SRF2017 - List of Keywords (HOM)

Paper	Title	Other Keywords	Page
MOXA04	Superconducting Accelerator for ERL Based FEL EUV Light Source at KEK	ion, cavity, linac, operation	13
	H. Sakai, E. Kako, T. Konomi, T. Kubo, K. Umemori KEK, Ibaraki, Japan T. Ota Toshiba, Yokohama, Japan M. Sawamura QST, Tokai, Japan
	An energy recovery linac (ERL)-based free electron laser (FEL) is a possible candidate of a tens of kW EUV source and open the era for next generation EUV-lithography. We have designed the 10 mA class ERL-based EUV-FEL source to generate more than 10 kW power. One of the key technologies is CW superconducting cavities to realize the energy recovery of high beam current of more than 10 mA by suppressing HOMs and high gradient acceleration of higher than 12 MV/m. This CW superconducting cavity had been developed through the construction of the Compact ERL facility in KEK and it successfully achieved the energy recovery of 1 mA CW beam until now. In this talk, first we express our design strategies of SRF cavities of the main linac of ERL-EUV light sources not only to suppress the HOMs but also to overcome the field emission problem by modifying the main linac cavity of Compact ERL more sophisticatedly. Next we show the recent development works for ERL-EUV superconducting cavity about HOM damper, cryomodule, and its clean string-assembly work by using horizontal test stand.
	Slides MOXA04 [5.938 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOXA04
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MOYA02	BESSY VSR: SRF Challenges and Developments for a Variable-pulse Length Next-generation Light Source	ion, cavity, SRF, 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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MOPB001	Concepts and Design for Beamline HOM Dampers for eRHIC	ion, cavity, impedance, linac	39
	P. Kolb, Y. Gao, D. Holmes, K.S. Smith, W. Xu BNL, Upton, Long Island, New York, USA Y. Gao PKU, Beijing, People's Republic of China
	Funding: Work supported by LDRD program of Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. DOE. In the design of eRHIC at BNL, HOM power plays a major role for the SRF installation. Depending on the final accelerator design and choice of cavity, up to 100kW of HOM power is estimated to be generated, presenting a big challenge for the HOM damping concept. Due to this high amount of HOM power, all current concepts for eRHIC would use room temperature beam line absorbers equipped with silicone-carbide dielectrics to absorb HOM power. Concepts, designs and simulations for these beam line absorbers will be presented.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOPB001
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MOPB009	Progress of 650 MHz SRF Cavity for eRHIC SRF Linac	cavity, ion, SRF, 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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MOPB017	Multiphysics Simulations of the Wide Opened Waveguide Crab-cavity	ion, cavity, impedance, dipole	90
	K. Papke, A. Amorim Carvalho, A. Grudiev, C. Zanoni CERN, Geneva, Switzerland
	In the frame of a FCC study a first prototype of a compact superconducting crab-cavity, using Nb-on-Cu-coating technique is being manufactured and investigated. The design, which is based on the ridged waveguide resonator, is subjected to multipacting and pressure sensitivity simulations. First results of theses simulations are presented and compared to those of other SRF cavities. Furthermore, several aspects related to the design of the fundamental mode coupler and HOM dampers are presented.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOPB017
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MOPB028	HOM Coupler Design for CEPC Cavities	ion, cavity, damping, collider	115
	H.J. Zheng, F. Meng, 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) In this paper，it will be presented the higher order mode (HOM) coupler design for the Circular Electron-Positron Collider (CEPC) 650 MHz 2-cell cavity. The higher order modes excited by the intense beam bunches must be damped to avoid additional cryogenic loss and multi-bunch instabilities. To keep the beam stable, the impedance budget and the HOM damping requirement are given. A double notch coaxial HOM coupler, which will be mounted on the beam pipe, is planned to extract the HOM power below the cut-off frequency of the beam pipe. This paper summarizes the RF design of the HOM coupler, tolerance analysis, thermal analysis as well as mechanical structures.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOPB028
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MOPB045	JLab New Injector Cryomodule Design, Fabrication and Testing	cavity, ion, cryomodule, cryogenics	158
	G. Cheng, M.A. Drury, J.F. Fischer, R. Kazimi, K. Macha, H. Wang JLab, Newport News, Virginia, USA
	Funding: U.S. DOE Contract No. DE-AC05-06OR23177. A new Injector Cryomodule (INJ CM) aimed to replace the existing Quarter Cryomodule in the CEBAF tunnel has been developed at Jefferson Lab (JLab). It is sched-uled to be first tested in the Cryomodule Test Facility (CMTF) for module performance then the Upgraded Injector Test Facility (UITF) with electron beam. This new cryomodule, hosting a 2-cell and 7-cell cavity, is designed to boost the electron energy from 200 keV to 5 MeV and permit 380 uA - 1.0 mA of beam current. The 2-cell cavity is a new design whereas the 7-cell cavity is refurbished from a low loss cavity from the retired JLab Renascence Cryomodule. The INJ CM adopts quite a few designs from the JLab 12 GeV Upgrade Cryomodule (C100). Examples of this include having the cold mass hung from a spaceframe structure by use of axial and transverse Nitronic rods, cavities to be tuned by scissor-jack style tuners and the end cans are actually modified from C100 style end cans. However, this new INJ CM is not a quarter of the C100 Cryomodule. This paper focuses on the major design features, fabrication and alignment process and testing of the module and its components. Authored by Jefferson Science Associates, LLC. The U.S. Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce this manuscript for Government purposes.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOPB045
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MOPB049	Upgraded Cavities for the CEBAF Cryomodule Rework Program	cavity, ion, cryomodule, GUI	168
	R.A. Rimmer, G. Cheng, G. Ciovati, W.A. Clemens, E. Daly, G.K. Davis, J. Follkie, D. Forehand, F. Fors, J. Guo, J. Henry, K. Macha, F. Marhauser, G.R. Myneni, L. Turlington JLab, Newport News, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. The CEBAF cryomodule rework program has been a successful tool to recover and maintain the energy reach of the original baseline 6 GeV accelerator. The weakest original modules with eight five-cell cavities assembled in four 'pairs', with a specification when new of 20 MV per cryomodule (5 MV/m), are disassembled, re-cleaned with modern techniques and re-qualified to at least 50 MV (12.5 MV/m), (leading to the acronym 'C50'). The cost per recovered MV is much less than building new modules. However over time the stock of weak modules is being used up and the voltage gain per rework cycle is diminishing. In an attempt to increase the gain per cycle it is proposed to rework the cavities by replacing the original accelerating cells with new ones of an improved shape and better material. The original CEBAF HOM and FPC end groups are retained. The goal is to achieve up to 75 MV (18.75 MV/m) for the reworked module ('C75'). We report on the fabrication experience and test results of the first trial pair, containing two such reworked cavities.
