SRF2017 - List of Keywords (simulation)

Paper	Title	Other Keywords	Page
MOPB011	CEA Cryomodules Design for SARAF Phase 2	ion, cavity, cryomodule, vacuum	70
	C. Madec CEA, Gif-sur-Yvette, France N. Bazin, D. Chirpaz-Cerbat, R. Cubizolles CEA/IRFU, Gif-sur-Yvette, France P. Brédy CEA/DSM/IRFU, France R. Bruce, P. Hardy, F. Leseigneur, Th. Plaisant, J. Plouin CEA/DRF/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 40.1 MeV. The SCL consists in 4 cryomodules separated by warm diagnostics housing beam diagnostics. The first two identical cryomodules host 6 half-wave resonator (HWR) low beta cavities (β = 0.091), 176 MHz. The last two identical cryomodules are equipped with 7 HWR high-beta cavities (β = 0.181), 176 MHz. The beam is focused through superconducting solenoids located between cavities housing steering coils. A Beam Position Monitor is placed upstream each solenoid. A diagnostic box containing a beam profiler and a vacuum pump will be placed at the end of each cryomodule. The cryomodules and the warm sections are being designed. These studies will be presented in this poster.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOPB011
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MOPB052	Dual-ridge Waveguide Load Design for eRHIC	ion, GUI, HOM, cavity	177
	P. Kolb, Y. Gao, C. Pai, R. Porqueddu, K.S. Smith, W. Xu BNL, Upton, Long Island, New York, USA Y. Gao PKU, Beijing, People's Republic of China
	Funding: Work supported by LDRD program of Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. DOE. To increase the real estate gradient in the eRHIC electron accelerator waveguide HOM couplers are being considered. These significantly reduce the length of individual cavities and address inter-cavity trapped modes, allowing for an increased number of cavities per cryomodule, which would increase the real estate gradient. The choice of waveguide went to a dual ridge waveguide due to a smaller size compared to rectangular waveguides. The waveguide termination, to convert the RF energy into thermal energy, is a custom designed load based on a silicon carbide dielectric that is already being used in beamline absorbers. Simulations of the RF properties of the load are presented as well as first measurements on a prototype.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOPB052
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MOPB054	Design of Fundamental Power Coupler for High Intensity Heavy-ion Accelerator	ion, electron, cavity, multipactoring	183
	B. Bing, T.M. Huang, Q. Ma, F. Meng, W.M. Pan IHEP, Beijing, People's Republic of China K.X. Gu Institute of High Energy Physics (IHEP), Chinese Academy of Sciences, Beijing, People's Republic of China
	A single-window coaxial coupler at warm has been designed for high intensity heavy-ion accelerator. The coupler is designed to handle 100 kW CW power of 325 MHz and is currently being fabricated. T-bend transition and doorknob have been taken into account. The length of the T-bend short circuit is sensitive to S parameters and contributes to the online adjustment of VSWR in RF conditioning. The doorknob type is adopted to realize the transition from a half-height WR 2300 waveguide to a coaxial line ended with a coupling antenna. This paper describes the RF design, thermal stress and heat load analysis of the coupler as well as multipacting simula-tions.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOPB054
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MOPB064	High Power Test for Plug-compatible STF-type Power Coupler for ILC	ion, electron, vacuum, GUI	199
	Y. Yamamoto, E. Kako, T. Matsumoto, S. Michizono, A. Yamamoto KEK, Ibaraki, Japan C. Julie, E. Montesinos CERN, Geneva, Switzerland
	From the view point of plug-compatibility for the power coupler in the ILC, recommended by Linear Collider Collaboration in 2013, new STF-type power couplers with 40mm of input port diameter were re-designed, fabricated and successfully high-power-tested. Moreover, from the view point of the cost reduction for the ILC, another type of power couplers with TiN coating-free ceramic were also fabricated and high-power-tested by the collaboration between CERN and KEK. In this paper, the detailed results for the both power couplers will be presented.
	Poster MOPB064 [6.671 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOPB064
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MOPB068	Development of 4-way 81.25 MHz 20 kW High Power Combiner Using Parallel Plate Structure	ion, cavity, rfq, impedance	213
	K.T. Son, C.O. Choi, H. Jang, H.C. Jung, D.Y. Lee IBS, Daejeon, Republic of Korea
	The recent development of semiconductor technology has proved that solid-state RF amplifier is a quite effective alternative high power RF source for numerous accelerator applications. To develop a high power SSPA system, high power combiner is required to combine the RF power from a lot of solid-state RF module. The parallel plate RF power combiner, which is designed to combine various high power modules, is developed for RAON(Rare the rare isotope accelerator complex for on-line experiment). In this presentation, the status of developed 81.25 MHz 20 kW power combiner will be described.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOPB068
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MOPB071	The Recent Research of HOM Damper for Superconducting Cavity in IHEP	ion, HOM, cavity, site	223
	F. Meng, T.M. Huang, H.Y. Lin, Q. Ma, W.M. Pan, J.Y. Zhai, P. Zhang, H.J. Zheng IHEP, Beijing, People's Republic of China
	Funding: This study was supported by National Key Programme for S&T Research and Development (Grant NO.: 2016YFA0400400) For high current accelerator, the efficient higher-order mode (HOM) damping is always an important issue. HOM damper with microwave absorbing material is a key component for high power and broadband HOM damping application. To pursue the high damping efficiency, some ideal material with good microwave absorbing capacity is essential during the RF design and fabrication phase. Sometimes the selection and test of material is the first step and also a long step. This paper will present the recent work on HOM dampers for BEPCII 500MHz cavity and CEPC 650MHz cavity in IHEP.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOPB071
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MOPB078	Power Coupler Design for the LUCRECE Project	ion, radiation, coupling, cavity	245
	H. Guler, D. Auguste, J. Bonis, O. Bouras, M. El Khaldi, W. Kaabi LAL, Orsay, France
