07 Accelerator Technology Main Systems
T07 Superconducting RF

Paper	Title	Page
WEPRO005	Development of Superconducting Spoke Cavity for Laser Compton Scattered Photon Sources	1946
	M. Sawamura, R. Hajima, R. Nagai JAEA, Ibaraki-ken, Japan H. Fujisawa, Y. Iwashita, H. Tongu Kyoto ICR, Uji, Kyoto, Japan T. Kubo KEK, Ibaraki, Japan
	Funding: This work is supported by Photon and Quantum Basic Research Coordinated Development Program. We have launched a 5-year research program to develop superconducting spoke cavity for laser Compton scattered (LCS) photon sources. For realizing a wide use of LCS X-ray and gamma-ray sources in academic and industrial applications, we adopt 325-MHz superconducting spoke cavity to electron beam drivers for the LCS sources. The spoke cavity, originally invented for ion and proton acceleration, can be used for electron accelerators, in which we can make best use of features of spoke cavity: relative compactness in comparison with a TM cavity of the same frequency, robustness with respect to manufacturing inaccuracy due to its strong cell-to-cell coupling, couplers on outer conductor for the better packing in a linac, and so on. In this paper, we present our research plan and results of cavity shape optimization.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPRO005
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WEPME024	Power Coupler Manufacturing and Quality Control at CPI	2308
	S.J. Einarson, T.A. Treado CPI, Beverley, Massachusetts, USA
	CPI has been designing and manufacturing fundamental power couplers for superconducting accelerators for over a dozen years. We have manufactured approximately 200 power couplers of 16 different designs. Power coupler frequencies have ranged from 175 MHz to 3.9 GHz and power levels have ranged from 5 kW to 500 kW average power. We have developed and qualified several key manufacturing processes including a high-RRR copper plating process and a titanium nitride coating process. In addition, we have established uniform quality control and inspection processes which ensure that the power couplers will meet the requirements for the intended use in superconducting accelerators. These processes have been developed, improved and/or qualified in collaboration with colleagues at superconducting accelerator facilities throughout the world. This paper will provide an overview of these critical manufacturing and quality control processes.
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WEPME058	Development of Thin Films for Superconducting RF Cavities	2406
	S. Wilde, B. Chesca Loughborough University, Loughborough, Leicestershire, United Kingdom A.N. Hannah, D.O. Malyshev, O.B. Malyshev, S.M. Pattalwar, R. Valizadeh STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom G.B.G. Stenning STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom
	Superconducting coatings for superconducting radio frequency (SRF) cavities is an intensively developing field that should ultimately lead to acceleration gradients better than those obtained by bulk Nb RF cavities. ASTeC has built and developed experimental systems for superconducting thin-film deposition, surface analysis and measurement of Residual Resistivity Ratio (RRR). Nb thin-films were deposited by magnetron sputtering in DC or pulsed DC mode (100 to 350 kHz with 50% duty cycle) with powers ranging from 100 to 600 W at various temperatures ranging from room temperature to 800 °C on Si (100) substrates. The first results gave RRR in the range from 2 to 22 with a critical temperature Tc=~9.5 K. Scanning electron microscopy (SEM), x-ray diffraction (XRD), electron back scattering diffraction (EBSD) and DC SQUID magnetometry revealed significant correlations between the film structure, morphology and superconducting properties.
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WEPRI001	Clean Room Integration of the European XFEL Cavity Strings	2474
	S. Berry, O. Napoly, B. Visentin CEA/DSM/IRFU, France F. Chastel, A. Clippet, M. Mbeleg, P. Pluvy ALSYOM, Argebteuil, France C. Cloué, C. Madec, T. Trublet CEA/IRFU, Gif-sur-Yvette, France
	The 101 cryomodules of the XFEL cold linac will be integrated at Saclay under the CEA responsability by the industrial operator ALSYOM, at the production rate of cryomodule per week. Each cryomodule includes a string of 8 Niobium superconducting cavities and a BPM-quadripole unit (downstream end). To avoid particle contamination of the RF cavities, the strings are assembled in an ISO4 cleanroom by following strict cleaning and high-vacuum procedures. The major technical challenge of the string integration thus lies in the capacity to realize 25 connections in two weeks while protecting the cavity and coupler RF surfaces and to check their leak-tightness up to 10-10 hPA.l/s. The partial demonstration was made by the CEA team with the first pre-series module XM-3 which achieves a total accelerating voltage of 232 MV preserving the individual performances of cavities. In this paper the status and challenges of the production line is presented, including the quality management, equipment and operator training aspects. The optimisation process toward a faster assembly while preserving or actually decreasing the cavity exposure to contamination sources is also described.
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WEPRI002	Status and First Results of Two High Beta Prototype Elliptical Cavities for ESS	2477
	F. Peauger, P. Bosland, P. Carbonnier, G. Devanz, F. Éozénou, X. Hanus, P. Hardy, V.M. Hennion, J. Plouin, D. Roudier, C. Servouin CEA/DSM/IRFU, France C. Darve, S. Molloy ESS, Lund, Sweden L. Maurice CEA/IRFU, Gif-sur-Yvette, France G. Olivier IPN, Orsay, France
	Two prototypes of elliptical superconducting cavities have been designed and manufactured in the frame of the French-Swedish agreement for ESS. These 5-cell cavities have a beta value of 0.86 and their frequency is 704.42 MHz. The nominal accelerating gradient on the ESS accelerator is 19.9 MV/m at 2K. We present the manufacturing status of the cavities by two different vendors as well as the specific means which have been developed for the cavity treatments performed at CEA after delivery. We emphasis the activities performed on the first bare cavities recently received at CEA such as the RF measurement and tuning operations, the cleaning and chemical treatments and the clean room assembly including high pressure rinsing. Finally, first test results at 2K in vertical cryostat are reported.
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WEPRI004	Operational Experience and Upgrades of the SOLEIL Storage Ring RF System	2480
	P. Marchand, J.P. Baete, R.C. Cuoq, H.D. Dias, M. Diop, J.L. Labelle, R. Lopes, M. Louvet, C.M. Monnot, L.S. Nadolski, S. Petit, F. Ribeiro, T. Ruan, R. Sreedharan, K. Tavakoli SOLEIL, Gif-sur-Yvette, France
	In the SOLEIL storage ring, two cryomodules provide to the electron beam an accelerating voltage of 3-4 MV and a power of 575 kW at 352 MHz. Each cryomodule contains a pair of superconducting cavities, cooled with liquid Helium at 4.5 K, which is supplied by a single 350 W cryogenic plant. The RF power is provided by four solid state amplifiers, each delivering up to 180 kW. The parasitic impedances of the high order modes (HOM) are strongly mitigated by means of four coaxial couplers, located on the central pipe connecting the two cavities. Eight years of operational experience with this system, as well as its upgrades, are reported.
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WEPRI005	Processing and Testing of the SRF Photoinjector Cavity for BERLinPro	2484
	A. Burrill, W. Anders, A. Frahm, J. Knobloch, A. Neumann HZB, Berlin, Germany G. Ciovati, W.A. Clemens, P. Kneisel, L. Turlington JLab, Newport News, Virginia, USA E.N. Zaplatin FZJ, Jülich, Germany
	Funding: Work supported by German Bundesministerium für Bildung und Forschung, Land Berlin, and grants of Helmholtz Association The BERLinPro project is a compact, c.w. SRF energy recovery linac (ERL) that is being built to develop the accelerator physics and technology required to operate the next generation of high current ERLs. The machine is designed to produce a 50 MeV 100 mA beam, with better than 1 mm-mrad emittance. The electron source for the ERL will be a SRF photoinjector equipped with a multi-alkali photocathode. In order to produce a SRF photoinjector to operate reliably at this beam current HZB has undertaken a 3 stage photoinjector development program to study the operation of SRF photoinjectors in detail. The 1.4 cell cavity being reported on here is the second stage of this development, and represents the first cavity designed by HZB for use with a high quantum efficiency multi-alkali photocathode. This paper will describe the work done to prepare the cavity for RF testing in the vertical testing dewar at Jefferson Laboratory as well as the results of these RF tests.