	Poster MOPB049 [1.503 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOPB049
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MOPB052	Dual-ridge Waveguide Load Design for eRHIC	ion, GUI, cavity, simulation	177
	P. Kolb, Y. Gao, C. Pai, R. Porqueddu, K.S. Smith, W. Xu BNL, Upton, Long Island, New York, USA Y. Gao PKU, Beijing, People's Republic of China
	Funding: Work supported by LDRD program of Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. DOE. To increase the real estate gradient in the eRHIC electron accelerator waveguide HOM couplers are being considered. These significantly reduce the length of individual cavities and address inter-cavity trapped modes, allowing for an increased number of cavities per cryomodule, which would increase the real estate gradient. The choice of waveguide went to a dual ridge waveguide due to a smaller size compared to rectangular waveguides. The waveguide termination, to convert the RF energy into thermal energy, is a custom designed load based on a silicon carbide dielectric that is already being used in beamline absorbers. Simulations of the RF properties of the load are presented as well as first measurements on a prototype.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOPB052
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MOPB053	RF Energy Harvesting of HOM Power	ion, GUI, cavity, distributed	180
	C. Xu, I. Ben-Zvi, Q. Wu, T. Xin BNL, Upton, Long Island, New York, USA I. Ben-Zvi Stony Brook University, Stony Brook, USA
	In an accelerator cavity, Higher Order Modes (HOM) are generated by the current of the beam. The HOM power can reach tens of kilowatts in a high current accelerator, depending on the details of the beam and cavity design. In this report, we propose a novel RF harvesting system to recover the HOM power into DC power which can further used for various purposes such as driving a solid state or klystron RF amplifier to supply fundamental RF power at other frequencies, charge batteries etc. The efficiency would be a product of the energy recovery and regeneration efficiencies, where the state of art is 90%. The proposed HOM power recycling system contains a multiple band harmonic RF coupler, broadband RF antenna system, a high power rectifier diode circuit and a DC load. 1) Collider-Accelerator Department, Brookhaven National Lab, Upton, NY 11973, USA 2) Physics & Astronomy Department, Stony Brook University, Stony Brook, NY 11794, USA
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOPB053
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MOPB062	Development of HOM Absorbers for CW Superconducting Cavities in Energy Recovery Linac	ion, cavity, superconducting-cavity, linac	191
	T. Ota, A. Miyamoto, K. Sato, M. Takasaki, M. Yamada Toshiba, Yokohama, Japan E. Kako, T. Konomi, H. Sakai, K. Umemori KEK, Ibaraki, Japan
	Higher Order Modes (HOM) absorbers for superconducting cavities have been developing at TOSHIBA in collaboration with High Energy Accelerator Research Organization (KEK) since 2015. Prototype HOM absorbers for 1.3 GHz 9-cell superconducting cavity were fabricated. An AlN lossy dielectrics cylinder was brazed with a copper cylinder, and the cool-down tests by nitrogen gas was carried out. Copper cylinders and SUS flanges were joined by electron beam welding to fabricate a whole prototype HOM absorber. Fabrication process of the prototype HOM absorber will be presented in this paper.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOPB062
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MOPB071	The Recent Research of HOM Damper for Superconducting Cavity in IHEP	ion, cavity, simulation, site	223
	F. Meng, T.M. Huang, H.Y. Lin, Q. Ma, W.M. Pan, J.Y. Zhai, P. 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) For high current accelerator, the efficient higher-order mode (HOM) damping is always an important issue. HOM damper with microwave absorbing material is a key component for high power and broadband HOM damping application. To pursue the high damping efficiency, some ideal material with good microwave absorbing capacity is essential during the RF design and fabrication phase. Sometimes the selection and test of material is the first step and also a long step. This paper will present the recent work on HOM dampers for BEPCII 500MHz cavity and CEPC 650MHz cavity in IHEP.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOPB071
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MOPB074	Analysis of Higher Order Modes of the Superconducting Cavities for the China-ADS Injector-II in IMP	dipole, ion, cavity, higher-order-mode	231
	C. Zhang, L. Chen, Y. He, S.C. Huang, Y.L. Huang, T.C. Jiang, Y.M. Li, F. Pan, R.X. Wang, A.D. Wu, Q.J. Wu, W.M. Yue, S.H. Zhang, S.X. Zhang IMP/CAS, Lanzhou, People's Republic of China
	Funding: funded by Natural Science Foundation of China， No.11505253 The influence of the higher order modes on the beam dynamics and the cryogenic losses has been studied for the superconducting section of the CIADS project in this paper. In addition, the necessity of HOM dampers in the Superconducting (SC) cavities is discussed.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOPB074
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MOPB079	HOM Coupler Alterations for the LHC DQW Crab Cavity	ion, cavity, impedance, simulation	249
	J.A. Mitchell Lancaster University, Lancaster, United Kingdom G. Burt, N.C. Shipman Cockcroft Institute, Lancaster University, Lancaster, United Kingdom R. Calaga CERN, Geneva, Switzerland S. Verdú-Andrés, Q. Wu, B. P. Xiao BNL, Upton, Long Island, New York, USA
	As part of the High Luminosity Large Hadron Collider (HL-LHC) project, 16 crab cavities are to be installed in the LHC in 2025. The two crab cavity designs are the Double Quarter Wave (DQW) and Radio Frequency Dipole (RFD). Preliminary beam tests in the Super Proton Synchrotron (SPS) are planned for both cavity types, with the DQW scheduled for testing in 2018. In reference to to Higher Order Mode (HOM) damping, the DQW has three identical on-cell HOM couplers. These HOM couplers provide a band-stop response at the frequency of the fundamental mode and act as a transmission path for the cavity HOMs. For the SPS cavity design, several geometric constraints exist. These give rise to dimensional limitations which in-turn impose limitations on the RF performance of the HOM couplers. As such, for the LHC assembly, the HOM coupler design is re-visited to take into account the relaxed geometric limitations, hence allowing the feasibility of an increased RF performance to be investigated. In addition to the RF performance, several geometric alterations were incorporated to ease manufacturing processes, tolerances and costs.
	Poster MOPB079 [2.038 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOPB079
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MOPB088	Experience on In-situ Module Repair and Set Up of Non XFEL Cavity Strings at DESY	ion, cavity, FEL, pick-up	269
	M. Schmökel, A. Daniel, N. Krupka, A. Matheisen, S. Saegebarth, M. Schalwat, P. Schilling DESY, Hamburg, Germany