	The LUCRECE project aims at developing an elementary RF system (cavity, power source, LLRF and controls) suitable for continuous (CW) operation at 1.3 GHz. This effort is made in the framework of the advanced and compact FEL project LUNEX5 (free electron Laser Using a New accelerator for the Exploitation of X-ray radiation of 5th generation), using superconducting linac technology for high repetition rate and multi-user operation (http://www.lunex5.com). In this context, based on its large experience on coupler design and RF conditioning, LAL Laboratory is in charge of the design and the fabrication of RF couplers that could operate at up to 15-20 kW in CW mode. For this purpose, couplers based on CORNELL 65kW CW couplers (RF power couplers for the Cornell ERL injector) are under consideration and will be adapted to the LUCRECE needs. Electromagnetic simulations and associated thermal heating will be discussed. Methods to decrease the thermal impact will be considered.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOPB078
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MOPB079	HOM Coupler Alterations for the LHC DQW Crab Cavity	ion, cavity, HOM, impedance	249
	J.A. Mitchell Lancaster University, Lancaster, United Kingdom G. Burt, N.C. Shipman Cockcroft Institute, Lancaster University, Lancaster, United Kingdom R. Calaga CERN, Geneva, Switzerland S. Verdú-Andrés, Q. Wu, B. P. Xiao BNL, Upton, Long Island, New York, USA
	As part of the High Luminosity Large Hadron Collider (HL-LHC) project, 16 crab cavities are to be installed in the LHC in 2025. The two crab cavity designs are the Double Quarter Wave (DQW) and Radio Frequency Dipole (RFD). Preliminary beam tests in the Super Proton Synchrotron (SPS) are planned for both cavity types, with the DQW scheduled for testing in 2018. In reference to to Higher Order Mode (HOM) damping, the DQW has three identical on-cell HOM couplers. These HOM couplers provide a band-stop response at the frequency of the fundamental mode and act as a transmission path for the cavity HOMs. For the SPS cavity design, several geometric constraints exist. These give rise to dimensional limitations which in-turn impose limitations on the RF performance of the HOM couplers. As such, for the LHC assembly, the HOM coupler design is re-visited to take into account the relaxed geometric limitations, hence allowing the feasibility of an increased RF performance to be investigated. In addition to the RF performance, several geometric alterations were incorporated to ease manufacturing processes, tolerances and costs.
	Poster MOPB079 [2.038 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOPB079
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MOPB082	A Preliminary Scheme for X-ray Emission Based on Micro-pulse Electron Gun	ion, electron, target, radiation	259
	Y. Yang, B.T. Li, X.Y. Lu, W.W. Tan, L. Xiao, D.Y. Yang, Z.Q. Yang, J. Zhao PKU, Beijing, People's Republic of China
	X-ray is now widely used in many areas of physics, biology, chemistry and materials. And how to achieve emission, monochrome, and focusing of x-ray is of great significance to study. Micro-pulse electron gun (MPG) is a new type of electron source, with characteristics of high repetition frequency, short-pulse and low cost. Generating x-ray with better monochromaticity is one of the potential applications of MPG. And a preliminary scheme of X-ray based on MPG is proposed in this paper. The scheme is designed by comparing different anode materials and the thickness of filters. The simulation results based on the software MCNP5 show that the proposed scheme can effectively improve the monotonicity of the generated X-rays.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOPB082
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MOPB090	Sub-micro-Tesla Magnetic Shielding Design for Cryomodules in the High-gradient Program at CERN	ion, shielding, cavity, cryomodule	278
	S. Papadopoulos, L. Dassa, F. Gerigk, F. Pillon, S. Ramberger, P. Yilmazer CERN, Geneva, Switzerland J. Dequaire Intitek, Lyon, France
	In the framework of the High-Gradient R\&D program at CERN a cryomodule, consisting of four superconducting 5-cell cavities, has been designed. In order to reduce flux trapping in the surface of the superconductor and to minimize Q degradation during a quench, highly effective magnetic shielding is needed. The solution proposed includes cold and warm passive shielding enhanced by four compensating coils. In this paper the magneto-static simulation results are presented illustrating different design considerations that led to a final design. Finally the shielding ability of the vacuum vessel is investigated experimentally through ambient magnetic field measurements.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOPB090
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TUPB013	Advanced Manufacturing Techniques for the Fabrication of Hl-LHC Crab Cavities at CERN	ion, cavity, niobium, MMI	409
	M. Garlaschè CERN, Geneva, Switzerland
	RF Crab Cavities are an essential part of the HL-LHC upgrade at CERN. Two concepts of such systems are being developed: the Double Quarter Wave (DQW) and the RF Dipole (RFD). The following paper describes the advanced manufacturing techniques developed for the fabrication of the DQW cavity prototype with an outlook on the upcoming RFD prototype production.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB013
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TUPB016	Redesign of CERN's Quadrupole Resonator for Testing of Superconducting Samples	ion, cavity, quadrupole, alignment	420
	V. del Pozo Romano, R. Betemps, F. Gerigk, R. Illan Fiastre, T. Mikkola CERN, Geneva, Switzerland
	The Quadrupole Resonator (QPR) was constructed in 1997 to measure the surface resistance of niobium samples at 400 MHz, the technology and RF frequency chosen for the LHC. It allows measurement of the RF properties of superconducting films deposited on disk-shaped metallic substrates. The samples are used to study different coatings which is much faster than the coating, stripping and re-coating of sample cavities. An electromagnetic and mechanical re-design of the existing QPR has been done with the goal of doubling the magnetic peak fields on the samples. Electromagnetic simulations were carried out on a completely parameterized model, using the actual CERN's QPR as baseline and modifying its dimensions. The aim was to optimize the measurement range and resolution by increasing the ratio between the magnetic peak fields on the sample and in the cavity. Increasing the average magnetic field on the sample leads to a more homogenous field distribution over the sample, which in turn gives a better resolution. Some of the modifications were based on the work already done by Helmholtz-Zentrum-Berlin for their upgraded version of the QPR.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB016