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WEPRI006	High Power RF Input Couplers and Test Stand for the BERLinPro Project	2487
	V.F. Khan, W. Anders, A. Burrill, J. Knobloch, A. Neumann HZB, Berlin, Germany
	Funding: Work supported by German Federal Ministry of Education and Research, Land Berlin, and grants of the Helmholtz Association The BERLinPro project, under construction at HZB, is a 100 mA, 50 MeV superconducting RF (SRF) energy recovery linac (ERL) being built to study the accelerator physics of operating a high current SRF ERL. For this high current operation, coaxial RF power couplers capable of handling 130 kW of power, c.w. at 1.3 GHz are required for both the SRF gun and booster cavities. In order to achieve this power level a coupler has been designed based on the high power coupler currently in use at the KEK-cERL. A key improvement that was made to the coupler was the modification of the coupler tip, termed a golf-tee. This modification is incorporated so as to achieve the desired coupling, Qext ~105, with minimal coupler penetration into the beampipe. Herein, we discuss the RF design and properties of the high-power coaxial coupler for the gun as well as booster cavity of BERLinPro, along with the design of the test stand for conditioning a pair of couplers.
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WEPRI007	Booster Cavity and Fundamental Power Coupler Design Issues for BERLinPro	2490
	A. Neumann, M. Abo-Bakr, W. Anders, A. Burrill, V.F. Khan, J. Knobloch, S. Wesch HZB, Berlin, Germany
	Funding: Work supported by German Bundesministerium für Bildung und Forschung, Land Berlin and grants of Helmholtz Association HZB has started building the 50MeV, 100mA demonstrator energy-recovery-linac (ERL) facility BERLinPro. The high power injector system needs to deliver this beam at 6.5MeV by combining the energy gain of a 1.4 cell SRF photo-injector and three Cornell style 2-cell booster cavities. One booster cavity will be operated at zero-crossing for bunch energy chirping. Thus two booster cavities have to deliver 2MV each requiring a strong coupling with a loaded Q of 105. To house the two envisaged KEK fundamental power couplers (FPC) with the cavity, the geometry was slightly modified. Further, to increase coupling and reduce transverse kick effects to the beam, a ”golf-tee” antenna tip was designed. This paper summarizes the SRF challenges for the booster cavities, the operational conditions and the modification to the KEK couplers, including tracking calculations to estimate the coupler kick effect to higher order.
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WEPRI008	First Cavity Design Studies for the BESSY-VSR Upgrade Proposal	2493
	A. Neumann, A. Burrill, P. Goslawski, A. Jankowiak, J. Knobloch, M. Ries, M. Ruprecht, A.V. Vélez, G. Wüstefeld HZB, Berlin, Germany
	Funding: Work supported by German Bundesministerium für Bildung und Forschung and Land Berlin Recently HZB proposed an upgrade of the 3rd generation synchrotron light source BESSY II allowing simultanous long and short pulse operation*. For this scheme to work superconducting higher harmonic cavities of the fundamental 500 MHz at two frequencies need to be installed in the BESSY II storage ring. Given an appropiate choice of the higher harmonics the resulting gradient leads to a beating effect of the effective longitudinal focussing voltage at the stable fix points resulting in different bunch lengths in subsequent buckets. This project places stringent requirements on the cavity performance, as high accelerating fields, excellent HOM damping capabilities and high reliability as they will operate in a 300 mA 24/7 user facility. In this paper we describe the requirements for the cavity design and first designs steps. * G. Wüstefeldt et al., Simultaneous Long and Short Electron Bunches in the BESSY II Storage Ring, Proc. of IPAC'11, San Sebástian, Spain
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WEPRI009	Parameter Studies and Geometry Optimization on Superconducting Multicell RF Cavity Resonators	2496
	B.D. Isbarn, B. Riemann, M. Sommer, T. Weis DELTA, Dortmund, Germany
	Funding: Work partly supported by the BMBF under contract No. 05K13PEB Modern accelerator concepts for high intensity electron beams often require superconducting multicell RF-cavity-resonators in circular accelerators (e.g. storage rings). Caused by strong beam-cavity interaction and due to high quality factors of superconducting RF-structures special care of lower order (LOM) and higher order (HOM) modes must be taken. Various numerical studies were performed to numerically calculate the dependence of different figures of merit (e.g. external quality factors Qext) with respect to the geometry parameters and cell number of the RF-structure, focused on the propagation and damping of low and higher order modes. To ease the numerical effort an optimization routine has been developed which automatically optimizes the geometry based on goal functions. In this context it turned out that cell geometries defined by spline functions have advantages compared to the standard elliptical parametrization regularly used. The number of free parameters is substantially reduced which facilitates the search for optimum solutions.
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WEPRI011	Progress of R&D on SRF Cavities at DESY towards the ILC Performance Goal	2499
	A. Navitski DESY, Hamburg, Germany A. Prudnikava, Y. Tamashevich Uni HH, Hamburg, Germany
	Funding: BMBF project 05H12GU9, Alexander von Humboldt Foundation, CRISP (No. 283745) and ”Construction of New Infrastructures-Preparatory Phase” ILC-HiGrade (No. 206711) of the EU 7th FP7/2007-2013 Programme. The R&D program of the ILC-HiGrade group at DESY aims at a solid understanding and control of the industrial mass-production process of the superconducting radio-frequency accelerating cavities that are being manufactured for the European X-ray Free Electron Laser (EXFEL). This accelerator is currently under construction at DESY. As well as the main production cavities for XFEL, 24 additional cavities are being constructed as part of the ILC-HiGrade program. The goal is to identify the gradient-limiting factors and further refine the cavity-treatment technique to understand how to achieve gradients above 35 MV/m at >90% production yield in an industrial context. Techniques such as 2nd sound and temperature mapping for the quench detection, OBACHT optical inspections, as well as Centrifugal Barrel Polishing (CBP) and Local Grinding repair are foreseen as tools. Actual status, details, and achievements will be reported.
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WEPRI012	Euclid Modified SRF Conical Half-wave Resonator Design	2502
	E.N. Zaplatin FZJ, Jülich, Germany T.L. Grimm, A. Rogacki Niowave, Inc., Lansing, Michigan, USA A. Kanareykin Euclid TechLabs, LLC, Solon, Ohio, USA V.P. Yakovlev Fermilab, Batavia, Illinois, USA
	Funding: This Work is supported by the DOE SBIR Program, contract # DE-SC0006302. The new low-beta conical Half-Wave Resonator (cHWR) is suggested for CW proton accelerators of new generation with relatively low beam loading, where frequency detune caused by microphonics and helium pressure fluctuations is essential. This particular design, considered in the paper, has operation frequency of 162.5 MHz, b=v/c=0.11, and is suitable for the first section of the PIP-II superconducting accelerator which is under development at Fermilab. The main idea of the cHWR design is to provide a self-compensation cavity design together with its helium vessel to minimize the resonant frequency dependence on external loads. A unique cavity side-tuning option is also under development. Niowave, Inc. proposed a series of cavity and helium vessel modifications to simplify their manufacturing. The whole set of numerical simulations has been generated to verify that the main parameters of the initial structure design were not affected by the proposed modifications. Here we present the main results of the cavity and helium vessel modified design.
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WEPRI013	Investigation of Cryomodules for the Mainz Energy-recovering Superconducting Accelerator MESA	2505
	F. Schlander, K. Aulenbacher, R.G. Heine, D. Simon IKP, Mainz, Germany A. Arnold HZDR, Dresden, Germany
	Funding: Work supported by the German Federal Ministery of Education and Research (BMBF) and German Research Foundation (DFG) under the Cluster of Excellence "PRISMA" For the multiturn accelerator MESA it is planned to employ superconducting technology for the main linac, which is supposed to provide an energy gain of 50 MeV per turn. As continuous wave operation is mandatory for the experiments, it is important to minimise the cryogenic losses, hence to find cavities and the corresponding cryomodule meeting the framework conditions for the accelerator. The findings and the current statuts will be reported.
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WEPRI016	Status of the Vertical Testing of the XFEL Third Harmonic Cavity Series	2508
SUSPSNE091	use link to see paper's listing under its alternate paper code
	J.F. Chen, M. Bertucci, A. Bosotti, M. Fusetti, C. Maiano, P. Michelato, L. Monaco, M. Moretti, C. Pagani, R. Paparella, P. Pierini, D. Sertore INFN/LASA, Segrate (MI), Italy
	The prototype cavities of the XFEL 3rd harmonic system at the XFEL injector have been tested vertically before their final integration into the He tank. The Vertical Test facility has been upgraded in preparation of the series and the results so far obtained are presented.