	All components installed to the European XFEL cavity string modules underwent an intensive inspection and quality control before acceptance for installation to cavities or modules. Even though some RF feed throughs for HOM coupler- and Pick Up antennas showed leaks at the ceramic insulation after module test at 2 K. Due to time restriction and continuity of production the exchange of these parts needed to be done without reentering the cleanroom. Successful repair of these modules took place by setting up a local cleanroom onto the cavity string. In collaboration with Helmholtz-Zentrum Dresden-Rossendorf (HZDR), a cavity string for the ELBE project was assembled at DESY and transported to HZDR for installation to the vacuum vessel. A spare module with 3.9 GHz Resonators for the European XFEL was set up at DESY and will be tested and qualified for the European XFEL. Due to delay in delivery of the power couplers, four power couplers were installed after string assembly.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOPB088
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MOPB096	Estimation of Alignment Error by Measuring Higher-order-mode of Injector Superconducting Cavity at KEK-cERL	cavity, ion, dipole, alignment	286
	Y. Honda, E. Kako, T. Konomi, T. Miyajima, T. Obina, H. Sakai, K. Umemori KEK, Ibaraki, Japan
	Precise alignment of accelerator cavities is important in realizing a low emittance beam. Especially in the cases of superconducting cavities installed in a cryomodule, it is difficult to mechanically measure the position of the cavities. By measuring higher-order-modes (HOM) excited by a beam, the electrical center of the cavities can be estimated. We have developed a HOM measurement system for the injector superconducting accelerator cavities of KEK ERL test accelerator (cERL).Comparing the HOM signals of the three independent cavities in the cryomodule, we estimated the relative positioning errors of the three cavities.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOPB096
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TUXAA01	CEPC SRF System Design and Challenges	ion, cavity, SRF, 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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TUPB001	338 MHz Crab Cavity Design for the eRHIC Hadron Beam	cavity, ion, proton, electron	382
	S. Verdú-Andrés, I. Ben-Zvi, Q. Wu, B. P. Xiao BNL, Upton, Long Island, New York, USA I. Ben-Zvi Stony Brook University, Stony Brook, USA
	Funding: Work supported by the US Department of Energy via Brookhaven Science Associates LLC under contract no. DE-AC02-98CH10886. Crab crossing is an essential mechanism to restore high luminosity and avoid synchro-betatron resonances in the electron-hadron collider eRHIC. The current ring-ring eRHIC design envisages a set of crab cavities operating at 338 MHz. This set of cavities will provide the crabbing kick to the hadron beam of eRHIC. Double-Quarter Wave (DQW) cavities are compact, superconducting RF deflecting cavities appropriate for crab crossing. This paper summarizes the main design requirements and presents an optimized RF design of a DQW cavity for the crabbing system of the ring-ring eRHIC hadron beam.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB001
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TUPB002	Novel HOM Damper Design for High Current SRF Cavities	ion, GUI, cavity, SRF	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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TUPB004	HOM damping with an enlarged beam tube for HEPS 166.6 MHz SC cavities	ion, cavity, damping, impedance	389
	H.X. Hao, Z.Q. Li, F. Meng, P. Zhang, X.Y. Zhang IHEP, Beijing, People's Republic of China
	The 166.6 MHz superconducting cavities have been proposed for the High Energy Photon Source (HEPS) storage ring, which is initiated by the Institute of High Energy Physics in Beijing. Their higher order modes (HOMs) have to be damped sufficiently in order to limit coupled-bunch instabilities and parasitic mode losses. In order to keep the beam stable, the impedance budget and the HOM damping requirement are given. As one HOM damping option, an enlarged beam tube allows HOMs to propagate and subsequently be absorbed by downstream HOM dampers installed on the inner surface of the beam tube. And the conventional coaxial HOM coupler, which will be mounted on the big beam tube, is planned to extract the HOM power below the cut-off frequency of the beam pipe.
	Poster TUPB004 [1.132 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB004
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TUPB032	Study on 650MHz 5-cell Prototype Cavities at IHEP	ion, cavity, SRF, 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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TUPB033	Tests of the High Current Slotted Superconducting Cavity with Extremely Low Impedance	cavity, ion, GUI, damping	451
	Z.C. Liu, J. Gao, F.S. He, S. Jin, Z.H. Mi, T.X. Zhao, H.J. Zheng IHEP, Beijing, People's Republic of China F. Wang, D.H. Zhuang PKU, Beijing, People's Republic of China
	Slotted superconducting cavity is a novel structure with extremely low impedance and high BBU threshold. It can be used in various high current applications. A 1.3 GHz 3-cell slotted superconducting cavity was designed and tested. The room temperature test results show the cavity has an extremely low impedance. The vertical test results show the cavity gradient can reach several MV/m, but it was limited by the test end group made of steel.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB033
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TUPB034	The 166.6 MHz Proof-of-principle SRF Cavity for HEPS-TF	cavity, ion, storage-ring, SRF	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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TUPB040	Design and Optimization of Medium and High Beta Superconducting Elliptical Cavities for the CW Linac in CIADS	cavity, ion, multipactoring, linac	478
	Y.L. Huang, L. Chen, Y. He, Y.M. Li, S.H. Zhang IMP/CAS, Lanzhou, People's Republic of China
	Superconducting technology is adopted in the main accelerating section of the CW Linac in China Initiative Accelerator Driven System (CIADS) to accelerate the 10 mA proton beam from 2.1 MeV up to 1.5 GeV. The high energy section of the superconducting linac is composed of two families of SC elliptical cavities with optimum beta 0.62 and 0.82 for the acceleration of proton beam from 178 MeV to 1.5 GeV. In this paper, the design and optimization of the 650 MHz medium and high beta elliptical cavities are discussed, including the RF design, multipacting analysis, high order modes (HOMs) analysis, generator RF power calculation, and the mechanical design.
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TUPB052	Higher Order Modes Damping in 9-cell Superconducting Cavity with Grooved Beam Pipe	cavity, ion, damping, quadrupole	502
	A.M. Bulygin, R.V. Donetskiy, Ya.V. Shashkov MEPhI, Moscow, Russia
	This paper is focused on higher order modes (HOM) damping efficiency analysis in 9-cell superconducting cavities with HOM couplers and with grooved beam pipe. Comparison of two methods of HOM damping is presented. In order to increase efficiency of damping of trapped modes the end cells of the structure were modified. Higher order modes, tesla, SRF
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TUPB053	Lessons Learned from RF-Dipole Prototype Cavities for LHC High Luminosity Upgrade	cavity, ion, dipole, luminosity	506
	S.U. De Silva, J.R. Delayen ODU, Norfolk, Virginia, USA Z. Li SLAC, Menlo Park, California, USA H. Park JLab, Newport News, Virginia, USA