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TUPB020	Microphonics Passive Damping	ion, cavity, SRF, operation	423
	E.N. Zaplatin FZJ, Jülich, Germany A. Kanareykin Euclid TechLabs, LLC, Solon, Ohio, USA V.P. Yakovlev Fermilab, Batavia, Illinois, USA
	Different types of external loads on the resonator walls predetermine the main working conditions of the SRF cavities. The most important of them are very high electromagnetic fields that result in strong Lorentz forces and the pressure on cavity walls from the helium tank that also deforms the cavity shape. For pulsed operation, the Lorentz forces usually play the decisive role for the cavity design. For CW operation, the liquid helium vessel pressure instability even for 2K operations is the source of large microphonics. All deformations resulting from any type of external loads on cavity walls lead to shifts in the working RF frequency in the range of hundreds of kHz. Taking into account high Q-factor of SC cavities such a large frequency shift takes the cavity out of operation. Here we present and discuss the achievements and problems of microphonics passive damping in different type SRF cavities.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB020
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TUPB021	First Considerations on HZB High Frequency Elliptical Resonator Stiffening	ion, cavity, SRF, cryomodule	428
	E.N. Zaplatin FZJ, Jülich, Germany H.-W. Glock, J. Knobloch, A. Neumann, A.V. Vélez HZB, Berlin, Germany
	There are two projects that currently are under development and construction at HZB which utilize high frequency elliptical resonators ' Energy Recovery Linac Prototype (BERLinPro, 7-cell, 1300 MHz, β=1) and BESSY Variable pulse-length Storage Ring (VSR, 5-cell, 1500/1750 MHz, β=1). A critical issue of both projects is small effective beam loading in cavities operating at high CW fields (Eacc of 20 MV/m) with a narrow band width. This necessitates precise tuning and therefore good compensation of microphonics and coupled Lorentz-force detuning driven instabilities. Here we present a conceptual study of an integrated SRF resonator and helium vessel structure design to ensure a reduced resonance frequency dependence on pressure and Lorentz forces to minimize their impact on the accelerating field profile.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB021
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TUPB032	Study on 650MHz 5-cell Prototype Cavities at IHEP	ion, cavity, HOM, SRF	448
	S. Jin, J. Gao, D.J. Gong, Z.C. Liu, P. Sha, J.Y. Zhai, T.X. Zhao, H.J. Zheng IHEP, Beijing, People's Republic of China
	CEPC Pre CDR pointed that the 650 MHz 5-cell SRF cavity could be a candidate for the main ring of the single-ring pretzel scheme at the Higgs energy in 2015. Then EM design of 5-cell cavities were published later. So, the study on the fabrication of a 5-cell prototype cavity with waveguide HOM couplers were carried on at IHEP. In the paper, we will mainly report the mechanical design and fabrication progress of the 5-cell prototype. Besides, fabrication of a bare 2-cell prototype cavity was also carried on according to the further study after Pre-CDR. Challenges and possible solutions for the prototypes development will also be discussed.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB032
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TUPB035	Frequency Pre-tuning of the 166.6 MHz Proof-of-principle SRF Cavity for HEPS-TF	cavity, ion, SRF, target	459
	P. Zhang, H.X. Hao, Z.Q. Li, X.Y. Zhang IHEP, Beijing, People's Republic of China
	Funding: This work has been supported by HEPS-TF project and also partly supported by Pioneer 'Hundred Talents Program' of Chinese Academy of Sciences. A 166.6 MHz proof-of-principle SRF cavity has been designed for the High Energy Photon Source - Test Facility (HEPS) at IHEP in Beijing. The cavity is a β=1 quarter-wave resonator made of bulk niobium operating at 4 K. A pre-tuning scheme was made to accommodate the cavity frequency shift mainly due to mechanical tolerances during cavity production, the subsequent surface treatment and cooldown process. To this end, the length of the cavity outer conductor was chosen as a free parameter for the pre-tuning. The cavity frequency was carefully monitored during the production, post-processing steps and vertical test. The measurement results agree well with our calculations. It is worth noticing that the pre-tuning method only involves one-time measurement of the cavity resonant frequency and its outer conductor length.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB035
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TUPB041	Design of a Triple Spoke Cavity for the HIF Demo Injector	ion, cavity, heavy-ion, linac	481
	W. Ma, L. Lu, L. Yang IMP/CAS, Lanzhou, People's Republic of China
	Funding: This work was supported by National Nature Science Foundation of China under Grant No. 11475232 and No. 11535016. A 325 MHz triple spoke type superconducting cavity for lead beams with β=0.3 is designed for the heavy ion inertial fusion (HIF) Demo facility. The design and simulations of the triple spoke will be reported in this paper, including the electromagnetic (EM) design and mechanical study using CST microwave studio (MWS) and ANSYS workbench.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB041
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TUPB047	Passband Modes Excitation Triggered by Field Emission in ESS Medium Beta Cavity Prototype	ion, cavity, site, electron	489
	J.F. Chen, M. Bertucci, A. Bosotti, P. Michelato, L. Monaco, R. Paparella, D. Sertore INFN/LASA, Segrate (MI), Italy M. Eshraqi, M. Lindroos, S. Pirani ESS, Lund, Sweden C. Pagani Università degli Studi di Milano & INFN, Segrate, Italy T.P.Å. Åkesson Lund University, Department of Physics, Lund, Sweden
	During the first vertical test of ESS Medium Beta large-grain prototype cavity in INFN-LASA, a phenomenon of coexisting two passband-modes was observed – 4π/6 mode was excited spontaneously during the power rise of 3π/6 mode. This phenomenon is most likely due to the field-emission electrons that transfer their energy gained from the 3π/6 mode to the 4π/6 mode. In this paper, we present the experimental results, the excitation mechanism and the related simulation results.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB047
