07 Accelerator Technology
T07 Superconducting RF

Paper	Title	Page
WEPMB003	Design of the HWR Cavities for SARAF	2119
	G. Ferrand, L. Boudjaoui, D. Chirpaz-Cerbat, P. Hardy, F. Leseigneur, C. Madec, N. Misiara, N. Pichoff CEA/IRFU, Gif-sur-Yvette, France
	CEA is committed to delivering a Medium Energy Beam Transfer line and a superconducting linac (SCL) for SARAF accelerator in order to accelerate 5mA beam of either protons from 1.3 MeV to 35 MeV or deuterons from 2.6 MeV to 40 MeV. The SCL consists in 4 cryomodules. The first two identical cryomodules host 6 half-wave resonator (HWR) low beta cavities (β = 0.09) at 176 MHz. The last two identical cryomodule will host 7 HWR high-beta cavities (β = 0.18) at 176 MHz. Low-beta and high beta cavities have been optimized to limit electric and magnetic peak fields in the cavity, and to minimize the dissipated power. Manufacturing constraints and helium cooling were taken into consideration to minimize the risk during manufacturing and operation. Preliminary mechanical studies of the cavity and of the tuning system, as well as preliminary studies of the couplers and pick-up antennas were carried out. This work will be presented in this poster.
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WEPMB005	Manufacturing of the IFMIF Series Power Couplers	2122
	H. Jenhani, N. Bazin, N. Berton, G. Devanz, P. Hardy, V.M. Hennion CEA/IRFU, Gif-sur-Yvette, France
	In the framework of the International Fusion Materials Irradiation Facility (IFMIF), which consists of two high power CW accelerator drivers, each delivering a 125 mA deuteron beam at 40 MeV, a Linear IFMIF Prototype Accelerator (LIPAc) is presently under construction for the first phase of the project. Eight power couplers are needed for the cryomodule of LIPAc. After the validation of the two prototypes, the manufacturing of the Series Power Couplers was lunched. This paper will report the status of the manufacturing progress. It will also describe the acceptance tests in addition to the criteria adopted for these critical RF power units. The manufacturing imperfections and some finishing techniques used for the different parts will be also presented and discussed.
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WEPMB006	XFEL Couplers RF Conditioning at LAL	2125
	H. Guler, A. Gallas, W. Kaabi, D.J.M. Le Pinvidic, C. Magueur, M. Oublaid, A. Thiebault, A. Verguet LAL, Orsay, France
	The industrialization and the RF conditioning of 800 power couplers for the European XFEL have been performed by LAL-Orsay from fall 2013 to spring 2016. LAL laboratory has in charge the industrial monitoring, the quality control and the RF conditioning of the couplers fabricated by two different suppliers. It was the first experience of coupler production at such scale. The faced challenges, the different issues, and the lessons learned during the mass production will be reported. And finally the huge amount of RF conditioning data will be shown as one of key point on the conditioning process.
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WEPMB007	Error Estimation in Cavity Performance Test for the European XFEL at DESY	2128
	Y. Yamamoto KEK, Ibaraki, Japan W.-D. Möller, D. Reschke DESY, Hamburg, Germany
	The cavity performance tests, that is, vertical test (V.T.) and cryomodule test (C.T.), in the cavity/cryomodule mass production for XFEL have been done since 2012 at DESY, and is still on-going at present. At the comparatively initial stage of the mass production, the error estimation in the cavity performance tests was done for understanding how precisely those measurements are done at AMTF (Accelerator Module Test Facility). There are two parameters for the error estimation in V.T. One is the cable calibration parameter, and the other is the external Q-value, which is related to the power emitted from cavity. The measurement precision in the external Q-value depends on the measurement of coupling coefficient (β) strongly. Therefore, it is essential not to miss the β measurement for the precise measurement in V.T. On the other hand, as for C.T., the change of parameter (Kt), which is related to the evaluation of accelerating gradient, was used. As the result of the data analysis for Kt, the error was estimated to be 6%, and is related to the cavity performance degradation from V.T. to C.T. In this paper, the detailed data analysis and error estimation will be presented.
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WEPMB009	Status of the Superconducting Cryomodules and Cryogenic System for the Mainz Energy-recovering Superconducting Accelerator MESA	2134
	T. Stengler, K. Aulenbacher, F. Hug, D. Simon, P. Weber IKP, Mainz, Germany F. Schlander ESS, Lund, Sweden N. Wiehl Johannes Gutenberg University Mainz, Institut of Nuclear Chemistry, Mainz, Germany
	Funding: Work supported by the German Research Foundation (DFG) under the Cluster of Excellence "PRISMA" SRF and the cryogenic system are mandatory for the operation of MESA at the Institut für Kernphysik at Johannes Gutenberg-Universität Mainz. The cryomodule production project is running for one year right now and the recent developments and measurements are presented. Further on the cryogenic concept required for the operation of MESA will be discussed.
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WEPMB011	ESS Medium and High Beta Cavity Prototypes	2138
	P. Michelato, A. Bellandi, M. Bertucci, A. Bignami, A. Bosotti, J.F. Chen, L. Monaco, R. Paparella, P. Pierini, D. Sertore INFN/LASA, Segrate (MI), Italy C.G. Maiano DESY, Hamburg, Germany C. Pagani Università degli Studi di Milano & INFN, Segrate, Italy S. Pirani ESS, Lund, Sweden
	In the framework of the ESS activity in progress at INFN-LASA, we are designing and developing 704.42 MHz Medium (β=0.67) and High (β=0.86) beta prototype cavities plug compatible with the ESS cryomodule design. The cells of one Medium and one High beta cavity are fabricated with high quality CBMM Large Grain Niobium (480 mm dia. Ingot, RRR=300, sliced by Heraeus) while a Medium beta cavity is done with Fine Grain material for comparison. The prototype cavities will be produced by the firm Ettore Zanon S.p.A. under the supervision of INFN - LASA group.
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WEPMB012	Production and Investigation of Superconducting 9-Cell Cavity Made of Large Grain Nb in KEK	2141
	T. Dohmae, H. Inoue, K. Umemori, Y. Watanabe, M. Yamanaka KEK, Ibaraki, Japan
	For CW operation of superconducting cavity, reduction of heat load at cavity surface is one of important topics, since generated heat load is much higher than that of pulse wave. Using Large Grain (LG) Nb for superconducting cavity has possibility to reach higher Q0 than using Fine Grain Nb, which reduces heat load to 2K Helium. KEK Cavity Fabrication Facility(CFF) group had successfully produced superconducting 1-cell cavity made of LG Nb in 2013, and reached high Q0 at the vertical test (maximum field of 45 MV/m). Then, KEK CFF group started producing first superconducting 9-cell LG cavity in 2015, which will be completed in the end of December 2015. Whole processes of producing this cavity from sliced Nb are done in KEK. In this report, process flow and strategies of producing 9-cell cavity and results of vertical test will be presented in detail.
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WEPMB013	Long Term Cavity Performance in Compact-ERL Injector Cryomodule	2145
	E. Kako, T. Konomi, T. Miura, H. Sakai, K. Umemori KEK, Ibaraki, Japan
	Degradation of cavity performance due to heavy field emission was observed in three 2-cell cavities after beam operation at 5 MeV for 2 years.
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WEPMB014	Cavity Performance of the Prototype KEK Superconducting RF Gun	2148
	T. Konomi, E. Kako, E. Kako, Y. Kobayashi, Y. Kobayashi, K. Umemori, K. Umemori, S. Yamaguchi KEK, Ibaraki, Japan R. Matsuda Mitsubishi Heavy Industries Ltd. (MHI), Takasago, Japan T. Yanagisawa MHI, Hiroshima, Japan
	A superconducting RF (SRF) gun can generate a high current and high energy beam. It has a possibility to achieve requirement from high performance ERL and high repetition FEL. Target values of the L-band KEK SRF gun are that beam repetition is 1.3 GHz, beam current is 100 mA, beam energy is 2 MeV, emittance is 1 mm mrad or less. The number of cell is 1.5. Accelerating energy of 2 MeV corresponds to 42 MV/m of maximum surface field. The photocathode is designed to be illuminated by excitation laser from backside. The SRF gun cavity consists of the 1.5 cell accelerating cavity, cathode plug and choke filter for protecting the heating of cathode plug. To evaluate these parts individually, these parts are added step by step. High gradient test of the accelerating cell without cathode plug and choke filter was done. The surface peak electric field reached 66 MV/m, and this meet the target value 42 MV/m sufficiently. Next high gradient test will be done after adding the choke filter. The choke filter is designed to be simple to wash choke cell easier. In this conference, we will report the design, fabrication and high gradient performance of the SRF gun cavity with choke filter.