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WEPRI018	Status of the Fabrication of the XFEL 3.9 GHz Cavity Series	2512
	C. Maiano, M. Bertucci, A. Bosotti, J.F. Chen, P. Michelato, L. Monaco, M. Moretti, C. Pagani, R. Paparella, P. Pierini, D. Sertore INFN/LASA, Segrate (MI), Italy
	The third harmonic system at 3.9 GHz of the European XFEL (E-XFEL) injector section will linearize the bunch RF curvature, induced by first accelerating module, before the first compression stage and it is a joint INFN and DESY contribution to the project. This paper presents the status of the fabrication of the 3.9 GHz cavity series in view of the XFEL injector commissioning in 2015.
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WEPRI020	Mechanical Analysis of the XFEL 3.9 GHz Cavities in support of PED Qualification	2515
SUSPSNE094	use link to see paper's listing under its alternate paper code
	M. Moretti, P. Pierini INFN/LASA, Segrate (MI), Italy A. Schmidt DESY, Hamburg, Germany
	We present the FEA stress analysis under different mechanical conditions of the XFEL 3.9 GHz superconducting cavities. The analysis is being performed in support of the necessary qualification according to the Pressure Equipment Directive European Norms, for the operating conditions set in the European XFEL project.
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WEPRI022	In-house Production of a Large-Grain Single-Cell Cavity at Cavity Fabrication Facility and Results of Performance Tests	2519
	T. Kubo, Y. Ajima, H. Inoue, K. Umemori, Y. Watanabe, M. Yamanaka KEK, Ibaraki, Japan
	We studied electron beam welding (EBW) conditions for large grain Nb, and fabricated a single cell cavity in Cavity Fabrication Facility (CFF), KEK. Vertical-test results of the cavity made from large grain Nb are also presented.
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WEPRI023	Review of the Multilayer Coating Model	2522
	T. Kubo, T. Saeki KEK, Ibaraki, Japan Y. Iwashita Kyoto ICR, Uji, Kyoto, Japan
	Structures of alternating layers of superconducting (Sc) and insulating films formed on a bulk Sc proposed by A. Gurevich in 2006 are actively discussed these years, because of their great possibility in reducing power consumptions and in enhancing RF breakdown field of the Sc RF cavity. On Apr. 2013, we submitted general formulae for the vortex penetration field of the Sc layer and the shielded magnetic field on the bulk Sc for a structure with a single Sc layer and a single insulator layer formed on a bulk Sc, by which a combination of the thicknesses of Sc and insulator layers that can realize the enhanced RF breakdown field can be found for any given materials. In this contribution, we will show progresses during the last year. Comparisons between the formulae and experimental results, and extended formulae for more realistic models, such as a model with surface defects, will be shown. T. Kubo, Y. Iwashita, and T. Saeki, Appl. Phys. Lett. 104, 032603 (2014); arXiv:1304.6876 [physics.acc-ph]; arXiv:1306.4823 [physics.acc-ph]; arXiv:1307.0583 [physics.acc-ph].
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WEPRI024	Two-Dimensional Models of the Magnetic-Field Enhancement at Pit and Bumps	2525
	T. Kubo KEK, Ibaraki, Japan
	Analytical models of the magnetic field enhancement at pits were presented at SRF2013 last year*. Other simple models will be addressed in this paper. * Proceedings of SRF2013, Paris, France (2013), p. 430
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WEPRI025	Studies of Fabrication Procedure of 9-cell SRF Cavity for ILC Mass-production at KEK.	2528
	T. Saeki, Y. Ajima, K. Enami, H. Hayano, H. Inoue, E. Kako, S. Kato, S. Koike, T. Kubo, S. Noguchi, M. Satoh, M. Sawabe, T. Shishido, A. Terashima, N. Toge, K. Ueno, K. Umemori, K. Watanabe, Y. Watanabe, S. Yamaguchi, A. Yamamoto, Y. Yamamoto, M. Yamanaka, K. Yokoya KEK, Ibaraki, Japan Y. Iwashita Kyoto ICR, Uji, Kyoto, Japan N. Kawabata, H. Nakamura, K. Nohara, M. Shinohara SPS, Funabashi-shi, Japan F. Yasuda The University of Tokyo, Institute of Physics, Tokyo, Japan
	We had been constructing a new facility for the fabrication of superconducting RF cavity at KEK from 2009 to 2011. In the facility, we have installed a deep-drawing machine, a half-cup trimming machine, an electron-beam welding machine, and a chemical etching room in one place. We started the studies on the fabrication of 9-cell cavity for International Linear Collier (ILC) using this facility. The studies are focusing on the cost reduction with keeping high performance of cavity, and the goal is the establishment of mass-production procedure for ILC. We already finished the fabrication of two 9-cell cavities in this facility. This article reports the current status of the studies.
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WEPRI026	Mechanical Vibration Search of Compact ERL Main Linac Superconducting Cavities in Cryomodule	2531
	M. Satoh, K. Enami, T. Furuya, S. Michizono, T. Miura, F. Qiu, H. Sakai, K. Shinoe, K. Umemori KEK, Ibaraki, Japan E. Cenni Sokendai, Ibaraki, Japan M. Sawamura JAEA, Ibaraki-ken, Japan
	In 2014, we will start the beam operation in Compact ERL(cERL) by using main linac cryomodule, which contained the two 9-cell cavities. In principle, thanks to the mechanism of energy recovery, the input power of main linac of cERL is very small even if the beam current will be higher than 100mA. Therefore, the coupling is very weak. However, this coupling is perfectly not matched to the unloaded Q-value of the superconducting cavity like 1x1010. The minimum input power will be restricted by the cavity detuning due to the microphonics from the cryomodule itself. We designed the lower loaded Q-valued of (1-4)x107 to reduce the effect of the michrophonics from the expected outer disturbance At present, we successfully suppressed the michrophonics to meet our requirement. However we found the enhancement of the detuning angle when we did not optimize the feedback loop of LLRF. This enhancement will be expected coming from the mechanical resonance frequencies of cavity and/or cryomodule. In this paper, we reported the correlation between the measured microphincs spectrum with LLRF in a beam operation and the results of the measured resonance frequencies spectrum at the test bench.
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WEPRI027	Performance Evaluation of ERL Main Linac Tuner	2534
	K. Enami, D.A. Arakawa, T. Furuya, S. Michizono, T. Miura, F. Qiu, H. Sakai, M. Satoh, K. Shinoe, K. Umemori KEK, Ibaraki, Japan E. Cenni Sokendai, Ibaraki, Japan M. Sawamura JAEA, Ibaraki-ken, Japan
	cERL project is now progressing. We are carrying on R&D for cERLmain linac consisted of 1.3GHz superconductive cavity. We evaluate slide jack tuner, which is component part of cryomodule. A slide jack tuner has 2 mechanism to tune frequency. One is slide jack mechanism that tunes roughly and the other is piezo mechanism that tunes finely. We carried out basic experiment and cold experiment. We finally confirmed that slide jack tuning system can tuning to target frequency 1.3GHz.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPRI027
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WEPRI028	Operation Status of Compact ERL Main Linac Cryomodule	2537
	K. Umemori, K. Enami, T. Furuya, S. Michizono, T. Miura, F. Qiu, H. Sakai, M. Satoh, K. Shinoe KEK, Ibaraki, Japan E. Cenni Sokendai, Ibaraki, Japan M. Sawamura JAEA, Ibaraki-ken, Japan
	We have developed a main linac cryomodule, in which two nine-cell HOM damped SRF cavities were mounted, for the Compact ERL (cERL) project in Japan. The main linac cryomodule is operated by a 2K refrigerator system, whose cooling ability is 80W. RF power is fed to each cavity from an IOT or a solid state amplifier. Amplitude and phase of RF stabilization is done by using a digital LLRF system. Cavity resonant frequency is controlled by using mechanical and piezo tuners. Before beam operation, performance test of the cryomodule has been carried out. Generally the cryomodule works well, but heavy field emission is rather problem. After construction of cERL circulation ring, we have a plan to do first beam operation with energy recovery mode, in this winter. Electron beam are accelerated up to 20 MeV. Heavy heat load to 2K Helium, caused by field emission, restrict cavity operation voltage. We report about a series of performance tests and a first experiment from beam operation.