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TUPB056	Study on a Low Beta High Current Taper Type Superconducting Half Wave Resonator for BISOL	cavity, ion, experiment, ISOL	516
	F. Zhu, M. Chen, L.W. Feng, S.W. Quan, F. Wang, H.T.X. Zhong PKU, Beijing, People's Republic of China
	Funding: Work supported by National Basic Research Project (No. 2014CB845504) Beijing isotope separation on line type rare ion beam facility (BISOL) for both basic science and applications is a project proposed by China Institute of Atomic Energy and Peking University. Deuteron driver accelerator of BISOL would adopt superconducting half wave resonator (HWR) with low beta and high current. For pre-research of BISOL, a β=0.09 162.5 MHz taper type HWR cavity has been designed for accelerating deuteron beam with several tens of mA. The Design, fabrication, post-processing and room temperature RF measurement of the HWR cavity will be presented in this paper.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB056
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TUPB078	SUBU Characterisation: Bath Fluid Dynamics vs Etching Rate	ion, cavity, ISOL, software	575
	A. Perez Rodriguez, L.M.A. Ferreira, A. Sublet CERN, Geneva, Switzerland
	The chemical polishing bath SUBU is widely used at CERN to prepare copper RF cavities surfaces before niobium thin film coating; examples are HIE-ISOLDE, LHC and future FCC accelerating cavities. The performance of the polishing process is affected by bath temperature and fluid dynamics. As part of on-going activities to characterise SUBU, the actual study was done to identify a correlation between the etching rate and physical parameters linked to the bath fluid dynamics. A first approach was made using experimental data from a simplified model setup, transposing them via numerical simulation to a real cavity geometry and verifying the agreement with an experiment in a real size (HIE-ISOLDE) mock-up. In a second approach to improve the accuracy of the calculation, the relation of the measured local etching rates, extracted from the mock-up, to flow dynamics quantities extracted from simulation was investigated. As a result, a correlation between the local etching rate and the turbulence kinetic energy was obtained. This correlation can be exploited to improve the polishing tools and so optimise the current process, as well as to predict the etching rate in other cavity geometries.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB078
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TUPB100	Determining BCP Etch Rate and Uniformity in High Luminosity LHC Crab Cavities	ion, cavity, experiment, SRF	635
	T.J. Jones STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom G. Burt Cockcroft Institute, Lancaster University, Lancaster, United Kingdom R. Calaga, O. Capatina, L.M.A. Ferreira, R. Leuxe CERN, Geneva, Switzerland T.J. Jones, J.A. Mitchell Lancaster University, Lancaster, United Kingdom S.M. Pattalwar STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom S. Verdú-Andrés, B. P. Xiao BNL, Upton, Long Island, New York, USA
	The compact SRF Crab Cavities required for HL-LHC have complex geometries making prediction of average and local BCP etch rates a difficult task. This paper describes a series of experiments and simulations used to determine the etch uniformity and rate within these structures. An initial experiment was conducted to determine the correlation between etch rate and flow rate in a Nb tube. These results were then incorporated into Computational Fluid Dynamics simulations of acid flow in the Double Quarter Wave (DQW) cavity to predict etch rates across the surface and allow optimisation of the BCP setup. There were several important findings from the work; one of which is that the flow rate in the relatively large body of the cavity is predominantly driven by natural convection due to the exothermic reaction. During BCP processing of the DQW cavity a significant difference in etching was observed between upper and lower horizontal surfaces which was mitigated by etching in several orientations. Two DQW cavities manufactured by CERN have received a heavy BCP of 200μm followed by 2 light BCPs of 30μm each with subsequent vertical cold tests showing performance exceeding specification.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB100
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THPB019	Simulation of the Thermoelectrically Generated Magnetic Field in a SC Nine-cell Cavity	ion, cavity, experiment, ECR	771
	J.M. Köszegi, J. Knobloch, O. Kugeler HZB, Berlin, Germany
	Several studies showed that thermocurrents generate a magnetic field in a horizontal cavity test assembly or cryomodul, which may get trapped during the superconducting phase transition. The trapped flux causes additional dissipation during operation and can therefore significantly degrade the cavity's quality factor. We simulated the distribution of the generated magnetic field for different temperature distributions and compared the results to experimental findings. Furthermore, the impact of a growing superconducting area was investigated. The simulations complement the experimental studies because measurements were only feasible with a limited number of probes and restricted to selected locations and orientations. The simulations allow to analyze this data in the context of the whole system.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-THPB019
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THPB025	A Crystal Plasticity Study on Influence of Dislocation Mean Free Path on Stage II Hardening in Nb Single Crystals	ion, experiment, cavity, niobium	783
	T. Maiti, A. Chakrabarty, P. Eisenlohr MSU, East Lansing, USA T.R. Bieler, D. Kang Michigan State University, East Lansing, Michigan, USA
