Gettmann, T. Kürzeder, M. Miski-Oglu
HIM, Mainz, Germany
K. Aulenbacher
IKP, Mainz, Germany
W.A. Barth, M. Heilmann, S. Yaramyshev
GSI, Darmstadt, Germany
W.A. Barth, S. Yaramyshev
MEPhI, Moscow, Russia
M. Basten, H. Podlech, M. Schwarz
IAP, Frankfurt am Main, Germany

Very compact accelerating-focusing structures, as well as short focusing periods, high accelerating gradients and very short drift spaces are strongly required for superconducting (sc) accelerator sections operating at low and medium beam energies. To keep the GSI-Super Heavy Element program competitive on a high level and even beyond, a standalone sc continuous wave Linac in combination with the GSI High Charge State injector, upgraded for cw-operation, is envisaged. The first LINAC section (financed by HIM and GSI) as a demonstration of the capability of 216 MHz multi gap Crossbar H-structures (CH) is still in the beam commissioning phase, while an accelerating gradient of 9.6 MV/m (4 K) at a sufficient quality factor has been already reached. Recently the overall Linac design, based on a standard cryomodule, comprising three CH cavities, a rebuncher section and two 9.3 T-solenoidal lenses, has to be fixed. This paper presents the status of the Linac layout studies as well as the integration in the GSI accelerator facility.

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MOPB031

Fabrication and Cold Test Result of FRIB β=0.53 Pre-production Cryomodule

ion, cavity, cryomodule, solenoid

120

H. Ao, J. Asciutto, B. Bird, N.K. Bultman, E.E. Burkhardt, F. Casagrande, C. Compton, K.D. Davidson, K. Elliott, A. Ganshyn, I. Grender, W. Hartung, L. Hodges, I.M. Malloch, S.J. Miller, D.G. Morris, P.N. Ostroumov, J.T. Popielarski, L. Popielarski, M.A. Reaume, K. Saito, M. Shuptar, S. Stark, J.D. Wenstrom, M. Xu, T. Xu, Z. Zheng
FRIB, East Lansing, USA
A. Facco
INFN/LNL, Legnaro (PD), Italy

Funding: Work supported by the U.S. Department of Energy Office of Science under Cooperative Agreement DE-SC0000661
The driver linac for the Facility for Rare Isotope Beams (FRIB) comprises four kinds of cavities (β=0.041, 0.085, 0.29, and 0.53) and six types of cryomodules including matching modules. FRIB has completed the fabrication and the cold test of a β=0.53 pre-production cryomodule, which is the first prototype for a half-wave (β=0.29 and 0.53) cavity. This paper describes the fabrication and the cold test result of the β=0.53 pre-production cryomodule including lessons learned.

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MOPB035

Cryogenic Probe Station at Old Dominion University Center for Accelerator Science

ion, cavity, cryogenics, niobium

128

J. Makita, J.R. Delayen, A.V. Gurevich
ODU, Norfolk, Virginia, USA
G. Ciovati
JLab, Newport News, Virginia, USA

With a growing effort in research and development of an alternative material to bulk Nb for a superconducting radiofrequency (SRF) cavity, it is important to have a cost effective method to benchmark new materials of choice. At Old Dominion University's Center for Accelerator Science, a cryogenic probe station (CPS) will be used to measure the response of superconductor samples under RF fields. The setup consists of a closed-cycle refrigerator for cooling a sample wafer to a cryogenic temperature, a superconducting magnet providing a field parallel to the sample, and DC probes in addition to RF probes. The RF probes will extract a quality factor from a sample patterned in a coplanar waveguide resonator structure on a 2' wafer. From the measured quality factor, the surface resistance and the penetration depth as a function of temperature and magnetic field will be calculated. This paper will discuss the design and measurement procedures of the current CPS setup.

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MOPB036

The Study of Deposition Method of Nb3Sn Film on Cu Substrate

ion, niobium, cavity, superconductivity

131

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

Our work is mainly focused on the fabrication methods of Nb3Sn films on Cu substrates and film's properties. There are diffraction peaks of Nb3Sn in the X-ray diffraction patterns in which without diffraction peaks of copper compounds. Scanning electron microstructures of Nb3Sn film reflect its nice compactness and binding force between film and substrate.

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MOPB040

ESS High-beta Cavity Test Preparations at Daresbury Laboratory

ion, cavity, niobium, LLRF

137

P.A. Smith, L. Bizel-Bizellot, K.D. Dumbell, M. Ellis, P. Goudket, A.J. Moss, E.F. Palade, S.M. Pattalwar, M.D. Pendleton, A.E. Wheelhouse
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom

Science and Technology Facility Council is responsible for supplying, and testing 84 High beta elliptical SRF cavities, as part of the UK In Kind Contribution to the European Spallation Source (ESS). The High-β=0.86, cavities have been designed by CEA- Saclay and are a five cell Niobium cavity operating at 704.42 MHz. They are required to provide an accelerating gradient of 19.9 MV/m at an unloaded Q of 5x10⁹. Preparations are underway to upgrade the cryogenic and RF facilities at Daresbury laboratory prior to the arrival of the first cavities. As part of these arrangements, a niobium coaxial resonator has been manufactured, to validate the test facility. The design considerations, for the coaxial resonator are presented, along with preliminary results. The RF measurement system to perform the cavity conditioning and testing is also presented.

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MOPB041

Status of the SOLEIL Superconducting RF System

ion, cavity, operation, GUI

141

M. Diop, J.P. Baete, R.C. Cuoq, H.D. Dias, J.L. Labelle, L.R. Lopes, M. Louvet, P. Marchand, C.M. Monnot, S. Petit, F. Ribeiro, T. Ruan, R. Sreedharan, K.T. Tavakoli
SOLEIL, Gif-sur-Yvette, France

The 352 MHz SOLEIL SRF systems consist in two cryomodules, each containing a pair of SC Nb/Cu cavities, cooled with LHe at 4K from a single 350 W cryogenic plant. In order to store 500 mA, a power of 575 kW and an accelerating voltage of 3-4 MV are required. The RF power is provided by 4 SSPA's delivering up to 180 kW each. The original cavity input power couplers, which are LEP-type antennas designed to handle up to 200 kW, are being replaced by upgraded versions, able to operate at 300 kW CW. This will open the possibility to operate at full beam current with only one active cryomodule. The SRF system operational experience over the past ten years as well as the different upgrades will be reported here.

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MOPB046

LCLS-II Cryomodule Production at JLab

ion, cryomodule, cavity, vacuum

163

R.A. Legg, G. Cheng, E. Daly, G.K. Davis, M.A. Drury, J.F. Fischer, T. Hiatt, N.A. Huque, L.K. King, J.P. Preble, A.V. Reilly, M. Stirbet, K.M. Wilson
JLab, Newport News, Virginia, USA

Funding: This work was supported by the LCLS-II Project and the U.S. Department of Energy, Contract DE-AC02-76SF00515.
The LCLS-II cryomodule construction program leverages the mature XFEL cryomodule design to produce technologically sophisticated cryomodules with a minimum of R&D according to an accelerated manufacturing schedule. Jlab, as one of the partner labs, is producing 18 cryomodules for LCLS-II. To meet the quality and schedule demands of LCLS-II, many upgrades to the JLAB cryomodule assembly infrastructure and techniques have been made. JLab has installed a new cleanroom for string assembly and instituted new protocols to minimize particulate transfer into the cavities during the cryomodule construction process. JLab has also instituted a set of magnetic hygiene protocols to be used during the assembly process to minimize magnetic field impingement on the finished cavity structure. The goal has been to have gradients, both maximum and field emission onset, that do not degrade between the cavity vertical test and final cryomodule qualification, while maximizing the Q0 of each finished cavity. Results from the prototype cryomodule assembly are presented.

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MOPB050

Cavity Processing and Testing Activities at Jefferson Lab for LCLS-II Production

cavity, ion, FEL, cryomodule

173

L. Zhao, G.K. Davis, J. Follkie, D. Forehand, K. Macha, A.D. Palczewski, A.V. Reilly
JLab, Newport News, Virginia, USA

Funding: Work supported by Jefferson Science Associates, LLC under U.S. DOE Contracts DE-AC05-06OR23177 and DE-AC02-76SF00515 for the LCLS-II Project.
Cryomodule production for LCLS-II is well underway at Jefferson Lab. This paper explains the process flow for production cavities, from being received at the Test Lab to being assembled onto cavity strings. Taking our facility and infrastructure into consideration, process optimization and process control are implemented to ensure high quality products.

Poster MOPB050 [2.338 MB]

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MOPB063

Fundamental Studies for the STF-type Power Coupler for ILC

ion, vacuum, FEL, cavity

194

Y. Yamamoto, E. Kako, T. Matsumoto, S. Michizono, A. Yamamoto
KEK, Ibaraki, Japan
M. Irikura, M. Ishibashi, H. Yasutake
Toshiba Electron Tubes & Devices Co., Ltd (TETD), Tochigi, Japan

From the view point of mass-production for the power coupler in ILC, the fundamental studies for the STF-type power coupler are under progress by the collaboration between KEK and TETD. At present, there are various rinsing procedures for power coupler in the world-wide laboratories. In this R&D, the main topic is to investigate the various rinsing effects in the copper plating and the ceramic through the high power test. In this paper, the first results will be presented.

Poster MOPB063 [2.237 MB]

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MOPB065

Development of Hybrid Superconducting Photocathodes on Niobium Using High QE Coatings

ion, cathode, electron, site

205

M. Warren, A.R. Denchfield, N. Samuelson, J. Zasadzinski
IIT, Chicago, Illinois, USA
W. Gai, J.H. Shao, E.E. Wisniewski
ANL, Argonne, Illinois, USA
L.K. Spentzouris, Z.M. Yusof
Illinois Institute of Technology, Chicago, Illinois, USA

High power, low emittance electron beams require superconducting RF photoinjectors, typically made of pure Nb, and a superconducting photocathode is desired. However, superconductivity and high photocathode quantum efficiency (QE) are not compatible, e.g. QE for pure Nb is only 10^-5 at 260 nm wavelength. Here is presented the current status of the development of hybrid superconducting photocathodes by the deposition of thin films of a high QE metal or semiconductor on Nb. Nb plugs coated with 10-100 nm of Mg have been tested for adhesion and dark current under RF fields as high as 60MV/m. QE measurements show significant enhancements over Nb. In another test, ultra thin films of the high QE material Cs2Te deposited on Nb are reported. Using the standard deposition procedure, QE ~12% is found for films ~ 200Å. As the thickness is reduced QE maintains a high value ~ 6% for films as thin as 2.0 nm. These results are quite promising for future superconducting photocathodes.

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MOPB086

First Results of the IFMIF/EVEDA-SaTHoRI Tests

ion, cavity, controls, cryomodule

262

O. Piquet, N. Bazin, P. Carbonnier, J.K. Chambrillon, M. Desmons, G. Devanz, H. Jenhani, C. Servouin
CEA/DRF/IRFU, Gif-sur-Yvette, France
P. Cara
Fusion for Energy, Garching, Germany
J.F. Denis, L. Maurice, J. Relland
CEA/IRFU, Gif-sur-Yvette, France
F. Éozénou, P. Hardy, E. Jacques, Y. Lussignol, P. Sahuquet
CEA/DSM/IRFU, France
D. Gex, A. Jokinen, G. Phillips
F4E, Germany
I. Moya, P. Méndez
CIEMAT, Madrid, Spain

The SaTHoRI test stand (Satellite de Tests Horizontal des Résonateurs IFMIF) aims to characterize a jacketed and fully dressed cavity with its coupler and tuner. A dedicated test cryostat has been manufactured and is connected to an existing horizontal test cryostat which provides the cryogenic coolant. A RF source ' provided by the IFMIF collaboration, one of the four RF sources which will be used for the cryomodule at Rokkasho ' has been installed and commissioned at CEA. This paper describes the test stand and presents the first results.