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WEPMB015	Construction and 2K Cooling Test of Horizontal Test Cryostat at KEK	2151
	K. Umemori, K. Hara, E. Kako, Y. Kobayashi, Y. Kondo, H. Nakai, H. Sakai, S. Yamaguchi KEK, Ibaraki, Japan
	A horizontal test cryostat was designed and constructed at AR East building on KEK. Main purposes of test stand are improvement of module assembly technique and effective development of module components. Diameter of vacuum chamber is 1 m and its length is 3 m, which is enough to realize performance test of L-band 9-cell cavity with full assembly, including input couplers, HOM dampers/couplers and frequency tuners. On the sides, several ports are prepared to access to components, such as coupler and tuners. A cold box is placed on the top of the chamber. Liquid He is filled in a 4K-pod and 2K He is supplied through a J-T valve. A He pumping system is prepared. Inside of the chamber was covered with 80K shield, which is cooled by Liquid nitrogen. A cavity is supported on 5K table, which is also used as 5K thermal anchors. After cooling down to 80K using liquid Nitrogen, 4K He was stored and pumped down to 2K. The cooling test was successful. In this presentation, details of design and construction of the horizontal test cryostat is described and results of the cooling tests are shown. High power tests will be realized in near future.
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WEPMB016	Vertical Test Results of Nitrogen Doped SRF Cavities at KEK	2154
	K. Umemori, H. Inoue, E. Kako, T. Konomi, T. Kubo, H. Sakai, H. Shimizu, M. Yamanaka KEK, Ibaraki, Japan H. Hara, K. Sennyu, T. Yanagisawa MHI-MS, Kobe, Japan
	Recently Nitrogen doping(N-doping) technique was proposed and drastic improvements of Q-values were reported. Since high-Q operation of SRF cavities are very attractive for CW machine, we started investigation on performance of Nitrogen doped SRF cavities. Nitrogen doping systems were prepared on two vacuum furnaces, which have been used for annealing of SRF cavities. Two fine grain single cell cavities have been used for the study. After 800 degree, 3 hours annealing, N-doping were carried out under several Pa of Nitrogen pressure and followed by post annealing. Three kind of different conditions, pressure and duration time, were attempted. After applying EP-2, cavity performances were evaluated by vertical tests. Against our expectations, we observed lower Q-values, at every measurements, than those measured without N-doping. In this presentation, we describe details about N-doping system and parameters and results obtained by vertical tests. Some discussions are also given against our results.
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WEPMB017	High Gradient Cavity Performance in STF-2 Cryomodule for the ILC at KEK	2158
	Y. Yamamoto, T. Honma, E. Kako, Y. Kojima, T. Matsumoto, H. Nakai, T. Shishido KEK, Ibaraki, Japan
	The high power test for STF-2 cryomodule has completed successfully in 2015. Before cooldown of cryomodule, at first, the input coupler conditioning at room temperature is done with detuned cavities. After cooldown, the cavity conditioning, which is the main part in the performance test, is done by monitoring the radiation level measured at three locations around the cryomodule, and the heating and RF output at two HOM (Higher Order Mode) couplers. Consequently, it became clear the average accelerating gradient is 30 MV/m for STF-2 cryomodule (39 MV/m at max. and 15 MV/m at min.), and the second cavity string with four cavities had the significant performance degradation by heavy field emission due to the additional clean room work in the STF tunnel. As the following next steps, there are the LFD (Lorenz Force Detuning) measurement, LFD compensation by piezo, and long run for check of stable operation at high gradient. In the long run around 32 MV/m, each cavity without degradation showed the stable operation with the successful LFD compensation by piezo and RF feedback system. In this paper, the detailed test result will be presented.
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WEPMB018	Multipactor Simulations in 650 MHz Superconducting Spoke Cavity for an Electron Accelerator	2161
	T. Kubo, T. Saeki KEK, Ibaraki, Japan E. Cenni CEA/IRFU, Gif-sur-Yvette, France R. Hajima, M. Sawamura JAEA, Ibaraki-ken, Japan H. Hokonohara, Y. Iwashita, H. Tongu Kyoto ICR, Uji, Kyoto, Japan
	Funding: The work is supported by Photon and Quantum Basic Research Coordinated Development Program from the Ministry of Education, Culture, Sports, Science and Technology, Japan. In order to realize a compact industrial-use X-ray source based on the laser-Compton scattering, a superconducting spoke cavity for an electron accelerator operated at 4K is under development. While the initially proposed operating frequency was 325MHz considering the 4K operation, we decided to start from the half scale model at 650MHz to accumulate our production experience of spoke cavity within our limited resources. In the present contribution, procedures and results of multipactor simulations for 650MHz spoke cavities are briefly introduced.
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WEPMB019	Magnetic Fields in Bulk, Film, and Multilayer Superconductors in Front of a Multi-turn Coil	2164
	T. Kubo KEK, Ibaraki, Japan
	Funding: JSPS Young Scientists(B) #26800157, JSPS Challenging Exploratory Research #26600142, MEXT Photon and Quantum Basic Research Coordinated Development Program The magnetic field distribution formulae in a bulk superconductor, a superconducting film, and an SIS multilayer structure in front of a multi-turn coil are derived, which may be useful for a detailed analysis in a vortex field measurement by using the third harmonic method. * See for example the invited oral presentation by T. Kubo, "Theory of multilayer coating for proof-of-concept experiments", at SRF2015 ** C.Z.Antoine et al., Appl. Phys. Lett. 102, 102603 (2013)
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WEPMB021	Construction of Measurement System for Superconducting Characteristics on Thin-film Samples at KEK	2167
	T. Saeki, H. Hayano, T. Kubo KEK, Ibaraki, Japan Y. Iwashita Kyoto ICR, Uji, Kyoto, Japan H. Oikawa Utsunomiya University, Utsunomiya, Japan
	We set up a measurement system for superconducting characteristics on thin-film samples at KEK. The system includes small-sized and middle-sized cryostats, where critical temperature, critical magnetic field, Residual Resistiviy Ratio (RRR), Superconducting RF (SRF) resistivity can be measured on thin-film samples. A small-sized cryostat has a compact refrigerator to cool down samples for the measurements of critical temperature and RRR. On the other had, we can cool down various setups with a middle-sized cryostat by using liquid helium. A thin-film sample is set into a mushroom cavity and the SRF characteristics of the thin-film sample can be measured. In another setup, a sample is set with a small coil and the third harmonic measurement is done on the sample around the critical temperature. Finally, a thin-film sample is set into the bore-center of superconducting magnet and the magnetization of sample is measured with external magnetic field around the critical temperature. This article presents the details of the system and some measurements of samples by the system.
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WEPMB023	Hydroforming SRF Three-cell Cavity from Seamless Niobium Tube	2170
	M. Yamanaka, T. Dohmae, H. Inoue, G.-T. Park, K. Umemori KEK, Ibaraki, Japan A. Hocker Fermilab, Batavia, Illinois, USA T. Tajima LANL, Los Alamos, New Mexico, USA
	We are developing the manufacturing method for superconducting radio frequency (SRF) cavities by using a hydroforming instead of using conventional electron beam welding. We expect higher reliability and reduced cost with hydroforming. For successful hydroforming, high-purity seamless niobium tubes with good formability as well as advancing the hydroforming technique are necessary. Using a seamless niobium tube from ATI Wah Chang, we were able to successfully hydroform a 1.3 GHz three-cell TESLA-like cavity and obtained an Eacc of 32 MV/m. A barrel polishing process was omitted after the hydroforming. The vertical test was carried out with very rough inside surface. We got amazing and interesting result.
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WEPMB024	Study on Nondestructive Inspections for Super-conducting Cavity	2174
	H. Tongu, H. Hokonohara, Y. Iwashita Kyoto ICR, Uji, Kyoto, Japan R. Hajima, M. Sawamura JAEA, Ibaraki-ken, Japan H. Hayano, T. Kubo, T. Saeki, Y. Yamamoto KEK, Ibaraki, Japan
	Funding: The work is supported by Photon and Quantum Basic Research Coordinated Development Program from the Ministry of Education, Culture, Sports, Science and Technology, Japan. We have been studying nondestructive inspections for super-conducting spoke cavities. The temperature mapping (T-map) and X-ray mapping (X-map) are powerful inspection methods to locate a hot spot during the vertical RF tests. There would be a defect under the hot spot and the defect may be the cause of a quench. Our XT-map system (a combined system of T-map and X-map) has a high resolution in space. Because the huge amount of sensor signals are multiplexed at a hi-speed scanning rate in the vicinity of the sensors, the small number of signal lines makes the installation process easy and reduces the system complexity. Our XT-map got useful results on finding a defect in vertical RF tests of International Linear collider super-conducting cavity. The XT-map system is useful as low cost nondestructive inspections for superconducting spoke cavity. The study will be reported. progresses will be reported.
