IPAC2015 - List of Keywords (HOM)

Paper	Title	Other Keywords	Page
MOBD2	Design and Prototyping of HL-LHC Double Quarter Wave Crab Cavities for SPS Test	cavity, luminosity, proton, simulation	64
	S. Verdú-Andrés, S.A. Belomestnykh, I. Ben-Zvi, J. Skaritka, Q. Wu, B. P. Xiao BNL, Upton, Long Island, New York, USA L. Alberty, K. Artoos, R. Calaga, O. Capatina, T. Capelli, F. Carra, N. Kuder, R. Leuxe, C. Zanoni CERN, Geneva, Switzerland S.A. Belomestnykh, I. Ben-Zvi Stony Brook University, Stony Brook, USA Z. Li SLAC, Menlo Park, California, USA A. Ratti LBNL, Berkeley, California, USA
	Funding: Work supported by US DOE via US LARP program, through BSA LLC contract No.DE-AC02-98CH10886 and by EU FP7 HiLumi LHC grant No.284404. Used NERSC resources by US DOE contract No.DE-AC02-05CH11231. The LHC high luminosity project envisages the use of the crabbing technique for increasing and levelling the LHC luminosity. Double-Quarter Wave (DQW) resonators are compact cavities especially designed to meet the technical and performance requirements for LHC beam crabbing. A couple of DQW crab cavities are under preparation and will be tested with beam in the Super Proton Synchrotron (SPS) of CERN by 2017. This paper describes the design and prototyping of DQW crab cavities for the SPS test.
	Slides MOBD2 [6.909 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-MOBD2
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MOPWA032	Aspects of SRF Cavity Optimization for BESSY-VSR Upgrade	cavity, SRF, higher-order-mode, storage-ring	171
	T. Galek, K. Brackebusch, T. Flisgen, J. Heller, U. van Rienen Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany B.D. Isbarn, B. Riemann, M. Sommer, T. Weis DELTA, Dortmund, Germany
	Funding: Work supported by Federal Ministry for Research and Education BMBF under contract 05K13HR1. In this work we present a preliminary study of a long chain of cavities and some aspects involved in the optimization procedure. It is important to numerically model and optimize the SRF cavities with respect to external quality factors of the most dangerous higher order modes. BESSY-VSR is an upgrade scheme for the existing BESSY II storage ring aiming to simultaneously support variable electron pulse lengths. Currently, BESSY II supports long 15 ps bunches in the standard user optics configuration and short 1.5 ps bunches in a so-called low-α optics mode. In order to develop BESSY II into a variable electron pulse length storage ring, additional two sets of SRF higher-harmonic cavities will be installed. The present RF acceleration system operates at 0.5 GHz and the additional 3rd harmonic and 3rd sub-harmonic cavities will operate at 1.5 GHz and 1.75 GHz, respectively. These cavities are essential to produce short 1.5 ps bunches with a design current of up to 0.8 mA per bunch. The total current in the storage ring is limited by the higher order mode damping capabilities of the SRF cavities.
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MOPWA056	Transverse Multi-Pass Beam Breakup Simulation for KEK ERL Light Source	cavity, simulation, linac, cryomodule	248
	S. Chen, N. Nakamura, M. Shimada, D. Zhou KEK, Ibaraki, Japan S. Huang, K.X. Liu PKU, Beijing, People's Republic of China
	In this paper, the multi-pass BBU of such a high energy ERL is studied based on the simulation on a 3 GeV ERL light source proposed by KEK.
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MOPJE069	General Functionality for Turn-Dependent Element Properties in SixTrack	simulation, cavity, collimation, optics	468
	K.N. Sjobak, H. Burkhardt, R. De Maria, A. Mereghetti, A. Santamaría García CERN, Geneva, Switzerland
	In order to facilitate studies of how dynamically changing element attributes affect the dynamics of the beam and beam losses, the functionality for dynamic kicks (DYNK) of SixTrack has been significantly extended. This functionality can be used for the simulation of dynamic scenarios, such as when crab cavities are switched on, orbit bumps are applied, optics are changed, or failures occur. The functionality has been extended with a more general and flexible implementation, such that arbitrary time-dependent functions can be defined and applied to different attributes of families or individual elements, directly from the user input files. This removes the need for source code manipulation, and it is compatible with LHC@Home which offers substantial computing resources from volunteers. In this paper, the functionality and implementation of DYNK is discussed, along with examples of application to the HL-LHC crab cavities.
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MOPJE083	Implications of Manufacturing Errors on Higher Order Modes and on Beam Dynamics in the ESS Linac	cavity, coupling, linac, wakefield	514
	A. Farricker, R.M. Jones UMAN, Manchester, United Kingdom S. Molloy ESS, Lund, Sweden
	The European Spallation Source (ESS) in Lund, Sweden, will be a facility for fundamental physics studies of atomic structure using a spallation source of unparalleled brightness. To achieve this end, protons will be accelerated up to 2 GeV using a suite of cavities. Here we focus on the Medium Beta (β =0.67) elliptical superconducting cavities and we assess the influence of potential errors in fabrication to shift eigenmode frequencies onto an harmonic of the bunch frequency. If this occurs, and countermeasures are not adopted, the beam quality will be appreciably diluted . We provide details on the geometrical parameters which are particularly sensitive to frequency errors from intensive finite element simulations of the electromagnetic fields. A circuit model is also employed to rapidly assess the shift in the eigenmodes from their anticipated design values due a variety of potential errors. Aaron Farricker et al, Physics Procedia, Proceedings of HOMSC14 (in press), 2014.
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MOPMA016	Coupler RF Kick in the Input 1.3 GHz Accelerating Cavity of the LCLS-II Linac	cavity, focusing, accelerating-gradient, emittance	571
	A. Lunin, N. Solyak, A.I. Sukhanov, V.P. Yakovlev Fermilab, Batavia, Illinois, USA
	Main and HOM couplers break the cavity axial symmetry, distort RF field and, thus, create a transverse kick, even for a particle moving along the cavity axes. Dependence of a kick on the RF phase causes a beam emittance dilution and degrade the FEL radiation quality. The transverse kick is most dangerous for a beam passing through the first accelerating structure of a linac, where particles energy and their relativistic mass are low. In the paper we analyze the coupler RF kick in the first accelerating structure of the LCSL-II linac.
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MOPTY014	An Experimental Study of Higher-Order Modes Excited by High Repetition Rate Electron Beam in an SRF Cavity	electron, SRF, cavity, experiment	965
	Y. Gao, J.E. Chen, L.W. Feng, J.K. Hao, S. Huang, L. Lin, K.X. Liu, X. Luo, S.W. Quan, F. Wang, Zh.W. Wang PKU, Beijing, People's Republic of China
	Funding: National Natural Science Foundation of China (No. 11275014) Higher-order modes (HOMs) excited by electron beam traversing a superconducting rf (SRF) cavity contain lots of information and can be used for intra-cavity electron beam diagnostics. Unlike single bunch, multiple bunches would excite HOMs with a much complicated spectrum. In this paper, we present our recent research on HOMs excited by a high repetition rate electron beam in an SRF cavity. Especially, we focus on the integer multiple frequency peaks in the HOM spectrum, which are determined by the nearest eigen HOM peaks. The experiments were carried out on the DC-SRF photoinjector, which was operated at MHz repetition rate. The results agree well with theoretic analysis.
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TUPJE065	Multi-Bunch Stability Analysis of the Advanced Photon Source Upgrade Including the Higher-Harmonic Cavity	damping, impedance, simulation, radiation	1784
	L. Emery, T.G. Berenc, M. Borland, R.R. Lindberg ANL, Argonne, Ilinois, USA