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MOPB087

Frequency Tuner Development and Testing at Cornell for the RAON Half-wave-resonator

ion, cavity, cryogenics, cryomodule

266

M. Ge, F. Furuta, J.E. Gillette, T. Gruber, S.W. Hartman, M. Liepe, T.I. O'Connell, P.J. Pamel, P. Quigley, J. Sears, V. Veshcherevich
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
B.H. Choi, J. Joo, J.W. Kim, W.K. Kim, J. Lee, I. Shin
IBS, Daejeon, Republic of Korea

The half-wave-resonators (HWRs) for the RAON project require a slow frequency tuner that can provide >80 kHz tuning range. Cornell University is currently in the process of designing, prototyping, and testing this HWR tuner. In this paper, we present the optimized tuner design, prototype fabrication, test insert preparation, and cryogenic test results. The performance of the tuner is analysed in detail.

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MOPB104

Development of a Novel Supporting System for High Luminosity LHC SRF Crab Cavities

ion, cavity, cryomodule, interface

304

T.J. Jones
STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom
K. Artoos, R. Calaga, O. Capatina, T. Capelli, M. Sosin, J.S. Swieszek, C. Zanoni
CERN, Geneva, Switzerland
G. Burt
Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
T.J. Jones
Lancaster University, Lancaster, United Kingdom

Compact SRF Crab Cavities are integral to the HL-LHC upgrade. This paper details the design of support structures within the SPS (Super Proton Synchrotron) Crab Cavity Cryomodule. For ease of alignment each cavity is supported with the mechanical tuner and RF Fundamental Power Coupler (FPC) via a common support plate. To reduce heat leak and remove bellows in the FPC it was determined that this would be the fixed support for the cavity (V. Parma, 2013). In addition, novel flexural blades were designed to give increased stiffness yet allow for thermal contraction of the cavity towards the fixed point of the FPC. This approach was superior when compared via simulation to several alternative techniques. A detailed simulation model was used for optimisation of directional stiffness, identification of vibration modes and minimising thermal stresses. A transmission matrix was developed in MS Excel to assess modal deflection for given ground vibration conditions. The spreadsheet gives an instantaneous yet comparable result to time consuming random vibration FE Analyses. The final engineering design of the supporting system is now complete and will also be described in this paper.
References
V. Parma, R. B. (2013). Status of the Superconducting Proton Linac (SPL) Cryomodule. SRF2013.

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MOPB110

Results of Accelerated Life Testing of LCLS-II Cavity Tuner Motor

ion, cavity, cryomodule, operation

323

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

An Accelerated Life Test (ALT) of the Phytron stepper motor used in the LCLS-II cavity tuner has been conducted at JLab. Since the motor will reside inside the cryomodule, any failure would lead to a very costly and arduous repair. As such, the motor was tested for the equivalent of 30 lifetimes before being approved for use in the production cryomodules. The 9-cell LCLS-II cavity is simulated by disc springs with an equivalent spring constant. Plots of the motor position vs. tuner position ' measured via an installed linear variable differential transformer (LVDT) ' are used to measure motor motion. The titanium spindle was inspected for loss of lubrication. The motor passed the ALT, and is set to be installed in the LCLS-II cryomodules.

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TUXAA01

CEPC SRF System Design and Challenges

ion, cavity, HOM, cryomodule

332

J.Y. Zhai, Y.L. Chi, J. Dai, J. Gao, R. Ge, D.J. Gong, R. Han, T.M. Huang, S. Jin, Z.Q. Li, B. Liu, Z.C. Liu, Q. Ma, F. Meng, Z.H. Mi, G. Pei, Q. Qin, P. Sha, Q.Y. Wang, T.X. Zhao, H.J. Zheng
IHEP, Beijing, People's Republic of China
C. Pagani
Università degli Studi di Milano & INFN, Segrate, Italy

Funding: Work supported by National Key Programme for S&T Research and Development of China (Grant NO.: 2016YFA0400400)
CEPC is a 100 km circular electron positron collider operating at 90-240 GeV center-of-mass energy of Z, W and Higgs bosons. CEPC and its successor SPPC, a 100 TeV center-of-mass super proton-proton collider, will ensure the elementary particle physics a vibrant field for decades to come. The conceptual design report (CDR) of CEPC will be completed in the end of 2017 as an important step to move the project forward. In this contribution, CEPC SRF system CDR design and challenges will be introduced, including the system layout and parameter choices, configuration at different operation energies, transient beam loading and its compensation, cavity fundamental mode (FM) and higher order mode (HOM) induced coupled bunch instabilities (CBI) and the beam feedback requirement, etc. The SRF technology R&D plan and progress as well as the SRF infrastructure and industrialization plan are discussed at last.

Slides TUXAA01 [9.124 MB]

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TUXAA03

Progress of FRIB SRF Production

ion, cavity, cryomodule, linac

345

T. Xu, H. Ao, B. Bird, N.K. Bultman, F. Casagrande, C. Compton, K.D. Davidson, K. Elliott, A. Facco, V. Ganni, A. Ganshyn, W. Hartung, M. Ikegami, P. Knudsen, S.M. Lidia, E.S. Metzgar, S.J. Miller, D.G. Morris, P.N. Ostroumov, J.T. Popielarski, L. Popielarski, M.A. Reaume, K. Saito, S. Shanab, M. Shuptar, S. Stark, D.R. Victory, J. Wei, J.D. Wenstrom, M. Xu, Y. Xu, Y. Yamazaki
FRIB, East Lansing, Michigan, USA
A. Facco
INFN/LNL, Legnaro (PD), Italy
K. Hosoyama
KEK, Ibaraki, Japan
M.P. Kelly
ANL, Argonne, Illinois, USA
R.E. Laxdal
TRIUMF, Vancouver, Canada
M. Wiseman
JLab, Newport News, Virginia, USA

Funding: Work supported by the U.S. Department of Energy Office of Science under Cooperative Agreement DE-SC0000661
The Facility for Rare Isotope Beams (FRIB), under construction at Michigan State University, will utilize a driver linac to accelerate stable ion beams from protons to uranium up to energies of >200 MeV per nucleon with a beam power of up to 400 kW. The FRIB linac consists of 46 cryomodules containing a total of 324 superconducting radio-frequency (SRF) resonators and 69 superconducting solenoids. The design of all six type cryomodules has been completed. The critical SRF components are tested as subsystem and validated in the pre-production cryomodules. The mass production of SRF cryomodules is underway. Here we report on the progress of the technical construction of FRIB superconducting linac.

Slides TUXAA03 [4.006 MB]

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TUYAA01

The Importance of the Electron Mean Free Path for Superconducting RF Cavities

cavity, ion, niobium, electron

359

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

Theoretical results offer a potential explanation for the anti-Q-slope, the phenomenon of decreasing microwave surface resistance with increasing radiofrequency electromagnetic field strength. This effect has been observed in niobium doped with impurities, chiefly nitrogen, and has been put to use in the Linac Coherent Light Source II (LCLS-II) accelerator currently under construction. Our work, presented here, finds a strong link between the electron mean free path, the main measure of impurity doping, to the overheating of quasiparticles in the RF penetration layer. This is an important effect that adjusts the magnitude of the theoretical anti-Q-slope by providing a mechanism to counteract it and introduce a surface resistance that increases with field strength. We discuss our findings in a study of niobium cavities doped at high temperature (800-990 °C) as well as new analysis of low-temperature-doped cavities.

Slides TUYAA01 [6.988 MB]

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TUYBA01

Progress on Characterization and Optimization of Multilayers

ion, cavity, site, niobium

368

C.Z. Antoine
CEA/DSM/IRFU, France
M. Aburas, A. Four
CEA/DRF/IRFU, Gif-sur-Yvette, France
H. Hayano, S. Kato, T. Kubo, T. Saeki
KEK, Ibaraki, Japan
Y. Iwashita
Kyoto ICR, Uji, Kyoto, Japan

Multilayers MgO/NbN/MgO/Nb with several thicknesses are being tested by local magnetometry, Scanning tunneling and various standard structural techniques experiment providing usefull information to compare experiments and recent theoretical advances proposed by A. Gurevich or T. Kubo.

Slides TUYBA01 [5.819 MB]

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TUPB002

Novel HOM Damper Design for High Current SRF Cavities

HOM, ion, GUI, cavity

385

W. Xu, I. Ben-Zvi, M. Blaskiewicz, Y. Gao, D. Holmes, P. Kolb, G.T. McIntyre, R. Porqueddu, K.S. Smith, R. Than, F.J. Willeke, B. P. Xiao, T. Xin, C. Xu, A. Zaltsman
BNL, Upton, Long Island, New York, USA
I. Ben-Zvi
Stony Brook University, Stony Brook, USA
Y. Gao
PKU, Beijing, People's Republic of China

Funding: This work is supported by LDRD program of Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. DOE.
ERL-Ring eRHIC aims to build a new high current (50 mA), multi-pass (6 passes) ERL to provide 3-18 GeV electron beams to collide with proton beams from existing RHIC. One critical challenge for eRHIC is to damp HOMs. The average HOM power is up to 8 kW per cavity, and it will get worse when the electron beam spectrum overlaps with cavity HOM spectrum. A novel HOM damping scheme by employing ridge waveguides has been worked out at BNL, which is able to well damp both longitudinal and transversal modes. This paper will describe the design of the HOM damping scheme, including RF design, HOM damping results, progress of prototyping.

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TUPB005

Developed Spoke Cavity Module for Main Linac of China ADS HOM Simulations and Damping Scheme for CEPC Cavities

cavity, ion, linac, niobium

393

Z.Q. Li, J.S. Cao, Y.L. Chi, F.S. He, S.P. Li, H.Y. Lin, Q. Ma, Z.H. Mi, W.M. Pan, P. Sha, B. Xu, J.Y. Zhai, X.Y. Zhang
IHEP, Beijing, People's Republic of China

During past five year, two kind of spoke of Beta equal 0.21 and 0.40 were developed at IHEP CAS, the spoke cavity of beta 0.21 was adopted to accelerate proton from 10 to 32MeV, and 32 to 160MeV for beta 0.40 spoke cavity. Up to now, two kind of naked spoke cavities have been test in vertical, also the module of beta 0.21 spoke cavity, which equipped the liquid helium jacket, magnetic shield layer and frequency tuner has been fulfilled and test, the performance of all of components reach the design requirements.

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TUPB008

Performance of SRF Half-wave-resonators Tested at Cornell for the RAON Project

cavity, ion, radiation, multipactoring

396

M. Ge, F. Furuta, J.E. Gillette, T. Gruber, S.W. Hartman, M. Liepe, T.I. O'Connell, P.J. Pamel, J. Sears, V. Veshcherevich
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
B.H. Choi, J. Joo, J.W. Kim, W.K. Kim, J. Lee, I. Shin
IBS, Daejeon, Republic of Korea

Two prototype half-wave-resonators (HWR; 162.5MHz and β=0.12) for the RAON project were tested at Cornell University. In this paper, we report and analyse detailed results from vertical tests, including tests of the HWRs without and with helium tank. Surface preparation at Research Instruments is discussed, as well as the development of new HWR preparation and test infrastructure at Cornell.