	The rf-dipole cavity has successfully demonstrated the principles of using a compact cavity operating in TE11-like mode in generating a transverse kick. Several proof-of-principle rf-dipole cavities have been fabricated and the rf tests have demonstrated high transverse gradients. The rf-dipole geometry has been adapted into a square-shaped geometry designed to meet the dimensional constraints for the LHC also maintaining crabbing in both horizontal and vertical planes. Recently, two prototype rf-dipole cavities intended for the test at SPS for have been completed that is designed to accommodate the FPC and HOM dampers. The performance during the rf tests have shown excellent results on achieving the design requirements of operation for the crab cavities for SPS. This paper presents the experiences and lessons learned during the cavity preparation and testing, including process validation, frequency tracking.
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TUPB054	RF Tests of RF-Dipole Prototype Crabbing Cavities for LHC High Luminosity Upgrade	cavity, ion, dipole, luminosity	509
	S.U. De Silva, J.R. Delayen ODU, Norfolk, Virginia, USA Z. Li SLAC, Menlo Park, California, USA H. Park JLab, Newport News, Virginia, USA
	The superconducting rf-dipole crabbing cavity is one of the two crabbing cavity designs proposed for the LHC high luminosity upgrade. The proof-of-principle (P-o-P) rf-dipole cavity operating at 400 MHz has demonstrated performance exceeding the design specifications. The prototype cavity for SPS beam test has been designed to include the fundamental power coupler, HOM couplers, and all the ancillary components intended to meet the design requirements. The crab cavities will be installed in the SPS beam line prior to the installation in LHC; this will be the first crabbing cavity operation on a proton beam. The fabrication of two prototype rf-dipole cavities is currently being completed at Jefferson Lab. This paper presents the details on cavity processing and cryogenic test results of the rf-dipole cavities.
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TUPB070	INFN-LASA Cavity Design for PIP-II LB650 Cavity	cavity, ion, coupling, operation	547
	C. Pagani Università degli Studi di Milano & INFN, Segrate, Italy M. Bertucci, A. Bignami, A. Bosotti, J.F. Chen, P. Michelato, L. Monaco, R. Paparella, D. Sertore INFN/LASA, Segrate (MI), Italy S. Pirani ESS, Lund, Sweden
	INFN-LASA is going to join the international partnership for Fermilab PIP-II project and to provide a novel design for the 650 MHz cavity of the 0.61 beta linac section, plug compatible with the Fermilab Cryomodule design. This paper reports the cavity design features both from the electro-magnetic and mechanical aspects, with focus on the rationales at the basis of the choice of main parameters. Furthermore, the current plans for the future R&D activity are here reported, including the production of two single cells and two complete cavities.
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THXA03	Crab Cavities for the High-luminosity LHC	ion, cavity, luminosity, cryomodule	695
	R. Calaga CERN, Geneva, Switzerland
	Funding: This work has been supported by the HL-LHC project (and by DOE or any other collaborating institutes, when applicable). As a first step towards the realization of crab crossing for HL-LHC, two superconducting crab cavities are foreseen to be tested with proton beams for the first time in the SPS. The progress on the cavity fabrication, RF test results, cryomodule development and integration into the SPS are presented. Some aspects of the beam tests with crab cavities in the SPS are outlined.
	Slides THXA03 [12.629 MB]
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THPB040	SRF Theory Developments from the Center for Bright Beams	ion, cavity, SRF, experiment	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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THPB054	Advanced Method to Extract the Surface Resistance From Q0 Measurements	ion, cavity, factory, quadrupole	867
	R. Kleindienst, S. Keckert, J. Knobloch, O. Kugeler HZB, Berlin, Germany
	Funding: The research leading to these results has received funding from the European Commission under the FP7 Research Infrastructures project EuCARD-2, grant agreement No. 312453. The quality factor of an RF cavity and the surface resistance are typically related with a constant geometry factor. The implicit assumption made is that the surface resistance is field independent, which is however not observed experimentally in superconducting cavities. The approximation error due to this assumption becomes larger the less homogeneous the magnetic field distribution along the cavity walls is. In this paper we calculate the surface resistance error for different cavity types. An iterative method to correct for this error is presented.
	Poster THPB054 [0.196 MB]
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THPB059	Simulation and Measurements of Crab Cavity HOMs and HOM Couplers for HL-LHC	ion, cavity, damping, simulation	881
	J.A. Mitchell, T.J. Jones Lancaster University, Lancaster, United Kingdom R. Apsimon, G. Burt, N.C. Shipman Cockcroft Institute, Lancaster University, Lancaster, United Kingdom I. Ben-Zvi, S. Verdú-Andrés, B. P. Xiao BNL, Upton, Long Island, New York, USA R. Calaga, A. Castilla, A. Macpherson, N.C. Shipman, A. Zwozniak CERN, Geneva, Switzerland T. Powers, H. Wang JLab, Newport News, Virginia, USA N.C. Shipman UMAN, Manchester, United Kingdom
	Two Superconducting Radio-Frequency (SRF) crab cavities are foreseen for the High Luminosity LHC (HL-LHC) upgrade. Preliminary beam tests of the Double Quarter Wave (DQW) crab cavity will take place in the Super Proton Synchrotron (SPS) in 2018. For damping of the cavity's Higher Order Modes (HOMs) the DQW has three identical on-cell, superconducting HOM couplers. The couplers are actively cooled by liquid heluim. In this paper, electromagnetic simulations of the HOMs and HOM couplers are presented. A novel approach to pre-installation spectral analysis of the HOM couplers is then presented, detailing both simulated and measured data. Measurements of the cavity HOMs at warm and in Vertical Test Facilities (VTFs) at both JLAB and CERN are detailed, comparing the measured characteristics of each mode to that of the simulated data-sets. Finally, the measured cavity data is compared with the test box measurements to see by what extent any reduction in damping can be predicted.
	Poster THPB059 [8.192 MB]
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FRXAA02	High-efficiency, High-current Optimized Main-linac ERL Cryomodule	ion, cavity, linac, cryomodule	935
	F. Furuta, N. Banerjee, A.C. Bartnik, J. Dobbins, R.G. Eichhorn, M. Ge, G.H. Hoffstaetter, M. Liepe, P. Quigley, D.M. Sabol, J. Sears, E.N. Smith, V. Veshcherevich Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	The Main Linac Cryomodule (MLC) prototype is a key component of the Cornell-BNL ERL Test Accelerator (CBETA) project, which is a 4-turn FFAG ERL currently under construction at Cornell University. This novel cryomodule is the first SRF module ever to be fully optimized simultaneously for high efficient SRF cavity operation and for supporting very high CW beam currents. After a successful initial MLC testing, the MLC has now been moved into its final location for the CBETA ring. For a first beam test of the MLC and CBETA, the Cornell ERL high voltage DC gun and SRF injector cryomodule were connected to MLC via an entry beam line; a beam stop assembly was also installed at the exit line. In this paper, we summarize the performance of this novel ERL cryomodule including the results of the first beam test and the additional tests focused on RF field stability and cavity microphonics.
	Slides FRXAA02 [8.792 MB]
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Paper