	Funding: Work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357 Multi-bunch stability simulations were done for the very-low-emittance hybrid seven-bend-achromat (H7BA) lattice proposed for the Advanced Photon Source (APS) upgrade. The simulations, performed using tracking code elegant, were meant to determine whether the long-term wakefields of the higher-order modes (HOMs) of the main 352-MHz cavities will produce an instability. The multi-particle simulations include the important effects of the Higher-Harmonic Cavity (HHC) and the longitudinal impedance of the new vacuum chamber. These realistic simulations show that the HHC provides additional damping in the form of the Landau damping. Still, the HOMs may likely produce a multi-bunch instability which can be cured with more effective HOM damping or a longitudinal feedback system.
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WEPJE008	Experimental Study of Wakefields in an X-band Photonic Band Gap Accelerating Structure	wakefield, higher-order-mode, coupling, electron	2689
	E.I. Simakov, S. Arsenyev, C.E. Buechler, R.L. Edwards, W.P. Romero LANL, Los Alamos, New Mexico, USA M.E. Conde, G. Ha, C.-J. Jing, J.G. Power, E.E. Wisniewski ANL, Argonne, Illinois, USA C.-J. Jing Euclid TechLabs, LLC, Solon, Ohio, USA
	Funding: This work is supported by U.S. Department of Energy (DOE) Office of Science Early Career Research Program. We designed an experiment to conduct a detailed investigation of higher order mode spectrum in a room-temperature traveling-wave photonic band gap (PBG) accelerating structure at 11.7 GHz. It has been long recognized that PBG structures have great potential in reducing long-range wakefields in accelerators. The first ever demonstration of acceleration in room-temperature PBG structures was conducted at MIT in 2005. Since then, the importance of that device has been recognized by many research institutions. However, the full experimental characterization of the wakefield spectrum in a beam test has not been performed to date. The Argonne Wakefield Accelerator (AWA) test facility at the Argonne National Laboratory represents a perfect site where this evaluation could be conducted with a single high charge electron bunch and with a train of bunches. Here we describe fabrication and tuning of PBG cells, the final cold-test of the traveling-wave accelerating structure, and the results of the beam testing at AWA.
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WEPMA013	Hom Damping Optimization Design Studies for BESSY VSR Cavities	damping, cavity, impedance, SRF	2774
	A.V. Vélez, H.-W. Glock, J. Knobloch, A. Neumann HZB, Berlin, Germany
	The BESSY VSR project is a future upgrade of the 3rd generation BESSY II light source. By using the same "standard" user optics, simultaneously long (ca. 15ps) and short (ca. 1.5ps) bunches will be stored. Thus, superconducting higher harmonic cavities of the fundamental 500 MHz at two frequencies need to be installed in the BESSY II storage ring. This work describes the optimizations studies for the Waveguide-based HOM dampers and the adjustable fundamental power coupler for the 1.5 GHz first SRF cavity prototype.
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WEPMA029	Design of a Normal Conducting Cavity for Arrival Time Stabilization at FLASH	cavity, wakefield, coupling, simulation	2818
	M. Fakhari, K. Flöttmann, S. Pfeiffer, H. Schlarb DESY, Hamburg, Germany J. Roßbach Uni HH, Hamburg, Germany
	It has been shown, that beam-based feedback loops stabilize the bunch arrival time in the femtoseconds range. However, further minimizing the bunch arrival time jitter requires a faster actuator that is a normal conducting cavity with higher bandwidth compared to narrow-band superconducting cavities. We present the design of a 4-cell normal conducting cavity that is going to be used in a fast beam-based feedback at free-electron laser FLASH at Hamburg. The input power will be injected to the cavity via a loop coupler from the side of the first cell. The operating frequency of the designed cavity is about 3 GHz with an adjustable bandwidth. The long range longitudinal wakefield calculation results are reported to investigate the cavity performance for multi-beam operation up to 3 MHz bunch repetition rate. The results declare that the influence of the long range wakefield on the arrival time jitter is less than 1 fs.
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WEPMA046	Studies on Innovative Production methods of HOM Coupler for SRF 9-cell Cavity	cavity, SRF, controls, target	2869
	K. Nohara, N. Kawabata, K. Miyajima, M. Shinohara SPS, Funabashi-shi, Japan H. Hayano, S. Kato, T. Saeki, A. Yamamoto, M. Yamanaka KEK, Ibaraki, Japan
	Pure Nb as the material of SRF cavity bears hard workability in general. This is why both the inner and outer conductors of HOM coupler for 9-cell cavity have been conventionally produced by full machining, backward extrusion accompanied with annealing and so on. However, in the mass production of 9-cell cavities in ILC, further cost reduction is required. We produced both the inner and outer conductors of HOM coupler for 9-cell cavity in the advanced press forming methods aiming at cost reduction. Press forming of a pure Nb sheet for the outer conductor of HOM coupler was performed with fewer processes free from intermediate annealing and primary machining. For the inner conductor of HOM coupler, water jet cutting and press cold-forging of a plate was performed. The above advanced press forming methods showed favored results, leading to a possibility of simple mass-production of components and cost reduction. The vertical test on a 9-cell cavity with the press formed HOM couplers achieved 36 MV/m that is beyond ILC qualification. The R＆D works are ongoing for further improvement.
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WEPMN046	Compassion of Higher Order Modes Damping Techniques for Superconducting 9-Cell Structure	damping, quadrupole, cavity, dipole	3030
	Ya.V. Shashkov, A.A. Mitrofanov, N.P. Sobenin MEPhI, Moscow, Russia V. Zvyagintsev TRIUMF, Vancouver, Canada
	Funding: Work supported by Ministry of Education and Science grant 3.245.2014/r Modern types of accelerators, such as Energy recovery linacs, require low values of higher order modes (HOM) Qext. In accelerators with high current HOM could lead to high losses for the modes excitation, beam instability and beam break up. HOM couplers and waveguides are often used in such structures for HOM damping. Unfortunately they could lead to a violation of the axial symmetry of the accelerating field and negatively affect the beam emittance. Also these devices are subject for multipactor discharge and could be difficult in maintaining and fabrication. In this paper we examine several ways of HOM damping with ridged, fluted and corrugated drift tubes which are devoid of the above-mentioned drawbacks. The influence of the parameters of the drift tube on the HOM damping and on the parameters of the fundamental wave were analyzed. Higher order modes, ERL, SRF
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WEPMN047	Suppression of Higher Order Modes in an Array of Cavities Using Waveguides	damping, impedance, cavity, wakefield	3033
	Ya.V. Shashkov, N.P. Sobenin MEPhI, Moscow, Russia M. Zobov INFN/LNF, Frascati (Roma), Italy
	Funding: Work is supported by Ministry of Education and Science grant 3.245.2014/r и and by the EU FP7 HiLumi LHC - Grant Agreement 284404 In the frameworks of the High Luminosity LHC upgrade program an application of additional harmonic cavities operating at multiplies of the main RF system frequency of 400 MHz is currently under discussion. A structure consisting of two 800 MHz single cell superconducting cavities with grooved beam pipes coupled by drift tubes has been suggested for implementation. However, it is desirable to increase the number of single cells installed in one cryomodule in order to decrease the number of transitions between “warm” and “cold” parts of the collider vacuum chamber. Unfortunately it can lead to the appearance of higher order modes (HOM) trapped between the cavities. In order to solve this problem the methods of HOM damping with rectangular waveguides connected to the drift tubes were investigated and compared. In this paper we describe the results obtained for arrays of 2, 4 and 8 cavities.
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WEPTY008	Superconducting Harmonic Cavity for the Advanced Photon Source Upgrade	cavity, photon, cryomodule, SRF	3267
	M.P. Kelly, A. Barcikowski, J. Carwardine, Z.A. Conway, D. Horan, S.H. Kim, P.N. Ostroumov, G.J. Waldschmidt ANL, Argonne, Illinois, USA J. Rathke, T. Schultheiss AES, Medford, New York, USA