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WEPRI029	Simulations and Measurements of Beam Pipe Modes excited in 9-cell Superconducting Cavities	2540
	A. Kuramoto Sokendai, Ibaraki, Japan N. Baboi DESY, Hamburg, Germany H. Hayano KEK, Ibaraki, Japan
	Higher order modes (HOM) excited in 9-cell superconducting cavities have been studied to detect cavity alignment. Dipole modes have been monitored, since their magnitude is proportional to beam offsets from their electrical centers. Detection of cavity alignment is important for the ILC to confirm alignment accuracy and furthermore possible source of emittance growth. We are particularly interested in beam pipe modes because they are localized in both ends of the cavity. We measured beam-induced HOM in the STF accelerator at KEK in 2012 – 2013. From the results of the measurement, we found some modes whose behaviors are like dipole mode at around 2.1 GHz instead of 2.28 GHz as calculated by R. Wanzenberg for an ideal cavity [TESLA 2001-33, September 2001]. We also measured beam induced HOM in the TESLA superconducting cavities in FLASH at DESY. In order to identify beam pipe modes and to compare the measurement with the calculation, we calculate beam pipe modes of 9-cell superconducting cavity by CST MICROWAVE STUDIO 2012 and HFSS 12. We will discuss about these calculations and the measurement.
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WEPRI030	Multipactor Simulation on Superconducting Spoke Cavity for Laser Compton Scattered Photon Sources	2543
	Y. Iwashita, H. Fujisawa, H. Tongu Kyoto ICR, Uji, Kyoto, Japan R. Hajima, R. Nagai, M. Sawamura JAEA, Ibaraki-ken, Japan T. Kubo KEK, Ibaraki, Japan
	Funding: This work is supported by Photon and Quantum Basic Research Coordinated Development Program. Superconducting spoke cavity for laser Compton scattered (LCS) photon sources is under development. The operating frequency is 325-MHz to accelerate electron beam for the LCS sources, where the size of the spoke cavity is less than a elliptical cavities with the same frequency. Because of the complicated shape of the cavity, it may be suffered from a strong multipactor effect. The recent results on the multipactor analysis will be presented.
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WEPRI032	First Cryomodule Test at AMTF Hall for The European X-ray Free Electron Laser (XFEL)	2546
	K. Kasprzak, B. Dzieza, W. Gaj, D. Karolczyk, L.M. Kolwicz-Chodak, A. Kotarba, A. Krawczyk, K. Krzysik, W. Maciocha, A. Marendziak, K. Myalski, S. Myalski, T. Ostrowicz, B. Prochal, M. Sienkiewicz, M. Skiba, J. Świerbleski, M. Wiencek, J. Zbroja, P. Ziolkowski, A. Zwozniak IFJ-PAN, Kraków, Poland
	The Accelerator Module Test Facility (AMTF) at DESY in Hamburg is dedicated to the tests of RF cavities and accelerating cryomodules for the European X-ray Free Electron Laser (XFEL). The AMTF hall is equipped with two vertical cryostats, which are used for RF cavities testing and three test benches that will be used for tests of the accelerating cryomodules. Recently, the first cryomodule teststand (XATB3) was commissioned and the first XFEL cryomodule (XM-2) was tested by team of physicists, engineers and technicians from The Henryk Niewodniczanski Institute of Nuclear Physics Polish Academy of Sciences in Kraków, Poland, as a part of Polish in-kind contribution to XFEL. This paper describes the preparation for the cryomodule test, differences with the old teststands CryoModule Test Bench (CMTB), the cryomodule test and the test procedure updates done at the AMTF test bench. The first test of the accelerating cryomodule on the AMTF was successfully performed and the preliminary test results are presented.
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WEPRI034	Analysis of BCP Characteristics for SRF Cavities	2549
	Y. Jung, H.J. Kim IBS, Daejeon, Republic of Korea H.H. Lee, H.C. Yang KRICT, Daejoen, Republic of Korea
	A chemical polishing process is well-known critical process for improving superconducting cavities such as a quality factor and an acceleration electric filed with additional temperature treatment. Especially, Buffered Chemical Polishing (BCP) has been widely used in SRF (Superconducting Radio Frequency) cavity processing. We performed BCP experiments with 1:1:1 and 1:1:2 of an etchant ratio (HF:HNO3:H3PO4). In fact, BCP experiments were carried out by using both undeformed (as-receoved) and deformed niobium samples. We will report baseline BCP results by analyzing surface states of niobium samples such as optical photographs, etch rates and AFM (Atomic Force Microscopy) depending on temperature and time.
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WEPRI035	Stiffening Structure of the HWR at RISP	2552
	G.-T. Park, H.J. Cha, H. Kim, H.J. Kim, W.K. Kim IBS, Daejeon, Republic of Korea
	The HWR being developed in RISP, Korea is in its final stage of the design. We consider the effects of the stiffeners in the presence of the helium vessel on the various detunings such as cool down, helium pressure fluctuation, Lorentz pressure. The interaction of the stiffened cavity with the helium jacket is studied via the coupled simulation by ANSYS and the optimal specification of the stiffeners are determined. In addition, the expected frequency shift is predicted to establish the target frequency bfor the manufacturing. The effect of the vibrational motion is also studied.
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WEPRI037	Comparison of High Order Modes Damping Techniques for 800 MHz Single Cell Superconducting Cavities	2558
SUSPSNE096	use link to see paper's listing under its alternate paper code
	Ya.V. Shashkov, N.P. Sobenin MEPhI, Moscow, Russia M. Zobov INFN/LNF, Frascati (Roma), Italy
	Currently, applications of 800 MHz harmonic cavities in both bunch lengthening and shortening regimes are under consideration and discussion in the framework of the High Luminosity LHC project. In this paper we study electromagnetic characteristics of high order modes (HOM) for a single cell 800 MHz superconducting cavity and arrays of such cavities connected by drifts tubes. Different techniques for the HOM damping such as beam pipe grooves, coaxial-notch loads, fluted beam pipes etc. are investigated and compared. The influence of the sizes and geometry of the drift tubes on the HOM damping is analyzed.
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WEPRI039	LIPAc SRF Linac Couplers Conditioning	2562
	D. Regidor, I. Kirpitchev, J. Mollá, P. Méndez, M. Weber, C. de la Morena CIEMAT, Madrid, Spain S. Chel, M. Desmons, G. Devanz, H. Jenhani CEA/IRFU, Gif-sur-Yvette, France H. Dzitko CEA, Pontfaverger-Moronvilliers, France
	The LIPAc SRF Linac is a cryomodule with eight superconducting HWR cavities at 175 MHz powered by RF couplers capable of transmitting up to 200 kW in CW. To prepare the couplers for operation, cleaning and high power RF processing are needed. When performed, the couplers will be ready for integration in the cryomodule. The Couplers Test Bench has been designed to perform the RF conditioning by pairs, providing good matching, low losses and the required UHV level. To preserve the cleanliness of the internal surfaces, after the test bench manufacturing, an ISO5 clean room has been used for the vacuum parts assembly. The size and number of particles was carefully controlled during the assembly process. The RF conditioning was performed at the IFMIF-EVEDA RF Integration Facility using the Prototype RF Module in travelling wave and standing wave modes. The process started with short pulses at low power and finished when full power CW was reached. Vacuum, multipacting, arcs and matching were continuously monitored to control the process avoiding damages. An overview of the process applied to the prototypes and the RF conditioning results are presented in this paper.
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WEPRI040	On the Optimal Design of Elliptical Superconducting Cavities	2565
SUSPSNE092	use link to see paper's listing under its alternate paper code
	G. Costanza Lund University, Lund, Sweden
	In this paper a linear regression analysis is used to analyze the behavior of the inner cell of an elliptical cavity. The aim is to understand how the RF parameters are correlated to each other and how they are affected by the change of the geometric parameters. This is done by fitting the RF data to a linear model. The data is obtained by simulating a set of different inner cells automatically by the use of a script. The results are useful in several ways: first of all the analysis sheds light on the behavior of elliptical cavities, in particular on its limitations. The analysis is carried out in the framework of optimal design so it is useful for the cavity designer since it allows to choose the geometry at an early stage of the design. It is also possible to make predictions on the performance of the cavity which are in very good agreement with the simulations. Such predictions facilitate the design of the accelerator when choosing the type and number of cavities and when writing the specifications for the cavities to be used in the accelerator.