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WEPMB025	Fabrication of Superconducting Spoke Cavity for Laser Compton Scattered Photon Sources	2177
	M. Sawamura, R. Hajima QST, Tokai, Japan H. Hokonohara, Y. Iwashita, H. Tongu Kyoto ICR, Uji, Kyoto, Japan T. Kubo, T. Saeki KEK, Ibaraki, Japan
	Funding: The work is supported by Photon and Quantum Basic Research Coordinated Development Program from the Ministry of Education, Culture, Sports, Science and Technology, Japan. 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 γ-ray sources in academic and industrial applications, we adopt the super-conducting spoke cavity to electron beam drivers. The spoke cavity has advantages such as relative compactness in comparison with an elliptical cavity of the same frequency, robustness with respect to manufacturing inaccuracy due to its strong cell-to-cell coupling, the better packing in a linac to install couplers on outer conductor. On the other hand the spoke cavity has disadvantage of more complicated structure than an elliptical cavity. Though our proposal design for the photon source consists of the 325 MHz spoke cavities in 4K operation, we have begun to fabricate the half scale model of 650 MHz spoke cavity in order to accumulate our cavity production experience by effective utilization of our limited resources. In this paper, we present our fabrication status.
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WEPMB026	MHI-MS's Production Activities of Superconducting Cavity	2180
	H. Hara, A. Miyamoto, K. Sennyu, T. Yanagisawa MHI-MS, Kobe, Japan E. Kako, T. Konomi, H. Nakai, K. Umemori KEK, Ibaraki, Japan
	Mitsubishi Heavy Industries Mechatronics Systems, Ltd. (MHI-MS), a subsidiary of MHI, took over MHI's accelerator business on October 1, 2015, and has been developing the business since that time. MHI-MS has developed manufacturing process of superconducting cavities continuously. In this presentation, recent progress will be reported.
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WEPMB028	High HOM Damping Structure Study for CEPC	2183
	Z.C. Liu, J. Gao, S. Jin, Y. Wang, H.J. Zheng IHEP, Beijing, People's Republic of China
	Both large circular collider such as CEPC and high current ERL facility need high HOM damping superconducting cavity. The slotted cavity is an option for such applications. It has three slotted waveguides which can highly damp the HOM and extract high HOM power out. However, the HOM absorbers for such facility are usually put outside of the cryomodule to decrease the influence of HOM power on the cryogenic system. Large slot waveguide need to make smaller transition structure to adapt this situation. A rectangular waveguide to coaxial waveguide structure was designed to the slotted cavity. In this paper, we will show the cavity HOM damping design scheme with this structure.
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WEPMB029	Research of Nitrogen Doping at IHEP	2186
	P. Sha Institute of High Energy Physics (IHEP), Chinese Academy of Sciences, Beijing, People's Republic of China J.P. Dai IHEP, Beijing, People's Republic of China F. Jiao PKU, Beijing, People's Republic of China
	Funding: Work funded by National Natural Science Foundation of China, Grant No. 11505197 Recently, nitrogen doping (N-doping) technology has been proved to increase Q0 of superconducting cavity obviously, which lowers the BCS surface resistance. After N-doping, Q0 of 9-cell 1.3 GHz cavity can be increased to 3*1010 at Eacc = 16 MV/m, while 1.5*1010 without N-doping [1]. Since 2013, there have been over 60 cavities nitrogen doped at FNAL, JLAB and Cornell. The Circular Electron Collider (CEPC) has been proposed by IHEP in China, while requests Q0=4e10@Eacc=15.5 MV/m for 650 MHz cavity. It's hard to achieve without N-doping. So research of N-doping was begun in cooperation with Peking University in early 2015. Experiments of niobium samples have showed that nitrogen concentration at niobium surface increased a lot after N-doping. After then, several single-cell 1.3 GHz cavities completed vertical tests, but there're no successful test results of Q0 increasing, yet.
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WEPMB030	Design Study of a Compact Deflecting Cavity at IHEP	2188
	J.P. Dai, B. Ni, J.Y. Zhai, J.R. Zhang IHEP, Beijing, People's Republic of China
	For the XFEL project proposed by IHEP, a sophisticated beam spreader is required to separate a single beam into multiple beams. One of the deflecting cavities used in the spreader has been investigated and optimized. It is a 325 MHz, compact RF-dipole superconducting cavity, with the transverse R/Q of 2900Ω, geometrical factor G of 88.5 Ω, and the Helium pressure sensitivity df/dp of 3.4 Hz/mbar. At the nominal deflecting voltage of 7MV, the peak electric field Epeak is 41 MV/m and peak magnetic field Bpeak is 48 mT. This paper will present the detailed RF and mechanical designs.
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WEPMB031	Post Processing of Spoke Type Superconducting Cavities at Institute of High Energy Physics	2191
	J. Dai, J.P. Dai, F.S. He, X. Huang, L.H. Li, Z.Q. Li, H.Y. Lin, Z.C. Liu, B. Ni, W.M. Pan, P. Sha, G.W. Wang, Q.Y. Wang, Z. Xue, X.Y. Zhang, G.Y. Zhao IHEP, Beijing, People's Republic of China
	Funding: Work supported by Chinese Academy of Science strategic Priority Research Program-Future Advanced Nuclear Fission Energy. After upgrading the post-processing system, several superconducting cavities were RF tested at Institute of High Energy Physics (IHEP) in China recently. The test results of 14 spoke 012 cavities and 6 spoke 021 cavities which used at China ADS injector I and linac all exceeds our design objective. Moreover, a spoke 040, a 650MHz elliptical cavity and a 325MHz HWR cavity are also vertical tested and the test results are all significantly surpass our design value. The post processing of these cavities including Buffered Chemical Polishing (BCP), high temperature heat treatment and High Pressure water Rinsing (HPR) is presented here. daijin@pku.edu.cn
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WEPMB032	Fabrication and Testing Status of IHEP03	2194
	T.X. Zhao, J. Gao, S. Jin, Z.Q. Li, Y.L. Liu, Z.C. Liu, Y. Wang, J.Y. Zhai, H.J. Zheng IHEP, Beijing, People's Republic of China M. Asano, E. Kako KEK, Ibaraki, Japan H. Yu, H. Yuan BIAM, Beijing, People's Republic of China
	After the successful development of the IHEP01 and IHEP02 1.3GHz 9cell superconducting cavity, we developed a 1.3GHz Tesla-Like 9cell superconducting cavities in collaboration with KEK. The cavity was made by niobium material produced in OTIC, Ningxia, China. After completeing welding, leakage check, BCP, HPR, we sent the cavity to KEK and used the standard procedures of ILC cavity for processing. These include electron polishing, vacuum furnace outgassing, tuning for field flatness and frequency, light EP, baking and vertical test. We target to have a high Q0 cavity for this experiment. In this paper, we will report the experimental status of the IHEP03 cavity.
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WEPMB034	Analysis of Niobium Quality Control for SRF Cavity	2197
	M.J. Joung IBS, Daejeon, Republic of Korea
	Funding: the Ministry of Science, ICT and Future Planning (MSIP) and the National Research Foundation (NRF) of the Republic of Korea under Contract 2013M7A1A1075764. Clean and smooth surface is important to get low sur-face resistance for superconducting material. SRF (Super-conducting Radio Frequency) cavity made of niobium which is superconducting material and also one of the rare metal. The procedure of niobium quality control was set up to get high performance SRF cavity. The procedure consists of three parts; certificates check, Nb specification verification, and surface inspection and measurements of thickness, roughness, flatness. Three important properties which are RRR value, chemical composition and me-chanical properties were verified to conform Nb specifica-tion. The range of thickness, roughness and flatness for niobium as SRF cavity raw material were obtained by measurement.
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WEPMB035	SRF Cavities for RAON	2200
	H.C. Jung, J. Joo, J. Lee IBS, Daejeon, Republic of Korea R.E. Laxdal, Z.Y. Yao TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada
	SRF cavities of superconducting linear accelerators in RAON are developed and tested at 2K/4K. 1st Quarter Wave Resonator (QWR) and Half Wave Resonator (HWR) are fabricated by a domestic vender and tested in the TRIUMF's facility. The measured Q factors are above the required values at the operating gradients. And the predicted multipacting phenomena are observed in the test and easily conditioned. The Q factors decreased after a slow cooldown and enhanced at 4K tests by a low temperature baking. Based on these tests, modified bare cavities are newly developed, jacketed and will be tested with tuners and power couplers.
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WEPMB036	High Pressure Rinsing for Niobium Superconducting Cavity	2202
	Y. Jung, M.J. Joung, M. Lee IBS, Daejeon, Republic of Korea J. Lee, J. Seo Vitzrotech Co., Ltd., Ansan City, Kyunggi-Do, Republic of Korea
	Niobium superconducting cavity is treated with high pressure rinsing to clean the inner surface of the cavity. Either organic or inorganic residues on the inner surface of the cavity can cause serious problems during the cavity operation. A thermal quenching - superconducting material loses its superconductivity - is a typical phenomenon brought out by harmful defects by increasing critical temperature. We have performed high pressure rinsing experiments to check out a prototype HPR machine. HPR experiments were performed with a simplified cavity structure, and analyzed as a function of the pressure, the distance from a nozzle, and the sizes of defects on the niobium surface. In this presentation, we will discuss the performance of the prototype HPR machine.