	Funding: Financial support from the Department of Energy through grant DE-SC0009962 is gratefully acknowledged. This work was supported in part by MSU through computational resources provided by the ICER. Constitutive models based on thermally-activated stress-assisted dislocation kinetics have been successful in predicting deformation behavior of crystalline materials, particularly in face-centered cubic (fcc) metals. In body-centered cubic (bcc) metals, success has been more or less limited, owing to ill-defined nature of slip planes and non-planar spreading of 1/2\hkl<111> screw dislocation cores. As a direct consequence of this, bcc metals show a strong dependence of flow stress on temperature and strain rate, and violation of Schmid law. We present high-resolution full-field crystal plasticity simulations of single crystal Niobium under tensile loading with an emphasis on multi-stage hardening, orientation dependence, and non-Schmid behavior. A dislocation density-based constitutive model with storage and recovery rates derived from Discrete Dislocation Dynamics is used to model strain hardening in stage II. The influence of dislocation mean free path and initial dislocation content on stage II hardening is simulated and compared with in-situ tensile experiments.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-THPB025
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THPB048	Double Cathode Configuration for the Nb Coating of HIE-ISOLDE Cavities	ion, cathode, cavity, ISOL	854
	A. Awais NCP, Islamabad, Pakistan A. Awais, A.J.G. Lunt, G.J. Rosaz, A. Sublet, M. Taborelli CERN, Geneva, Switzerland
	The Quarter Wave Resonator (QWR) cavities for HIE-ISOLDE project at CERN have entered their ending phase of production. Some R&D is still required to improve the uniformity of the Nb layer thickness on the cavity surface. In order to improve this behaviour one approach which has been proposed is to replace the single cathode with a double cathode and test the suitability of different deposition techniques. With this change it is possible to control the plasma and power distribution separately for the inner and outer part of cavity and thereby potentially improve film uniformity throughout the cavity and coating duration. In this study a comparison between the deposition rates obtained using a single cathode and a double cathode using Direct Current (DC)-bias diode sputtering, DC-magnetron sputtering (DCMS) and Pulsed DC-magnetron sputtering (PDCMS) is presented. The morphology of the thin film samples were compared using Focused Ion Beam (FIB) cross section milling and Scanning Electron Microscopy (SEM) analysis.
	Poster THPB048 [3.715 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-THPB048
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THPB052	Error Analysis of Surface Resistance Fits to Experimental Data	ion, cavity, experiment, data-analysis	859
	S. Keckert, J. Knobloch, O. Kugeler HZB, Berlin, Germany
	Funding: This work is part of EuCARD-2, partly funded by the European Commission, GA 312453. Superconducting material properties such as energy gap, mean free path or residual resistance are commonly extracted by fitting experimental surface resistance data. Depending on the measurement setup, both, temperature range and the number of points are limited. In order to obtain significant results, systematic as well as statistical uncertainties have to be taken into account. In this contribution different classes of errors and their impact on systematic and statistical deviations of the fitted parameters are discussed. In particular, past measurements have yielded contradictory conclusions that, we believe, result from the use of insufficient data in the necessary temperature range. Furthermore, this study is applied to the boundary conditions of the Quadrupole Resonator and its measurement accuracy.
	Poster THPB052 [1.034 MB]
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THPB059	Simulation and Measurements of Crab Cavity HOMs and HOM Couplers for HL-LHC	ion, HOM, cavity, damping	881
	J.A. Mitchell, T.J. Jones Lancaster University, Lancaster, United Kingdom R. Apsimon, G. Burt, N.C. Shipman Cockcroft Institute, Lancaster University, Lancaster, United Kingdom I. Ben-Zvi, S. Verdú-Andrés, B. P. Xiao BNL, Upton, Long Island, New York, USA R. Calaga, A. Castilla, A. Macpherson, N.C. Shipman, A. Zwozniak CERN, Geneva, Switzerland T. Powers, H. Wang JLab, Newport News, Virginia, USA N.C. Shipman UMAN, Manchester, United Kingdom
	Two Superconducting Radio-Frequency (SRF) crab cavities are foreseen for the High Luminosity LHC (HL-LHC) upgrade. Preliminary beam tests of the Double Quarter Wave (DQW) crab cavity will take place in the Super Proton Synchrotron (SPS) in 2018. For damping of the cavity's Higher Order Modes (HOMs) the DQW has three identical on-cell, superconducting HOM couplers. The couplers are actively cooled by liquid heluim. In this paper, electromagnetic simulations of the HOMs and HOM couplers are presented. A novel approach to pre-installation spectral analysis of the HOM couplers is then presented, detailing both simulated and measured data. Measurements of the cavity HOMs at warm and in Vertical Test Facilities (VTFs) at both JLAB and CERN are detailed, comparing the measured characteristics of each mode to that of the simulated data-sets. Finally, the measured cavity data is compared with the test box measurements to see by what extent any reduction in damping can be predicted.
	Poster THPB059 [8.192 MB]
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THPB079	Simulations of RF Field-induced Thermal Feedback in Niobium and Nb3Sn Cavities	ion, cavity, niobium, feedback	920
	J. Ding, D.L. Hall Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA M. Liepe Cornell University, Ithaca, New York, USA
	Thermal feedback is a known limitation for SRF cavities made of low-purity niobium, as the increased losses at higher temperature described by BCS theory create a feedback mechanism that can eventually result in a runaway effect and associated cavity quench. In a similar manner, niobium cavities coated with Nb3Sn may also be subject to increased losses from thermal feedback, as Nb3Sn is possessed of a much lower thermal conductivity than niobium, although this effect will be mitigated by the thin film nature of the coating. In order to better understand the degree to which thermal feedback plays a role in the performance of Nb3Sn cavities, it is necessary to understand how the various components of the problem play a role in the outcome. In this paper, we present the first results from simulations performed at Cornell University that model RF induced thermal feedback in both conventional niobium cavities and niobium cavities coated with a thin film of Nb3Sn. The impacts of layer thickness, niobium substrate thermal conductivity, and trapped flux on the performance of the cavity are discussed.
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Paper