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TUPB009

High-frequency SRF Cavities

cavity, ion, cryogenics, ECR

400

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

Historically, the frequency of SRF cavities has been limited by cryogenic power dissipation increasing rapidly with frequency, due to the BCS surface resistance having a quadratic dependence on frequency. Now, new SRF surfaces using doped niobium and compound superconductors like Nb3Sn can drastically reduce the BCS part of the surface resistance. The temperature independent part of the surface resistance (residual resistance) can therefore become dominant, and has its own, different frequency dependence. We have developed a model to analyze cryogenic cooling power requirements for SRF cavities as function of operating frequency, temperature, and trapped flux to evaluate the impact of the novel low-loss SRF surfaces on the questions of optimal operating frequency and frequency limit. We show that high-frequency SRF cavities now become a realistic option for future SRF driven accelerators. As the transverse cavity size decreases inversely with respect to its resonant frequency, such high-frequency SRF cavities could greatly reduce cost.

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TUPB020

Microphonics Passive Damping

ion, cavity, simulation, operation

423

E.N. Zaplatin
FZJ, Jülich, Germany
A. Kanareykin
Euclid TechLabs, LLC, Solon, Ohio, USA
V.P. Yakovlev
Fermilab, Batavia, Illinois, USA

Different types of external loads on the resonator walls predetermine the main working conditions of the SRF cavities. The most important of them are very high electromagnetic fields that result in strong Lorentz forces and the pressure on cavity walls from the helium tank that also deforms the cavity shape. For pulsed operation, the Lorentz forces usually play the decisive role for the cavity design. For CW operation, the liquid helium vessel pressure instability even for 2K operations is the source of large microphonics. All deformations resulting from any type of external loads on cavity walls lead to shifts in the working RF frequency in the range of hundreds of kHz. Taking into account high Q-factor of SC cavities such a large frequency shift takes the cavity out of operation. Here we present and discuss the achievements and problems of microphonics passive damping in different type SRF cavities.

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TUPB021

First Considerations on HZB High Frequency Elliptical Resonator Stiffening

ion, cavity, simulation, cryomodule

428

E.N. Zaplatin
FZJ, Jülich, Germany
H.-W. Glock, J. Knobloch, A. Neumann, A.V. Vélez
HZB, Berlin, Germany

There are two projects that currently are under development and construction at HZB which utilize high frequency elliptical resonators ' Energy Recovery Linac Prototype (BERLinPro, 7-cell, 1300 MHz, β=1) and BESSY Variable pulse-length Storage Ring (VSR, 5-cell, 1500/1750 MHz, β=1). A critical issue of both projects is small effective beam loading in cavities operating at high CW fields (Eacc of 20 MV/m) with a narrow band width. This necessitates precise tuning and therefore good compensation of microphonics and coupled Lorentz-force detuning driven instabilities. Here we present a conceptual study of an integrated SRF resonator and helium vessel structure design to ensure a reduced resonance frequency dependence on pressure and Lorentz forces to minimize their impact on the accelerating field profile.

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TUPB023

Further Tests on the SC 325 MHz CH-cavity and Power Coupler Test Setup

ion, cavity, linac, pick-up

437

M. Busch, M. Basten, H. Podlech, U. Ratzinger, M. Schwarz
IAP, Frankfurt am Main, Germany
W.A. Barth
MEPhI, Moscow, Russia
W.A. Barth
GSI, Darmstadt, Germany
W.A. Barth, F.D. Dziuba, V. Gettmann
HIM, Mainz, Germany

Funding: Work supported by BMBF contr. No. 05P15RFRBA
The 325MHz CH-cavity which has been developed and successfully vertically tested at the Institute for Applied Physics, Frankfurt, has has been welded to the helium vessel at the frontal joints of the cavity and further vertical and horizontal tests are in preparation. Finally a beam test with a 11.4 AMeV, 10 mA ion beam at GSI, Darmstadt is projected. Furthermore a newly developed, dedicated test stand for the 217 MHz power couplers has been set up for the cavities of the sc cw-LINAC project at GSI.

Poster TUPB023 [2.579 MB]

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TUPB028

Improvement of Magnetic Condition for KEK-STF Vertical Test Facility Toward High-Q Study

ion, cavity, solenoid, controls

444

K. Umemori, T. Dohmae, E. Kako, T. Konomi, T. Kubo, M. Masuzawa, G.-T. Park, A. Terashima, K. Tsuchiya, R. Ueki
KEK, Ibaraki, Japan
T. Okada
Sokendai, Ibaraki, Japan

Improvement of unloaded Q-values of SRF cavities are important to reduce surface loss of cavity and heat loads of He refrigerators. R&D activities have been developed worldwide. We also started work toward high-Q, but soon realized that magnetic condition of KEK-STF vertical test facility was not good enough to carry out high-Q measurements. First, magnetized components were searched. Shafts to move variable coupler were found to be most magnetized one and exceed more than 1 Gauss. Magnetized components were exchanged to non-magnetized one. In order to further reduce remnant magnetic field, a solenoid coil was prepared and used to cancel it. To suppress flux trapping, a heater was located around an upper beampipe of cavity and made thermal gradient. Owing to these efforts, Q-value of more than 1x10¹¹ can be measured with a condition of residual resistance of ~3 nΩ. Clear flux expulsion signal can be also observed. In this presentation, we report about efforts to reduce ambient magnetic field and to realize high-Q measurements. Results of vertical tests, including flux expulsion measurements, are also presented.

Poster TUPB028 [1.961 MB]

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TUPB032

Study on 650MHz 5-cell Prototype Cavities at IHEP

ion, cavity, HOM, simulation

448

S. Jin, J. Gao, D.J. Gong, Z.C. Liu, P. Sha, J.Y. Zhai, T.X. Zhao, H.J. Zheng
IHEP, Beijing, People's Republic of China

CEPC Pre CDR pointed that the 650 MHz 5-cell SRF cavity could be a candidate for the main ring of the single-ring pretzel scheme at the Higgs energy in 2015. Then EM design of 5-cell cavities were published later. So, the study on the fabrication of a 5-cell prototype cavity with waveguide HOM couplers were carried on at IHEP. In the paper, we will mainly report the mechanical design and fabrication progress of the 5-cell prototype. Besides, fabrication of a bare 2-cell prototype cavity was also carried on according to the further study after Pre-CDR. Challenges and possible solutions for the prototypes development will also be discussed.

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TUPB034

The 166.6 MHz Proof-of-principle SRF Cavity for HEPS-TF

cavity, ion, HOM, storage-ring

454

P. Zhang, J. Dai, H.X. Hao, T.M. Huang, Z.Q. Li, H.Y. Lin, Q. Ma, F. Meng, Z.H. Mi, W.M. Pan, Y. Sun, G.W. Wang, Q.Y. Wang, X.Y. Zhang
IHEP, Beijing, People's Republic of China

Funding: This work has been supported by HEPS-TF project and also partly supported by Pioneer "Hundred Talents Program" of Chinese Academy of Sciences.
The 166.6 MHz superconducting RF cavities have been proposed for the High Energy Photon Source (HEPS), a 6 GeV kilometer-scale light source. The cavity is of quarter-wave type made of bulk niobium with β =1. Each cavity will be operated at 4 K providing 1.2 MV accelerating voltage and 145 kW of power to the electron beam. During the HEPS - Test Facility (HEPS-TF) phase, a proof-of-principle cavity of 166.6 MHz has been designed in IHEP and manufactured in Beijing. The subsequent BCP was conducted in Ningxia, while HPR, cleanroom assembly and 120 degree baking was done in IHEP. The cavity was finally vertical tested at both 4K and 2K in IHEP. The cavity Q0 at nominal gradient at 4 K was measured to be 2.4·10⁹ with Epeak of 42 MV/m and Bpeak of 65 mT. The maximum Epeak and Bpeak reached 86MV/m and 131 mT respectively at both 4 K and 2 K, and the corresponding Q0 was measured to be 5.10⁸ (4 K) and 3.3·10⁹ (2 K). The residual surface resistance was measured to be 2.3 nOhm.

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TUPB035

Frequency Pre-tuning of the 166.6 MHz Proof-of-principle SRF Cavity for HEPS-TF

cavity, ion, simulation, target

459

P. Zhang, H.X. Hao, Z.Q. Li, X.Y. Zhang
IHEP, Beijing, People's Republic of China

Funding: This work has been supported by HEPS-TF project and also partly supported by Pioneer 'Hundred Talents Program' of Chinese Academy of Sciences.
A 166.6 MHz proof-of-principle SRF cavity has been designed for the High Energy Photon Source - Test Facility (HEPS) at IHEP in Beijing. The cavity is a β=1 quarter-wave resonator made of bulk niobium operating at 4 K. A pre-tuning scheme was made to accommodate the cavity frequency shift mainly due to mechanical tolerances during cavity production, the subsequent surface treatment and cooldown process. To this end, the length of the cavity outer conductor was chosen as a free parameter for the pre-tuning. The cavity frequency was carefully monitored during the production, post-processing steps and vertical test. The measurement results agree well with our calculations. It is worth noticing that the pre-tuning method only involves one-time measurement of the cavity resonant frequency and its outer conductor length.

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TUPB036

R&D of CEPC Cavity

cavity, ion, cryomodule, experiment

463

P. Sha
Institute of High Energy Physics (IHEP), Chinese Academy of Sciences, Beijing, People's Republic of China
B. Liu, Z.H. Mi, J.Y. Zhai, X.Y. Zhang, H.J. Zheng
IHEP, Beijing, People's Republic of China

Funding: This study was supported by National Key Programme for S&T Research and Development (Grant NO.: 2016YFA0400400) and National Natural Science Foundation of China (Grant NO.: 11505197)
CEPC will use 650 MHz cavities for the collider (Main Ring) and 1.3 GHz cavities for the Booster. Each booster cryomodule contains eight 1.3 GHz 9-cell cavities, which is similar as LCLS-II. Each collider cryomodule contains six 650 MHz 2-cell cavities, which is totally new. So our R&D of CEPC cavity mainly focuses on the 650 MHz 2-cell cavity. A cryomodule which consists of two 650 MHz 2-cell cavities has began in early 2017. In this thesis, the RF and mechanical design is displayed with Helium Vessel. Besides, multipacting is analyzed. In order to achieve high Q, N-doping is also studied.

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TUPB037

A 166.6 MHz Proof-of-principle SRF Cavity for HEPS-TF: Mechanical Design and Fabrication

ion, cavity, storage-ring, superconducting-RF

466

X.Y. Zhang
Institute of High Energy Physics (IHEP), Chinese Academy of Sciences, Beijing, People's Republic of China
H.X. Hao, Z.Q. Li, H.Y. Lin, Y. Sun, P. Zhang
IHEP, Beijing, People's Republic of China

166.6 MHz superconducting RF cavities operating at 4.2 K have been proposed by IHEP for the High Energy Photon Source - Test Facility (HEPS-TF). The cavity is a quarter wave resonator with beam going through the cavity inner conductor. The cavity and its stiffness were designed and optimized to meet pressure safety requirement and to reduce frequency sensitivity due to helium pressure fluctuations. Tuning sensitivity, Lorentz force detuning and microphonics were also simulated. Most calculations have been validated by experiments. This paper reports the mechanical design and fabrication details of the first proof-of-principle cavity.

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TUPB038

Mechanical Design of a 650 MHz Superconducting RF Cavity for CEPC

ion, cavity, collider, positron

471

X.Y. Zhang
Institute of High Energy Physics (IHEP), Chinese Academy of Sciences, Beijing, People's Republic of China
F.S. He, Q. Ma, Z.H. Mi, P. Sha, J.Y. Zhai
IHEP, Beijing, People's Republic of China

Funding: This study was supported by National Key Programme for S&T Research and Development (Grant NO.: 2016YFA0400400)
The 650 MHz superconducting RF cavities have been proposed by IHEP for the Circular Electron-Positron Collider (CEPC). The major components are a 2-cell elliptical cavity, end groups, stiffness and helium vessel, which have been optimized to meet the design requirement. The minimization of the Lorentz force detuning and the sensitivity of resonance frequency to Helium pressure variations was the main goal of the optimization. Also detailed stress analysis, tuning and microphonics performance of dresses cavity will be presented in this paper.