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WEPRI041	Progress of HOM Couplers for CERN SPL Cavities	2568
SUSPSNE095	use link to see paper's listing under its alternate paper code
	K. Papke, F. Gerigk CERN, Geneva, Switzerland U. van Rienen Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
	Funding: Work supported by the Wolfgang-Gentner-Programme of the Bundesministerium für Bildung und Forschung (BMBF) In this paper we present the progress of the Higher-Order-Mode (HOM) coupler design for the high beta CERN SPL (Superconducting Proton Linac) cavities. This includes the RF transmission behavior as well as mechanical and thermal requirements and their optimizations. Warm RF measurements are presented for the first four high beta SPL Cavities made of bulk niobium. Moreover the first prototype of a HOMcoupler will be introduced and we discuss its characteristics and its tuning possibilities.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPRI041
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WEPRI042	Nb Coated HIE-ISOLDE QWR Superconducting Accelerating Cavities: From Process Development to Series Production	2571
	A. Sublet, I. Aviles Santillana, B. Bártová, S. Calatroni, N.M. Jecklin, I. Mondino, M. Therasse, W. Venturini Delsolaro, P. Zhang CERN, Geneva, Switzerland M. Cantoni EPFL, Lausanne, Switzerland
	The new HIE-ISOLDE accelerator at CERN requires the production of 32 superconducting cavities (20 high-beta and 12 low-beta) in order to increase the energy of the rare isotope beam delivered to the experiments. The Quarter Wave Resonators (QWRs) cavities (0.3m diameter and 0.8m height) are made of OFE 3D-forged copper and are coated by DC-bias diode sputtering with a thin superconducting layer of niobium. Following a preliminary process development phase, the series production of the high-beta cavities has started. An overview of the development phase is presented, describing the key parameters varied to match the HIE-ISOLDE specifications (operation at 4.5 K with an accelerating field of 6 MV/m at 10W RF losses and Q0=4.5x108) and the resulting niobium film characteristics. The first series of cavities, produced using the baseline coating recipe, and their RF performance is reviewed.
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WEPRI044	Final Structure and Design Parameters of TARLA RF System	2577
	Ö. Karslı, A.A. Aksoy, Ç. Kaya, İ.B. Koc, E.Ç. Polat, Ö. Yavaş Ankara University, Accelerator Technologies Institute, Golbasi / Ankara, Turkey M. Doğan Dogus University, Istanbul, Turkey S. Özkorucuklu Istanbul University, Istanbul, Turkey
	Funding: Work supported by Turkish Ministry of Development (Grant No: DPT2006K-120470) Turkish Accelerator and Radiation Laboratory in Ankara (TARLA) is an oscillator mode IR-FEL facility which is under construction since 2011. ELBE licensed superconducting modules housing TESLA RF cavities have been manufacturing for one year and the first module will be delivered in 2015. He Cryogenic System has also started to be manufacturing at similar time with the accelerator structures. It will be delivered in 2014. High Power RF amplifiers are started to tender procedures and delivery time is planning as 2015. The installation of high power transmission lines have to be completed at the same time with the delivery date of HPRF amplifiers to test the cavities and amplifiers. In this study, the final structural design of high power RF transmission lines and design parameters of RF amplifiers for TARLA is discussed. On behalf of TARLA Collaboration, www.tarla.org.tr
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WEPRI045	Key Design Features of Crab-Cavity Cryomodule for HiLumi LHC	2580
	S.M. Pattalwar, A.J. May, P.A. McIntosh, A.E. Wheelhouse STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom G. Burt, B.D.S. Hall Cockcroft Institute, Lancaster University, Lancaster, United Kingdom O. Capatina CERN, Geneva, Switzerland T.J. Jones, N. Templeton STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom T.H. Nicol Fermilab, Batavia, Illinois, USA
	A prototype Superconducting RF (SRF) cryomodule, comprising multiple compact crab cavities is foreseen to realise a local crab crossing scheme for the “Hi-Lumi LHC”, a project launched by CERN to increase the luminosity performance of LHC. A cryomodule with two cavities will be initially installed and tested on the SPS drive accelerator at CERN to evaluate performance with high-intensity proton beams. STFC in collaboration with, University of Lancaster, CERN and FNAL has developed a concept cryomodule that has overcome most of the critical challenges imposed by a series of boundary conditions arising from; the complexity of the cavity design, the requirement for multiple RF couplers, the close proximity to the second LHC beam pipe and the tight space constraints in the SPS tunnel. This paper highlights some of the key design features of the cryomodule with the results of the associated mechanical and thermal analysis.
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WEPRI046	Commissioning of the ERL Cryomodule on ALICE at Daresbury Laboratory	2583
	A.E. Wheelhouse, R.K. Buckley, S.R. Buckley, P.A. Corlett, L.S. Cowie, P. Goudket, A.R. Goulden, L. Ma, P.A. McIntosh, A.J. Moss, S.M. Pattalwar STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
	The ERL cryomodule with two identical 7-cell, 1.3 GHz cavities developed as part of a international collaborative program has been installed in the linac stage on the ALICE (Accelerators and Lasers in Combined Experiments) facility at Daresbury Laboratory replacing the existing 9-cell cryomodule. The cavities have been cooled to 2 K and commissioning of the cryomodule is underway. This paper describes the conditioning and the characterisation tests performed on the two superconducting RF cavities.
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WEPRI048	Testing and Dressed Cavity Design for the HL-LHC 4R Crab Cavity	2589
	B.D.S. Hall, G. Burt Cockcroft Institute, Lancaster University, Lancaster, United Kingdom R. Calaga, S. Calatroni, E. Jensen, A. Macpherson, M. Navarro-Tapia CERN, Geneva, Switzerland T.J. Jones, N. Templeton STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom A.J. May, P.A. McIntosh, S.M. Pattalwar, A.E. Wheelhouse STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
	The High luminosity upgrade to the LHC (HL-LHC) calls for crab cavities to reduce the luminosity loss due to the crossing angle and help provide luminosity levelling. The 4 Rod Crab Cavity (4RCC) is one of three proposed options under consideration. A bare cavity has been prototyped and has undergone recent vertical tests and the results are presented. The dressed cavity includes a power coupler, a lower order mode coupler and two HOM couplers will be presented and discussed.
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WEPRI049	Optimization of Window Position on Diamond SCRF Cavities	2592
	S.A. Pande, C. Christou DLS, Oxfordshire, United Kingdom
	The Diamond storage ring uses CESR type superconducting cavities. These cavities have a fixed coupling resulting in fixed Qext which is considerably higher than the optimum. We use 3 stub tuners to match the cavities under these non-optimum conditions. Diamond Cavity-1 will soon be refurbished. This opportunity could be used to lower the Qext on the cavity. One of the options is to modify the coupling tongue geometry along with a matching section. This may require cutting off the beam tube with the coupler for rework or it may need to be newly fabricated. We investigated another option to lower the Qext of the cavity by optimising the location of the window with respect to the cavity, maintaining the same coupling tongue geometry. The height of the waveguide on the vacuum side of the window differs from that of the coupling waveguide on the cavity resulting in a step. The location of window with respect to the cavity makes a significant difference to the ultimate Qext obtained after putting the window in place. In this paper we present the results of our numerical simulations comparing the present and the proposed window position under different operating conditions.
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WEPRI050	Development and Test Results of a Quasi-waveguide Multi-cell Resonator	2595
	Z.A. Conway, A. Barcikowski, S.M. Gerbick, M. Kedzie, M.P. Kelly, J.S. Kerby, S.H. Kim, S.V. Kutsaev, R.C. Murphy, A. Nassiri, P.N. Ostroumov, T. Reid, T.L. Smith, A. Zholents ANL, Argonne, Illinois, USA
	Funding: Work supported by the U.S. Department of Energy, Offices of Nuclear Physics and Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. This paper reports the successful fabrication and test results of a novel 2815 MHz superconducting deflecting cavity operating in a TE-mode trapped in a quasi-waveguide structure with extremely high shunt impedance. The waveguide structure of this cavity allows for the free propagation of all higher order modes (HOMs) out of the cavity via the beam ports, eliminating the need for HOM dampers inside the cavity when operated with high beam current. The absence of HOM dampers greatly simplifies the cavity fabrication and operation at cryogenic temperatures. This cavity with its high shunt impedance is ideal for the spatial rotation of short bunches in a small physical space, a requirement for the generation of sub-picosecond short pulse x-rays in electron storage rings or luminosity upgrades of colliders. Results characterizing the fabrication accuracy and precision, the RF performance at 2 K, and frequency tuning considerations will be discussed here.