	A new bunch lengthening cryomodule using a single-cell ‘higher-harmonic’ superconducting cavity (HHC) based on the TESLA shape and operating at the 4th harmonic (1408 MHz) of the main RF is under development at Argonne. The system will be used to improve the Touschek lifetime and increase the single-bunch current limit in the upgraded multibend achromat lattice of the Advanced Photon Source electron storage ring. The 4 K cryomodule will fit within one half of a straight section, ~2.5 meters, of the ring. The system will use a pair of moveable 20 kW (each) CW RF power couplers to adjust the loaded Q and extract power from the beam. This will provide the flexibility to adjust the impedance presented to the beam and run at various beam currents. Higher-order modes (HOMs) induced by the circulating electron beam will be extracted along the beam axis and damped using a pair of room temperature beam line absorbers. Engineering designs and the prototyping status for the cavity, power couplers and HOM absorbers are discussed.
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WEPTY069	Complection of the Cornell High Q CW Full Linac Cryo-module	linac, cavity, cryomodule, alignment	3440
	R.G. Eichhorn, B. Bullock, B. Clasby, J.V. Conway, B. Elmore, F. Furuta, G.M. Ge, G.H. Hoffstaetter, M. Liepe, T.I. O'Connel, P. Quigley, D.M. Sabol, J. Sears, E.N. Smith, V. Veshcherevich Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA Y. He Fermilab, Batavia, Illinois, 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 individual HOM absorbers and one magnet/ BPM section. In pushing the limits, a high quality factor of the cavities (2x10¹⁰) and high beam currents (100 mA accelerated plus 100 mA decelerated) were targeted. We will review the design shortly and present the results of the components tested before the assembly. This includes data of the quality-factors of all 6 cavities that we produced and treated in-house, the HOM absorber performance measured with beam on a test set-up as well as testing of the couplers and the tuners.
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WEPTY071	Time Resolved Cryogenic Cooling Analysis of the Cornell Injector Cryomodule	simulation, cryogenics, operation, impedance	3443
	R.G. Eichhorn, S.R. Markham, P. Quigley, E.N. Smith Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Managing parallel cryogenic flows has become a key challenge in designing efficient and smart cryo-modules for particle accelerators. In analyzing the heating dynamics of the cornell high current injector module a power-full computational tool has been set-up allowing time resolved analysis and optimization. We will describe the computational methods and data sets we have used, report the results and compare them to measured data from the module being in good agreement. Mitigation strategies developed on basis of this model have helped pushing the operational limitations.
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WEPTY082	High Gradient Testing of the Five-cell Superconducting RF Module with a PBG Coupler Cell	cavity, linac, SRF, coupling	3471
	S. Arsenyev, W.B. Haynes, D.Y. Shchegolkov, E.I. Simakov, T. Tajima LANL, Los Alamos, New Mexico, USA C.H. Boulware, T.L. Grimm, A. Rogacki Niowave, Inc., Lansing, Michigan, USA
	We report results of high-gradient testing of the first 5- cell superconducting radio frequency (SRF) module with a photonic band gap cell (PBG). Higher order mode (HOM) damping is vital for preserving the quality of high-current electron beams in novel SRF accelerators. Because HOMs are not confined by the PBG array, they can be effectively damped in order to raise the current threshold for beam instabilities. The PBG design increases the real-estate gradient of the linac because both HOM damping and the fundamental power coupling can be done through the PBG cell instead of via the beam pipe at the ends of the cavity. A superconducting multi-cell cavity with a PBG damping cell is therefore an attractive option for high-current linacs. The first-ever SRF multi-cell cavity incorporating a PBG cell was designed a LANL and built at Niowave Inc. The cavity was tuned to a desired gradient profile and underwent surface treatment at Niowave. A vertical test (VTS) was then performed at LANL, demonstrating an abnormally low cavity quality factor in the accelerating mode of 1.6*10⁶. Future tests are proposed to determine the source of the losses and resolve the problem.
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WEPTY083	Five-cell Superconducting RF Module with a PBG Coupler Cell: Design and Cold Testing of the Copper Prototype	cavity, factory, damping, impedance	3475
	S. Arsenyev, D.Y. Shchegolkov, E.I. Simakov LANL, Los Alamos, New Mexico, USA C.H. Boulware, T.L. Grimm, A. Rogacki Niowave, Inc., Lansing, Michigan, USA
	We report the design and experimental data for a copper prototype of a superconducting radio-frequency (SRF) accelerator module. The five-cell module has an incorporated photonic band gap (PBG) cell with couplers. The purpose of the PBG cell is to achieve better higher order mode (HOM) damping which is vital for preserving the quality of highcurrent electron beams. Better HOM damping raises the current threshold for beam instabilities in novel SRF accelerators. The PBG design also increases the real-estate gradient of the linac because both HOM damping and the fundamental power coupling can be done through the PBG cell instead of on the beam pipe via complicated end assemblies. First, we will discuss the design and accelerating properties of the structure. The five-cell module was optimized to provide good HOM damping while maintaining the same accelerating properties as conventional elliptical-cell modules. We will then discuss the process of tuning the structure to obtain the desired accelerating gradient profile. Finally, we will list measured quality factors for the accelerating mode and the most dangerous HOMs.
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WEPWI004	FPC and Hi-Pass Filter HOM Coupler Design for the RF Dipole Crab Cavity for the LHC HiLumi Upgrade	cavity, dipole, coupling, damping	3492
	Z. Li SLAC, Menlo Park, California, USA S.U. De Silva, J.R. Delayen, R.G. Olave, H. Park ODU, Norfolk, Virginia, USA
	Funding: Work partially supported by the US DOE through the US LHC Accelerator Research Program (LARP), and by US DOE under contract number DE-AC02-76SF00515. A 400-MHz compact RF dipole (RFD) crab cavity design was jointly developed by Old Dominion University and SLAC under the support of US LARP program for the LHC HiLumi upgrade. The RFD cavity design is consisted of a rounded-square tank and two ridged deflecting poles, operating with a TE11-like dipole mode, which is the lowest mode of the cavity. A prototype RFD cavity is being manufactured and will be tested on the SPS beam line at CERN. The coaxial fundamental Power Coupler (FPC) of the prototype cavity was re-optimized to minimizing the power heating on the coupler internal antenna. A hi-pass filter HOM damping coupler was developed to achieve the required wakefield damping while maintaining a compact size to fit into the beam line space. In this paper, we will discuss the details of the RF optimization and tolerance analyses of the FPC and HOM couplers.
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WEPWI015	BNL 56 MHz HOM Damper Prototype Fabrication at JLab	niobium, cavity, network, vacuum	3521
	N.A. Huque, W.A. Clemens, E. Daly JLab, Newport News, Virginia, USA S. Bellavia, G.T. McIntyre, S.K. Seberg, Q. Wu BNL, Upton, Long Island, New York, USA
	A prototype Higher-Order Mode (HOM) Damper was fabricated at JLab for the Relativistic Heavy-Ion Collider’s (RHIC) 56 MHz cavity at Brookhaven National Laboratory (BNL). Primarily constructed from high RRR Niobium and Sapphire, the coaxial damper presented significant challenges in electron-beam welding (EBW), brazing and machining via acid etching. The results of the prototype operation brought about changes in the damper design, due to overheating braze alloys and possible multi-pacting. Five production HOM dampers are currently being fabricated at JLab. This paper outlines the challenges faced in the fabrication process, and the solutions put in place.
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WEPWI030	Injector Cavities Fabrication, Vertical Test Performance and Primary Cryomodule Design	cavity, cryomodule, dipole, impedance	3551