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TUPB039

Electropolishing of Niobium from Deep Eutectic Solvents Based on Choline Chloride

ion, ECR, cavity, niobium

475

Q.W. Chu, H. Guo, Y. He, L. Li, P.R. Xiong, Z.M. You, S.H. Zhang
IMP/CAS, Lanzhou, People's Republic of China

Niobium (Nb) was successfully electropolished from a green ionic liquid, choline chloride/urea deep eutectic solvent (DES). This paper was to investigate the influence of various electropolishing parameters, including electropolishing time, temperature and voltage, on the electropolishing rate, surface roughness, glossiness and microstructure of Nb. The result showed that the electropolishing parameters had a significant impact on the performance of Nb. Based on surface analysis by scanning electron microscope (SEM) and atomic force microscope (AFM), smooth Nb can be achieved under properly controlled conditions.

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TUPB049

Design Study on the Superconducting HWR for Secondary Particle Generation at KOMAC

ion, cavity, proton, linac

499

H.S. Kim
KAERI, Daejon, Republic of Korea
Y.-S. Cho, J.J. Dang, H.S. Jeong, H.-J. Kwon, S. Lee
Korea Atomic Energy Research Institute (KAERI), Gyeongbuk, Republic of Korea

Funding: This work has been supported through KOMAC (Korea of Multi-purpose Accelerator Complex) operation fund of KAERI by MSIP (Ministry of Science, ICT and Future Planning).
A 100-MeV proton linac has been operated since 2013 at KOMAC (Korea Multi-purpose Accelerator Complex) and provides the accelerated proton beam to various users from the research institutes, universities and industries. To expand the utilization fields of the accelerator, we have a plan to develop a secondary particle utilization facility including a pulsed neutron source and radio-isotope beam based on the 100-MeV linac. According to the preliminary analysis, the neutron yields can be increased by about 2.5 times if the incident proton beam energy increases from 100 MeV to 160 MeV. Therefore, we carried out design study on the SRF linac based on half-wave resonator to increase the proton beam energy. Baseline design parameters include 350 MHz operating frequency, 2 K operation temperature, and peak electric field and magnetic field less than 35 MV/m and 70 mT, respectively. The available space at existing accelerator tunnel was also taken into consideration. Details on the design study on the SRF linac based on HWR cavity for the secondary particle utilization facility at KOMAC will be given in this presentation.

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TUPB055

Nb3Sn Thin Film Deposition On Copper By DC Magnetron Sputtering

ion, target, cavity, niobium

512

W.W. Tan, B.T. Li, X.Y. Lu, L. Xiao, D. Xie, D.Y. Yang, Y. Yang, Z.Q. Yang, J. Zhao
PKU, Beijing, People's Republic of China

Nb3Sn for SRF cavities has been coated on copper samples by DC magnetron Sputtering. Pure Nb target and pure Sn target were installed separately in the magnetron sputtering device. Nb3Sn precursor was coated on copper in the Ar atmosphere of 0.5 Pa. The Nb3Sn precursor was annealed in the vacuum furnace whose pressure is 10^-4 Pa. The XRD results demonstrate the exist of Nb3Sn crystal, and MPMS results show superconductivity of Nb3Sn. The highest critical temperature obtained is 15K.

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TUPB060

Innovative Cryogenic Test Facility for Testing SRF Cavity Series Production

ion, cavity, operation, cryogenics

520

L. Bizel-Bizellot, M. Ellis, S.M. Pattalwar, M.D. Pendleton, P.A. Smith, A.E. Wheelhouse
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom

Testing SRF cavities in a vertical cryostat is the first step in qualifying the performance of SRF cavities before being integrated into a cryomodule. The European Spallation Source (ESS) requires 84 high-beta 5 cells, 704 MHz cavities which will be manufactured and qualified for their RF performance in a vertical cryostat at Science and Technology Facility Council (STFC) Daresbury Laboratory (United-kingdom). Taking a conventional approach each vertical test would require a large cryostat demanding more than 7000 litres of liquid helium per test for testing 3 cavities simultaneously. In order to reduce the overall operating cost, we plan to develop an alternative method to divide the liquid helium consumption by 5 by filling liquid helium only in each individual helium vessels enclosing each cavity placed horizontally in the cryostat. Therefore the test is performed in more realistic conditions such as in a cryomodule and reduces the operating time. This also reduces the mass flow-rate to be handled by a factor 10, leading to 2 g/s, thus reducing the size of the associated components such as the 2 K pumps, the safety device, the valves and transfer lines.

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TUPB065

Design of Multi-frequency Coaxial Test Resonators

ion, cavity, niobium, operation

531

Z.Y. Yao, T. Junginger, R.E. Laxdal, B. Matheson, B.S. Waraich, V. Zvyagintsev
TRIUMF, Vancouver, Canada

A significant issue in low beta resonators is medium field Q-slope (MFQS) at 4K. To study the MFQS and the field dependence of surface resistance in low beta resonators, a quarter-wave resonator (QWR) and a half-wave resonator (HWR) were designed to be tested at integer harmonic frequencies of 200MHz, and up to 1.2GHz. A series of chemistry and heat treatments will be applied to these cavities so that a systemic study on the surface resistance of the coaxial resonators associating with post-processing, RF field, and frequency can be done. The detail design of these cavities and the status of cavity fabrication will be reported in this paper.

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TUPB066

RF Results of Nb Coated SRF Accelerator Cavities via HiPIMS

ion, cavity, lattice, site

535

M.C. Burton, M. Beebe, R.A. Lukaszew
The College of William and Mary, Williamsburg, Virginia, USA
A.D. Palczewski, H.L. Phillips, C.E. Reece
JLab, Newport News, Virginia, USA

Funding: Jefferson Lab
Bulk Nb SRF cavities are the preferred method for acceleration of charged particles. However, bulk Nb cavities suffer from variable RF performance, high cost and impose material & design restrictions on other components of a particle accelerator. Since SRF is a shallow surface phenomena, a proposed solution is to deposit a Nb thin film on the interior of a cavity made of an alternative material such as Cu. While this approach has been attempted in the past, new energetic condensation techniques, such as High Power Impulse Magnetron Sputtering (HiPIMS), offer the opportunity to create Nb films with improved properties compared to traditional methods. To test HiPIMS, a study was performed in which Nb films were deposited on samples in multiple 'series' where only one parameter (Ion Fraction, Condensation Energy'etc.) is varied. Sample properties were then characterized using: XRD, AFM, SEM'etc., and correlations made between deposition parameters and film properties. Nb films were then deposited on 1.3GHz Cu cavities at select parameter sets and RF tested. Here we present the results from the Nb film studies and correlate the sample properties to RF results of Nb/Cu cavities.

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TUPB067

Insights into Formation of Nb3Sn Film During the Vapor Diffusion Process

ion, niobium, experiment, cavity

539

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
M.J. Kelley, J. Tuggle
Virginia Polytechnic Institute and State University, Blacksburg, USA

Funding: Supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC05-06OR23177 and Office of High Energy Physics under grant DE-SC-0014475.
The potential of Nb3Sn for SRF cavities is widely recognized and renewed R&D efforts continue to bring new insights about material structure and its properties. We have systematically coated niobium with Nb3Sn using "vapor diffusion" under varying coating conditions to elucidate the reaction of tin with niobium at the temperatures of interest. The analysis of the coated samples is revealing new understanding about the two-stage nucleation/deposition ("vapor diffusion") process that allows us to form a hypothesis regarding Nb3Sn formation mechanism. The essential aspect of nucleation is the deposition of a high coverage, nanoscale thin tin film with particle assemblage by decomposition of tin chloride on the niobium surface at temperatures sufficient for reduction of the thick niobium oxide film, usually at about 500°C. The deposition is followed by the reaction of tin from tin vapor with the niobium surface to form Nb3Sn at about 1200°C, where the surface and grain boundaries start to play key role in the formation process initiation and progression. These findings improve understanding of the Nb3Sn growth in the typical vapor diffusion process used for accelerator cavity coatings.

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TUPB069

Rigorous Data Processing and Automatic Documentation of SRF Cold Tests

ion, LabView, software, cavity

543

K.G. Hernández-Chahín
Universidad de Guanajuato, División de Ciencias e Ingenierías, León, Mexico
S. Aull, P.F. Fernández López, K.G. Hernández-Chahín, N. Schwerg, N. Stapley
CERN, Geneva, Switzerland

Performance curves for SRF cavities are derived from primary quantities which are processed by software. Commonly, the mathematical implementation of this analysis is hidden in software such as Excel or LabVIEW, making it difficult to verify or to trace, while text-based programming like Python and MATLAB require some programming skills for review and use. As part of an initiative to consolidate and standardise SRF data analysis tools, we present a Python program converting a module containing the collection of all commonly used functions into a \LaTeX (PDF) document carrying all features of the implementation and allowing for a review by SRF experts, not programmers. The resulting document is the reference for non-experts, beginners and test stand operators. The module is imported in any subsequent processing and analysis steps like the symbolic analysis of the measurement uncertainties or the study of sensitivities. As an additional layer of protection the functions can be further wrapped including assertions, type and sanity checks. This process maximises function reuse, reduces the risk of human errors and guarantees automatically validated and documented cold test results.

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TUPB072

Investigation of BCP Parameters for Mastery of SRF Cavity Treatment

ion, cavity, niobium, experiment

558

F. Éozénou
CEA/DSM/IRFU, France
E. Cenni, G. Devanz, T. Percerou, Th. Proslier, C. Servouin
CEA/DRF/IRFU, Gif-sur-Yvette, France
M.L.L. Nghiem
UPMC, Paris, France

Mastery of Standard Buffered Chemical Polishing (with mixture of hydrofluoric, nitric and phosphoric acids) is of paramount importance for the treatment of SRF resonators with complex geometry has IFMIF half-wave resonators, in order to control accurately their frequency evolution. Furthermore, strong and unexpected asymmetry in removals has recently been observed after BCP treatment of ESS-medium beta resonators. The goal of this study is to investigate accurately influence of parameters such as surface geometry and orientation, acid temperature, agitation and their coupling on the removal rate. We will also focus on the influence of by-products such has NOx on kinetics. The mixture used is HF(40%)- HNO3(65%)-H3PO4(85%) with ratio 1-1-2.4.

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TUPB073

Vertical Electro-polishing Collaboration Between Cornell, KEK, and Marui Galvanizing Co. Ltd

cathode, cavity, ion, linac

563

F. Furuta, M. Ge, T. Gruber, J.J. Kaufman, M. Liepe, 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, KEK, and Marui Galvanizing Co. Ltd (MGI) have collaborated since 2014 on Vertical Electro-Polishing (VEP) R&D as a part of a US/Japan Program for Cooperation in High Energy Physics. We have focused on an improvement of removal uniformity during the VEP process. MGI and KEK have developed their original VEP cathode named i-cathode Ninja®, which has four retractable wing-shape parts per cell. Cornell processed one single cell cavity with VEP using this cathode and performed a vertical test. KEK also provided one 9-cell cavity to Cornell. Cornell then performed surface treatments including Cornell VEP and RF test on this 9-cell cavity. The progress by the VEP collaboration and RF test results are presented in this paper.