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WEPMB039	Operation Techniques for HWR1 Cryomodule	2205
	H. Kim, J.W. Choi, Y.W. Jo, W.K. Kim, Y. Kim, M. Lee IBS, Daejeon, Republic of Korea
	Control systems such as PLC and EPICS are developed for a half-wave resonator (HWR) cryomodule. PLC rack is fabricated for the HWR1 cryomodule. The PLC controls pumps, heaters and valves. The PLC communicates with temperature monitors through Ethernet. HMI of PLC and EPICS controls and monitors pumps, heaters, valves and temperature sensors through switching hub. The PLC HMI is developed and EPICS is also developed. The CSS of EPICS consists of control, monitor, parameter set-up, alarm and data browser screen.
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WEPMB041	Design of RF Power Coupler for RISP Half Wave Resonator	2208
	S. Lee, E.-S. Kim Korea University Sejong Campus, Sejong, Republic of Korea I. Shin IBS, Daejeon, Republic of Korea
	RF power couplers for half wave resonators are under development for the Rare Isotope Science Project (RISP) in Korea. It is required to deliver up to 6 kW RF power at 162.5 MHz to the HWR in CW mode. The RF coupler is a coaxial capacitive type using a disc type ceramic window. Design studies of 2nd prototype HWR RF coupler are presented.
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WEPMB044	Development of RF Conditioning System for RISP RF Power Couplers	2211
	C.K. Sung, E.-S. Kim Korea University Sejong Campus, Sejong, Republic of Korea S. Lee, I. Shin IBS, Daejeon, Republic of Korea
	RF power coupler prototypes have been conditioned for a heavy ion accelerator of the Rare Isotope Science Project (RISP) in Korea. The RF couplers operate for 162.5 MHz half-wave resonators at 6 kW RF power. The RF couplers are a 50-Ohm coaxial structure with a disk type ceramic window at room temperature. The control system using Labview software supported automatic process for RF conditioning, data acquisition and interlock system. The conditioning system and the result of conditioning of RF coupler are presented in this paper.
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WEPMB045	Measurement of Higher Order Modes Electrodynamic Characteristics for Array of Two 2400 MHz Cavities	2214
	Ya.V. Shashkov, R.V. Donetskiy, M.V. Lalayan, N.P. Sobenin MEPhI, Moscow, Russia A. Orlov NRNU, Moscow, Russia
	Funding: *Work supported by Ministry of Education and Science grant 3.245.2014/r and the EU FP7 HiLumi LHC ' Grant Agreement 284404 In the frameworks of the High Luminosity Large hadron collider (HL-LHC) upgrade program an application of additional superconducting harmonic cavities operating at 800 MHz is currently under discussion. As a candidate, the two cavities with grooved beam pipes connected by the drift tube were suggested. In this article of measurements of Qload are performed for the aluminum model of array of two cavities connected by drift tube. Field distribution of Fundamental Mode (FM) and Higher Order Modes (HOM) were measured for aluminum prototype with a frequency of the operational mode of 2400 MHz, and their comparison with the simulation results. Higher order modes
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WEPMB047	Higher Order Modes Couplers for 800 MHz Harmonic Cavity	2217
	Ya.V. Shashkov, R.V. Donetskiy, M. Gusarova, N.P. Sobenin MEPhI, Moscow, Russia
	Funding: *Work supported by Ministry of Education and Science grant 3.245.2014/r For the higher order modes damping (HOM) in the 800 MHz superconducting single cell cavity the HOM coupler was developed. Several versions of the coupler design were shown. For the chain of two cavities with couplers the calculations of external Q-factor are presented. The calculations of multipactor discharge of cavity were also conducted. Higher order modes, Tesla, couplers
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WEPMB048	Macros for Identification of Higher Order Modes Types, Their Transverse Shunt Impedance and Kick Factor	2220
	Ya.V. Shashkov MEPhI, Moscow, Russia A. Orlov NRNU, Moscow, Russia
	Funding: *Work supported by Ministry of Education and Science grant 3.245.2014/r During the design studies of accelerating cavities one of the most time-consuming tasks is classification of the higher order modes (HOM) types. To automate the process of identification of HOM types special macros for CST Microwave studio was written. This article describes the programs algorithm of mode recognition and the results of the analysis on the example of single cell and 9 cell cavities. Macros for the calculation of the HOM transverse shunt impedance upon Q-factor values and kick-factor was also written. Higher order modes, electrodynamic characteristics, macros
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WEPMB050	RF Test of ESS Superconducting Spoke Cavities at Uppsala University	2227
	H. Li, A.K. Bhattacharyya, V.A. Goryashko, L. Hermansson, R.J.M.Y. Ruber, R. Santiago Kern Uppsala University, Uppsala, Sweden N. Gandolfo, G. Olry IPN, Orsay, France
	The European Spallation Source (ESS) is an accelerator-driven neutron spallation source built in Sweden. It will deliver the first protons to a rotating tungsten target by 2019 and will reach the full 5 MW average beam power in the following years. The superconducting Spoke cavities are considered compact structures at low frequencies and having an excellent RF performance in both low and medium velocity regimes, therefore ESS will include a total of 26 double-spoke cavities. The testing of the double-spoke prototype cavity at high power has been conceded to Uppsala University, Sweden, where the Facility for Research Instrumentation and Accelerator development (FREIA) has been equipped with superconducting cavity test facility. A bare spoke cavity has been tested at the FREIA Laboratory with a self-exited loop at low power level to confirm its vertical test performance at IPNO. Similar test results as IPNO's previous test were obtained with FREIA system. In this paper we present the methods and preliminary study results of the cavity performance.
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WEPMB051	HIE-ISOLDE: First Commissioning Experience	2230
	W. Venturini Delsolaro, E. Bravin, N. Delruelle, M. Elias, J.A. Ferreira Somoza, M.A. Fraser, J. Gayde, Y. Kadi, G. Kautzmann, F. Klumb, Y. Leclercq, M. Martino, V. Parma, J.A. Rodriguez, S. Sadovich, E. Siesling, D. Smekens, L. Valdarno, D. Valuch, P. Zhang CERN, Geneva, Switzerland
	The HIE ISOLDE project [1] reached a major milestone in October 2015, with the start of the first physics run with radioactive ion beams. This achievement was the culminating point of intense months during which the first cryomodule of the HIE ISOLDE superconducting Linac and its high-energy beam transfer lines were first installed and subsequently brought into operation. Hardware commissioning campaigns were conducted in order to define the envelope of parameters within which the machine could be operated, to test and validate software and controls, and to investigate the limitations preventing the systems to reach their design performance. Methods and main results of the first commissioning of HIE ISOLDE post accelerator, including the performance of the superconducting cavities with beam, will be reviewed in this contribution.
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WEPMB052	System Integration and Beam Commissioning of the 500-MHz RF Systems for Taiwan Photon Source	2234
	Ch. Wang, L.-H. Chang, M.H. Chang, C.-T. Chen, L.J. Chen, F.-T. Chung, M.-C. Lin, Z.K. Liu, C.H. Lo, G.-H. Luo, C.L. Tsai, H.H. Tsai, M.H. Tsai, M.-S. Yeh, T.-C. Yu NSRRC, Hsinchu, Taiwan
	The accelerator complex of the Taiwan Photon Source (TPS) consists of two 500-MHz RF systems: one RF system with two KEKB-type single-cell SRF modules is operated for the 3-GeV storage ring of circumference 518 m, and the other with one five-cell Petra cavity at room temperature is for the concentric full-energy booster synchrotron. This report overviews the installation, system integration, commissioning, and initial operation of the 500-MHz RF systems for the TPS with emphasis on our solution to approach the highly reliable SRF operation at its maximum design beam current of 500-mA. Lessons learned during the project are reviewed.
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WEPMB056	CVD Deposition of Nb Based Materials for SRF Cavities	2241
	P. Pizzol, P. Chalker, T. Heil The University of Liverpool, Liverpool, United Kingdom O.B. Malyshev, S.M. Pattalwar, R. Valizadeh STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom G.B.G. Stenning STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom
	Bulk niobium cavities are widely employed in particle accelerators to create high accelerating gradient despite their high material and operation cost. Advancements in technology have taken bulk niobium close to its theoretical operational limits, pushing the research to explore novel materials, such as niobium based alloys. Nitrides of niobium offer such an alternative, exhibiting a higher Tc compared to bulk niobium. Replacing then the niobium with a material with better thermal conductivity, such as copper, coated with thin films of nitrides in a multilayer S-I-S would lead to improved performance at reduced cost. Physical vapour deposition (PVD) is currently used to produce these coatings, but it suffers from lack of conformity. This issue can be resolved by using chemical vapour deposition (CVD), which is able to produce high quality coatings over surfaces with a high aspect ratio. This project explores the use of CVD techniques to deposit NbN thin films starting from their chlorinated precursors. The samples obtained are characterized via SEM, FIB, XRD, and EDX.