Title

Other Keywords

Page

MOPB011

CEA Cryomodules Design for SARAF Phase 2

ion, cavity, cryomodule, vacuum

70

C. Madec
CEA, Gif-sur-Yvette, France
N. Bazin, D. Chirpaz-Cerbat, R. Cubizolles
CEA/IRFU, Gif-sur-Yvette, France
P. Brédy
CEA/DSM/IRFU, France
R. Bruce, P. Hardy, F. Leseigneur, Th. Plaisant, J. Plouin
CEA/DRF/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 40.1 MeV. The SCL consists in 4 cryomodules separated by warm diagnostics housing beam diagnostics. The first two identical cryomodules host 6 half-wave resonator (HWR) low beta cavities (β = 0.091), 176 MHz. The last two identical cryomodules are equipped with 7 HWR high-beta cavities (β = 0.181), 176 MHz. The beam is focused through superconducting solenoids located between cavities housing steering coils. A Beam Position Monitor is placed upstream each solenoid. A diagnostic box containing a beam profiler and a vacuum pump will be placed at the end of each cryomodule. The cryomodules and the warm sections are being designed. These studies will be presented in this poster.

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MOPB052

Dual-ridge Waveguide Load Design for eRHIC

ion, GUI, HOM, cavity

177

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

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

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MOPB054

Design of Fundamental Power Coupler for High Intensity Heavy-ion Accelerator

ion, electron, cavity, multipactoring

183

B. Bing, T.M. Huang, Q. Ma, F. Meng, W.M. Pan
IHEP, Beijing, People's Republic of China
K.X. Gu
Institute of High Energy Physics (IHEP), Chinese Academy of Sciences, Beijing, People's Republic of China

A single-window coaxial coupler at warm has been designed for high intensity heavy-ion accelerator. The coupler is designed to handle 100 kW CW power of 325 MHz and is currently being fabricated. T-bend transition and doorknob have been taken into account. The length of the T-bend short circuit is sensitive to S parameters and contributes to the online adjustment of VSWR in RF conditioning. The doorknob type is adopted to realize the transition from a half-height WR 2300 waveguide to a coaxial line ended with a coupling antenna. This paper describes the RF design, thermal stress and heat load analysis of the coupler as well as multipacting simula-tions.

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MOPB064

High Power Test for Plug-compatible STF-type Power Coupler for ILC

ion, electron, vacuum, GUI

199

Y. Yamamoto, E. Kako, T. Matsumoto, S. Michizono, A. Yamamoto
KEK, Ibaraki, Japan
C. Julie, E. Montesinos
CERN, Geneva, Switzerland

From the view point of plug-compatibility for the power coupler in the ILC, recommended by Linear Collider Collaboration in 2013, new STF-type power couplers with 40mm of input port diameter were re-designed, fabricated and successfully high-power-tested. Moreover, from the view point of the cost reduction for the ILC, another type of power couplers with TiN coating-free ceramic were also fabricated and high-power-tested by the collaboration between CERN and KEK. In this paper, the detailed results for the both power couplers will be presented.

Poster MOPB064 [6.671 MB]

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MOPB068

Development of 4-way 81.25 MHz 20 kW High Power Combiner Using Parallel Plate Structure

ion, cavity, rfq, impedance

213

K.T. Son, C.O. Choi, H. Jang, H.C. Jung, D.Y. Lee
IBS, Daejeon, Republic of Korea

The recent development of semiconductor technology has proved that solid-state RF amplifier is a quite effective alternative high power RF source for numerous accelerator applications. To develop a high power SSPA system, high power combiner is required to combine the RF power from a lot of solid-state RF module. The parallel plate RF power combiner, which is designed to combine various high power modules, is developed for RAON(Rare the rare isotope accelerator complex for on-line experiment). In this presentation, the status of developed 81.25 MHz 20 kW power combiner will be described.

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MOPB071

The Recent Research of HOM Damper for Superconducting Cavity in IHEP

ion, HOM, cavity, site

223

F. Meng, T.M. Huang, H.Y. Lin, Q. Ma, W.M. Pan, J.Y. Zhai, P. Zhang, H.J. Zheng
IHEP, Beijing, People's Republic of China

Funding: This study was supported by National Key Programme for S&T Research and Development (Grant NO.: 2016YFA0400400)
For high current accelerator, the efficient higher-order mode (HOM) damping is always an important issue. HOM damper with microwave absorbing material is a key component for high power and broadband HOM damping application. To pursue the high damping efficiency, some ideal material with good microwave absorbing capacity is essential during the RF design and fabrication phase. Sometimes the selection and test of material is the first step and also a long step. This paper will present the recent work on HOM dampers for BEPCII 500MHz cavity and CEPC 650MHz cavity in IHEP.

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MOPB078

Power Coupler Design for the LUCRECE Project

ion, radiation, coupling, cavity

245

H. Guler, D. Auguste, J. Bonis, O. Bouras, M. El Khaldi, W. Kaabi
LAL, Orsay, France

The LUCRECE project aims at developing an elementary RF system (cavity, power source, LLRF and controls) suitable for continuous (CW) operation at 1.3 GHz. This effort is made in the framework of the advanced and compact FEL project LUNEX5 (free electron Laser Using a New accelerator for the Exploitation of X-ray radiation of 5th generation), using superconducting linac technology for high repetition rate and multi-user operation (http://www.lunex5.com). In this context, based on its large experience on coupler design and RF conditioning, LAL Laboratory is in charge of the design and the fabrication of RF couplers that could operate at up to 15-20 kW in CW mode. For this purpose, couplers based on CORNELL 65kW CW couplers (RF power couplers for the Cornell ERL injector) are under consideration and will be adapted to the LUCRECE needs. Electromagnetic simulations and associated thermal heating will be discussed. Methods to decrease the thermal impact will be considered.

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MOPB079

HOM Coupler Alterations for the LHC DQW Crab Cavity

ion, cavity, HOM, impedance

249

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

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

Poster MOPB079 [2.038 MB]

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MOPB082

A Preliminary Scheme for X-ray Emission Based on Micro-pulse Electron Gun

ion, electron, target, radiation

259

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

X-ray is now widely used in many areas of physics, biology, chemistry and materials. And how to achieve emission, monochrome, and focusing of x-ray is of great significance to study. Micro-pulse electron gun (MPG) is a new type of electron source, with characteristics of high repetition frequency, short-pulse and low cost. Generating x-ray with better monochromaticity is one of the potential applications of MPG. And a preliminary scheme of X-ray based on MPG is proposed in this paper. The scheme is designed by comparing different anode materials and the thickness of filters. The simulation results based on the software MCNP5 show that the proposed scheme can effectively improve the monotonicity of the generated X-rays.