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TUPB074

RF Performance of Multi-cell Scale Niobium SRF Cavities Prepared with HF Free Bipolar Electro-polishing at Faraday Technology

cavity, ion, niobium, MMI

567

F. Furuta, M. Ge, T. Gruber, J.J. Kaufman, M. Liepe, J. Sears
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
T.D. Hall, M.E. Inman, R. Radhakrishnan, S.T. Snyder, E.J. Taylor
Faraday Technology, Inc., Clayton, Ohio, USA

Cornell's SRF group and Faraday Technology, Inc. have been collaborating on two phase-II SBIR projects. One of them is the development and commissioning of a 9-cell scale HF free Bipolar Electro-Polishing (BEP) system. Faraday Technology had completed the proof of principle on BEP with single cell scale prior to the work reported here, and has now developed a new 9-cell scale BEP system. Cornell has fabricated three single cell cavities and has assembled them together as a 9-cell scale test string. The 9-cell scale test string has received BEP at Faraday Technology and RF testing has been performed on the three single cell cavities one-by-one at Cornell. Here we give a status update on the new 9-cell scale BEP system commissioning and on results from RF tests of the BEP cavities.

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TUPB075

Vertical Electro Polishing of Superconducting Single-and Multi Cell Gun Resonators

gun, cavity, ion, cathode

571

N. Steinhau-Kühl, R. Bandelmann, A. Matheisen, S. Saegebarth, M. Schmökel
DESY, Hamburg, Germany
A. Arnold
HZDR, Dresden, Germany

At DESY activities on surface treatment of superconducting RF gun cavity resonators at 1.3 GHz are ongoing. Due to the small opening on the endplate for insertion of cathodes, no reasonable acid flow can be realized with the existing set up for horizontal electro polishing. To benefit from electro polishing of Niobium surfaces, an adapter to the existing horizontal electro polishing bench at DESY was set up and is in operation now. Vertical EP was applied on 1.3 GHz SRF gun resonators with 1.6 and 3.5 cell geometry. Work flow, process conditions as well as test results of gun cavities treated so far at DESY are described.

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TUPB082

Setup of a Spatially Resolving Vector Magnetometry System for the Investigation of Flux Trapping in Superconducting Cavities

ion, cavity, niobium, superconducting-cavity

580

B. Schmitz, K. Alomari, J. Knobloch, O. Kugeler, J.M. Köszegi, Y. Tamashevich
HZB, Berlin, Germany

Flux trapping is the major contribution to the residual resistance of superconducting cavities. In order to gain a better understanding of the mechanisms involved and aiming at an eventual minimization of trapped flux, a measurement setup based on AMR sensors was devised that allows for monitoring the magnetic field vector at various positions near the cavity surface. First results of the efforts are presented.

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TUPB083

Post Processing of a 166.6 MHz HEPS-TF Cavity at Institute of High Energy Physics

cavity, ion, photon, target

583

J. Dai, Z.Q. Li, P. Zhang
IHEP, Beijing, People's Republic of China

Funding: Work supported by High Energy Photon Source Test Facility (HEPS-TF) project
A 166.667 MHz Proof-of-Principle (PoP) superconducting RF cavity has been fabricated by IHEP for the High Energy Photon Source Test Facility (HEPS-TF) [1]. After a series of post-processing including chemical etching (BCP), high temperature heat treatment, High Pressure water Rinsing (HPR) and 120°C baking, the cavity was cold RF tested and reached E_peak=86.5 MV/m and B_peak=132.1 mT with Q₀=5.1×〖10〗⁸ at 4.2K. The cavity was RF tested again at 2K, and reached E_peak=85.5 MV/m and B_peak=131.1 mT with Q₀=3.3×〖10〗⁹.
daijin@ihep.ac.cn

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TUPB084

EP System Development at IHEP

cavity, ion, controls, cathode

586

S. Jin, J. Dai, J. Gao, D.J. Gong, F.S. He, Z.Q. Li, Z.C. Liu, P. Sha, J.Y. Zhai, P. Zhang, T.X. Zhao
IHEP, Beijing, People's Republic of China

Electropolishing (EP) System is a critical facility for SRF cavity treatment, especially for high performance cavities which are necessary for several great projects like LCLS-II, CEPC, Shanghai XFEL, and so on. So, an EP system was under development at IHEP. At this stage, we would like a horizontal EP facility. Main purpose is for elliptical SRF Nb cavities like 500MHz single cell cavities. Besides, it should be compatible for other frequency cavities, such as 650MHz and 1.3GHz cavities. In this paper, we will mainly report the preliminary design for the EP system. Several key points in the design will be also discussed.

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TUPB085

Quench Detection on Superconducting Cavity by Second Sound

ion, cavity, detector, site

589

Z.C. Liu, J. Gao, F.S. He, H.Y. Lin, P. Zhang
IHEP, Beijing, People's Republic of China

High gradient is very important for superconducting cavity, however it may be limited by quench on the cavity high field region. Quench can be caused by various reasons. To locate the position is the key to reveal the mysteries of quench. OST sensor was widely used to locate the quench position. Now we are developing the quench position detection system by RTD sensors such as Cernox. In this paper, we will show the design of the second sound system and testing results on the QWR cavity.

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TUPB086

Study on Local Chemical Treatment for Recovery From Surface Oxidation by HPR Process on SRF Cavities

cavity, ion, experiment, niobium

592

H. Guo, Y. He, Y.M. Li, T. Tan, A.D. Wu, P.R. Xiong, Z.M. You, W.M. Yue, S.H. Zhang
IMP/CAS, Lanzhou, People's Republic of China

High pressure rinsing (HPR) with ultra-pure water (UPW) is the last step which is commonly used for SRF cavities cleaning. The serious surface damage will be caused due to the failure of the distance control between the jet and cavity surface or the breakdown of the jet rotation. The surface of taper HWR cavities which are used for CIADS project was damaged in HPR process. Two methods were used for surface recovery and the result will be presented in this paper.

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TUPB090

Investigation of High Temperature Baking of Jacketed Quarter Wave Resonators

ion, cavity, linac, niobium

598

A. Rai, D. Kanjilal, K.K. Mistri, P. Patra, P.N. Potukuchi, S.K. Sonti
IUAC, New Delhi, India

The Superconducting booster Linac at IUAC has been delivering accelerated beams for scheduled experiments since 2013. It has three accelerating modules with 8 Quarter Wave Resonators (QWR)in each. The QWRs for the first module were built at Argonne National Laboratory while those for the second and third modules have been built in-house. During the electropolishing of one of the indigenously built resonators (QWR # I03) the RF surface got spoiled due to a wrong acid mixture that was being used for etching. In subsequent cold tests of the cavity, its performance was poor (2.6 MV/m @ 4W). There was evidence of Q disease also, as the performance deteriorated further (~20%) when the cavity was held at 100-120K for ~8 hours .In an attempt to recover the cavity it was baked at 650 °C for 10 hours along with its stainless steel jacket. A series of tests were conducted thereafter wherein, a substantial improvement (factor of two) in the performance was observed. Encouraged with the results another QWR designed for a lower beta (β=0.05) was also heat treated identically. This paper presents the different treatments followed to enhance the cavity performance vis-à-vis the test results.

Poster TUPB090 [1.240 MB]

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TUPB095

Modeling the Hydroforming of a Large Grain Niobium Tube With Crystal Plasticity

ion, cavity, niobium, experiment

616

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

Current SRF cavities are made from fine grained polycrystalline niobium half-cells welded together. Hot spots are commonly found in the heat-affected zone, making seamless hydroformed cavities attractive. Large grain cavities usually perform as well as fine grain cavities, often having a higher Q, presumably due to fewer grain boundaries. Large grain Nb forms non-uniformly, which introduces problems in manufacturing. A model that could realistically predict the deformation response of large grain Nb could facilitate the design of large grain hydroformed tubes. To this end, a crystal plasticity model was developed and calibrated with tensile stress-strain data of Nb single crystals. A seamless large grain tube was made from rolling a fine grain sheet into a tube, welded, and heat treated to grow large grains. The heat treatment resulted in a large grain tube with a single grain orientation in the center. The tube was hydroformed until it cracked. The hydroforming process was simulated with the crystal plasticity model, which was able to predict the deformed shape of the tube, the location of the crack and other localized areas with heterogeneous strain.

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TUPB096

SRF Cavity Assembly in Clean Room with Horizontal Laminar Flow

ion, cavity, GUI, cryomodule

620

A. Miyamoto, H. Hara, K. Sennyu, T. Yanagisawa
MHI-MS, Kobe, Japan

Mitsubishi Heavy Industries Mechatronics Systems(MHI-MS) has developed manufacturing process of superconducting cavitis for a long time. In this presentation, recent progress will be reported.

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TUPB097

R&D of Electro-polishing (EP) Process with HF-free Neutral Electrolyte by Bipolar-pulse (BP) Method

ion, experiment, cavity, cathode

623

J. Taguchi, Y. Mochida, T. Nakajima
Nomura Plating Co, Ltd., Osaka, Japan
H. Hayano, T. Saeki
KEK, Ibaraki, Japan
S. Kakudo, M. Kunieda
The University of Tokyo, Tokyo, Japan

Currently the Electro-Polishing (EP) process of Superconducting Radio-Frequency (SRF) accelerating cavity is performed with the electrolyte that is the mixture of hydrofluoric and sulfuric acids. However, the electrolyte is very dangerous and the environmental load in the disposal process of electrolyte is very heavy. This is the reason why the high cost is necessary in the safe design of facility and the safe operation of process in the conventional EP method. In such situation, considering the reduction of cost and environmental load in the EP process, we performed the R&D of novel EP process with HF-free neutral electrolyte by Bipolar-Pulse (BP) method. In this presentation, we will report the removal rate, surface roughness and the results of surface analysis for the Nb-coupon samples that were processed by the BP-EP with HF-free neutral electrolyte.

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TUPB098

The Effect of Process Parameters on the Surface Properties of Niobium During Plasma Etching

ion, plasma, cavity, experiment

628

J.J. Peshl, S. Popović, L. Vušković
ODU, Norfolk, Virginia, USA
J. Upadhyay
LANL, Los Alamos, New Mexico, USA
A-M. Valente-Feliciano
JLab, Newport News, Virginia, USA

Funding: This work is supported by the Department of Energy, Grant DE-SC0014397.
We have shown that plasma etching using an electronegative Ar/Cl2 discharge can effectively remove surface oxide layers on Nb samples as well as bulk Nb from single cell SRF cavities*. With accelerating fields on the order of wet etching processes and a decrease in field emission the use of plasma assisted etching for bulk Nb processing is a worthwhile endeavor. We are presenting the surface properties of plasma etched Nb. Cavity grade Nb coupons were made by water jet cutting, and then polished to achieve surface roughness equivalent to electropolishing (<1 micron). The coupons were plasma etched while process parameters (rf power, gas pressure, temperature and DC bias voltage) are varied. These samples are placed on the inner surface of the cylindrical cavity to be etched. The experimental setup is similar to the single cell cavity plasma etching setup. Each sample is weighed and scanned before and after plasma processing with an AFM, SEM, and digital optical microscope that provide both atomic composition and surface roughness profiles. Comparing the scans allows us to make conclusions about the effect of each parameter on the surface roughness.
J. Upadhyay et. al. 'Cryogenic rf test of the first plasma etched SRF cavity,' arXiv: 1605.06494 [physics.acc-ph] (2016).