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WEPRI051	Results from RF Tests of the First US-built High-gradient Superconducting Cryomodule	2598
	A. Hocker, C.M. Baffes, K. Carlson, B. Chase, D.J. Crawford, E. Cullerton, D.R. Edstrom, E.R. Harms, T. Kubicki, M.J. Kucera, J.R. Leibfritz, J.N. Makara, D. McDowell, O.A. Nezhevenko, D.J. Nicklaus, H. Pfeffer, Y.M. Pischalnikov, P.S. Prieto, J. Reid, W. Schappert, P. Stabile, P. Varghese Fermilab, Batavia, Illinois, USA
	Funding: United States Department of Energy, Contract No. DE-AC02-07CH11359 Fermilab has built a cryomodule comprised of eight 1.3 GHz superconducting RF cavities for use in its Advanced Superconducting Test Accelerator (ASTA) facility. This cryomodule (RFCA002) was intended to achieve the International Linear Collider (ILC) “S1” goal of demonstrating an average accelerating gradient of 31.5 MV/m, and is the first of its kind built in the United States. The module has been cooled down and operated without beam at ASTA in order to assess its performance. The results from these tests are presented here.
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WEPRI052	SRF Systems for ASTA at Fermilab	2601
	E.R. Harms, C.M. Baffes, K. Carlson, B. Chase, D.J. Crawford, E. Cullerton, D.R. Edstrom, M. Geynisman, A. Hocker, A.L. Klebaner, M.J. Kucera, J.R. Leibfritz, J.N. Makara, D. McDowell, S. Nagaitsev, O.A. Nezhevenko, D.J. Nicklaus, H. Pfeffer, Y.M. Pischalnikov, P.S. Prieto, J. Reid, W. Schappert, P. Stabile, P. Varghese Fermilab, Batavia, Illinois, USA
	Funding: Operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy. The Advanced Superconducting Test Accelerator (ASTA) at Fermilab now being commissioned is comprised of a number of superconducting RF systems including single-cavity cryomodules and a TESLA/ILC style 8-cavity cryomodule. Two of them, 'Capture Cavity 2' and 'Cryomodule 2', have been cooled to 2 Kelvin and brought into operation. We provide an overview of the unique characteristics of each of the systems, commissioning experience, and latest results including their respective operating characteristics.
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WEPRI053	Phase Method of Measuring Cavity Quality Factor	2604
	O.S. Melnychuk, R.V. Pilipenko, Y.M. Pischalnikov, W. Schappert, D.A. Sergatskov Fermilab, Batavia, Illinois, USA
	Novel method for measuring intrinsic quality factor of superconducting RF (SRF) cavities using both amplitude and phase information of forward, reflected, and transmitted cavity signal is discussed. Advantages of the method in comparison with traditional types of cavity quality factor measurements are highlighted. Computer simulations and evaluation of uncertainties for the measurements are described. Analysis of data collected at vertical test facility for SRF cavities at Fermilab is presented.
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WEPRI054	Medium Field Q-Slope Studies in Low Beta Resonators	2608
	O.S. Melnychuk, A. Grassellino, A.I. Sukhanov Fermilab, Batavia, Illinois, USA
	Studies of the phenomenon of Medium field Q-slope (MFQS, 30-80 mT) have been focused predominantly on high beta superconducting cavities. Complementing research on cavity losses with the analysis of low beta cavity data can provide additional insights into the nature of MFQS. We present MFQS measurements of 325MHz β=0.2 single spoke resonators and 650MHz β=0.9 elliptical single cell resonators at vertical test facility at FNAL. We compare our findings with those obtained for high frequency 1.3GHz cavities tested both at the same facility and other laboratories.
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WEPRI057	RF Control and DAQ Systems for the Upgraded Vertical Test Facility at Fermilab	2612
	Y.M. Pischalnikov, R.H. Carcagno, F.L. Lewis, R. Nehring, R.V. Pilipenko, W. Schappert Fermilab, Batavia, Illinois, USA
	Funding: Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy. The Fermilab Vertical Cavity Test Facility (VCTF) [1] is a used to test production cavities prior to their installation in cryomodules and to characterize the performance of research cavities as part of the extensive SRF cavity R&D program at FNAL. The performance of a variety of SRF cavities (325MHz, 650MHz, 1300MHz; bare and dressed) can be measured at VCTF. Recently FNAL upgraded the facility by adding two additional test stands (VTS2&3) in preparation for production of cavities for two new linear accelerators (LCLS II and PIP II). This paper provides an overview of the design features, technical parameters and experience with first operation of the upgraded RF control and DAQ systems.
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WEPRI058	Commissioning Status of the Advanced Superconducting Test Accelerator at Fermilab	2615
	J. Ruan, R. Andrews, C.M. Baffes, D.R. Broemmelsiek, K. Carlson, B. Chase, M.D. Church, D.J. Crawford, E. Cullerton, J.S. Diamond, N. Eddy, D.R. Edstrom, E.R. Harms, A. Hocker, A.S. Johnson, A.L. Klebaner, M.J. Kucera, J.R. Leibfritz, A.H. Lumpkin, J.N. Makara, S. Nagaitsev, O.A. Nezhevenko, D.J. Nicklaus, L.E. Nobrega, P.S. Prieto, J. Reid, J.K. Santucci, G. Stancari, D. Sun, M. Wendt, S.J. Wesseln Fermilab, Batavia, Illinois, USA P. Piot Northern Illinois University, DeKalb, Illinois, USA
	Funding: *Operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy. The Advanced Superconducting Test Accelerator (ASTA) is under construction at Fermilab. This accelerator will consist of a photo-electron gun, injector, ILC-type cryomodules, and multiple downstream beam-lines. Its purpose is to be a user-based facility for Advanced Accelerator R&D. . Following the successful commissioning of the photoinjector gun, a Tesla style 8-cavity cryomodule and a high gradient capture cavity have been cooled down to 2 K and powered commissioning and performance characterization has begun. We will report on the commissioning status and near-term future plans for the facility.
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WEPRI060	Investigation of Thermocurrents Limiting the Performance of Superconducting Cavities	2621
	R.G. Eichhorn, C.G. Daly, F. Furuta, A. Ganshin Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	As the surface resistance of superconducting cavities approach the theoretical limits parasitic effects limiting the performance came into focus of current research. One of these effects is that the quality factor of a cavity is impacted by the cooldown rate. We will present results from recent investigations on thermocurrents, driven by the temperature difference between the two material interfaces between the superconducting Niobium cavity and its Titanium helium-vessel, leading to the presence of a magnetic field while the cavity transits to the superconducting state.
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WEPRI061	Cornell's Main Linac Cryomodule for the Energy Recovery Linac Project	2624
	R.G. Eichhorn, B. Bullock, J.V. Conway, B. Elmore, F. Furuta, Y. He, G.H. Hoffstaetter, J.J. Kaufman, M. Liepe, T.I. O'Connel, 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
	Cornell University has been designing and building superconducting accelerators for various applications for more than 50 years. Currently, an energy-recovery linac (ERL) based synchrotron-light facility is proposed making use of the existing CESR facility. As part of the phase 1 R&D program funded by the NSF, critical challenges in the design were addressed, one of them being a full linac cryo-module. It houses 6 superconducting cavities- operated at 1.8 K in continuous wave (CW) mode - with individual HOM absorbers and one magnet/ BPM section. Pushing the limits, a high quality factor of the cavities (2•1010) and high beam currents (100 mA accelerated plus 100 mA decelerated) are targeted. We will present the status of the main linac cryomodule (MLC) fabrication and the findings on the cavity performance and component testing.
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WEPRI062	The Joint High Q0 R&D Program for LCLS-II	2627
	M. Liepe, R.G. Eichhorn, F. Furuta, G.M. Ge, D. Gonnella, G.H. Hoffstaetter Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA A.C. Crawford, A. Grassellino, A. Hocker, O.S. Melnychuk, A. Romanenko, A.M. Rowe, D.A. Sergatskov Fermilab, Batavia, Illinois, USA R.L. Geng, A.D. Palczewski, C.E. Reece JLab, Newport News, Virginia, USA M.C. Ross SLAC, Menlo Park, California, USA
	The superconducting RF linac for LCLS-II calls for 1.3 GHz 9-cell cavities with an average intrinsic quality factor Q0 of 2.7·1010 at 2K and 16 MV/m accelerating gradient. A collaborative effort between Cornell University, FNAL, and JLab has been set up with the goal of developing and demonstrating a cavity treatment protocol for the LCLS-II cavities meeting these specifications. The high Q0 treatment protocol is based on nitrogen doping of the RF surface layer during a high temperature heat treatment. This novel SRF cavity preparation was recently developed at FNAL and shown to result in SRF cavities of very high Q0 at 2K with an increase in Q0 from low to medium fields. N-doped single cell cavities at Cornell, FNAL, and JLab routinely exceed LCLS-II specification. 9-cell N-doped cavities at FNAL achieve an average Q0(T=2K, 16 MV/m) of ≈ 3.4·1010 with an average quench field of ≈ 19 MV/m, meeting therefore overall with good margin the LCLS-II specification.