	H. Wang, G. Cheng, W.A. Clemens, G.K. Davis, K. Macha, R.B. Overton, D. Spell JLab, Newport News, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. After the electromagnetic design * and the mechanical design ** of a β=0.6, 2-cell elliptical SRF cavity, the cavity has been fabricated. Then both 2-cell and 7-cell cavities have been bench tuned to the target values of frequency, coupling external Q and field flatness. After buffer chemistry polishing (BCP) and high pressure rinses (HPR), Vertical 2K cavity test results have been satisfied the specifications and ready for the string assembly. We will report the cavity performance including Lorenz Force Detuning (LFD) and Higher Order Modes (HOM) damping data. Its integration with cavity tuners to the cryomodule design will be reported. * H. Wang, etc., Proceeding of IPAC2013, Shanghai, China, WEPWO073. ** G. Cheng, etc., Proceeding of PAC2013, Pasadena, CA, WEPAC47.
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WEPWI036	Design and Prototyping of a 400 MHz RF-dipole Crabbing Cavity for the LHC High-Luminosity Upgrade	cavity, dipole, cryomodule, luminosity	3568
	S.U. De Silva, J.R. Delayen, H. Park ODU, Norfolk, Virginia, USA Z. Li SLAC, Menlo Park, California, USA T.H. Nicol Fermilab, Batavia, Illinois, USA
	LHC High Luminosity Upgrade is in need of two crabbing systems that deflects the beam in both horizontal and vertical planes. The 400 MHz rf-dipole crabbing cavity system is capable of crabbing the proton beam in both planes. At present we are focusing our efforts on a complete crabbing system in the horizontal plane. Prior to LHC installation the crabbing system will be installed for beam test at SPS. The crabbing system consists of two rf-dipole cavities in the cryomodule. This paper discusses the electromagnetic design and mechanical properties of the rf-dipole crabbing system for SPS beam test.
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WEPWI037	Imperfection and Tolerance Analysis of HOM Couplers for ODU/SLAC 400 MHz Crabbing Cavity	cavity, impedance, dipole, luminosity	3572
	S.U. De Silva, J.R. Delayen, H. Park ODU, Norfolk, Virginia, USA Z. Li SLAC, Menlo Park, California, USA R.G. Olave Old Dominion University, Norfolk, Virginia, USA
	In preparation for the LHC High Luminosity upgrade, a 400 MHz crab cavity has been developed jointly at ODU/SLAC, including two higher order mode couplers designed to dampen the wakefields in order to comply with the impedance budget specified for the LHC system. During fabrication, assembly, and processing of the couplers, a number of imperfections may arise that could modify the higher order mode spectrum and the associated impedance for each mode. We present here a detailed study of the imperfections of the horizontal- and vertical- HOM couplers, and the associated allowed tolerances for manufacture, assembly and processing.
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WEPWI039	Engineering Study of Crab Cavity HOM Couplers for LHC High Luminosity Upgrade	niobium, cavity, damping, luminosity	3578
	H. Park, S.U. De Silva, J.R. Delayen, R.G. Olave ODU, Norfolk, Virginia, USA T. Capelli CERN, Geneva, Switzerland S.U. De Silva, J.R. Delayen, H. Park JLab, Newport News, Virginia, USA Z. Li SLAC, Menlo Park, California, USA T.H. Nicol Fermilab, Batavia, Illinois, USA N. Templeton STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom
	The LHC is planning to employ crab cavities for the high luminosity upgrade. Old Dominion University and SLAC National Laboratory are developing the crab cavity completed with the HOM damping couplers. The HOM couplers are coaxial type and perform over broad band up to 2 GHz. The amount of extracted power requires active cooling using liquid helium. The electromagnetic study has provided expected power dissipation on the coupler. Correlations between the fabrication tolerance and its damping performance have been studied and the results are providing guidelines on how to manufacture the HOM couplers. This paper summarizes the engineering studies; mechanical strength as a part of pressure system, thermal stability, and fabrication method to ensure the required tolerance.
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WEPWI059	Higher Order Mode Filter Design for Double Quarter Wave Crab Cavity for the LHC High Luminosity Upgrade	cavity, impedance, luminosity, coupling	3627
	B. P. Xiao, S.A. Belomestnykh, I. Ben-Zvi, J. Skaritka, S. Verdú-Andrés, Q. Wu BNL, Upton, Long Island, New York, USA S.A. Belomestnykh, I. Ben-Zvi Stony Brook University, Stony Brook, USA G. Burt, B.D.S. Hall Cockcroft Institute, Lancaster University, Lancaster, United Kingdom G. Burt Lancaster University, Lancaster, United Kingdom R. Calaga, O. Capatina CERN, Geneva, Switzerland T.J. Jones STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom
	Funding: Work partly supported by US LARP, by US DOE under contract No. DE-AC02-05CH11231 and through BSA under contract No. DE-AC02-98CH10886. Research supported by EU FP7 HiLumi LHC - Grant Agreement 284404. A double quarter wave crab cavity (DQWCC) was designed for the Large Hadron Collider (LHC) luminosity upgrade. A compact Higher Order Mode (HOM) filter with wide stop band at the deflecting mode is developed for this cavity. Multi-physics finite element simulation results are presented. The integration of this design to the cavity cryomodule is described.
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THXB2	Crab Cavities: Past, Present, and Future of a Challenging Device	cavity, luminosity, collider, operation	3643
	Q. Wu BNL, Upton, Long Island, New York, USA
	Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with LARP and the U.S. Department of Energy and EU FP7 HiLumi LHC - Grant Agreement 284404 In two-ring facilities operating with a crossing angle collision scheme, the luminosity can be limited due to incomplete overlap of the colliding bunches. Crab cavities are introduced to restore head-on collisions by providing destined opposite deflection to the head and tail of the bunch. Luminosity increase has been demonstrated at KEKB with global crab crossing, and the Large Hardron Collider (LHC) at CERN is currently designing local crab crossing for the Hi-Lumi upgrade. Future colliders may investigate both approaches. This paper reviews the challenges in the technology and implementation of crab cavities, discusses experience in past colliders, ongoing R&D and proposed implementations for future facilities such as HL-LHC, CLIC, ILC, and eRHIC/MEIC.
	Slides THXB2 [4.307 MB]
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THPF033	The First Operation of 56 MHz SRF Cavity in RHIC	cavity, operation, SRF, cryomodule	3767
	Q. Wu, S.A. Belomestnykh, I. Ben-Zvi, M. Blaskiewicz, L. DeSanto, D. Goldberg, M. Harvey, T. Hayes, G.T. McIntyre, K. Mernick, P. Orfin, S.K. Seberg, F. Severino, K.S. Smith, R. Than, A. Zaltsman 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. A 56 MHz superconducting RF cavity has been designed, fabricated and installed in the Relativistic Heavy Ion Collider (RHIC). The cavity operated at 4.4 K with a “quiet helium source” to isolate the cavity from environmental acoustic noise. The cavity is a beam driven quarter wave resonator. It is detuned and damped during injection and acceleration cycles and is brought to operation only at store energy. For a first test operation, the cavity voltage was stabilized at 300 kV with full beam current. Within both Au + Au and asymmetrical Au + He3 collisions, luminosity improvement was detected from direct measurement, and the hourglass effect was reduced. One higher order mode (HOM) coupler was installed on the cavity. We report in this paper on our measurement of a broadband HOM spectrum excited by the Au beam.
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THPF062	CADS 650 MHz β=0.63 Elliptical Cavity Study	cavity, linac, proton, resonance	3836
	L.J. Wen, Y. He, Y.M. Li, S.H. Zhang IMP/CAS, Lanzhou, People's Republic of China
	The China Accelerator Driven Sub-critical System (CADS) is a high intensity proton facility to dispose of nuclear waste and generate electric power. CADS is based on 1.5 GeV, 10mA CW superconducting (SC) linac as a driver. The high-energy section of the linac is composed of two families of SC elliptical cavities which are designed for the geometrical beta 0.63 and 0.82. In this paper, the 650 MHz β=0.63 SC elliptical cavity was studied, including cavity optimization, multipacting, high order modes (HOM) and generator RF power calculation.
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Paper