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TUPB100

Determining BCP Etch Rate and Uniformity in High Luminosity LHC Crab Cavities

ion, cavity, experiment, simulation

635

T.J. Jones
STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom
G. Burt
Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
R. Calaga, O. Capatina, L.M.A. Ferreira, R. Leuxe
CERN, Geneva, Switzerland
T.J. Jones, J.A. Mitchell
Lancaster University, Lancaster, United Kingdom
S.M. Pattalwar
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
S. Verdú-Andrés, B. P. Xiao
BNL, Upton, Long Island, New York, USA

The compact SRF Crab Cavities required for HL-LHC have complex geometries making prediction of average and local BCP etch rates a difficult task. This paper describes a series of experiments and simulations used to determine the etch uniformity and rate within these structures. An initial experiment was conducted to determine the correlation between etch rate and flow rate in a Nb tube. These results were then incorporated into Computational Fluid Dynamics simulations of acid flow in the Double Quarter Wave (DQW) cavity to predict etch rates across the surface and allow optimisation of the BCP setup. There were several important findings from the work; one of which is that the flow rate in the relatively large body of the cavity is predominantly driven by natural convection due to the exothermic reaction. During BCP processing of the DQW cavity a significant difference in etching was observed between upper and lower horizontal surfaces which was mitigated by etching in several orientations. Two DQW cavities manufactured by CERN have received a heavy BCP of 200μm followed by 2 light BCPs of 30μm each with subsequent vertical cold tests showing performance exceeding specification.

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TUPB104

First Full Cryogenic Test of the SRF Thin Film Test Cavity

ion, cavity, cryogenics, niobium

644

R. Valizadeh, L. Bizel-Bizellot, P. Goudket, L. Gurran, O.B. Malyshev, N. Pattalwar, S.M. Pattalwar
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
G. Burt, L. Gurran
Lancaster University, Lancaster, United Kingdom
G. Burt, P. Goudket, O.B. Malyshev, S.M. Pattalwar, R. Valizadeh
Cockcroft Institute, Warrington, Cheshire, United Kingdom
L. Gurran
Cockcroft Institute, Lancaster University, Lancaster, United Kingdom

A test cavity that uses RF chokes, rather than a physical seal, to contain the field is a promising method of SRF sample testing, especially in thin films research where the rate of sample production far outstrips that of full SRF characterisation. Having the sample and cavity physically separate reduces the complexity involved in changing samples - major causes of low throughput rate and high running costs for other test cavities - and also allows direct measurement of the RF power dissipated in the sample via power calorimetry. Choked test cavities operating at 7.8 GHz with three RF chokes have been designed and tested at Daresbury Laboratory. As part of the commissioning of this system, we performed the first full SRF test with a bulk Nb sample and we verified that the system would perform as required for future superconducting thin film sample tests.

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TUPB106

Standardized Beamline Particulate Characterization Analysis: Initial Application to CEBAF and LCLS-II Cryomodule Components

ion, cavity, cryomodule, linac

647

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

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177
Despite continuously evolving efforts to minimize particulates in operational SRF accelerator systems, the presence of electron field emission from contaminating particulates on SRF surfaces with high surface electric fields remains a challenge. Jefferson Lab has recently initiated a standardized particulate sampling and characterization practice in order to gain more systematic knowledge of the particulates actually present. It is expected that patterns that emerge from such sampling will strengthen source attribution and guide improvement efforts. Initial samples were gathered from a cryomodule and adjoining warm girders removed from the CEBAF tunnel for reprocessing. The collection and analysis techniques were also used to characterize particulates on the inside of LCLS-II string components. Samples are transferred to clean industry-standard forensic GSR carbon tape spindles and examined via automated cleanroom SEM scanning for particle localization and sizing. The particulates are subsequently analyzed with EDS for elemental composition. A catalogue of particle types is being accumulated. The methods used and results obtained from these initial applications will be presented.

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TUPB108

Genesis of Topography in Buffered Chemical Polishing of Niobium for Application to Superconducting Radiofrequency Accelerator Cavities

ion, niobium, cavity, electron

651

L. Zhao, C.E. Reece
JLab, Newport News, Virginia, USA
M.J. Kelley
The College of William and Mary, Williamsburg, Virginia, USA

Funding: Supported by Office of High Energy Physics, U.S. Department of Energy, Grant SC0007907 to the College of William & Mary and by U.S. DOE Contract No. DE-AC05-06OR23177 to Jefferson Science Associates
Topography arising from the final etch step in preparing niobium superconducting radiofrequency (SRF) accelerator cavities is understood to significantly impact cavity performance at high field levels. This study investigated the effect of process temperature and time on the etch rate and topography arising from the widely-used buffered chemical polishing (BCP). This study aims to understand more thoroughly the genesis of topography in BCP of polycrystalline niobium, with the ultimate aim of finding a path to surface smoothness comparable to that obtained by electropolishing (EP). It was found that the etch process is controlled by the surface reaction; and that the etch rate varies with crystallographic orientation. The familiar micron-scale roughening necessarily results. Gas evolution has an impact, but is secondary. The major outcome is that surface smoothness comparable to EP appears to be inherently unachievable for polycrystalline niobium using BCP, setting an upper limit to the gradient for which it is useful.

Poster TUPB108 [3.782 MB]

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TUPB112

First Test of Electropolishing System at IMPCAS

ion, cavity, cathode, controls

660

L. Li, Q.W. Chu, H. Guo, Y. He, P.R. Xiong, Z.Q. Yang, Z.M. You, B. Zhang, S.H. Zhang, X. Zhu
IMP/CAS, Lanzhou, People's Republic of China

The first SRF cavity electropolishing system of China has been built by IMPCAS. We used two type of cathodes in different process parameters to test the typical Voltage-Current Density curves of 1.3GHz one-cell SRF cavity.

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WEXA01

High Performance Nb3Sn Cavities

ion, cavity, niobium, site

667

D.L. Hall, M. Liepe, R.D. Porter
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
T. Arias, P. Cueva, D. Liarte, D.A. Muller, J.P. Sethna, N. Sitaraman
Cornell University, Ithaca, New York, USA

In recent years, 1.3 GHz single-cell cavities coated with Nb3Sn at Cornell University have repeatedly demonstrated quality factors of >10¹⁰ at 4.2 K and >15 MV/m. Ongoing research is currently focussed on the impact of intrinsic and extrinsic factors that limit the quality factor and quench field in these cavities. New single-cell cavities have been commissioned to enable further exploration of the coating parameter space. Experimental studies on both cavities and sample coupons have been supplemented by theoretical work done on layer growth, trapped vortex motion and flux entry. In this paper, we provide a comprehensive overview of the latest developments on Nb3Sn cavities, including work conducted in collaboration with the new NSF Centre for Bright Beams, with a brief summary on work being done in the field at large.

Slides WEXA01 [10.681 MB]

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WEXA03

High-performance Thin-film Niobium Produced via Chemical Vapor Deposition (CVD)

niobium, ion, cavity, electron

674

R.D. Porter, D.L. Hall, M. Liepe, J.T. Maniscalco
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
V.M. Arrieta, S.R. McNeal, W.E. Williams
Ultramet, Pacoima, California, USA

Bulk niobium cavities have been the standard for superconducting particle accelerators for many years. However, the cost of high RRR niobium start materials makes them expensive. The use of Chemical Vapor Deposition (CVD) processing technologies to produce thin Nb films on low-cost substrates (e.g. copper) offers a method to significantly reduce the cost of accelerator cavity fabrication while increasing cavity performance capabilities. Recent optimization of CVD niobium processes for high RRR Nb films has led to RF performance approaching that of bulk Nb. In collaboration with Ultramet, Cornell continues to explore the potential of CVD techniques. This paper presents results from a detailed study of CVD thin film Nb materials produced by Ultramet on 5-inch diameter copper and molybdenum substrates, including RF performance results with T-mapping and detailed surface analysis of performance limiting regions. Our work shows that CVD-based cavity fabrication methods are a promising alternative to sheet-formed bulk cavities, and to other thin Nb film techniques, warranting further development. Additional results from the field will be discussed.

Slides WEXA03 [1.503 MB]

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WEYA05

Progress Toward 2 K High Performance Half-wave Resonators and Cryomodule

ion, cavity, cryomodule, cryogenics

692

Z.A. Conway, B.M. Guilfoyle, M. Kedzie, M.P. Kelly, T. Reid
ANL, Argonne, Illinois, USA
H. Guo
IMP/CAS, Lanzhou, People's Republic of China

Funding: This material is based upon work supported by the U.S. DOE, Office of Science's Office of Nuclear Physics and Office of High Energy Physics, contract numbers DE-AC02-06CH11357 and DE-AC02-76CH03000.
Argonne National Laboratory is implementing a novel 2.0 K superconducting cavity cryomodule operating at 162.5 MHz. This cryomodule is designed for the acceleration of 2 mA H-/proton beams from 2.1 to 10.3 MeV as part of the Fermilab Proton Improvement Project-II (PIP-II). The 2.0 K cryomodule is comprised of 8 half-wave cavities operated in the continuous wave mode with 8 superconducting magnets, one in front of each cavity. In this paper we will review recent cavity results which demonstrate continuous-wave operated cavities with low-field residual resistances of 2.5 nΩ which achieve peak surface fields up to 134 MV/m and 144 mT, electric and magnetic respectively, with field emission onset fields greater than 70 MV/m in the production cavities following the prototyping effort.

Slides WEYA05 [1.967 MB]

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THXA04

Fabrication, Treatment and Test of Large Grain Cavities

cavity, ion, superconducting-cavity, FEL

700

J.K. Hao, J.E. Chen, L.W. Feng, L. Lin, K.X. Liu, S.W. Quan, F. Wang, H.M. Xie, F. Zhu
PKU, Beijing, People's Republic of China

Development of SRF technology has been included in the project of Soft X-ray FEL (SXFEL) for a hard X-ray FEL plan in China which would be operated in CW mode. Six 9-cell TESLA type cavities as well as several single-cell cavities made of Ningxia large grain niobium material have been fabricated by Peking University for achieving high gradient and high intrinsic quality factor Q0. The measurements of gradient and Q0 have been carried out with a new vertical test system at PKU. The process of fabrication, surface treatment and test results of these large grain cavities will be presented.

Slides THXA04 [7.911 MB]

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THXA08

Review of Heat Treatments for Low Beta Cavities : What's So Different from Elliptical Cavities

ion, cavity, niobium, accelerating-gradient

708

D. Longuevergne
IPN, Orsay, France

Heat treatments done for low beta (low frequency) cavities are usually, due to the lack of feedback, inspired from elliptical (high frequency) cavity results. Is that still relevant now that experimental data are available thanks to the florishing business of low beta structures (Spiral2, ESS, FRIB, C-ADS, MYRRHA, PROJECTX, …). These 2 families are moreover not usually operating in the same resistance regime (BCS and residual). The paper will review procedures applied and results obtained on different type of cavities (Quarter-Wave resonator, Half-Wave resonator and Spoke) and different temperature treatments (low temperature baking, hydrogen degassing, nitrogen doping, …) and compare these to elliptical cavities.

Slides THXA08 [5.567 MB]

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THYA01

Performance Testing of FRIB Early Series Cryomodules

ion, cavity, cryomodule, linac

715

J.T. Popielarski, C. Compton, A. Ganshyn, W. Hartung, D. Luo, S.J. Miller, D.G. Morris, P.N. Ostroumov, L. Popielarski, K. Saito, S. Shanab, S. Stark, T. Xu, S. Zhao, Z. Zheng
FRIB, East Lansing, USA

Funding: U.S. Department of Energy Office of Science under Cooperative Agreement DE SC0000661.
Construction of a new accelerator for nuclear physics research, the Facility for Rare Isotope Beams (FRIB), is underway at Michigan State University (MSU). The FRIB linac will use superconducting resonators at an operating temperature of 2 K to accelerate ions to 200 MeV per nucleon. The linac requires 10⁶ quarter wave resonators (80.5 MHz, β = 0.043 and 0.086) and 248 half wave resonators (322 MHz, β = 0.29 and 0.54), all made from sheet Nb. Production resonators being delivered to MSU by cavity vendors. At MSU, the resonators are etched, rinsed, and tested in MSU's certification test facility. Certification testing is done before the installation of the high-power input coupler and the tuner. After certification, the resonators are tested in the cryomodule before installation into the FRIB tunnel. The cryomodule test goals are to verify integrated operation of the resonators, RF couplers, tuners, RF controls, and superconducting solenoids. To date, 10 cryomodules out of 48 have been fabricated, and 8 of the cryomodules have been certified. Cryomodule test results are presented in this paper.