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WEPRI063	Flux Trapping in Nitrogen-Doped and 120 C Baked Cavities	2631
	D. Gonnella, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: United States Department of Energy It is well known that external magnetic fields can cause higher residual resistance in superconducting RF cavities if the field is present during cooldown. However, the effect of cavity preparation and surface mean free path on the resulting residual resistance from magnetic field is less well studied. In this paper, we report on recent studies at Cornell in which two SRF cavities (one nitrogen-doped and one 120oC baked) were cooled through Tc in an applied uniform external magnetic field. Trapped flux and residual resistance were measured for a variety of cooldowns and applied magnetic fields. It was found that the residual resistance due to trapped flux in the nitrogen-doped cavity was three times larger than in the 120oC baked cavity.
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WEPRI064	New Insights into Heat Treatment of SRF Cavities in a Low-pressure Nitrogen Atmosphere	2634
SUSPSNE093	use link to see paper's listing under its alternate paper code
	D. Gonnella, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: United States Department of Energy Recent results from Cornell and FNAL have shown that superconducting RF cavities given a heat treatment in a nitrogen atmosphere of a few mTorr display an increase in Q0 with increasing accelerating field, opposite to the medium field Q slope usually observed. Three cavities was prepared at Cornell using this method and subsequently tested after different amounts of material removal. Cavity performance and material properties were extracted for each cavity and correlated with material removal. This has given new insights into how material properties and the anti-Q slope depend on cavity preparation.
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WEPRI065	SRF Material Performance Studies using a Sample Host Cavity	2638
	D.L. Hall, D. Gonnella, M. Liepe, I.S. Madjarov Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	A sample-host TE-mode cavity developed at Cornell for the purposes of studying novel superconducting materials has undergone further testing using a niobium sample plate. In initial testing the peak field achieved on the sample plate was (45 ± 4.5) mT, although this was limited by the amount of input power available. New tests have been performed using both an improved RF power system and a temperature mapping system for precision measurements of surface resistance as a function of location on the sample plate. Results of the most recent test, in which the cavity achieved a peak sample plate field of (81 ± 4) mT using a high-RRR niobium sample plate, are presented and future work on the cavity is discussed.
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WEPRI066	Recent Progress in Nb3Sn SRF Cavity Development at Cornell	2641
	S. Posen, D. Gonnella, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Nb3Sn coatings on niobium SRF cavities have the potential to significantly reduce cryogenic costs due to their extremely small surface resistance (Rs). In this paper, we present new results showing the repeatability of Cornell's fabrication process, which produces high Q0 cavities that reach medium fields with minimal Q-slope. We also show the results of attempts to smooth RF surfaces and reduce defects via material removal. However, both HF rinsing and centrifugal barrel polishing resulted in strong performance degradation.
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WEPRI067	Multi-Physics Analysis of CW Superconducting Cavity for the LCLS-II using ACE3P	2645
	Z. Li, C. Adolphsen, O. Kononenko, T.O. Raubenheimer, C.H. Rivetta, M.C. Ross, L. Xiao SLAC, Menlo Park, California, USA
	Funding: Work was supported by the U.S. DOE contract DE-AC02-76SF00515 and used the resources of NERSC at LBNL under US DOE Contract No. DE-AC03-76SF00098. The LCLS-II linac utilizes superconducting technology operating at continuous wave to accelerate the 1-MHz electron beams to 4 GeV to produce tunable FELs. The TESLA 9-cell superconducting cavity is adopted as the baseline design for the linac. The design gradient is approximately 16 MV/m. The highest operating current is 300 μA. Assuming that the RF power is matched at the highest current, the optimal loaded QL of the cavity is found to be around 4·107. Because of the high QL, the cavity bandwidth approaches the background microphonic detuning, and the performance of the cavity is tightly coupled to the mechanical perturbations of the cavity/cryomodule system. The resulting large phase and amplitude variations in the cavity require active feedback to achieve the 0.01% amplitude and phase stability requirements. To understand the cavity RF response and feedback requirements to the microphonics and Lorentz Force detuning, we have developed a simulation model of the RF-mechanical coupled system using parameters obtained with the multi-physics solver ACE3P. We will present the simulation results of the LCLS-II linac under different power feed scenarios and feedback schemes.
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WEPRI068	Conceptual Design of an Ideal Variable Coupler for Superconducting Radiofrequency 1.3 GHz Cavities	2648
	C. Xu, S.G. Tantawi SLAC, Menlo Park, California, USA
	We present a new type of fundamental mode accelerator structure coupler. This coupler has a very simplified mechanical structure and is equipped with a novel vacuum window structure that allows the coupler to be divided into two parts. These two parts are fully thermally isolated, only coupled by thermal radiation. The rf power on the other hand get coupled perfectly from one part to the other. This is truly novel approach which is quite different than the conventional approach to this problem such as chock structure. The structure in general is slightly overmoded. We show that this structure can also be adopted to change the coupling coefficient and thus be tuned for an external Q. This could be of great utility for CW operation. We show the analytical and numerical calculation for a two window variable coupler.
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WEPRI069	Reproducibility of High-Q SRF Cavities by High Temperature Heat Treatment	2651
	P. Dhakal, G. Ciovati, P. Kneisel, G.R. Myneni JLab, Newport News, Virginia, USA
	Funding: This manuscript has been authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177 Recent work on high-temperature (> 600 °C) heat treatment of ingot Nb cavities in a customized vacuum furnace for several hours showed the possibility of achieving Q0-values of up to ~5×1010 at 2.0 K, 1.5 GHz and accelerating gradients of ~20 MV/m. This contribution presents results on further studies of the heat treatment process to produce cavities with high Q0 values for continuous-wave accelerator application. Single-cell cavities of different Nb purity have been processed through few cycles of heat-treatments and chemical etching. Measurements of Q0 as a function of temperature at low RF field and of Q0 as a function of the RF field at or below 2.0 K have been made after each treatment. Measurements by TOF-SIMS of the impurities’ depth profiles were made on samples heat treated with the cavities.
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WEPRI070	Mechanical Properties of Ingot Nb Cavities	2654
	G. Ciovati, P. Dhakal, P. Kneisel, J.D. Mammosser, J. Matalevich, G.R. Myneni JLab, Newport News, Virginia, USA
	Funding: This manuscript has been authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. This contribution presents the results of measurements of the resonant frequency and of strain along the contour of a single-cell cavity made of ingot Nb subjected to increasing uniform differential pressure, up to 6 atm. The data were used to infer mechanical properties of this material after cavity fabrication, by comparison with the results from simulation calculations done with ANSYS. The objective is to provide useful information about the mechanical properties of ingot Nb cavities which can be used in the design phase of SRF cavities intended to be built with this material.
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WEPRI072	High Power Co-axial Couplers for SRF Cavities	2657
	J. Guo, J. Henry, R.A. Rimmer, H. Wang, R.S. Williams JLab, Newport News, Virginia, USA A. Dudas, M.L. Neubauer Muons, Inc, Illinois, USA
	Funding: Work supported by Dept. of Energy grant no. DE-SC0002769 High Power RF couplers are required in a wide range of accelerator projects using superconducting RF cavities. We have proposed a novel robust coax SRF coupler design using two pre-stressed disc windows without the need of additional matching elements. The matching frequency and the power handling capacity can be easily scaled by changing the diameter and the spacing of the windows. In this paper, we will present our latest progress in the fabrication and the testing of the windows.
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WEPRI073	High Order Modes Survey and Mitigation of the CEBAF C100 Cryomodules	2660
	J. Guo, M. Stirbet, H. Wang, S. Wang JLab, Newport News, Virginia, USA
	Funding: Funding Agency: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177 Ten new C100 cryomodules have been installed for the CEBAF 12GeV upgrade in the last few years. The high order modes (HOM) of these cryomodules need to be controlled to avoid beam breakup (BBU) instability. We surveyed the HOM for all the 80 cavities of the C100 modules in both the JLab cryomodule test facility (CMTF) and the CEBAF tunnel. Additional measures such as waveguide filters were applied to bring down out of spec modes. In this paper, we will present the HOM survey setup and results. The mitigation measures and their effects will also be discussed.