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MOPB090

Sub-micro-Tesla Magnetic Shielding Design for Cryomodules in the High-gradient Program at CERN

ion, shielding, cavity, cryomodule

278

S. Papadopoulos, L. Dassa, F. Gerigk, F. Pillon, S. Ramberger, P. Yilmazer
CERN, Geneva, Switzerland
J. Dequaire
Intitek, Lyon, France

In the framework of the High-Gradient R\&D program at CERN a cryomodule, consisting of four superconducting 5-cell cavities, has been designed. In order to reduce flux trapping in the surface of the superconductor and to minimize Q degradation during a quench, highly effective magnetic shielding is needed. The solution proposed includes cold and warm passive shielding enhanced by four compensating coils. In this paper the magneto-static simulation results are presented illustrating different design considerations that led to a final design. Finally the shielding ability of the vacuum vessel is investigated experimentally through ambient magnetic field measurements.

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TUPB013

Advanced Manufacturing Techniques for the Fabrication of Hl-LHC Crab Cavities at CERN

ion, cavity, niobium, MMI

409

M. Garlaschè
CERN, Geneva, Switzerland

RF Crab Cavities are an essential part of the HL-LHC upgrade at CERN. Two concepts of such systems are being developed: the Double Quarter Wave (DQW) and the RF Dipole (RFD). The following paper describes the advanced manufacturing techniques developed for the fabrication of the DQW cavity prototype with an outlook on the upcoming RFD prototype production.

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TUPB016

Redesign of CERN's Quadrupole Resonator for Testing of Superconducting Samples

ion, cavity, quadrupole, alignment

420

V. del Pozo Romano, R. Betemps, F. Gerigk, R. Illan Fiastre, T. Mikkola
CERN, Geneva, Switzerland

The Quadrupole Resonator (QPR) was constructed in 1997 to measure the surface resistance of niobium samples at 400 MHz, the technology and RF frequency chosen for the LHC. It allows measurement of the RF properties of superconducting films deposited on disk-shaped metallic substrates. The samples are used to study different coatings which is much faster than the coating, stripping and re-coating of sample cavities. An electromagnetic and mechanical re-design of the existing QPR has been done with the goal of doubling the magnetic peak fields on the samples. Electromagnetic simulations were carried out on a completely parameterized model, using the actual CERN's QPR as baseline and modifying its dimensions. The aim was to optimize the measurement range and resolution by increasing the ratio between the magnetic peak fields on the sample and in the cavity. Increasing the average magnetic field on the sample leads to a more homogenous field distribution over the sample, which in turn gives a better resolution. Some of the modifications were based on the work already done by Helmholtz-Zentrum-Berlin for their upgraded version of the QPR.

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TUPB020

Microphonics Passive Damping

ion, cavity, SRF, operation

423

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

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

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TUPB021

First Considerations on HZB High Frequency Elliptical Resonator Stiffening

ion, cavity, SRF, cryomodule

428

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

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

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TUPB032

Study on 650MHz 5-cell Prototype Cavities at IHEP

ion, cavity, HOM, SRF

448

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

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

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TUPB035

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

cavity, ion, SRF, target

459

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

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

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TUPB041

Design of a Triple Spoke Cavity for the HIF Demo Injector

ion, cavity, heavy-ion, linac

481

W. Ma, L. Lu, L. Yang
IMP/CAS, Lanzhou, People's Republic of China

Funding: This work was supported by National Nature Science Foundation of China under Grant No. 11475232 and No. 11535016.
A 325 MHz triple spoke type superconducting cavity for lead beams with β=0.3 is designed for the heavy ion inertial fusion (HIF) Demo facility. The design and simulations of the triple spoke will be reported in this paper, including the electromagnetic (EM) design and mechanical study using CST microwave studio (MWS) and ANSYS workbench.

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TUPB047

Passband Modes Excitation Triggered by Field Emission in ESS Medium Beta Cavity Prototype

ion, cavity, site, electron

489

J.F. Chen, M. Bertucci, A. Bosotti, P. Michelato, L. Monaco, R. Paparella, D. Sertore
INFN/LASA, Segrate (MI), Italy
M. Eshraqi, M. Lindroos, S. Pirani
ESS, Lund, Sweden
C. Pagani
Università degli Studi di Milano & INFN, Segrate, Italy
T.P.Å. Åkesson
Lund University, Department of Physics, Lund, Sweden

During the first vertical test of ESS Medium Beta large-grain prototype cavity in INFN-LASA, a phenomenon of coexisting two passband-modes was observed – 4π/6 mode was excited spontaneously during the power rise of 3π/6 mode. This phenomenon is most likely due to the field-emission electrons that transfer their energy gained from the 3π/6 mode to the 4π/6 mode. In this paper, we present the experimental results, the excitation mechanism and the related simulation results.

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TUPB056

Study on a Low Beta High Current Taper Type Superconducting Half Wave Resonator for BISOL

cavity, ion, experiment, ISOL

516

F. Zhu, M. Chen, L.W. Feng, S.W. Quan, F. Wang, H.T.X. Zhong
PKU, Beijing, People's Republic of China

Funding: Work supported by National Basic Research Project (No. 2014CB845504)
Beijing isotope separation on line type rare ion beam facility (BISOL) for both basic science and applications is a project proposed by China Institute of Atomic Energy and Peking University. Deuteron driver accelerator of BISOL would adopt superconducting half wave resonator (HWR) with low beta and high current. For pre-research of BISOL, a β=0.09 162.5 MHz taper type HWR cavity has been designed for accelerating deuteron beam with several tens of mA. The Design, fabrication, post-processing and room temperature RF measurement of the HWR cavity will be presented in this paper.

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TUPB078

SUBU Characterisation: Bath Fluid Dynamics vs Etching Rate

ion, cavity, ISOL, software

575

A. Perez Rodriguez, L.M.A. Ferreira, A. Sublet
CERN, Geneva, Switzerland

The chemical polishing bath SUBU is widely used at CERN to prepare copper RF cavities surfaces before niobium thin film coating; examples are HIE-ISOLDE, LHC and future FCC accelerating cavities. The performance of the polishing process is affected by bath temperature and fluid dynamics. As part of on-going activities to characterise SUBU, the actual study was done to identify a correlation between the etching rate and physical parameters linked to the bath fluid dynamics. A first approach was made using experimental data from a simplified model setup, transposing them via numerical simulation to a real cavity geometry and verifying the agreement with an experiment in a real size (HIE-ISOLDE) mock-up. In a second approach to improve the accuracy of the calculation, the relation of the measured local etching rates, extracted from the mock-up, to flow dynamics quantities extracted from simulation was investigated. As a result, a correlation between the local etching rate and the turbulence kinetic energy was obtained. This correlation can be exploited to improve the polishing tools and so optimise the current process, as well as to predict the etching rate in other cavity geometries.