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Other Keywords

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MOBD2

Design and Prototyping of HL-LHC Double Quarter Wave Crab Cavities for SPS Test

cavity, luminosity, proton, simulation

64

S. Verdú-Andrés, S.A. Belomestnykh, I. Ben-Zvi, J. Skaritka, Q. Wu, B. P. Xiao
BNL, Upton, Long Island, New York, USA
L. Alberty, K. Artoos, R. Calaga, O. Capatina, T. Capelli, F. Carra, N. Kuder, R. Leuxe, C. Zanoni
CERN, Geneva, Switzerland
S.A. Belomestnykh, I. Ben-Zvi
Stony Brook University, Stony Brook, USA
Z. Li
SLAC, Menlo Park, California, USA
A. Ratti
LBNL, Berkeley, California, USA

Funding: Work supported by US DOE via US LARP program, through BSA LLC contract No.DE-AC02-98CH10886 and by EU FP7 HiLumi LHC grant No.284404. Used NERSC resources by US DOE contract No.DE-AC02-05CH11231.
The LHC high luminosity project envisages the use of the crabbing technique for increasing and levelling the LHC luminosity. Double-Quarter Wave (DQW) resonators are compact cavities especially designed to meet the technical and performance requirements for LHC beam crabbing. A couple of DQW crab cavities are under preparation and will be tested with beam in the Super Proton Synchrotron (SPS) of CERN by 2017. This paper describes the design and prototyping of DQW crab cavities for the SPS test.

Slides MOBD2 [6.909 MB]

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MOPWA032

Aspects of SRF Cavity Optimization for BESSY-VSR Upgrade

cavity, SRF, higher-order-mode, storage-ring

171

T. Galek, K. Brackebusch, T. Flisgen, J. Heller, U. van Rienen
Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
B.D. Isbarn, B. Riemann, M. Sommer, T. Weis
DELTA, Dortmund, Germany

Funding: Work supported by Federal Ministry for Research and Education BMBF under contract 05K13HR1.
In this work we present a preliminary study of a long chain of cavities and some aspects involved in the optimization procedure. It is important to numerically model and optimize the SRF cavities with respect to external quality factors of the most dangerous higher order modes. BESSY-VSR is an upgrade scheme for the existing BESSY II storage ring aiming to simultaneously support variable electron pulse lengths. Currently, BESSY II supports long 15 ps bunches in the standard user optics configuration and short 1.5 ps bunches in a so-called low-α optics mode. In order to develop BESSY II into a variable electron pulse length storage ring, additional two sets of SRF higher-harmonic cavities will be installed. The present RF acceleration system operates at 0.5 GHz and the additional 3rd harmonic and 3rd sub-harmonic cavities will operate at 1.5 GHz and 1.75 GHz, respectively. These cavities are essential to produce short 1.5 ps bunches with a design current of up to 0.8 mA per bunch. The total current in the storage ring is limited by the higher order mode damping capabilities of the SRF cavities.

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MOPWA056

Transverse Multi-Pass Beam Breakup Simulation for KEK ERL Light Source

cavity, simulation, linac, cryomodule

248

S. Chen, N. Nakamura, M. Shimada, D. Zhou
KEK, Ibaraki, Japan
S. Huang, K.X. Liu
PKU, Beijing, People's Republic of China

In this paper, the multi-pass BBU of such a high energy ERL is studied based on the simulation on a 3 GeV ERL light source proposed by KEK.

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MOPJE069

General Functionality for Turn-Dependent Element Properties in SixTrack

simulation, cavity, collimation, optics

468

K.N. Sjobak, H. Burkhardt, R. De Maria, A. Mereghetti, A. Santamaría García
CERN, Geneva, Switzerland

In order to facilitate studies of how dynamically changing element attributes affect the dynamics of the beam and beam losses, the functionality for dynamic kicks (DYNK) of SixTrack has been significantly extended. This functionality can be used for the simulation of dynamic scenarios, such as when crab cavities are switched on, orbit bumps are applied, optics are changed, or failures occur. The functionality has been extended with a more general and flexible implementation, such that arbitrary time-dependent functions can be defined and applied to different attributes of families or individual elements, directly from the user input files. This removes the need for source code manipulation, and it is compatible with LHC@Home which offers substantial computing resources from volunteers. In this paper, the functionality and implementation of DYNK is discussed, along with examples of application to the HL-LHC crab cavities.

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MOPJE083

Implications of Manufacturing Errors on Higher Order Modes and on Beam Dynamics in the ESS Linac

cavity, coupling, linac, wakefield

514

A. Farricker, R.M. Jones
UMAN, Manchester, United Kingdom
S. Molloy
ESS, Lund, Sweden

The European Spallation Source (ESS) in Lund, Sweden, will be a facility for fundamental physics studies of atomic structure using a spallation source of unparalleled brightness. To achieve this end, protons will be accelerated up to 2 GeV using a suite of cavities. Here we focus on the Medium Beta (β =0.67) elliptical superconducting cavities and we assess the influence of potential errors in fabrication to shift eigenmode frequencies onto an harmonic of the bunch frequency. If this occurs, and countermeasures are not adopted, the beam quality will be appreciably diluted *. We provide details on the geometrical parameters which are particularly sensitive to frequency errors from intensive finite element simulations of the electromagnetic fields. A circuit model is also employed to rapidly assess the shift in the eigenmodes from their anticipated design values due a variety of potential errors.
* Aaron Farricker et al, Physics Procedia, Proceedings of HOMSC14 (in press), 2014.

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MOPMA016

Coupler RF Kick in the Input 1.3 GHz Accelerating Cavity of the LCLS-II Linac

cavity, focusing, accelerating-gradient, emittance

571

A. Lunin, N. Solyak, A.I. Sukhanov, V.P. Yakovlev
Fermilab, Batavia, Illinois, USA

Main and HOM couplers break the cavity axial symmetry, distort RF field and, thus, create a transverse kick, even for a particle moving along the cavity axes. Dependence of a kick on the RF phase causes a beam emittance dilution and degrade the FEL radiation quality. The transverse kick is most dangerous for a beam passing through the first accelerating structure of a linac, where particles energy and their relativistic mass are low. In the paper we analyze the coupler RF kick in the first accelerating structure of the LCSL-II linac.

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MOPTY014

An Experimental Study of Higher-Order Modes Excited by High Repetition Rate Electron Beam in an SRF Cavity

electron, SRF, cavity, experiment

965

Y. Gao, J.E. Chen, L.W. Feng, J.K. Hao, S. Huang, L. Lin, K.X. Liu, X. Luo, S.W. Quan, F. Wang, Zh.W. Wang
PKU, Beijing, People's Republic of China

Funding: National Natural Science Foundation of China (No. 11275014)
Higher-order modes (HOMs) excited by electron beam traversing a superconducting rf (SRF) cavity contain lots of information and can be used for intra-cavity electron beam diagnostics. Unlike single bunch, multiple bunches would excite HOMs with a much complicated spectrum. In this paper, we present our recent research on HOMs excited by a high repetition rate electron beam in an SRF cavity. Especially, we focus on the integer multiple frequency peaks in the HOM spectrum, which are determined by the nearest eigen HOM peaks. The experiments were carried out on the DC-SRF photoinjector, which was operated at MHz repetition rate. The results agree well with theoretic analysis.