Slides THYA01 [31.165 MB]

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THPB003

An Innovative Design of a Flexible Temperature-mapping System

cavity, ion, electron, superconducting-cavity

746

M. Ge, F. Furuta, M. Liepe, P.J. Pamel
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

A temperature-mapping (T-Map) system is an essential tool for fundamental SRF research as it provides spatial information of RF power dissipation and so allows localizing hot-spots on a cavity surface at cryogenic temperatures. However, the temperature sensors are mounted on rigid boards in most current systems, so each can only work for one specific cavity size and shape. In this paper, we proposed a flexible design, which allows this temperature mapping system to work for different cavity shapes.

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THPB005

Design Updates on Cavity to Measure Suppression of Microwave Surface Resistance by DC Magnetic Fields

ion, cavity, niobium, experiment

754

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

Our research has shown good agreement between experimental measurements of the anti-Q-slope in niobium SRF cavities and predictions from a recent theoretical model of the suppression of the microwave surface resistance with applied RF field. To confirm that this mechanism is indeed what causes the anti-Q-slope in impurity-doped niobium, it will be necessary to measure the theory's prediction that the same effect may be achieved by applying a constant (i.e. DC) magnetic field parallel to the RF surface. This will also allow for systematic studies of the proposed fundamental effect of the anti-Q-slope and of the behavior of the anti-Q-slope for many surface preparations and alternative materials, since it provides a cleaner measurement by eliminating the counteracting quasiparticle overheating and the complexifying oscillation of the screening currents. In this report we give an update on work at Cornell to design and build a coaxial cavity to measure this effect.

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THPB007

Nitrogen Infusion R&D on Single Cell Cavities at DESY

ion, cavity, niobium, injection

759

M. Wenskat, D. Reschke, J. Schaffran
DESY, Hamburg, Germany
A.L. Prudnikava
University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany

A first series of single cell cavities underwent the "Nitrogen Infusion" treatment at DESY. Samples, which were in the furnace together with the cavities, underwent a series of SEM/EDX measurements and showed some unexpected structures. In parallel, the cavity performance deteriorated after the treatment. The furnace pressure and temperature and the residual gases during the treatment were analyzed and the possible cause for the deterioration has been found. Steps to prevent this deterioration in following treatments are discussed and first results are shown.

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THPB018

Towards the Perfect Meissner State: A Magneto-Optical Study on Competing Pinning Centers in Niobium

ion, niobium, cavity, background

766

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

Over the past years trapped magnetic flux has emerged as a main limiting factor of high quality factors in SRF cavities. Several studies investigated how the ambient magnetic field can be minimized or how the flux expulsion during the phase transition can be improved. We now present a study that targets the pinning centers which allow for the flux to remain inside the superconductor in the first place. Using magneto-optical imaging we were able to not only measure the amount of trapped flux but in addition we managed to image its distribution with a resolution below 10μm and correlate it with electron backscatter diffraction maps. As a result we found that the grain boundaries did not play a major role as pinning centers nor did the crystal orientation influence the amount of trapped flux signifi-cantly. Niobium hydrides which formed during the cool down to cryogenic temperatures however were found to enhance trapping.

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THPB021

Trial of Nitrogen Infusion and Nitrogen Doping by Using J-PARC Furnace

ion, cavity, niobium, controls

775

T. Konomi, T. Dohmae, Y. Hori, E. Kako, T. Kubo, G.-T. Park, H. Sakai, K. Umemori
KEK, Ibaraki, Japan
J. Kamiya, K. Takeishi
JAEA/J-PARC, Tokai-mura, Japan
T. Nagata
ULVAC, Inc., Tsukuba, Japan

KEK has been carrying out SRF cavity developments toward higher Q-values and higher accelerating gradients. In the past nitrogen-doping was tested using the KEK furnaces, but it did not succeed. This time nitrogen infusion and nitrogen doping are tested using the J-PARC's furnace, which has an oil-free pumping system and is mainly pumped by a 10000 L/s cryopump and three 3000 L/s turbo pumps. Nitrogen pressure is controlled by a variable leak valve and an additional turbo pump. To avoid performance degradation during heat treatment, flanges of cavities are covered by Nb caps and foils. Nitrogen infusion at 120 degrees was applied to a single cell cavity and cavity performance was measured by vertical tests after HPR and assembly. Nitrogen doping at 800 degrees is also applied to another single cell cavity. After applying EP and HPR, vertical tests were carried out. Nb samples were also installed into the furnace during heat treatment. Surfaces are analyzed by SIMS and XPS. In this presentation, we report procedure of nitrogen infusion and doping, vertical test results and results of surface analysis.

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THPB024

Investigation on Depth Profiling of Niobium Surface Composition and Work Function of SRF Cavities

ion, niobium, cavity, electron

779

A.D. Wu, L. Chen, Q.W. Chu, H. Guo, Y. He, Y.M. Li, F. Pan, L. Yang, S.H. Zhang, H.W. Zhao
IMP/CAS, Lanzhou, People's Republic of China

The niobium samples were prepared by different surface treatments that commonly applied for the superconducting RF cavities preparation, as the following of electrochemical polishing, the buffered chemical polishing and high temperature annealing. In order to understand the property of niobium surface, especially the relationship between the composition and the work function value, the X-ray and ultraviolet photoelectron spectra depth profiling has been studied. The intensity photoelectrons signals of O1s, C1s and the Nb3d were identified for composition of the niobium oxide and the hydrocarbon contamination. And the work function of sample surface was measured via the means of the ultraviolet photoelectron spectra band width. To make a depth profiling, the sputtering of Argon ions was used to remove surface material gradually under by control the sputtering times. The results shown that the value of work function strongly depends on the chemical composition.

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THPB026

Investigation of the Effect of Strategically Selected Grain Boundaries on Superconducting Properties of SRF Cavity Niobium

ion, niobium, cavity, cryogenics

787

M. Wang, T.R. Bieler
Michigan State University, East Lansing, Michigan, USA
S. Balachandran, P.J. Lee
NHMFL, Tallahassee, Florida, USA
S. Chetri, A. Polyanskii
ASC, Tallahassee, Florida, USA
C. Compton
FRIB, East Lansing, Michigan, USA

Funding: Research supported by DOE/OHEP contracts DE-SC0009962, DE-SC0009960, NSF-DMR-1157490, and the State of Florida.
High purity Nb is commonly used for fabricating SRF cavities due to its high critical temperature and its formability. However, microstructural defects such as dislocations and grain boundaries in niobium can serve as favorable sites for pinning centers of magnetic flux that can degrade SRF cavity performance. In this study, two bi-crystal niobium samples extracted from strategically selected grain boundaries were investigated for the effect of grain misorientation on magnetic flux behavior. Laue X-ray and EBSD-OIM crystallographic analyses were used to characterize grain orientations and orientation gradients. Cryogenic Magneto-Optical Imaging (MOI) was used to directly observe magnetic flux penetration at about 5-8 K. Flux penetration was observed along one of the grain boundaries, as well as along a low angle boundary that was not detected prior to MOI imaging. Hydride scars on the sample surface after MOI were examined using atomic force microscopy (AFM) analysis. The relationships between dislocation content, cryo-cooling, flux penetration and grain boundaries are examined.

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THPB027

Characterization of Microstructural Defects in SRF Cavity Niobium using Electron Channeling Contrast Imaging

ion, cavity, niobium, electron

792

M. Wang, T.R. Bieler, D. Kang
Michigan State University, East Lansing, Michigan, USA
C. Compton
FRIB, East Lansing, Michigan, USA

Funding: Research supported by DOE/OHEP contract DE-SC0009962
Although the quality factor of niobium cavities has improved, performance variability arises from microstructural defects such as dislocations and grain boundaries that can trap magnetic flux, block heat transfer, and perturb superconducting currents. Microstructural defect evolution is compared in four samples extracted from a 2.8 mm thick large-grain niobium slice, with tensile axes chosen to generate desired dislocation structures during deformation. The four samples are 1) as-extracted, 2) extracted and annealed, 3) extracted and then deformed to 40% strain, and 4) extracted, annealed at 800 °C 2 hours, and deformed to 40% strain. Electron Channeling Contrast Imaging (ECCI) was performed on all samples to characterize initial dislocation density, dislocation structure evolution due to annealing and deformation, and related to the mechanical behavior observed in stress-strain curves. The orientation evolution and geometrically necessary dislocation (GND) density were characterized with electron backscattered diffraction (EBSD) maps. Fundamental understanding of dislocation evolution in niobium is necessary to develop models for computational cavity design.

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THPB029

XPS Studies of Nitrogen Doping Nb Samples before and after GCIB Etching

ion, niobium, cavity, electron

802

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

The surface chemical composition of nitrogen doping Nb samples used for the fabrication of superconducting radio frequency (SRF) cavities, followed by the subsequent successive EP with different amounts of material removal, has been studied by XPS. The chemical composition of Nb, O, C and N was presented before and after Gas Cluster Ion Beams (GCIB) etching. No signals of bad superconducting nitrides NbNx was found in any doped and un-doped samples before etching. However, in the depth range greater than 30nm, the content of N elements is below the XPS detection precision scope even in the samples directly after nitrogen doping treatment.

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THPB031

Magnetic Properties of Nitrogen Doping Niobium Samples

ion, cavity, niobium, experiment

809

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

Nitrogen doping study on Niobium samples used for the fabrication of superconducting radio frequency (SRF) cavities was carried out. The samples' surface treatments were attempted to replicate that of the cavities, which included heavy electropolishing (EP), nitrogen doping and the subsequent successive EP with different amounts of material removal. The magnetization curves of both doped and un-doped samples have been measured, from which the lower critical field Hffp (First Flux Penetration, ffp) and upper critical field Hc2 was extracted. The thermodynamic critical field Hc, superheating field Hsh and superconducting parameters of samples with different treatments was calculated from the determined reversible magnetization curves. Hsh of doped samples is obviously smaller than that of un-doped samples, which may be a possible reason for the reduction of achievable accelerating gradient in SRF niobium cavities after nitrogen doping treatments.

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THPB034

Development of High Purity Niobium Components and Cavities for SRF Accelerator

cavity, ion, electron, niobium

814

T. Nagata, H. Masui, S. Shinozawa
ULVAC, Inc, Chiba, Japan
H. Inoue, E. Kako, M. Yamanaka
KEK, Ibaraki, Japan
M. Murakami
ULVAC, Inc., Tsukuba, Japan

Comprehensive cavity fabrication process from Niobium ingot was investigated. In order to purify ingots, A 600 kW electron beam furnace was introduced in ULVAC. It makes possible the stable quality of Niobium sheets and tubes. In evaluation of chemical components, mechanical properties, and RRR of our materials, all the value satisfies the ASTM Type 5 (superconducting grade) specification. In this study, we performed the trial manufacturing of welding-type and seamless-type cavities were made of our high purity Niobium ingots (RRR > 300). Accelerating gradient over 40 MV/m was shown in both cavities. We also tried to manufacture a 3-cell seamless cavity as scale up study. A seamless tube with a length of 830 mm, an inner diameter of 131 mm and a thickness of 3.5 mm was prepared. We succeed in direct forming from tube to cavity shape by using a hydroforming process. Cavity surface could be smoother than that of single cell cavity caused by small crystal grain size.