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TUPB100

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

ion, cavity, experiment, SRF

635

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

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

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB100

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THPB019

Simulation of the Thermoelectrically Generated Magnetic Field in a SC Nine-cell Cavity

ion, cavity, experiment, ECR

771

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

Several studies showed that thermocurrents generate a magnetic field in a horizontal cavity test assembly or cryomodul, which may get trapped during the superconducting phase transition. The trapped flux causes additional dissipation during operation and can therefore significantly degrade the cavity's quality factor. We simulated the distribution of the generated magnetic field for different temperature distributions and compared the results to experimental findings. Furthermore, the impact of a growing superconducting area was investigated. The simulations complement the experimental studies because measurements were only feasible with a limited number of probes and restricted to selected locations and orientations. The simulations allow to analyze this data in the context of the whole system.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-THPB019

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THPB025

A Crystal Plasticity Study on Influence of Dislocation Mean Free Path on Stage II Hardening in Nb Single Crystals

ion, experiment, cavity, niobium

783

T. Maiti, A. Chakrabarty, P. Eisenlohr
MSU, East Lansing, USA
T.R. Bieler, D. Kang
Michigan State University, East Lansing, Michigan, USA

Funding: Financial support from the Department of Energy through grant DE-SC0009962 is gratefully acknowledged. This work was supported in part by MSU through computational resources provided by the ICER.
Constitutive models based on thermally-activated stress-assisted dislocation kinetics have been successful in predicting deformation behavior of crystalline materials, particularly in face-centered cubic (fcc) metals. In body-centered cubic (bcc) metals, success has been more or less limited, owing to ill-defined nature of slip planes and non-planar spreading of 1/2\hkl<111> screw dislocation cores. As a direct consequence of this, bcc metals show a strong dependence of flow stress on temperature and strain rate, and violation of Schmid law. We present high-resolution full-field crystal plasticity simulations of single crystal Niobium under tensile loading with an emphasis on multi-stage hardening, orientation dependence, and non-Schmid behavior. A dislocation density-based constitutive model with storage and recovery rates derived from Discrete Dislocation Dynamics is used to model strain hardening in stage II. The influence of dislocation mean free path and initial dislocation content on stage II hardening is simulated and compared with in-situ tensile experiments.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-THPB025

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THPB048

Double Cathode Configuration for the Nb Coating of HIE-ISOLDE Cavities

ion, cathode, cavity, ISOL

854

A. Awais
NCP, Islamabad, Pakistan
A. Awais, A.J.G. Lunt, G.J. Rosaz, A. Sublet, M. Taborelli
CERN, Geneva, Switzerland

The Quarter Wave Resonator (QWR) cavities for HIE-ISOLDE project at CERN have entered their ending phase of production. Some R&D is still required to improve the uniformity of the Nb layer thickness on the cavity surface. In order to improve this behaviour one approach which has been proposed is to replace the single cathode with a double cathode and test the suitability of different deposition techniques. With this change it is possible to control the plasma and power distribution separately for the inner and outer part of cavity and thereby potentially improve film uniformity throughout the cavity and coating duration. In this study a comparison between the deposition rates obtained using a single cathode and a double cathode using Direct Current (DC)-bias diode sputtering, DC-magnetron sputtering (DCMS) and Pulsed DC-magnetron sputtering (PDCMS) is presented. The morphology of the thin film samples were compared using Focused Ion Beam (FIB) cross section milling and Scanning Electron Microscopy (SEM) analysis.

Poster THPB048 [3.715 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-THPB048

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THPB052

Error Analysis of Surface Resistance Fits to Experimental Data

ion, cavity, experiment, data-analysis

859

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

Funding: This work is part of EuCARD-2, partly funded by the European Commission, GA 312453.
Superconducting material properties such as energy gap, mean free path or residual resistance are commonly extracted by fitting experimental surface resistance data. Depending on the measurement setup, both, temperature range and the number of points are limited. In order to obtain significant results, systematic as well as statistical uncertainties have to be taken into account. In this contribution different classes of errors and their impact on systematic and statistical deviations of the fitted parameters are discussed. In particular, past measurements have yielded contradictory conclusions that, we believe, result from the use of insufficient data in the necessary temperature range. Furthermore, this study is applied to the boundary conditions of the Quadrupole Resonator and its measurement accuracy.

Poster THPB052 [1.034 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-THPB052

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THPB059

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

ion, HOM, cavity, damping

881

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

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

Poster THPB059 [8.192 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-THPB059

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THPB079

Simulations of RF Field-induced Thermal Feedback in Niobium and Nb3Sn Cavities

ion, cavity, niobium, feedback

920

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

Thermal feedback is a known limitation for SRF cavities made of low-purity niobium, as the increased losses at higher temperature described by BCS theory create a feedback mechanism that can eventually result in a runaway effect and associated cavity quench. In a similar manner, niobium cavities coated with Nb3Sn may also be subject to increased losses from thermal feedback, as Nb3Sn is possessed of a much lower thermal conductivity than niobium, although this effect will be mitigated by the thin film nature of the coating. In order to better understand the degree to which thermal feedback plays a role in the performance of Nb3Sn cavities, it is necessary to understand how the various components of the problem play a role in the outcome. In this paper, we present the first results from simulations performed at Cornell University that model RF induced thermal feedback in both conventional niobium cavities and niobium cavities coated with a thin film of Nb3Sn. The impacts of layer thickness, niobium substrate thermal conductivity, and trapped flux on the performance of the cavity are discussed.

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reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-THPB079

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