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TUPJE065

Multi-Bunch Stability Analysis of the Advanced Photon Source Upgrade Including the Higher-Harmonic Cavity

damping, impedance, simulation, radiation

1784

L. Emery, T.G. Berenc, M. Borland, R.R. Lindberg
ANL, Argonne, Ilinois, USA

Funding: Work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357
Multi-bunch stability simulations were done for the very-low-emittance hybrid seven-bend-achromat (H7BA) lattice proposed for the Advanced Photon Source (APS) upgrade. The simulations, performed using tracking code elegant, were meant to determine whether the long-term wakefields of the higher-order modes (HOMs) of the main 352-MHz cavities will produce an instability. The multi-particle simulations include the important effects of the Higher-Harmonic Cavity (HHC) and the longitudinal impedance of the new vacuum chamber. These realistic simulations show that the HHC provides additional damping in the form of the Landau damping. Still, the HOMs may likely produce a multi-bunch instability which can be cured with more effective HOM damping or a longitudinal feedback system.

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WEPJE008

Experimental Study of Wakefields in an X-band Photonic Band Gap Accelerating Structure

wakefield, higher-order-mode, coupling, electron

2689

E.I. Simakov, S. Arsenyev, C.E. Buechler, R.L. Edwards, W.P. Romero
LANL, Los Alamos, New Mexico, USA
M.E. Conde, G. Ha, C.-J. Jing, J.G. Power, E.E. Wisniewski
ANL, Argonne, Illinois, USA
C.-J. Jing
Euclid TechLabs, LLC, Solon, Ohio, USA

Funding: This work is supported by U.S. Department of Energy (DOE) Office of Science Early Career Research Program.
We designed an experiment to conduct a detailed investigation of higher order mode spectrum in a room-temperature traveling-wave photonic band gap (PBG) accelerating structure at 11.7 GHz. It has been long recognized that PBG structures have great potential in reducing long-range wakefields in accelerators. The first ever demonstration of acceleration in room-temperature PBG structures was conducted at MIT in 2005. Since then, the importance of that device has been recognized by many research institutions. However, the full experimental characterization of the wakefield spectrum in a beam test has not been performed to date. The Argonne Wakefield Accelerator (AWA) test facility at the Argonne National Laboratory represents a perfect site where this evaluation could be conducted with a single high charge electron bunch and with a train of bunches. Here we describe fabrication and tuning of PBG cells, the final cold-test of the traveling-wave accelerating structure, and the results of the beam testing at AWA.

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WEPMA013

Hom Damping Optimization Design Studies for BESSY VSR Cavities

damping, cavity, impedance, SRF

2774

A.V. Vélez, H.-W. Glock, J. Knobloch, A. Neumann
HZB, Berlin, Germany

The BESSY VSR project is a future upgrade of the 3rd generation BESSY II light source. By using the same "standard" user optics, simultaneously long (ca. 15ps) and short (ca. 1.5ps) bunches will be stored. Thus, superconducting higher harmonic cavities of the fundamental 500 MHz at two frequencies need to be installed in the BESSY II storage ring. This work describes the optimizations studies for the Waveguide-based HOM dampers and the adjustable fundamental power coupler for the 1.5 GHz first SRF cavity prototype.

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WEPMA029

Design of a Normal Conducting Cavity for Arrival Time Stabilization at FLASH

cavity, wakefield, coupling, simulation

2818

M. Fakhari, K. Flöttmann, S. Pfeiffer, H. Schlarb
DESY, Hamburg, Germany
J. Roßbach
Uni HH, Hamburg, Germany

It has been shown, that beam-based feedback loops stabilize the bunch arrival time in the femtoseconds range. However, further minimizing the bunch arrival time jitter requires a faster actuator that is a normal conducting cavity with higher bandwidth compared to narrow-band superconducting cavities. We present the design of a 4-cell normal conducting cavity that is going to be used in a fast beam-based feedback at free-electron laser FLASH at Hamburg. The input power will be injected to the cavity via a loop coupler from the side of the first cell. The operating frequency of the designed cavity is about 3 GHz with an adjustable bandwidth. The long range longitudinal wakefield calculation results are reported to investigate the cavity performance for multi-beam operation up to 3 MHz bunch repetition rate. The results declare that the influence of the long range wakefield on the arrival time jitter is less than 1 fs.

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WEPMA046

Studies on Innovative Production methods of HOM Coupler for SRF 9-cell Cavity

cavity, SRF, controls, target

2869

K. Nohara, N. Kawabata, K. Miyajima, M. Shinohara
SPS, Funabashi-shi, Japan
H. Hayano, S. Kato, T. Saeki, A. Yamamoto, M. Yamanaka
KEK, Ibaraki, Japan

Pure Nb as the material of SRF cavity bears hard workability in general. This is why both the inner and outer conductors of HOM coupler for 9-cell cavity have been conventionally produced by full machining, backward extrusion accompanied with annealing and so on. However, in the mass production of 9-cell cavities in ILC, further cost reduction is required. We produced both the inner and outer conductors of HOM coupler for 9-cell cavity in the advanced press forming methods aiming at cost reduction. Press forming of a pure Nb sheet for the outer conductor of HOM coupler was performed with fewer processes free from intermediate annealing and primary machining. For the inner conductor of HOM coupler, water jet cutting and press cold-forging of a plate was performed. The above advanced press forming methods showed favored results, leading to a possibility of simple mass-production of components and cost reduction. The vertical test on a 9-cell cavity with the press formed HOM couplers achieved 36 MV/m that is beyond ILC qualification. The R＆D works are ongoing for further improvement.

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WEPMN046

Compassion of Higher Order Modes Damping Techniques for Superconducting 9-Cell Structure

damping, quadrupole, cavity, dipole

3030

Ya.V. Shashkov, A.A. Mitrofanov, N.P. Sobenin
MEPhI, Moscow, Russia
V. Zvyagintsev
TRIUMF, Vancouver, Canada

Funding: Work supported by Ministry of Education and Science grant 3.245.2014/r
Modern types of accelerators, such as Energy recovery linacs, require low values of higher order modes (HOM) Qext. In accelerators with high current HOM could lead to high losses for the modes excitation, beam instability and beam break up. HOM couplers and waveguides are often used in such structures for HOM damping. Unfortunately they could lead to a violation of the axial symmetry of the accelerating field and negatively affect the beam emittance. Also these devices are subject for multipactor discharge and could be difficult in maintaining and fabrication. In this paper we examine several ways of HOM damping with ridged, fluted and corrugated drift tubes which are devoid of the above-mentioned drawbacks. The influence of the parameters of the drift tube on the HOM damping and on the parameters of the fundamental wave were analyzed.
Higher order modes, ERL, SRF

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WEPMN047

Suppression of Higher Order Modes in an Array of Cavities Using Waveguides

damping, impedance, cavity, wakefield

3033

Ya.V. Shashkov, N.P. Sobenin
MEPhI, Moscow, Russia
M. Zobov
INFN/LNF, Frascati (Roma), Italy

Funding: Work is supported by Ministry of Education and Science grant 3.245.2014/r и and by the EU FP7 HiLumi LHC - Grant Agreement 284404
In the frameworks of the High Luminosity LHC upgrade program an application of additional harmonic cavities operating at multiplies of the main RF system frequency of 400 MHz is currently under discussion. A structure consisting of two 800 MHz single cell superconducting cavities with grooved beam pipes coupled by drift tubes has been suggested for implementation. However, it is desirable to increase the number of single cells installed in one cryomodule in order to decrease the number of transitions between “warm” and “cold” parts of the collider vacuum chamber. Unfortunately it can lead to the appearance of higher order modes (HOM) trapped between the cavities. In order to solve this problem the methods of HOM damping with rectangular waveguides connected to the drift tubes were investigated and compared. In this paper we describe the results obtained for arrays of 2, 4 and 8 cavities.