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Other Keywords

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MOXA04

Superconducting Accelerator for ERL Based FEL EUV Light Source at KEK

ion, cavity, linac, operation

13

H. Sakai, E. Kako, T. Konomi, T. Kubo, K. Umemori
KEK, Ibaraki, Japan
T. Ota
Toshiba, Yokohama, Japan
M. Sawamura
QST, Tokai, Japan

An energy recovery linac (ERL)-based free electron laser (FEL) is a possible candidate of a tens of kW EUV source and open the era for next generation EUV-lithography. We have designed the 10 mA class ERL-based EUV-FEL source to generate more than 10 kW power. One of the key technologies is CW superconducting cavities to realize the energy recovery of high beam current of more than 10 mA by suppressing HOMs and high gradient acceleration of higher than 12 MV/m. This CW superconducting cavity had been developed through the construction of the Compact ERL facility in KEK and it successfully achieved the energy recovery of 1 mA CW beam until now. In this talk, first we express our design strategies of SRF cavities of the main linac of ERL-EUV light sources not only to suppress the HOMs but also to overcome the field emission problem by modifying the main linac cavity of Compact ERL more sophisticatedly. Next we show the recent development works for ERL-EUV superconducting cavity about HOM damper, cryomodule, and its clean string-assembly work by using horizontal test stand.

Slides MOXA04 [5.938 MB]

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MOYA02

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

ion, cavity, SRF, 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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MOPB001

Concepts and Design for Beamline HOM Dampers for eRHIC

ion, cavity, impedance, linac

39

P. Kolb, Y. Gao, D. Holmes, K.S. Smith, W. Xu
BNL, Upton, Long Island, New York, USA
Y. Gao
PKU, Beijing, People's Republic of China

Funding: Work supported by LDRD program of Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. DOE.
In the design of eRHIC at BNL, HOM power plays a major role for the SRF installation. Depending on the final accelerator design and choice of cavity, up to 100kW of HOM power is estimated to be generated, presenting a big challenge for the HOM damping concept. Due to this high amount of HOM power, all current concepts for eRHIC would use room temperature beam line absorbers equipped with silicone-carbide dielectrics to absorb HOM power. Concepts, designs and simulations for these beam line absorbers will be presented.

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MOPB009

Progress of 650 MHz SRF Cavity for eRHIC SRF Linac

cavity, ion, SRF, 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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MOPB017

Multiphysics Simulations of the Wide Opened Waveguide Crab-cavity

ion, cavity, impedance, dipole

90

K. Papke, A. Amorim Carvalho, A. Grudiev, C. Zanoni
CERN, Geneva, Switzerland

In the frame of a FCC study a first prototype of a compact superconducting crab-cavity, using Nb-on-Cu-coating technique is being manufactured and investigated. The design, which is based on the ridged waveguide resonator, is subjected to multipacting and pressure sensitivity simulations. First results of theses simulations are presented and compared to those of other SRF cavities. Furthermore, several aspects related to the design of the fundamental mode coupler and HOM dampers are presented.

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MOPB028

HOM Coupler Design for CEPC Cavities

ion, cavity, damping, collider

115

H.J. Zheng, F. Meng, 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)
In this paper，it will be presented the higher order mode (HOM) coupler design for the Circular Electron-Positron Collider (CEPC) 650 MHz 2-cell cavity. The higher order modes excited by the intense beam bunches must be damped to avoid additional cryogenic loss and multi-bunch instabilities. To keep the beam stable, the impedance budget and the HOM damping requirement are given. A double notch coaxial HOM coupler, which will be mounted on the beam pipe, is planned to extract the HOM power below the cut-off frequency of the beam pipe. This paper summarizes the RF design of the HOM coupler, tolerance analysis, thermal analysis as well as mechanical structures.

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MOPB045

JLab New Injector Cryomodule Design, Fabrication and Testing

cavity, ion, cryomodule, cryogenics

158

G. Cheng, M.A. Drury, J.F. Fischer, R. Kazimi, K. Macha, H. Wang
JLab, Newport News, Virginia, USA

Funding: U.S. DOE Contract No. DE-AC05-06OR23177.
A new Injector Cryomodule (INJ CM) aimed to replace the existing Quarter Cryomodule in the CEBAF tunnel has been developed at Jefferson Lab (JLab). It is sched-uled to be first tested in the Cryomodule Test Facility (CMTF) for module performance then the Upgraded Injector Test Facility (UITF) with electron beam. This new cryomodule, hosting a 2-cell and 7-cell cavity, is designed to boost the electron energy from 200 keV to 5 MeV and permit 380 uA - 1.0 mA of beam current. The 2-cell cavity is a new design whereas the 7-cell cavity is refurbished from a low loss cavity from the retired JLab Renascence Cryomodule. The INJ CM adopts quite a few designs from the JLab 12 GeV Upgrade Cryomodule (C100). Examples of this include having the cold mass hung from a spaceframe structure by use of axial and transverse Nitronic rods, cavities to be tuned by scissor-jack style tuners and the end cans are actually modified from C100 style end cans. However, this new INJ CM is not a quarter of the C100 Cryomodule. This paper focuses on the major design features, fabrication and alignment process and testing of the module and its components.
Authored by Jefferson Science Associates, LLC. The U.S. Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce this manuscript for Government purposes.