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WEPMB057	First Results of Magnetic Field Penetration Measurements on Multilayer S-I-S Structures	2245
	O.B. Malyshev, K.D. Dumbell, L. Gurran, N. Pattalwar, S.M. Pattalwar, R. Valizadeh STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom A.V. Gurevich ODU, Norfolk, Virginia, USA L. Gurran Lancaster University, Lancaster, United Kingdom L. Gurran Cockcroft Institute, Lancaster University, Lancaster, United Kingdom O.B. Malyshev, S.M. Pattalwar, R. Valizadeh Cockcroft Institute, Warrington, Cheshire, United Kingdom
	The performance of superconducting RF cavities made of bulk Nb is limited by a breakdown field of Bp=~200 mT, close to the superheating field for Nb. A potentially promising solution to enhance the breakdown field of the SRF cavities beyond the intrinsic limits of Nb is a multilayer coating suggested in [1]. In the simplest case, such a multilayer may be a superconductor-insulator-superconductor (S-I-S) coating, for example, bulk niobium (S) coated with a thin film of insulator (I) followed by a thin layer of another superconductor (S) which could be e.g. dirty niobium [2]. Here we report the first results of our measurements of field penetration in Nb thin films and Nb-AlN-Nb multilayer samples at 4.2 K using the magnetic field penetration facility designed, built and tested in ASTeC.
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WEPMB058	LHC Crab Cavity Coupler Test Boxes	2248
	J.A. Mitchell Lancaster University, Lancaster, United Kingdom R. Apsimon, G. Burt, A.R.J. Tutte Cockcroft Institute, Lancaster University, Lancaster, United Kingdom R. Calaga, A. Macpherson, E. Montesinos CERN, Geneva, Switzerland S.D. Silva ODU, Norfolk, Virginia, USA B. P. Xiao BNL, Upton, Long Island, New York, USA
	The LHC double quarter wave (DQW) crab cavities have two different types of Higher Order Mode (HOM) couplers in addition to a fundamental power coupler (FPC). The FPC requires conditioning, so to achieve this we have designed a radio-frequency (RF) quarter wave resonator to provide high transmission between two opposing FPCs. For the HOM couplers we must ensure that the stop-band filter is positioned at the cavity frequency and that peak transmission occurs at the same frequencies as the strongest HOMs. We have designed two test boxes which preserve the cavity spectral response in order to test the couplers.
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WEPMB060	Modifications to the Pump Out Box to Lower the Qext of Diamond SCRF Cavities	2251
	S.A. Pande, C. Christou, P. Gu DLS, Oxfordshire, United Kingdom G. Burt Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
	Diamond's CESR-B cavities are iris coupled and have fixed Qext. For reliability, the cavities are operated at lower voltages. This results in the optimum condition for beam loading being satisfied at a much lower power typically about 100 kW. For operation at 300 mA with two cavities, the RF power needed per system exceeds 200 kW. Consequently, the cavities need to be operated under-coupled. To lower the Qext and move the optimum operating point nearer to 200kW, 3 stub tuners are used in the waveguide feed line. The difference in the height of the coupling waveguide on cavity and that of the vacuum side waveguide on the window assembly results in a step transition which affects the Qext. The present window/step location results in Qext higher than that without the window. The Qext can be lowered by re-locating the RF window or by shifting the step change in the waveguide cross-section from its present location. This needs modification to the Pump Out box. The pros and cons of the proposed modification to the pump out box in terms of standing waves and multipacting characteristics studied with CST Studio are discussed in this paper.
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WEPMR002	Ultimate Gradient Limitation in Niobium Superconducting Accelerating Cavities	2254
SUPSS091	use link to see paper's listing under its alternate paper code
	M. Checchin, A. Grassellino, M. Martinello, S. Posen, A. Romanenko Fermilab, Batavia, Illinois, USA M. Checchin, M. Martinello Illinois Institute of Technology, Chicago, Illlinois, USA J. Zasadzinski IIT, Chicago, Illinois, USA
	Funding: Fermilab is operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy. The present study is addressed to the theoretical description of the ultimate gradient limitation in SRF cavities. Our intent is to exploit experimental data to confirm models which provide feed-backs on how to improve the current state-of-art. New theoretical insight on the cavities limiting factor can be suitable to improve the quench field of N-doped cavities, and therefore to take advantage of high Q0 at high gradients.
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WEPMR003	Tailoring Surface Impurity Content to Maximize Q-factors of Superconducting Resonators	2258
SUPSS094	use link to see paper's listing under its alternate paper code
	M. Martinello, M. Checchin, A. Grassellino, O.S. Melnychuk, S. Posen, A. Romanenko, D.A. Sergatskov Fermilab, Batavia, Illinois, USA M. Checchin, M. Martinello Illinois Institute of Technology, Chicago, Illlinois, USA J. Zasadzinski IIT, Chicago, Illinois, USA
	Funding: Fermilab is operated by Fermi Research Alliance, LLC under contract No. DE-AC02-07CH11359 with the United States Department of Energy. Quality factor of superconducting radio-frequency (SRF) cavities is degraded whenever magnetic flux is trapped in the cavity walls during the cooldown. In this contribution we study how the trapped flux sensitivity, defined as the trapped flux surface resistance normalized for the amount of flux trapped, depends on the mean free path. A variety of 1.3 GHz cavities with different surface treatments (EP, 120 C bake and different N-doping) were studied in order to cover the largest range of mean free path nowadays achievable, from few to thousands of nanometers. A bell shaped trend appears for the range of mean free path studied. Over doped cavities falls at the maximum of this curve defining the largest values of sensitivity. In addition, we have also studied the trend of the BCS surface resistance contribution as a function of mean free path, revealing that N-doped cavities follow close to the theoretical minimum of the BCS surface resistance as a function of the mean free path. Adding these results together we unveil that optimal N-doping treatment allows to maximize Q-factor at 2 K and 16 MV/m until the magnetic field fully trapped during the cavity cooldown stays below 10 mG.
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WEPMR004	Cryomdoule Test Stand Reduced-Magnetic Support Design at Fermilab	2262
	M.W. McGee, S.K. Chandrasekaran, A.C. Crawford, E.R. Harms, J.R. Leibfritz, G. Wu Fermilab, Batavia, Illinois, USA
	Funding: Operated by Fermi Research Alliance, LLC, under Contract No. DE-AC02- 07CH11359 with the U.S. Department of Energy In a partnership with SLAC National Accelerator Laboratory (SLAC) and Jefferson Lab, Fermilab will assemble and test 17 of the 35 total 1.3 GHz cryomodules for the Linac Coherent Light Source II (LCLS-II) Project. These devices will be tested at Fermilab's Cryomodule Test Facility (CMTF) within the Cryomodule Test Stand (CMTS-1) cave. The problem of magnetic pollution became one of major issues during design stage of the LCLS-II cryomodule as the average quality factor of the accelerating cavities is specified to be 2.7 x 1010. One of the possible ways to mitigate the effect of stray magnetic fields and to keep it below the goal of 5 mGauss involves the application of low permeable materials. Initial permeability and magnetic measurement studies regarding the use of 316L stainless steel material indicated that cold work (machining) and heat affected zones from welding would be acceptable.
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WEPMR005	Investigation of Thermal Acoustic Effects on SRF Cavities within CM1 at Fermilab	2265
	M.W. McGee, E.R. Harms, A.L. Klebaner, J.R. Leibfritz, A. Martinez, Y.M. Pischalnikov, W. Schappert Fermilab, Batavia, Illinois, USA
	Funding: Operated by Fermi Research Alliance, LLC, under Contract No. DE-AC02- 07CH11359 with the U.S. Department of Energy. Two TESLA-style 8-cavity cryomodules have been operated at Fermilab Accelerator Science and Technology (FAST), formerly the Superconducting Radio Frequency (SRF) Accelerator Test Facility. Operational instabilities were revealed during Radio Frequency (RF) power studies. These observations were complemented by the characterization of thermal acoustic effects on cavity microphonics manifested by apparent noisy boiling of helium involving vapor bubble and liquid vibration. The thermal acoustic measurements also consider pressure and temperature spikes which drive the phenomenon at low and high frequencies.
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WEPMR006	Transport of LCLS-II 1.3 GHz Cryomodule to SLAC	2268
	M.W. McGee, T.T. Arkan, T.J. Peterson, Z. Tang Fermilab, Batavia, Illinois, USA S.R. Boo, M. Carrasco SLAC, Menlo Park, California, USA E. Daly, N.A. Huque JLab, Newport News, Virginia, USA
	Funding: Operated by Fermi Research Alliance, LLC, under Contract No. DE-AC02- 07CH11359 with the U.S. Department of Energy. In a partnership with SLAC National Accelerator Laboratory (SLAC) and Jefferson Lab, Fermilab will assemble and test 17 of the 35 total 1.3 GHz cryomodules for the Linac Coherent Light Source II (LCLS-II) Project. These include a prototype built and delivered by each Lab. Another two 3.9 GHz cryomodules will be built, tested and transported by Fermilab to SLAC. Each assembly will be transported over-the-road from Fermilab or Jefferson Lab using specific routes to SLAC. The transport system consists of a base frame, isolation fixture and upper protective truss. The strongback cryomodule lifting fixture is described along with other supporting equipment used for both over-the-road transport and local (on-site) transport at Fermilab. Initially, analysis of fragile components and stability studies will be performed in order to assess the risk associated with over-the-road transport of a fully assembled cryomodule.