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WEPTY008

Superconducting Harmonic Cavity for the Advanced Photon Source Upgrade

cavity, photon, cryomodule, SRF

3267

M.P. Kelly, A. Barcikowski, J. Carwardine, Z.A. Conway, D. Horan, S.H. Kim, P.N. Ostroumov, G.J. Waldschmidt
ANL, Argonne, Illinois, USA
J. Rathke, T. Schultheiss
AES, Medford, New York, USA

A new bunch lengthening cryomodule using a single-cell ‘higher-harmonic’ superconducting cavity (HHC) based on the TESLA shape and operating at the 4th harmonic (1408 MHz) of the main RF is under development at Argonne. The system will be used to improve the Touschek lifetime and increase the single-bunch current limit in the upgraded multibend achromat lattice of the Advanced Photon Source electron storage ring. The 4 K cryomodule will fit within one half of a straight section, ~2.5 meters, of the ring. The system will use a pair of moveable 20 kW (each) CW RF power couplers to adjust the loaded Q and extract power from the beam. This will provide the flexibility to adjust the impedance presented to the beam and run at various beam currents. Higher-order modes (HOMs) induced by the circulating electron beam will be extracted along the beam axis and damped using a pair of room temperature beam line absorbers. Engineering designs and the prototyping status for the cavity, power couplers and HOM absorbers are discussed.

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WEPTY069

Complection of the Cornell High Q CW Full Linac Cryo-module

linac, cavity, cryomodule, alignment

3440

R.G. Eichhorn, B. Bullock, B. Clasby, J.V. Conway, B. Elmore, F. Furuta, G.M. Ge, G.H. Hoffstaetter, M. Liepe, T.I. O'Connel, P. Quigley, D.M. Sabol, J. Sears, E.N. Smith, V. Veshcherevich
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
Y. He
Fermilab, Batavia, Illinois, 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 individual HOM absorbers and one magnet/ BPM section. In pushing the limits, a high quality factor of the cavities (2x10¹⁰) and high beam currents (100 mA accelerated plus 100 mA decelerated) were targeted. We will review the design shortly and present the results of the components tested before the assembly. This includes data of the quality-factors of all 6 cavities that we produced and treated in-house, the HOM absorber performance measured with beam on a test set-up as well as testing of the couplers and the tuners.

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WEPTY071

Time Resolved Cryogenic Cooling Analysis of the Cornell Injector Cryomodule

simulation, cryogenics, operation, impedance

3443

R.G. Eichhorn, S.R. Markham, P. Quigley, E.N. Smith
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Managing parallel cryogenic flows has become a key challenge in designing efficient and smart cryo-modules for particle accelerators. In analyzing the heating dynamics of the cornell high current injector module a power-full computational tool has been set-up allowing time resolved analysis and optimization. We will describe the computational methods and data sets we have used, report the results and compare them to measured data from the module being in good agreement. Mitigation strategies developed on basis of this model have helped pushing the operational limitations.

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WEPTY082

High Gradient Testing of the Five-cell Superconducting RF Module with a PBG Coupler Cell

cavity, linac, SRF, coupling

3471

S. Arsenyev, W.B. Haynes, D.Y. Shchegolkov, E.I. Simakov, T. Tajima
LANL, Los Alamos, New Mexico, USA
C.H. Boulware, T.L. Grimm, A. Rogacki
Niowave, Inc., Lansing, Michigan, USA

We report results of high-gradient testing of the first 5- cell superconducting radio frequency (SRF) module with a photonic band gap cell (PBG). Higher order mode (HOM) damping is vital for preserving the quality of high-current electron beams in novel SRF accelerators. Because HOMs are not confined by the PBG array, they can be effectively damped in order to raise the current threshold for beam instabilities. The PBG design increases the real-estate gradient of the linac because both HOM damping and the fundamental power coupling can be done through the PBG cell instead of via the beam pipe at the ends of the cavity. A superconducting multi-cell cavity with a PBG damping cell is therefore an attractive option for high-current linacs. The first-ever SRF multi-cell cavity incorporating a PBG cell was designed a LANL and built at Niowave Inc. The cavity was tuned to a desired gradient profile and underwent surface treatment at Niowave. A vertical test (VTS) was then performed at LANL, demonstrating an abnormally low cavity quality factor in the accelerating mode of 1.6*10⁶. Future tests are proposed to determine the source of the losses and resolve the problem.

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WEPTY083

Five-cell Superconducting RF Module with a PBG Coupler Cell: Design and Cold Testing of the Copper Prototype

cavity, factory, damping, impedance

3475

S. Arsenyev, D.Y. Shchegolkov, E.I. Simakov
LANL, Los Alamos, New Mexico, USA
C.H. Boulware, T.L. Grimm, A. Rogacki
Niowave, Inc., Lansing, Michigan, USA

We report the design and experimental data for a copper prototype of a superconducting radio-frequency (SRF) accelerator module. The five-cell module has an incorporated photonic band gap (PBG) cell with couplers. The purpose of the PBG cell is to achieve better higher order mode (HOM) damping which is vital for preserving the quality of highcurrent electron beams. Better HOM damping raises the current threshold for beam instabilities in novel SRF accelerators. The PBG design also increases the real-estate gradient of the linac because both HOM damping and the fundamental power coupling can be done through the PBG cell instead of on the beam pipe via complicated end assemblies. First, we will discuss the design and accelerating properties of the structure. The five-cell module was optimized to provide good HOM damping while maintaining the same accelerating properties as conventional elliptical-cell modules. We will then discuss the process of tuning the structure to obtain the desired accelerating gradient profile. Finally, we will list measured quality factors for the accelerating mode and the most dangerous HOMs.

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WEPWI004

FPC and Hi-Pass Filter HOM Coupler Design for the RF Dipole Crab Cavity for the LHC HiLumi Upgrade

cavity, dipole, coupling, damping

3492

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

Funding: Work partially supported by the US DOE through the US LHC Accelerator Research Program (LARP), and by US DOE under contract number DE-AC02-76SF00515.
A 400-MHz compact RF dipole (RFD) crab cavity design was jointly developed by Old Dominion University and SLAC under the support of US LARP program for the LHC HiLumi upgrade. The RFD cavity design is consisted of a rounded-square tank and two ridged deflecting poles, operating with a TE11-like dipole mode, which is the lowest mode of the cavity. A prototype RFD cavity is being manufactured and will be tested on the SPS beam line at CERN. The coaxial fundamental Power Coupler (FPC) of the prototype cavity was re-optimized to minimizing the power heating on the coupler internal antenna. A hi-pass filter HOM damping coupler was developed to achieve the required wakefield damping while maintaining a compact size to fit into the beam line space. In this paper, we will discuss the details of the RF optimization and tolerance analyses of the FPC and HOM couplers.

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WEPWI015

BNL 56 MHz HOM Damper Prototype Fabrication at JLab

niobium, cavity, network, vacuum

3521

N.A. Huque, W.A. Clemens, E. Daly
JLab, Newport News, Virginia, USA
S. Bellavia, G.T. McIntyre, S.K. Seberg, Q. Wu
BNL, Upton, Long Island, New York, USA

A prototype Higher-Order Mode (HOM) Damper was fabricated at JLab for the Relativistic Heavy-Ion Collider’s (RHIC) 56 MHz cavity at Brookhaven National Laboratory (BNL). Primarily constructed from high RRR Niobium and Sapphire, the coaxial damper presented significant challenges in electron-beam welding (EBW), brazing and machining via acid etching. The results of the prototype operation brought about changes in the damper design, due to overheating braze alloys and possible multi-pacting. Five production HOM dampers are currently being fabricated at JLab. This paper outlines the challenges faced in the fabrication process, and the solutions put in place.