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MOPB049

Upgraded Cavities for the CEBAF Cryomodule Rework Program

cavity, ion, cryomodule, GUI

168

R.A. Rimmer, G. Cheng, G. Ciovati, W.A. Clemens, E. Daly, G.K. Davis, J. Follkie, D. Forehand, F. Fors, J. Guo, J. Henry, K. Macha, F. Marhauser, G.R. Myneni, L. Turlington
JLab, Newport News, Virginia, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
The CEBAF cryomodule rework program has been a successful tool to recover and maintain the energy reach of the original baseline 6 GeV accelerator. The weakest original modules with eight five-cell cavities assembled in four 'pairs', with a specification when new of 20 MV per cryomodule (5 MV/m), are disassembled, re-cleaned with modern techniques and re-qualified to at least 50 MV (12.5 MV/m), (leading to the acronym 'C50'). The cost per recovered MV is much less than building new modules. However over time the stock of weak modules is being used up and the voltage gain per rework cycle is diminishing. In an attempt to increase the gain per cycle it is proposed to rework the cavities by replacing the original accelerating cells with new ones of an improved shape and better material. The original CEBAF HOM and FPC end groups are retained. The goal is to achieve up to 75 MV (18.75 MV/m) for the reworked module ('C75'). We report on the fabrication experience and test results of the first trial pair, containing two such reworked cavities.

Poster MOPB049 [1.503 MB]

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MOPB052

Dual-ridge Waveguide Load Design for eRHIC

ion, GUI, cavity, simulation

177

P. Kolb, Y. Gao, C. Pai, R. Porqueddu, K.S. Smith, W. Xu
BNL, Upton, Long Island, New York, USA
Y. Gao
PKU, Beijing, People's Republic of China

Funding: Work supported by LDRD program of Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. DOE.
To increase the real estate gradient in the eRHIC electron accelerator waveguide HOM couplers are being considered. These significantly reduce the length of individual cavities and address inter-cavity trapped modes, allowing for an increased number of cavities per cryomodule, which would increase the real estate gradient. The choice of waveguide went to a dual ridge waveguide due to a smaller size compared to rectangular waveguides. The waveguide termination, to convert the RF energy into thermal energy, is a custom designed load based on a silicon carbide dielectric that is already being used in beamline absorbers. Simulations of the RF properties of the load are presented as well as first measurements on a prototype.

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MOPB053

RF Energy Harvesting of HOM Power

ion, GUI, cavity, distributed

180

C. Xu, I. Ben-Zvi, Q. Wu, T. Xin
BNL, Upton, Long Island, New York, USA
I. Ben-Zvi
Stony Brook University, Stony Brook, USA

In an accelerator cavity, Higher Order Modes (HOM) are generated by the current of the beam. The HOM power can reach tens of kilowatts in a high current accelerator, depending on the details of the beam and cavity design. In this report, we propose a novel RF harvesting system to recover the HOM power into DC power which can further used for various purposes such as driving a solid state or klystron RF amplifier to supply fundamental RF power at other frequencies, charge batteries etc. The efficiency would be a product of the energy recovery and regeneration efficiencies, where the state of art is 90%. The proposed HOM power recycling system contains a multiple band harmonic RF coupler, broadband RF antenna system, a high power rectifier diode circuit and a DC load.
1) Collider-Accelerator Department, Brookhaven National Lab, Upton, NY 11973, USA 2) Physics & Astronomy Department, Stony Brook University, Stony Brook, NY 11794, USA

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MOPB062

Development of HOM Absorbers for CW Superconducting Cavities in Energy Recovery Linac

ion, cavity, superconducting-cavity, linac

191

T. Ota, A. Miyamoto, K. Sato, M. Takasaki, M. Yamada
Toshiba, Yokohama, Japan
E. Kako, T. Konomi, H. Sakai, K. Umemori
KEK, Ibaraki, Japan

Higher Order Modes (HOM) absorbers for superconducting cavities have been developing at TOSHIBA in collaboration with High Energy Accelerator Research Organization (KEK) since 2015. Prototype HOM absorbers for 1.3 GHz 9-cell superconducting cavity were fabricated. An AlN lossy dielectrics cylinder was brazed with a copper cylinder, and the cool-down tests by nitrogen gas was carried out. Copper cylinders and SUS flanges were joined by electron beam welding to fabricate a whole prototype HOM absorber. Fabrication process of the prototype HOM absorber will be presented in this paper.

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MOPB071

The Recent Research of HOM Damper for Superconducting Cavity in IHEP

ion, cavity, simulation, site

223

F. Meng, T.M. Huang, H.Y. Lin, Q. Ma, W.M. Pan, J.Y. Zhai, P. 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)
For high current accelerator, the efficient higher-order mode (HOM) damping is always an important issue. HOM damper with microwave absorbing material is a key component for high power and broadband HOM damping application. To pursue the high damping efficiency, some ideal material with good microwave absorbing capacity is essential during the RF design and fabrication phase. Sometimes the selection and test of material is the first step and also a long step. This paper will present the recent work on HOM dampers for BEPCII 500MHz cavity and CEPC 650MHz cavity in IHEP.

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MOPB074

Analysis of Higher Order Modes of the Superconducting Cavities for the China-ADS Injector-II in IMP

dipole, ion, cavity, higher-order-mode

231

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

Funding: funded by Natural Science Foundation of China， No.11505253
The influence of the higher order modes on the beam dynamics and the cryogenic losses has been studied for the superconducting section of the CIADS project in this paper. In addition, the necessity of HOM dampers in the Superconducting (SC) cavities is discussed.

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MOPB079

HOM Coupler Alterations for the LHC DQW Crab Cavity

ion, cavity, impedance, simulation

249

J.A. Mitchell
Lancaster University, Lancaster, United Kingdom
G. Burt, N.C. Shipman
Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
R. Calaga
CERN, Geneva, Switzerland
S. Verdú-Andrés, Q. Wu, B. P. Xiao
BNL, Upton, Long Island, New York, USA

As part of the High Luminosity Large Hadron Collider (HL-LHC) project, 16 crab cavities are to be installed in the LHC in 2025. The two crab cavity designs are the Double Quarter Wave (DQW) and Radio Frequency Dipole (RFD). Preliminary beam tests in the Super Proton Synchrotron (SPS) are planned for both cavity types, with the DQW scheduled for testing in 2018. In reference to to Higher Order Mode (HOM) damping, the DQW has three identical on-cell HOM couplers. These HOM couplers provide a band-stop response at the frequency of the fundamental mode and act as a transmission path for the cavity HOMs. For the SPS cavity design, several geometric constraints exist. These give rise to dimensional limitations which in-turn impose limitations on the RF performance of the HOM couplers. As such, for the LHC assembly, the HOM coupler design is re-visited to take into account the relaxed geometric limitations, hence allowing the feasibility of an increased RF performance to be investigated. In addition to the RF performance, several geometric alterations were incorporated to ease manufacturing processes, tolerances and costs.