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WEPMR009	Magnetic Flux Expulsion Studies in Niobium SRF Cavities	2277
	S. Posen, M. Checchin, A.C. Crawford, A. Grassellino, M. Martinello, O.S. Melnychuk, A. Romanenko, D.A. Sergatskov, Y. Trenikhina Fermilab, Batavia, Illinois, USA
	With the recent discovery of nitrogen doping treatment for SRF cavities, ultra-high quality factors at medium accelerating fields are regularly achieved in vertical RF tests. To preserve these quality factors into the cryomodule, it is important to consider background magnetic fields, which can become trapped in the surface of the cavity during cooldown and cause Q0 degradation. Building on the recent discovery that spatial thermal gradients during cooldown can significantly improve expulsion of magnetic flux, a detailed study was performed of flux expulsion on two cavities with different furnace treatments that are cooled in magnetic fields amplitudes representative of what is expected in a realistic cryomodule. In this contribution, we summarize these cavity results, in order to improve understanding of the impact of flux expulsion on cavity performance.
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WEPMR011	Simulations and Experimental Studies of Third Harmonic 3.9 Ghz CW Couplers for LCLS-II Project	2280
	N. Solyak, I.V. Gonin, E.R. Harms, S. Kazakov, T.N. Khabiboulline, A. Lunin Fermilab, Batavia, Illinois, USA
	LCLS-II linac is based on SRF technology developed for the XFEL project. The XFEL 3rd harmonic system built by INFN is based on the original designs of cavity and power coupler developed and built by Fermilab for the FLASH facility at DESY. For LCLS-II application both designs of the 3.9 GHz cavity and the power coupler have been modified for an operation in the continuous wave regime up to 2 kW average RF power. In this paper we discuss coupler modifications and the result multiphysics analysis for various operating regimes. For the initial test of a proposed design, we decided to modify two spare warm sections of power couplers, built for the FLASH facility, by shortening both of two inner bellows and making a thicker copper plating. Modification of the existing coupler test stand and the test program are briefly discussed in this paper.
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WEPMR013	Study of LCLS-II Fundamental Power Coupler Heating in HTS Integrated Cavity Tests	2286
	N. Solyak, I.V. Gonin, A. Grassellino, C.J. Grimm, T.N. Khabiboulline, J.P. Ozelis, K. Premo, O.V. Prokofiev, D.A. Sergatskov, G. Wu Fermilab, Batavia, Illinois, USA
	LCLS-II coupler based on modified design of TTF3 coupler for higher average power was assembled on high Q cavity and tested at HTS as part of integrated cavity test program. Couplers were thermally connected to thermal shields and equipped with diagnostics to control temperature in different locations and provide information about cryogenic heat loads at 2 K, 5 K and 80 K.Three dressed cavities with power couplers were tested in HTS at full specified RF power. Results are summarized in this paper and cross-checked with simulation.
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WEPMR014	RF Design of a High Average Beam-Power SRF Electron Source	2289
	N. Sipahi, S. Biedron, S.V. Milton CSU, Fort Collins, Colorado, USA I.V. Gonin, R.D. Kephart, T.N. Khabiboulline, V.P. Yakovlev Fermilab, Batavia, Illinois, USA
	There is a significant interest in developing high-average power electron sources, particularly in the area of electron sources integrated with Superconducting Radio Frequency (SRF) systems. For these systems, the electron gun and cathode parts are critical components for stable intensity and high-average powers. In this initial design study, we will present the design of a 9-cell accelerator cavity having a frequency of 1.3 GHz and the corresponding field optimization studies.
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WEPMR015	Surface Topography Techniques at Cornell University: Optical Inspection and Surface Replica	2292
	G.M. Ge, F. Furuta, D. Gonnella, D.L. Hall, G.H. Hoffstaetter, M. Liepe, T.I. O'Connell, J. Sears Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Surface imperfections significantly limit the performance of superconducting radio frequency (SRF) cavities. The development of surface topography techniques aims to locate the surface flaws in an SRF cavity and profile their geometry details. This effort plays an important role of quality control in cavity productions as well as provides contour information of the defects for understanding quench mechanisms. The surface topography techniques at Cornell University include an optical inspection system and surface replica technique. In this paper, we present the details of the techniques and show features found in the SRF cavities at Cornell.
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WEPMR016	Vertical Electropolishing Studies at Cornell with KEK and Marui	2295
	F. Furuta, G.M. Ge, T. Gruber, J.J. Kaufman, J. Sears Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA V. Chouhan, Y.I. Ida, K.N. Nii, T.Y. Yamaguchi MGH, Hyogo-ken, Japan H. Hayano, S. Kato, T. Saeki KEK, Ibaraki, Japan
	Cornell's SRF group has developed Vertical Electro-Polishing (VEP) and applied on 1.3GHz Niobium SRF cavities as the primary surface treatment. High-Q and high voltage performances of VEP'ed SRF cavities had been successfully demonstrated at Cornell. In 2014, new VEP R&D collaboration has started between Cornell, KEK, and Marui Galvanizing Co. Ltd. (MGI). MGI and KEK has developed their original VEP cathode named 'i-cathode Ninja'® which has four retractable wing-shape parts per cell for single-/9-cell cavities. We will report the results of VEP process using 'i-cathode Ninja'® on single cell cavity at Cornell.
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WEPMR018	Time Resolved Cryogenic Cooling Analysis of the Cornell Injector Cryomodule	2298
	R.G. Eichhorn, A.C. Bartnik, B.M. Dunham, G.M. Ge, G.H. Hoffstaetter, H. Lee, M. Liepe, S.R. Markham, T.I. O'Connell, P. Quigley, D.M. Sabol, J. Sears, E.N. Smith, V. Veshcherevich Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	To demonstrate key parameters of a an energy recovery linac (ERL) at Cornel, an injector based on a photo gun and an SRF cryomodule was designed and built. The goal was to demonstrate high current generation while achieving low emittances. While the emittance goal has been reached, the current achieved so far is 75 mA. Even though this is a world record, it is still below the targeted 100 mA. While ramping up the current we observed excessive heating in the fundamental power coupler which we were able to track down to insufficient cooling of the 80 K intercepts. These intercepts are cooled by a stream of parallel cryogenic flows which we found to be unbalanced. In this paper we will review the finding, describe the analysis we did, modeling of the parallel flow and the modifications made to the module to overcome the heating.
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WEPMR019	Development of Plasma Cleaning at Cornell University	2302
	G.M. Ge, F. Furuta, M. Liepe, V. Veshcherevich Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Cornell University is developing the plasma cleaning technology as an alternative cleaning technique for SRF cavity surface preparation. In experiments, we successfully ignited the plasma in a single-cell SRF cavity. However the experiments were limited by the peak electric-fields in the RF coupler. In this paper, we show the analysis of the limitation and propose a new design of the coupler which can eliminate the limitation.
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WEPMR020	First Cool-down of the Cornell ERL Main Linac Cryo-Module	2305
	R.G. Eichhorn, J.V. Conway, F. Furuta, G.M. Ge, D. Gonnella, T. Gruber, G.H. Hoffstaetter, J.J. Kaufman, M. Liepe, T.I. O'Connell, P. Quigley, D.M. Sabol, J. Sears, E.N. Smith, V. Veshcherevich Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Cornell University has finished building a 10 m long superconducting accelerator module as a prototype of the main linac of a proposed ERL facility. This module houses 6 superconducting cavities- operated at 1.8 K in continuous wave (CW) mode with a design field of 16 MV/m and a Quality factor of 2x1010. We wil shortly review the design and focus on reporting on the first cool-down of this module. We will giving data for various cool-down scenarios (fast/ slow), uniformity and performance
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WEPMR023	Surface Analysis Studies of Nb3Sn Thin Films	2316
	D.L. Hall, J.J. Kaufman, M. Liepe, J.T. Maniscalco Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	A recent study to optimise the coating of thin-film Nb3Sn cavities has resulted in coating procedures that can fabricate 1.3 GHz cavities capable of reproducibly achieving fields of >16 MV/m with record high Qs >1010 at 4.2 K. However, the performance of these next generation SRF cavities is as yet well below the theoretical maximum performance expected of Nb3Sn, thus giving ample room for further advancements. Current measurements strongly suggest that the current limits are due to local defects and irregularities in the coated surface. In this paper we analyse, using methods including SEM/EDS, TEM, XRD and EBSD, the surface of both sample coupons and cavity cut-outs, with a view to identifying and understanding the origin of surface non-uniformities that would lead to increased surface resistance and cavity quench.
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WEPMR024	RF Measurements on High Performance Nb3Sn Cavities	2320
SUPSS092	use link to see paper's listing under its alternate paper code
	D.L. Hall, M. Liepe, J.T. Maniscalco Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	A single-cell 1.3 GHz ILC-shape thin-film Nb3Sn-on-Nb cavity recently achieved accelerating gradients of >16 MV/m with a record Q0 of approx. 2·1010 at 4.2 K, exceeding the power efficiency seen in the current most efficient niobium cavities. A concurrent study of the coating process has resulted in a coating procedure that is capable of replicating this performance in other single-cell cavities. In this paper we demonstrate the RF performance and behaviour of these next generation SRF cavities, with an emphasis on both the impact from both external magnetic fields and the cavity cool down procedure on cavity performance.