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WEPWI030

Injector Cavities Fabrication, Vertical Test Performance and Primary Cryomodule Design

cavity, cryomodule, dipole, impedance

3551

H. Wang, G. Cheng, W.A. Clemens, G.K. Davis, K. Macha, R.B. Overton, D. Spell
JLab, Newport News, Virginia, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
After the electromagnetic design * and the mechanical design ** of a β=0.6, 2-cell elliptical SRF cavity, the cavity has been fabricated. Then both 2-cell and 7-cell cavities have been bench tuned to the target values of frequency, coupling external Q and field flatness. After buffer chemistry polishing (BCP) and high pressure rinses (HPR), Vertical 2K cavity test results have been satisfied the specifications and ready for the string assembly. We will report the cavity performance including Lorenz Force Detuning (LFD) and Higher Order Modes (HOM) damping data. Its integration with cavity tuners to the cryomodule design will be reported.
* H. Wang, etc., Proceeding of IPAC2013, Shanghai, China, WEPWO073.
** G. Cheng, etc., Proceeding of PAC2013, Pasadena, CA, WEPAC47.

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WEPWI036

Design and Prototyping of a 400 MHz RF-dipole Crabbing Cavity for the LHC High-Luminosity Upgrade

cavity, dipole, cryomodule, luminosity

3568

S.U. De Silva, J.R. Delayen, H. Park
ODU, Norfolk, Virginia, USA
Z. Li
SLAC, Menlo Park, California, USA
T.H. Nicol
Fermilab, Batavia, Illinois, USA

LHC High Luminosity Upgrade is in need of two crabbing systems that deflects the beam in both horizontal and vertical planes. The 400 MHz rf-dipole crabbing cavity system is capable of crabbing the proton beam in both planes. At present we are focusing our efforts on a complete crabbing system in the horizontal plane. Prior to LHC installation the crabbing system will be installed for beam test at SPS. The crabbing system consists of two rf-dipole cavities in the cryomodule. This paper discusses the electromagnetic design and mechanical properties of the rf-dipole crabbing system for SPS beam test.

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WEPWI037

Imperfection and Tolerance Analysis of HOM Couplers for ODU/SLAC 400 MHz Crabbing Cavity

cavity, impedance, dipole, luminosity

3572

S.U. De Silva, J.R. Delayen, H. Park
ODU, Norfolk, Virginia, USA
Z. Li
SLAC, Menlo Park, California, USA
R.G. Olave
Old Dominion University, Norfolk, Virginia, USA

In preparation for the LHC High Luminosity upgrade, a 400 MHz crab cavity has been developed jointly at ODU/SLAC, including two higher order mode couplers designed to dampen the wakefields in order to comply with the impedance budget specified for the LHC system. During fabrication, assembly, and processing of the couplers, a number of imperfections may arise that could modify the higher order mode spectrum and the associated impedance for each mode. We present here a detailed study of the imperfections of the horizontal- and vertical- HOM couplers, and the associated allowed tolerances for manufacture, assembly and processing.

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WEPWI039

Engineering Study of Crab Cavity HOM Couplers for LHC High Luminosity Upgrade

niobium, cavity, damping, luminosity

3578

H. Park, S.U. De Silva, J.R. Delayen, R.G. Olave
ODU, Norfolk, Virginia, USA
T. Capelli
CERN, Geneva, Switzerland
S.U. De Silva, J.R. Delayen, H. Park
JLab, Newport News, Virginia, USA
Z. Li
SLAC, Menlo Park, California, USA
T.H. Nicol
Fermilab, Batavia, Illinois, USA
N. Templeton
STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom

The LHC is planning to employ crab cavities for the high luminosity upgrade. Old Dominion University and SLAC National Laboratory are developing the crab cavity completed with the HOM damping couplers. The HOM couplers are coaxial type and perform over broad band up to 2 GHz. The amount of extracted power requires active cooling using liquid helium. The electromagnetic study has provided expected power dissipation on the coupler. Correlations between the fabrication tolerance and its damping performance have been studied and the results are providing guidelines on how to manufacture the HOM couplers. This paper summarizes the engineering studies; mechanical strength as a part of pressure system, thermal stability, and fabrication method to ensure the required tolerance.

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WEPWI059

Higher Order Mode Filter Design for Double Quarter Wave Crab Cavity for the LHC High Luminosity Upgrade

cavity, impedance, luminosity, coupling

3627

B. P. Xiao, S.A. Belomestnykh, I. Ben-Zvi, J. Skaritka, S. Verdú-Andrés, Q. Wu
BNL, Upton, Long Island, New York, USA
S.A. Belomestnykh, I. Ben-Zvi
Stony Brook University, Stony Brook, USA
G. Burt, B.D.S. Hall
Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
G. Burt
Lancaster University, Lancaster, United Kingdom
R. Calaga, O. Capatina
CERN, Geneva, Switzerland
T.J. Jones
STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom

Funding: Work partly supported by US LARP, by US DOE under contract No. DE-AC02-05CH11231 and through BSA under contract No. DE-AC02-98CH10886. Research supported by EU FP7 HiLumi LHC - Grant Agreement 284404.
A double quarter wave crab cavity (DQWCC) was designed for the Large Hadron Collider (LHC) luminosity upgrade. A compact Higher Order Mode (HOM) filter with wide stop band at the deflecting mode is developed for this cavity. Multi-physics finite element simulation results are presented. The integration of this design to the cavity cryomodule is described.

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THXB2

Crab Cavities: Past, Present, and Future of a Challenging Device

cavity, luminosity, collider, operation

3643

Q. Wu
BNL, Upton, Long Island, New York, USA

Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with LARP and the U.S. Department of Energy and EU FP7 HiLumi LHC - Grant Agreement 284404
In two-ring facilities operating with a crossing angle collision scheme, the luminosity can be limited due to incomplete overlap of the colliding bunches. Crab cavities are introduced to restore head-on collisions by providing destined opposite deflection to the head and tail of the bunch. Luminosity increase has been demonstrated at KEKB with global crab crossing, and the Large Hardron Collider (LHC) at CERN is currently designing local crab crossing for the Hi-Lumi upgrade. Future colliders may investigate both approaches. This paper reviews the challenges in the technology and implementation of crab cavities, discusses experience in past colliders, ongoing R&D and proposed implementations for future facilities such as HL-LHC, CLIC, ILC, and eRHIC/MEIC.

Slides THXB2 [4.307 MB]

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THPF033

The First Operation of 56 MHz SRF Cavity in RHIC

cavity, operation, SRF, cryomodule

3767

Q. Wu, S.A. Belomestnykh, I. Ben-Zvi, M. Blaskiewicz, L. DeSanto, D. Goldberg, M. Harvey, T. Hayes, G.T. McIntyre, K. Mernick, P. Orfin, S.K. Seberg, F. Severino, K.S. Smith, R. Than, A. Zaltsman
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.
A 56 MHz superconducting RF cavity has been designed, fabricated and installed in the Relativistic Heavy Ion Collider (RHIC). The cavity operated at 4.4 K with a “quiet helium source” to isolate the cavity from environmental acoustic noise. The cavity is a beam driven quarter wave resonator. It is detuned and damped during injection and acceleration cycles and is brought to operation only at store energy. For a first test operation, the cavity voltage was stabilized at 300 kV with full beam current. Within both Au + Au and asymmetrical Au + He3 collisions, luminosity improvement was detected from direct measurement, and the hourglass effect was reduced. One higher order mode (HOM) coupler was installed on the cavity. We report in this paper on our measurement of a broadband HOM spectrum excited by the Au beam.

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THPF062

CADS 650 MHz β=0.63 Elliptical Cavity Study

cavity, linac, proton, resonance

3836

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

The China Accelerator Driven Sub-critical System (CADS) is a high intensity proton facility to dispose of nuclear waste and generate electric power. CADS is based on 1.5 GeV, 10mA CW superconducting (SC) linac as a driver. The high-energy section of the linac is composed of two families of SC elliptical cavities which are designed for the geometrical beta 0.63 and 0.82. In this paper, the 650 MHz β=0.63 SC elliptical cavity was studied, including cavity optimization, multipacting, high order modes (HOM) and generator RF power calculation.

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