Poster MOPB079 [2.038 MB]

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MOPB088

Experience on In-situ Module Repair and Set Up of Non XFEL Cavity Strings at DESY

ion, cavity, FEL, pick-up

269

M. Schmökel, A. Daniel, N. Krupka, A. Matheisen, S. Saegebarth, M. Schalwat, P. Schilling
DESY, Hamburg, Germany

All components installed to the European XFEL cavity string modules underwent an intensive inspection and quality control before acceptance for installation to cavities or modules. Even though some RF feed throughs for HOM coupler- and Pick Up antennas showed leaks at the ceramic insulation after module test at 2 K. Due to time restriction and continuity of production the exchange of these parts needed to be done without reentering the cleanroom. Successful repair of these modules took place by setting up a local cleanroom onto the cavity string. In collaboration with Helmholtz-Zentrum Dresden-Rossendorf (HZDR), a cavity string for the ELBE project was assembled at DESY and transported to HZDR for installation to the vacuum vessel. A spare module with 3.9 GHz Resonators for the European XFEL was set up at DESY and will be tested and qualified for the European XFEL. Due to delay in delivery of the power couplers, four power couplers were installed after string assembly.

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MOPB096

Estimation of Alignment Error by Measuring Higher-order-mode of Injector Superconducting Cavity at KEK-cERL

cavity, ion, dipole, alignment

286

Y. Honda, E. Kako, T. Konomi, T. Miyajima, T. Obina, H. Sakai, K. Umemori
KEK, Ibaraki, Japan

Precise alignment of accelerator cavities is important in realizing a low emittance beam. Especially in the cases of superconducting cavities installed in a cryomodule, it is difficult to mechanically measure the position of the cavities. By measuring higher-order-modes (HOM) excited by a beam, the electrical center of the cavities can be estimated. We have developed a HOM measurement system for the injector superconducting accelerator cavities of KEK ERL test accelerator (cERL).Comparing the HOM signals of the three independent cavities in the cryomodule, we estimated the relative positioning errors of the three cavities.

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TUXAA01

CEPC SRF System Design and Challenges

ion, cavity, SRF, 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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TUPB001

338 MHz Crab Cavity Design for the eRHIC Hadron Beam

cavity, ion, proton, electron

382

S. Verdú-Andrés, I. Ben-Zvi, Q. Wu, B. P. Xiao
BNL, Upton, Long Island, New York, USA
I. Ben-Zvi
Stony Brook University, Stony Brook, USA

Funding: Work supported by the US Department of Energy via Brookhaven Science Associates LLC under contract no. DE-AC02-98CH10886.
Crab crossing is an essential mechanism to restore high luminosity and avoid synchro-betatron resonances in the electron-hadron collider eRHIC. The current ring-ring eRHIC design envisages a set of crab cavities operating at 338 MHz. This set of cavities will provide the crabbing kick to the hadron beam of eRHIC. Double-Quarter Wave (DQW) cavities are compact, superconducting RF deflecting cavities appropriate for crab crossing. This paper summarizes the main design requirements and presents an optimized RF design of a DQW cavity for the crabbing system of the ring-ring eRHIC hadron beam.

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TUPB002

Novel HOM Damper Design for High Current SRF Cavities

ion, GUI, cavity, SRF

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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TUPB004

HOM damping with an enlarged beam tube for HEPS 166.6 MHz SC cavities

ion, cavity, damping, impedance

389

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

The 166.6 MHz superconducting cavities have been proposed for the High Energy Photon Source (HEPS) storage ring, which is initiated by the Institute of High Energy Physics in Beijing. Their higher order modes (HOMs) have to be damped sufficiently in order to limit coupled-bunch instabilities and parasitic mode losses. In order to keep the beam stable, the impedance budget and the HOM damping requirement are given. As one HOM damping option, an enlarged beam tube allows HOMs to propagate and subsequently be absorbed by downstream HOM dampers installed on the inner surface of the beam tube. And the conventional coaxial HOM coupler, which will be mounted on the big beam tube, is planned to extract the HOM power below the cut-off frequency of the beam pipe.

Poster TUPB004 [1.132 MB]

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TUPB032

Study on 650MHz 5-cell Prototype Cavities at IHEP

ion, cavity, SRF, 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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TUPB033

Tests of the High Current Slotted Superconducting Cavity with Extremely Low Impedance

cavity, ion, GUI, damping

451

Z.C. Liu, J. Gao, F.S. He, S. Jin, Z.H. Mi, T.X. Zhao, H.J. Zheng
IHEP, Beijing, People's Republic of China
F. Wang, D.H. Zhuang
PKU, Beijing, People's Republic of China

Slotted superconducting cavity is a novel structure with extremely low impedance and high BBU threshold. It can be used in various high current applications. A 1.3 GHz 3-cell slotted superconducting cavity was designed and tested. The room temperature test results show the cavity has an extremely low impedance. The vertical test results show the cavity gradient can reach several MV/m, but it was limited by the test end group made of steel.

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TUPB034

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

cavity, ion, storage-ring, SRF

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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TUPB040

Design and Optimization of Medium and High Beta Superconducting Elliptical Cavities for the CW Linac in CIADS

cavity, ion, multipactoring, linac

478

Y.L. Huang, L. Chen, Y. He, Y.M. Li, S.H. Zhang
IMP/CAS, Lanzhou, People's Republic of China

Superconducting technology is adopted in the main accelerating section of the CW Linac in China Initiative Accelerator Driven System (CIADS) to accelerate the 10 mA proton beam from 2.1 MeV up to 1.5 GeV. The high energy section of the superconducting linac is composed of two families of SC elliptical cavities with optimum beta 0.62 and 0.82 for the acceleration of proton beam from 178 MeV to 1.5 GeV. In this paper, the design and optimization of the 650 MHz medium and high beta elliptical cavities are discussed, including the RF design, multipacting analysis, high order modes (HOMs) analysis, generator RF power calculation, and the mechanical design.

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TUPB052

Higher Order Modes Damping in 9-cell Superconducting Cavity with Grooved Beam Pipe

cavity, ion, damping, quadrupole

502

A.M. Bulygin, R.V. Donetskiy, Ya.V. Shashkov
MEPhI, Moscow, Russia

This paper is focused on higher order modes (HOM) damping efficiency analysis in 9-cell superconducting cavities with HOM couplers and with grooved beam pipe. Comparison of two methods of HOM damping is presented. In order to increase efficiency of damping of trapped modes the end cells of the structure were modified.
Higher order modes, tesla, SRF

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TUPB053

Lessons Learned from RF-Dipole Prototype Cavities for LHC High Luminosity Upgrade

cavity, ion, dipole, luminosity

506

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

The rf-dipole cavity has successfully demonstrated the principles of using a compact cavity operating in TE11-like mode in generating a transverse kick. Several proof-of-principle rf-dipole cavities have been fabricated and the rf tests have demonstrated high transverse gradients. The rf-dipole geometry has been adapted into a square-shaped geometry designed to meet the dimensional constraints for the LHC also maintaining crabbing in both horizontal and vertical planes. Recently, two prototype rf-dipole cavities intended for the test at SPS for have been completed that is designed to accommodate the FPC and HOM dampers. The performance during the rf tests have shown excellent results on achieving the design requirements of operation for the crab cavities for SPS. This paper presents the experiences and lessons learned during the cavity preparation and testing, including process validation, frequency tracking.