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WEPMR025	Improved N-Doping Protocols for SRF Cavities	2323
	D. Gonnella, R.G. Eichhorn, F. Furuta, G.M. Ge, T. Gruber, G.H. Hoffstaetter, J.J. Kaufman, P.N. Koufalis, M. Liepe, J.T. Maniscalco Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: NSF, DOE Nitrogen-doping has been shown to consistently produce better quality factors in SRF cavities than is achievable with standard preparation techniques. Unfortunately, nitrogen-doping typically brings with it lower quench fields and higher sensitivities of residual resistance to trapped magnetic flux. Here we present work to understand these effects in hopes of mitigating them while maintaining the high Q desired by future projects. Using a nitrogen diffusion simulation, material parameters of nitrogen-doped cavities can be predicted prior to doping. These simulations results are consistent with SIMS data taken from samples treated with cavities. The nature of doping's effect on quench field has also been studied using CW and pulsed measurements. These results have allowed us to better understand the nature of nitrogen-doping and its effect on cavity performance.
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WEPMR026	RF Losses from Trapped Flux in SRF Cavities	2327
	D. Gonnella, J.J. Kaufman, P.N. Koufalis, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: NSF Previous measurements at Cornell have shown that the sensitivity of residual resistance to trapped magnetic field in SRF cavities is heavily dependent on the mean free path of the RF penetration layer of the niobium. Here we report on a systematic study of ten cavity preparations with different mean free paths and the effect of these preparations on sensitivity to trapped magnetic flux. In the clean limit, longer mean free path leads to a lower sensitivity to trapped magnetic flux while in the dirty limit the opposite is true, shorter mean free path leads to lower sensitivity. These results are also shown to be in good agreement with theoretical predictions of RF losses due to oscillations of vortex lines.
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WEPMR027	Dependence of Surface Resistance on N-Doping Level	2331
	D. Gonnella, F. Furuta, G.M. Ge, J.J. Kaufman, P.N. Koufalis, M. Liepe, J.T. Maniscalco Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: NSF, DOE Nitrogen-doping has become a standard tool for reaching high quality factors in SRF cavities in the medium field region at 2 K. This high Q has been shown to be a result of lowering of the temperature dependent BCS resistance. Here we show that this lowering of the BCS resistance is due to interstitial nitrogen in the niobium lowering the mean free path. The BCS resistance extracted from experimental data is shown to be consistent with theoretical predictions from BCS theory; that there is an optimal doping of which the mean free path is lowered to about half the intrinsic coherence length. These results provide insight into understanding the mechanisms behind nitrogen-doping and allow us to more accurately predict doping parameters to reach optimal cavity performance.
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WEPMR028	Studies on the Field Dependence of the BCS Surface Resistance	2335
SUPSS116	use link to see paper's listing under its alternate paper code
	J.T. Maniscalco, D. Gonnella, G.H. Hoffstaetter, P.N. Koufalis, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Experiments have shown that the temperature-dependent portion of the RF surface resistance of SRF materials also exhibits a dependence on the magnitude of the surface field, manifested as a "Q-slope" or "anti-Q-slope" in the medium field region. Recent theoretical work proposes an explanation of the anti-Q-slope in dirty-limit superconductors. In this report, we compare theoretical predictions with the results of systematic experimental studies on the RF field dependence of the surface resistance using 1.3 GHz niobium SRF cavities with a wide range of mean free paths. We find very good agreement between theory and experiment in the dirty limit, with some divergence as the cavities approach the clean limit.
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WEPMR029	New Material Studies in the Cornell Sample Host Cavity	2338
	J.T. Maniscalco, D.L. Hall, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA O.B. Malyshev, R. Valizadeh, S. Wilde STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom S. Wilde Loughborough University, Loughborough, Leicestershire, United Kingdom
	Cornell has developed a TE mode sample host microwave cavity in order to study large, flat samples of novel SRF materials. In recent calibration tests, the cavity was shown to reach peak magnetic fields on the sample plate of >100 mT and a quality factor Q0 greater than 1010, making it a powerful system to study the performance of superconductors at high RF fields with nOhms sensitivity. In this report we present results of measurements of two samples of thin-film Nb deposited on Cu using HiPIMS at 500 C and at 800 C.
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WEPMR030	Pulsed Field Limits in SRF Cavities	2341
	J.T. Maniscalco, D. Gonnella, D.L. Hall, P.N. Koufalis, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	High-power pulsed (HPP) measurements of SRF cavities offer several different avenues of experimentation from standard continuous wave (CW) measurements by probing higher fields and reducing thermal effects. In this paper we report upon recent measurements of N-doped Nb and Nb3Sn cavities, investigating the limitations of the superheating field, flux entry field, and other maximum fields. We also investigate the potential of these materials for operation in a pulsed accelerator, which would partially or fully mitigate the effects of defects (i.e. thermal quenches).
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WEPMR033	Observation of Stable Low Surface Resistance in Large-Grain Niobium SRF Cavities	2344
	R.L. Geng JLab, Newport News, Virginia, USA S.C. Huang IMP/CAS, Lanzhou, People's Republic of China
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. Low surface resistance, or high unloaded quality factor (Q0), superconducting radio frequency (SRF) cavities are being pursued actively nowadays as their application in large-scale CW SRF accelerators can save capital and operational cost in cryogenics. There are different options in realization of such cavities. One of them is the large-grain (LG) niobium cavity. In this contribution, we present new experimental results in evaluation of LG niobium cavities cooled down in the presence of an external magnetic field. High Q0 values are achieved even with an ambient magnetic field of up to 100 mG. More over, it is observed that these high Q0 values are super-robust against repeated quench, literally not affected at all after the cavity being deliberately quenched for hundreds of times in the presence of an ambient magnetic field of up to 200 mG.
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WEPMR034	Analyses of 476 MHz and 952 MHz Crab Cavities for JLAB Electron Ion Collider	2348
SUPSS095	use link to see paper's listing under its alternate paper code
	H. Park, A. Castilla, S.U. De Silva, J.R. Delayen ODU, Norfolk, Virginia, USA V.S. Morozov JLab, Newport News, Virginia, USA
	Center for Accelerator Science at ODU has designed, fabricated and successfully tested a crab cavity for MEIC at Jefferson Lab*. This proof of principle cavity was based on the earlier MEIC design which used 748.5 MHz RF system. The updated MEIC design** utilizes the components from PEP-II. It results in the change on the bunch repetition rate of stored beam to 476.3 MHz. The ion ring collider will eventually require 952.6 MHz crab cavity. This paper will present the analyses of crab cavities of both 476 MHz and 952 MHz options. It compares advantages and disadvantages of the options which provides the MEIC design team important technical information for a system down selection. * Cryogenic Test of a 750 MHz Superconducting RF Dipole Crabbing Cavity, A. castilla et al, IPAC2014 ** MEIC Design Summary, S. Abeyratne et al, arXiv:1504.07961
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WEPMR036	Crab Cavities for eRHIC - A Preliminary Design	2351
	Q. Wu, I. Ben-Zvi, S. Verdú-Andrés, B. P. Xiao BNL, Upton, Long Island, New York, USA I. Ben-Zvi Stony Brook University, Stony Brook, USA
	Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy. The proposed eRHIC electron ion collider at BNL must use a relatively large crossing angle between the ion and electron beams for various reasons, including the reduction of long-range beam-beam effects and minimization of synchrotron radiation noise in the detector. To prevent significant loss of the luminosity due to this large crossing angle, the design of the collider requires the use of groups of crab cavities to provide local crabbing for both proton/ion and electron beams. We will base our design for eRHIC crab cavities based on our experience in the design of the 400 MHz double quarter wave crab cavity (DQWCC) for the Hi-Lumi upgrade of the Large Hadron Collider at CERN. This DQWCC design is scaled to different frequencies of a main crab cavity and its higher harmonics for eRHIC. In this paper, we discuss the preliminary designs of the eRHIC crab cavities and their major parameters.
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WEPMR037	Wakefield Analysis of the 56 MHz SRF Cavity	2354
	Q. Wu, Y. Hao BNL, Upton, Long Island, New York, USA
	Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy. The 56 MHz SRF cavity is a superconducting quarter-wave resonator installed in the common section of RHIC. Both beams share the cavity in an interwoven pattern over the entire store. The wake field excited in the cavity is the superposition of the two opposing bunches. This paper will discuss the wake field excited by both beams, and the higher order mode power as a result of the excited field.