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WEPRI074	Status of SRF Facilities at SNS	2663
	J. Saunders, R. Afanador, B. DeGraff, C.J. McMahan ORNL RAD, Oak Ridge, Tennessee, USA M.T. Crofford, M. Doleans, M.P. Howell, S.-H. Kim, S.W. Lee, T.S. Neustadt, S.E. Stewart, W.H. Strong ORNL, Oak Ridge, Tennessee, USA
	Funding: This work was supported by SNS through UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. DOE. As a part or an ongoing process to maintain and improve the performance of its Superconducting Linac (SCL) the Spallation Neutron Source (SNS) is building facilities for processing and testing Superconducting Radio Frequency (SRF) cavities. Recently both a High Pressure Rinse (HPR) tool and a Vertical Test Apparatus (VTA) have been built and commissioned. The HPR is a commercially fabricated piece of equipment which is customized for the SNS application. The VTA was specified, designed and developed by the SNS. This paper will outline the design features as well as the commissioning results for both systems.
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WEPRI075	A Compact Beam Spreader using RF Deflecting Cavities for the LCLS-II	2666
	S.U. De Silva, J.R. Delayen, R.G. Olave ODU, Norfolk, Virginia, USA L.R. Doolittle, M. Placidi, A. Ratti LBNL, Berkeley, California, USA P. Emma SLAC, Menlo Park, California, USA
	The LCLS-II project currently under development is designed to accelerate electron bunches up to 4 GeV and transport them to one of two FEL undulators located more than 2 km downstream of the end of the LCLS-II linac. The upgrade requires a spreader system to separate the baseline electron bunches and transport them to two undulator lines or a local dump. Fast bipolar kickers (FK) or transverse electric rf deflectors (RFD) are considered as fast-switching devices (FSD). In the RFD approach described here three design options operating at 325 MHz are studied including a superconducting rf-dipole cavity, a normal conducting rf-dipole cavity, and a normal conducting 4-rod cavity. Optional compact splitting schemes involving a combination of vertical and horizontal initial deflections are addressed.
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WEPRI076	Higher Order Mode Damping in Superconducting Spoke Cavities	2669
	C.S. Hopper, J.R. Delayen ODU, Norfolk, Virginia, USA
	Parasitic higher order modes (HOMs) can be severely detrimental to the performance of superconducting cavities. For this reason, the mode spectrum and beam coupling strength must be examined in detail to determine which modes must be damped. One advantage of the spoke cavity geometry is that couplers can be placed on the outer body of the cavity rather than in the beam line space. We present an overview of the HOM properties of spoke cavities and methods for suppressing the most harmful ones.
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WEPRI077	Cryogenic Test of a 750 MHz Superconducting RF Dipole Crabbing Cavity*	2672
	A. Castilla, J.R. Delayen ODU, Norfolk, Virginia, USA A. Castilla, J.R. Delayen, H. Park JLab, Newport News, Virginia, USA A. Castilla DCI-UG, León, Mexico
	Funding: *Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. With resources of NERSC, under U.S. DOE contract No. DE-AC02-05CH11231. A superconducting rf dipole cavity has been designed to address the challenges of a high repetition rate (750 MHz), high current for both electron/ion species (0.5/3 A per bunch), and large crossing angle (50 mrad) at the interaction points (IPs) crabbing system for the Medium Energy Electron-Ion Collider (MEIC) proposed by Jefferson Lab. The cavity prototype built at Niowave, Inc. has been tested at the Jefferson Lab facilities. In this work we present a detailed analysis of the prototype cavity performance at 4 K and 2 K, corroborating the absence of hard multipacting barriers that could limit the desired transverse fields, along with the surface resistance (Rs) temperature dependency.
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WEPRI078	Development of a Quarter-wave Coaxial Coupler for 1.3 GHz Superconducting Cavities	2675
	Y. Xie, A. Kanareykin Euclid TechLabs, LLC, Solon, Ohio, USA N. Solyak, V.P. Yakovlev Fermilab, Batavia, Illinois, USA
	Superconducting ILC-type cavities have an rf coupler that is welded on. A detachable coupler will reduce conditioning time (can be conditioned separately), reduce cost and improve reliability. The problem with placing an extra flange in the superconducting cavity is creating a possible quench spot. Euclid Techlabs LLC designed a coupler and optimized its geometry that yielding an area on the surface with zero magnetic field (hence zero surface current). By placing a flange in that area we are able to avoid disturbing surface currents that typically lead to a quench. The coupler is optimized to preserve the axial symmetry of the cavity and rf field. The rf test results of this type coupler with a 1.3 GHz ILC-type single-cell cavity at Fermilab will be reported and discussed.
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WEPRI081	Mechanical Design of the 704 MHz 5-cell SRF Cavity Cold Mass for CeC PoP Experiment	2678
	J.C. Brutus, S.A. Belomestnykh, I. Ben-Zvi, Y. Huang, V. Litvinenko, I. Pinayev, J. Skaritka, L. Snydstrup, R. Than, J.E. Tuozzolo, W. Xu BNL, Upton, Long Island, New York, USA T.L. Grimm, R. Jecks, J.A. Yancey Niowave, Inc., Lansing, Michigan, USA
	Funding: * Work is supported by Brookhaven Science Associates, LLC under contract No. DE-AC02-98CH10886 with the US DOE. A 5-cell SRF cavity operating at 704 MHz will be used for the Coherent Electron Cooling Proof of Principle (CeC PoP) system under development for the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory. The CeC PoP experiment will demonstrate the new technique of cooling proton and ion beams that may increase the beam luminosity in certain cases, by as much as tenfold. The 704 MHz cavity will accelerate 2 MeV electrons from a 112 MHz SRF gun up 22 MeV. Novel mechanical designs, including a super fluid heat exchanger, helium vessel, vacuum vessel and tuner mechanism are presented. Structural and thermal analysis, using ANSYS were performed to confirm the mechanical tuning system structural stability. This paper provides an overview of the design, the project status and schedule of the 704 MHz 5-cell SRF for CeC PoP experiment.
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THOBB01	Pursuing the Origin and Remediation of Low Q0 observed in the Original CEBAF Cryomodules	2828
	R.L. Geng, J.F. Fischer, C.E. Reece, A.V. Reilly JLab, Newport News, Virginia, USA F.S. He, Y.M. Li PKU, Beijing, People's Republic of China
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. We report on results of a new investigation into the Q0 degradation phenomenon observed in original CEBAF cavities when assembled into cryomodules. As a result, the RF dissipation losses increased by roughly a factor of two. The origin of the degradation, first observed in 1994, has remained unresolved up to current period, despite much effort. Recently, a new investigation has been launched, taking advantage of the latest cryomodule to undergo refurbishment. Systematic measurements are conducted with respect to the magnetic shielding effects of the double-layer shields and the magnetic properties of various components within the inner shield. This resulted in the new discovery of strongly magnetized strut springs as a major source of remnant magnetic flux near a cavity inside of all magnetic shielding. New springs with superior magnetic properties have been found, evaluated and implemented into the current cryomodule. In this contribution, we will review the data accumulated so far. Options for complete Q0 preservation of assembled cavities and possible Q0 remediation for those 330 cavities already installed in CEBAF will be presented.
	Slides THOBB01 [16.521 MB]
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THOBB02	Superconducting Cavity Cryomodule Designs for the Next Generation of CW Linacs: Challenges and Options	2831
	T.H. Nicol, Y.O. Orlov, T.J. Peterson, V.P. Yakovlev Fermilab, Batavia, Illinois, USA
	Funding: Supported by FRA under DOE Contract DE-AC02-07CH11359 The designs of nearly all superconducting RF (SRF) linacs over the last several years, with one notable exception being CEBAF at Jefferson Lab, have assumed pulsed beam operation with relatively low duty factors. These include the XFEL at DESY, the ILC, the original configuration for Project X at Fermilab, as well as several others. Recently proposed projects, on the other hand, including the LCLS-II at SLAC, the newly configured low and medium energy sections for Project X, and FRIB at Michigan State, to name a few, assume continuous wave or CW operation on quite a large scale with ambitious gradients and cavity performance requirements. This has implications in the cavity design as well as in many parts of the overall cryomodule due to higher dynamic heat loads in the cavities themselves and higher heat loads in the input and high-order-mode (HOM) couplers. Piping internal to the cryomodule, the effectiveness of thermal intercepts, the size of integrated heat exchangers, and many other aspects of the overall design are also affected. This paper will describe some of these design considerations as we move toward the next generation of accelerator projects.
	Slides THOBB02 [8.388 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THOBB02
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