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TUPB054

RF Tests of RF-Dipole Prototype Crabbing Cavities for LHC High Luminosity Upgrade

cavity, ion, dipole, luminosity

509

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

The superconducting rf-dipole crabbing cavity is one of the two crabbing cavity designs proposed for the LHC high luminosity upgrade. The proof-of-principle (P-o-P) rf-dipole cavity operating at 400 MHz has demonstrated performance exceeding the design specifications. The prototype cavity for SPS beam test has been designed to include the fundamental power coupler, HOM couplers, and all the ancillary components intended to meet the design requirements. The crab cavities will be installed in the SPS beam line prior to the installation in LHC; this will be the first crabbing cavity operation on a proton beam. The fabrication of two prototype rf-dipole cavities is currently being completed at Jefferson Lab. This paper presents the details on cavity processing and cryogenic test results of the rf-dipole cavities.

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TUPB070

INFN-LASA Cavity Design for PIP-II LB650 Cavity

cavity, ion, coupling, operation

547

C. Pagani
Università degli Studi di Milano & INFN, Segrate, Italy
M. Bertucci, A. Bignami, A. Bosotti, J.F. Chen, P. Michelato, L. Monaco, R. Paparella, D. Sertore
INFN/LASA, Segrate (MI), Italy
S. Pirani
ESS, Lund, Sweden

INFN-LASA is going to join the international partnership for Fermilab PIP-II project and to provide a novel design for the 650 MHz cavity of the 0.61 beta linac section, plug compatible with the Fermilab Cryomodule design. This paper reports the cavity design features both from the electro-magnetic and mechanical aspects, with focus on the rationales at the basis of the choice of main parameters. Furthermore, the current plans for the future R&D activity are here reported, including the production of two single cells and two complete cavities.

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THXA03

Crab Cavities for the High-luminosity LHC

ion, cavity, luminosity, cryomodule

695

R. Calaga
CERN, Geneva, Switzerland

Funding: This work has been supported by the HL-LHC project (and by DOE or any other collaborating institutes, when applicable).
As a first step towards the realization of crab crossing for HL-LHC, two superconducting crab cavities are foreseen to be tested with proton beams for the first time in the SPS. The progress on the cavity fabrication, RF test results, cryomodule development and integration into the SPS are presented. Some aspects of the beam tests with crab cavities in the SPS are outlined.

Slides THXA03 [12.629 MB]

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THPB040

SRF Theory Developments from the Center for Bright Beams

ion, cavity, SRF, experiment

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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THPB054

Advanced Method to Extract the Surface Resistance From Q0 Measurements

ion, cavity, factory, quadrupole

867

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

Funding: The research leading to these results has received funding from the European Commission under the FP7 Research Infrastructures project EuCARD-2, grant agreement No. 312453.
The quality factor of an RF cavity and the surface resistance are typically related with a constant geometry factor. The implicit assumption made is that the surface resistance is field independent, which is however not observed experimentally in superconducting cavities. The approximation error due to this assumption becomes larger the less homogeneous the magnetic field distribution along the cavity walls is. In this paper we calculate the surface resistance error for different cavity types. An iterative method to correct for this error is presented.

Poster THPB054 [0.196 MB]

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THPB059

Simulation and Measurements of Crab Cavity HOMs and HOM Couplers for HL-LHC

ion, cavity, damping, simulation

881

J.A. Mitchell, T.J. Jones
Lancaster University, Lancaster, United Kingdom
R. Apsimon, G. Burt, N.C. Shipman
Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
I. Ben-Zvi, S. Verdú-Andrés, B. P. Xiao
BNL, Upton, Long Island, New York, USA
R. Calaga, A. Castilla, A. Macpherson, N.C. Shipman, A. Zwozniak
CERN, Geneva, Switzerland
T. Powers, H. Wang
JLab, Newport News, Virginia, USA
N.C. Shipman
UMAN, Manchester, United Kingdom

Two Superconducting Radio-Frequency (SRF) crab cavities are foreseen for the High Luminosity LHC (HL-LHC) upgrade. Preliminary beam tests of the Double Quarter Wave (DQW) crab cavity will take place in the Super Proton Synchrotron (SPS) in 2018. For damping of the cavity's Higher Order Modes (HOMs) the DQW has three identical on-cell, superconducting HOM couplers. The couplers are actively cooled by liquid heluim. In this paper, electromagnetic simulations of the HOMs and HOM couplers are presented. A novel approach to pre-installation spectral analysis of the HOM couplers is then presented, detailing both simulated and measured data. Measurements of the cavity HOMs at warm and in Vertical Test Facilities (VTFs) at both JLAB and CERN are detailed, comparing the measured characteristics of each mode to that of the simulated data-sets. Finally, the measured cavity data is compared with the test box measurements to see by what extent any reduction in damping can be predicted.

Poster THPB059 [8.192 MB]

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FRXAA02

High-efficiency, High-current Optimized Main-linac ERL Cryomodule

ion, cavity, linac, cryomodule

935

F. Furuta, N. Banerjee, A.C. Bartnik, J. Dobbins, R.G. Eichhorn, M. Ge, G.H. Hoffstaetter, M. Liepe, P. Quigley, D.M. Sabol, J. Sears, E.N. Smith, V. Veshcherevich
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

The Main Linac Cryomodule (MLC) prototype is a key component of the Cornell-BNL ERL Test Accelerator (CBETA) project, which is a 4-turn FFAG ERL currently under construction at Cornell University. This novel cryomodule is the first SRF module ever to be fully optimized simultaneously for high efficient SRF cavity operation and for supporting very high CW beam currents. After a successful initial MLC testing, the MLC has now been moved into its final location for the CBETA ring. For a first beam test of the MLC and CBETA, the Cornell ERL high voltage DC gun and SRF injector cryomodule were connected to MLC via an entry beam line; a beam stop assembly was also installed at the exit line. In this paper, we summarize the performance of this novel ERL cryomodule including the results of the first beam test and the additional tests focused on RF field stability and cavity microphonics.

Slides FRXAA02 [8.792 MB]

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