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WEPMR038	Frequency Tuning for a DQW Crab Cavity	2357
	S. Verdú-Andrés, I. Ben-Zvi, J. Skaritka, Q. Wu, B. P. Xiao BNL, Upton, Long Island, New York, USA K. Artoos, R. Calaga, O. Capatina, R. Leuxe, C. Zanoni CERN, Geneva, Switzerland I. Ben-Zvi Stony Brook University, Stony Brook, USA
	Funding: Work supported by US DOE via BSA LLC contract No.DE-AC02-98CH10886, the US LARP program, US DOE contract No. DE-AC02-05CH1123 (NERSC resources) and by HiLumi project. The nominal operating frequency for the HL-LHC crab cavities is 400.79 MHz within a bandwidth of ±60kHz. Attaining the required cavity tune implies a good understanding of all the processes that influence the cavity frequency from the moment when the cavity parts are being fabricated until the cavity is installed and under operation. Different tuning options will be available for the DQW crab cavity of LHC. This paper details the different steps in the cavity fabrication and preparation that may introduce a shift in the cavity frequency and introduces the different tuning methods foreseen to bring the cavity frequency to meet the specifications.
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WEPMR040	HOM Absorber Study by Photon Diffraction Model	2360
	C. Xu, I. Ben-Zvi, V. Ptitsyn, P. Takas, W. Xu BNL, Upton, Long Island, New York, USA I. Petrushina SUNY SB, Stony Brook, New York, USA B. P. Xiao SBU, Stony Brook, New York, USA
	Photon diffraction model (PDM) is one of the most promising candidates to study High Order Mode (HOM) power absorption on absorbing materials for high current SRF cavities. Because at very high frequency (>10GHz), the wavelengths of HOMs are much smaller compared with accelerators dimension, the phase of those HOM will be negligible. Meanwhile, Finite Element Method (FEM) cannot lend a high resolution on evaluation the HOM field patterns due to limited meshing capability. This PDM model utilizes Monte Carlo simulation to trace the ray diffusive reflection in a cavity. This method can directly estimate the power absorption on the cavity and absorber wall. This method will help design the HOM damper setup for eRHIC HOM damper. In this report, we evaluate HOM absorption on the cavity wall with different absorber setup and give a possible solution for power damping scheme for high frequency HOMs.
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WEPMR041	RF and Mechanical Design of 647 MHz 5-Cell BNL4 Cavity for eRHIC ERL	2364
	W. Xu, I. Ben-Zvi, H. Hahn, G.T. McIntyre, C. Pai, R. Porqueddu, K.S. Smith, J.L. Tuozzolo, J.E. Tuozzolo, 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. A 647 MHz 5-cell cavity has been designed for the envisioned EIC at BNL which is configured as an eRHIC ERL with a FFAG lattice to achieve the necessary e-p luminosity. The cavity was optimized to allow propagation of all HOMs out of the cavity for high BBU threshold current and low HOM power (loss factor). eRHIC will collide the electron beam over a wide energy range with protons from 40 GeV to 250 GeV, which requires the cavity to tune up to 170 kHz at 2 K. This poses a true challenge to the mechanical design of the SRF cavity. This paper will present the RF and mechanical designs of the 647 MHz 5-cell cavity, and status of the cavity fabrication will be addressed as well.
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WEPMR042	Ridge Waveguide HOM Damping Scheme for High Current SRF Cavity	2367
	W. Xu, I. Ben-Zvi, Y. Gao, H. Hahn, G.T. McIntyre, R. Porqueddu, V. Ptitsyn, K.S. Smith, R. Than, J.L. Tuozzolo, C. Xu, 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. HOM damping is a challenge for high-current SRF linacs possibly generating HOM power at a level of 10 KW per cavity. A rectangular waveguide used as a natural high pass filter is a good option as high power, large spectrum HOM damper. However, its size is too big, causing a big challenge for the cooling and cryogenic system. A reliable, compact HOM damping scheme using a ridged waveguide is being developed to damp high power (> 10 kW), large spectrum HOMs ( up to 40 GHz) that may be generated in the 647 MHz 5-cell eRHIC ERL SRF linac. The size of a ridged waveguide is less than a quarter of the regular waveguide, which alleviates the thermal issue. This paper presents the design of a ridged waveguide and estimated HOM damping results using a ridged waveguide. The thermal or cooling design of the ridged waveguide will also be addressed.
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WEPMW041	Multiple Bunch HOM Evaluation for eRHIC Main Linac Cavities	2525
	C. Xu, I. Ben-Zvi, M. Blaskiewicz, Y. Hao, V. Ptitsyn BNL, Upton, Long Island, New York, 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. High current Superconducting Radiofrequency (SRF) 5-cell cavities are essential for the proposed ERL-based electron-ion collider eRHIC in BNL. The HOM power generated when a single bunch traverses the cavity is estimated by the corresponding loss factor. Multiple re-circulations through the ERL create a specific bunch pattern. In this case the loss factor can be different than the single bunch loss factor. The HOM power generation can be surveyed in the time and frequency domains. We estimate the average HOM power in the eRHIC 5-cell cavity with different ERL bunch patterns using both methods. We also discuss possible solutions to reduce this HOM power.
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WEPMW042	Trapped Modes Study and BBU Analysis in the 5-Cell 650 MHz Cavity	2529
	C. Xu, I. Ben-Zvi, Y. Hao, V. Ptitsyn, W. Xu BNL, Upton, Long Island, New York, USA I. Petrushina SUNY SB, Stony Brook, New York, 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. #chenxu@bnl.gov eRHIC project is a future electron-hadron collider proposed at BNL. The proposed electron accelerator will generate up to 20 GeV polarized electrons which will collide with proton beams with energy up to 250 GeV. The proposed collider will deliver electron-nucleon luminosity of 1033- 1034 cm-2 ses−1. A superconducting RF (SRF) 5-cell elliptical cavity will be utilized in electron accelerator. This paper presents a study of higher-order modes (HOM) for this 647 MHz SRF cavity. Different types of HOM modes and their BBU instabilities were investigated for frequencies up to 3.2 GHz. Threshold current values of beam breakup are estimated by GBBU code. Further improvement on this threshold current has been explored and discussed.
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WEPOY059	Axisymmetric Numerical Studies of Higher Order Mode Damping Techniques using Ring Ferrites for BESSY VSR	3132
	B. Riemann, B.D. Isbarn, M. Sommer, T. Weis DELTA, Dortmund, Germany
	Funding: Work supported by the BMBF under contract no. 05K13PEB. Utilizing superconducting multicell rf cavities with fundamental frequencies of 1.5 GHz and 1.75 GHz and therefore modulating the rf gradient, the upcoming BESSY II upgrade BESSY VSR aims to provide both short and long electron bunches simultaneously. However, beam induced excitation of higher order modes (HOM) inside those superconducting cavities is a major concern for beam stability in a recirculating accelerator. Thus it is important to develop and apply proper HOM damping techniques. Current design considerations involve HOM coupler which usually introduce discontinuities in the cross section while also breaking the axisymmetry. To circumvent these issues we investigate in a layout with ring ferrites as an alternative or additional HOM damping technique. We also present an alternative superstructure setup that uses two instead of four cavities for VSR.
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THYB01	Performance of Superconducting Cavities for the European XFEL	3186
	D. Reschke DESY, Hamburg, Germany
	The superconducting accelerator of the European XFEL consists of the injector part and the main linac. The injector includes one 1.3 GHz accelerator module and one 3.9 GHz third harmonic module, while the main linac consists of 100 accelerator modules, each housing eight 1.3 GHz TESLA-type cavities, operated at an average design gradient of 23.6 MV/m. The fabrication and surface treatment by industry as well as the vertical and cryomodule RF tests of the required 808 superconducting 1.3GHz cavities are analysed and presented.
	Slides THYB01 [3.227 MB]
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THOBB02	Impurity Doping of Superconducting Radio Frequency Cavities	3195
SUPSS093	use link to see paper's listing under its alternate paper code
	P.N. Koufalis, F. Furuta, G.M. Ge, D. Gonnella, J.J. Kaufman, M. Liepe, J.T. Maniscalco Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Funding: NSF PHYS-1416318 Impurity doping of bulk-niobium superconducting radio frequency (SRF) cavities is a relatively new field of study and the underlying physics is not yet fully understood. Previous studies have shown an increase in the intrinsic quality factor and the corresponding decrease of the temperature-dependent component of the surface resistance of nitrogen-doped cavities with increasing accelerating field.* Here we investigate the effects of alternative inert dopants on the surface resistance and thus the intrinsic quality factor of SRF cavities in pursuit of the optimal dopant and doping level. A. Grassellino et al., Nitrogen and Argon Doping of Niobium for Superconducting Radio Frequency Cavities. Supercond. Sci. Technol., 26(102001), 2013
	Slides THOBB02 [4.048 MB]
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THOBB03	Root Causes of Field Emitters in SRF Cavities Placed in CEBAF Tunnel	3198
	R.L. Geng JLab, Newport News, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. It has been suspected that appearance of new field emitters can occur in SRF cavities after their placement in accelerator tunnel for long term beam operation. This apparently has been the case for CEBAF. However, no physical evidence has been shown in the past. In this contribution, we will report on the recent results concerning the root cause of field emitters in SRF cavities placed in CEBAF tunnel. We will discuss these results in the context of high-reliability and low-cryogenic-loss operation of CEBAF.
	Slides THOBB03 [3.768 MB]
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