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THPB040

SRF Theory Developments from the Center for Bright Beams

ion, cavity, experiment, HOM

835

D. Liarte, T. Arias, M. Liepe, J.P. Sethna, N. Sitamaran
Cornell University, Ithaca, New York, USA
D.L. Hall
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
A.R. Pack, M.K. Transtrum
Brigham Young University, Provo, USA

Funding: This work was supported by the US National Science Foundation under Award OIA-1549132, the Center for Bright Beams.
We present theoretical studies of SRF materials from the Center for Bright Beams. First, we discuss the effects of disorder, inhomogeneities, and materials anisotropy on the maximum parallel surface field that a superconductor can sustain in an SRF cavity, using linear stability in conjunction with Ginzburg-Landau and Eilenberger theory. We connect our disorder mediated vortex nucleation model to current experimental developments of Nb3Sn and other cavity materials. Second, we use time-dependent Ginzburg-Landau simulations to explore the role of inhomogeneities in nucleating vortices, and discuss the effects of trapped magnetic flux on the residual resistance of weakly-pinned Nb3Sn cavities. Third, we present first-principles density-functional theory (DFT) calculations to uncover and characterize the key fundamental materials processes underlying the growth of Nb3Sn. Our calculations indicate that the observed tin-depleted regions may be the direct result of an exothermic reaction between Nb3Sn and Nb at the growing Nb/Nb3Sn interface. We suggest new growth protocols to mitigate the formation of tin depleted regions.

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THPB042

Field-dependence of the Sensitivity to Trapped Flux in Nb3Sn

ion, cavity, niobium, site

844

D.L. Hall, M. Liepe, R.D. Porter
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
D. Liarte, J.P. Sethna
Cornell University, Ithaca, New York, USA

The amount of residual resistance gained per unit of trapped flux ' referred to as the trapped flux sensitivity ' in Nb3Sn cavities has been found to be a function of the amplitude of the RF field. This behaviour is consistent with a scenario in which the trapped vortex dynamics are described by collective weak pinning. A model has been developed to describe this, and results in the observed linear dependence of trapped flux sensitivity with RF field. The model is used to discuss cavity preparation methods that might suppress this dependence, which would reduce the trapped flux requirements necessary to operate an Nb3Sn cavity at simultaneous high quality factors and accelerating gradients.

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THPB043

Effects of Chemical Treatments on the Surface Roughess and Surface Magnetic Field Ehancement of Niobium-3 Tin Films for Superconducting Radio-Frequency Cavities

ion, cavity, niobium, linac

848

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

Current niobium-3 tin (Nb3Sn) films produced via vapor diffusion have rougher surfaces than typical electropolished niobium surfaces causing significantly enhancement of the surface magnetic fields. Reducing surface roughness of Nb3Sn surfaces may be necessary to achieve higher gradient accelerator cavities with high Q. Previous work at Cornell has shown the impact of several chemical treatments on the surface roughness of Nb3Sn films; however, it had not been evaluated how the changes in surface roughness impact the surface magnetic field enhancement. In this paper we present simulations of the surface field enhancement of oxipolished Nb3Sn, which was shown to be effective at reducing the surface roughness of Nb3Sn. The surface magnetic field enhancement data is compared to those of unetched Nb3Sn to find that the surface magnetic field enhancement (and surface roughness) has been roughly halved.

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THPB044

Update on Sample Host Cavity Design Work for Measuring Flux Entry and Quench Field

cavity, ion, niobium, radio-frequency

851

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

Current state-of-the-art Niobium superconducting radio-frequency (SRF) accelerator cavities have reached surface magnetic field close to the theoretical maximum set by the superheating field. Further increasing accelerating gradients will require new superconducting materials for accelerator cavities that are capable of supporting higher surface magnetic fields. This necessitates measuring the quench fields of new materials in high power RF fields. Previous work at Cornell University has used electromagnetic simulations to optimize the shape of a dipole mode sample host cavity such that the surface magnetic fields on the sample are high compared to the energy inside the cavity and the surface magnetic field on the rest of the cavity. In this paper we present an update of the design that includes how to mount samples in the cavity and the addition of a low field chamber.

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THPB053

Surface Resistance Characterization of Nb3Sn Using the HZB Quadrupole Resonator

ion, quadrupole, cavity, niobium

863

S. Keckert, J. Knobloch, O. Kugeler
HZB, Berlin, Germany
D.L. Hall, M. Liepe
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Funding: This work is part of EuCARD-2, partly funded by the European Commission, GA 312453.
Nb3Sn is a very promising candidate material for future SRF cavities. With a critical temperature more than twice as the one of bulk niobium, higher operational temperatures with still lower surface resistance are theoretically possible. A sample prepared by Cornell University was characterized towards its SRF properties using the HZB Quadrupole Resonator. In comparison to a coated cavity this device enables SRF measurements at an extended parameter space (frequency, temperature and RF field) and easy access to physical quantities such as critical field and penetration depth. In this contribution we present surface resistance and RF critical field measurements.

Poster THPB053 [2.725 MB]

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THPB055

Plasma-enhanced ALD System for SRF Cavity

ion, cavity, niobium, plasma

870

S. Kato, H. Hayano
KEK, Ibaraki, Japan

Funding: This work was supported by Photon and Quantum Basic Research Coordinated Development Program by MEXT and partly by JST-CREST.
A remote PEALD (Plasma-enhanced Atomic Layer Deposition) system which would offer a high conformality and a low deposition temperature has been being developed for deposition of NbN on an SRF cavity. The deposition equipment consists of a deposition chamber, a remote plasma exciter, a precursor supply system, vacuum pumps, a quartz crystal microbalance (QCM) as a film growth rate meter, a detoxifying system and a safety system. An RF frequency of 13.56MHz was used for the inductively coupled plasma exciter of a reactant gas. The whole equipment is in a draft booth for operation safety. For ALD of an SRF cavity, the ALD system allows us to easily replace the deposition chamber with a single cell Nb cavity. The prepared precursors are tris[ethylmethylamido][tert-butylimido] niobium (TBTEMN) and trimethylaluminium (TMA). Ammonia, hydrogen and water are also prepared as reactants. We will report the ALD system design and result of the NbN deposition on sample coupons which are analysed with SEM, EDX and XPS.

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THPB057

Investigation of Nucleation Stage in Diffusion Coating of Nb3Sn on Nb

ion, niobium, experiment, cavity

873

F. Pan
IMP/CAS, Lanzhou, People's Republic of China

Nb3Sn has the potential to improve properties of SRF cavities, such as the gradients and the working tempera-tures. Institute of Modern Physics has launched its Nb3Sn thin film coated SRF cavity project in 2016. Samples have been successfully coated to study the process of tin vapor diffusion. The main part of the deposition system is a tube furnace, which working temperature can reach 1100°C. Basic material characterization of the Sn-Nb film will be presented in this work.

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THPB069

Surface Studies of Nb3Sn Coated Samples Prepared under Different Coating Conditions

ion, experiment, cavity, site

894

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
M.J. Kelley, J. Tuggle
Virginia Polytechnic Institute and State University, Blacksburg, USA

Funding: Supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DEAC0506OR23177 and Office of High Energy Physics under grant DESC0014475.
The promise of better performance and significant cost reduction make Nb3Sn-coated Nb SRF cavities an attractive option when compared to traditional Nb SRF cavities. Historically, the vapor diffusion technique for coating Nb cavities with Nb3Sn has proven to be the most successful, and is currently practiced in several research facilities with minor variations. Using modern characterization tools, we examined the Nb3Sn coating prepared in different systems and/or under different conditions. Identically prepared high RRR (~ 300) Nb samples were coated using existing standard protocols at different coating facilities. The microstructure and composition of Nb3Sn coatings were found to be similar when examined with scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Atomic force microscopy (AFM) was performed on each sample and the topographies of the samples were then compared in terms of power spectral densities (PSDs). Secondary ion mass spectrometry (SIMS) depth profiles revealed trace amounts of Ti in some of the samples.

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THPB070

Electrochemical Finishing Treatment of Nb3Sn Diffusion-coated Niobium

ion, niobium, cavity, experiment

900

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

Funding: Supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DEAC0506OR23177 and Office of High Energy Physics under grant DESC0014475.
Nb3Sn cavities are now routinely prepared by depositing few micron thick Nb3Sn coatings on Nb cavities using tin vapor diffusion process. For the¬¬ case of niobium there is a significant improvement after electropolishing (EP), but electrochemical finishing treatment on Nb3Sn coatings has not been studied. Controlled removal of the first few layers could lead to a smoother and cleaner surface that is conducive to better RF performance. Several samples, which were coated with Nb3Sn by vapor diffusion process in a JLab sample chamber, were used to explore polishing parameters, such as I-V characteristics, removal rate, topography, etc. Preliminary results from the first runs are discussed here.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-THPB070

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THPB076

Carbon-based Coatings for Electron Cloud Mitigation in SRF Photocathodes

ion, gun, cathode, electron

910

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

Funding: This research has been funded by the Federal Ministry of Education and Research of Germany in the framework of HOPE I (project number 05K13PS2).
During the past three years, we developed a coating along with a corresponding in-situ characterization process in order to realize SRF-gun surfaces featuring low secondary electron yield (SEY). Important aspects that have been accounted for are the homogeneity and adhesion of the coatings deposited on the cylindrical SRF-gun mantle. Furthermore, the correlation between SEY and crystallinity, morphology, and contamination was studied in detail. The SEY maximum can be tuned between 1.5 and less than 0.7 depending on the deposition conditions. In this work, we recap the results and present a general strategy for the effective mitigation of electron cloud multiplication.

Poster THPB076 [5.583 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-THPB076

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THPB078

Fabrication of Large-area MgB2 Films on Copper Substrates

ion, cavity, niobium, radio-frequency

917

X. Guo, K.X. Liu, Z. Ni
PKU, Beijing, People's Republic of China
Q. Feng, C. Yang
Peking University, Beijing, People's Republic of China

Magnesium diboride (MgB2) is a promising candidate material for SRF cavities because of its higher transition temperature and critical field compared with niobium. To meet the demand of RF test devices, the fabrication of large-area MgB2 films on metal substrates is needed. In this work, MgB2 films with 50-mm diameter were fabri-cated on Cu substrates by using an improved HPCVD setups at Peking University. The transition temperatures of MgB2 film on Cu substrate and with Mo buffer layer on Cu substrate are 36.2 K and 36.5 K, respectively. The fabrication processes, surface morphology, superconduct-ing properties of these large-area MgB2 films are present-ed.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-THPB078

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THPB080

Measurement of Frequency, Temperature, RF Field Dependent Surface Resistance Using Superconducting Half Wave Cavity

cavity, ion, experiment, factory

925

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

A theory of surface resistance of superconductor was rigorously formulated by Bardeen, Cooper, Schrieffer more than 50 years ago. Since then the accelerator community has been used the theory as a guideline to improve the surface resistance of the superconducting cavity. It has been observed that the surface resistance is dependent on frequency, temperature and rf field strength, and surface preparation. To verify these dependences, a well-controlled study is required. Although many different types of cavities have been tested, the typical superconducting cavities are built for specific frequencies of their application. They do not provide data other than at its own frequency. A superconducting half wave cavity is a cavity that enables us to collect the surface resistance data across frequencies of interest for particle accelerators and evaluate preparation techniques. This paper will present the design of the half wave cavity, its electromagnetic mode characteristics and experimental results.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-THPB080

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