Keyword: HOM
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MOOBC02 Status of Main Linac Cryomodule Development for Compact ERL Project linac, cavity, cryomodule, damping 67
 
  • K. Umemori, K. Enami, T. Furuya, H. Sakai, M. Satoh, K. Shinoe
    KEK, Ibaraki, Japan
  • E. Cenni
    Sokendai, Ibaraki, Japan
  • M. Sawamura
    JAEA, Ibaraki-ken, Japan
  
  The Compact ERL, which is a test facility of ERL, is under construction at KEK, in Japan. For the main linac, one cryomodule, containing two 9-cell superconducting cavities, is under development. The cryomodule has been designed under High Pressure Gas Safety Code in Japan. Thermal design and cavity alignment have been also carefully considered. Two 9-cell cavities were already fabricated and their performances were confirmed by vertical tests. They satisfied ERL main linac specifications. Their accelerating field reached to 25 MV/m, without field limits. Two input couplers, three HOM absorbers and two Slide-Jack tuners are also under fabrication for the cryomodule. High power processing will be applied for input couplers, at a test stand using a 300 kW klystron. Cooling tolerance and HOM damping abilities were tested for HOM absorbers. Some performance studies were also applied for the tuner at room temperature condition. Cryomodule assembly is planned on this summer. After cooling tests and high power tests will be carried out, ERL beam operation will be started.  
slides icon Slides MOOBC02 [3.849 MB]  
 
MOPPC059 Various Approaches to Electromagnetic Field Simulations for RF Cavities simulation, cavity, impedance, electromagnetic-fields 268
 
  • C. Liu, W. Ackermann, W.F.O. Müller, T. Weiland
    TEMF, TU Darmstadt, Darmstadt, Germany
  
  Funding: Work supported by BMBF under contract 05H09RD5.
The Superconducting Proton Linac (SPL) cavity is mainly designed and conducted by CERN. It is a part of the planned injector upgrade of the Large Hadron Collider (LHC). The SPL cavity is used to accelerate the ion beam from 160 MeV to 5GeV and served as a driver for neutrino facilities and radioactive beam facilities. In the Superconducting Proton Linac (SPL) cavity, it is very important to calculate the eigenmodes precisely, because many higher-order modes (HOMs) can lead to particle beam instabilities. We used and compared three different ways to calculate the eigenmodes in the SPL cavity: field simulation with hexahedron mesh in frequency domain, field simulation with hexahedron mesh in time domain, and field simulation with tetrahedral mesh and higher order curvilinear elements. In this paper the principles of the three numerical methods will be introduced and compared. Finally the calculated results will be presented. 		 
 
MOPPC062 Eigenmode Computation for Cavities with Perturbed Geometry Based on a Series Expansion of Unperturbed Eigenmodes cavity, factory, wakefield, higher-order-mode 277
 
  • K. Brackebusch, U. van Rienen
    Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
  
  Funding: Work supported by Federal Ministry for Research and Education BMBF under contracts 05H09HR5 and 05K10HRC.
The geometry of an accelerator cavity determines its eigenmodes and thereby its performance characteristics. Therefore, accelerating performance and wakefield characteristics may be improved by an intentional modification of the geometry. However, undesired geometry perturbations due to manufacturing tolerances and operational demands can likewise impair it. To analyze the effects of geometry variations on the eigenmodes, parameter studies are to be undertaken. Using common eigenmode solvers it usually is necessary to perform a full eigenmode computation for each variation step, even if the geometry is only slightly altered. Parameter studies for cavity perturbations thus tend to be computationally extensive and inefficient. In this paper, we present the fundamentals of an efficient eigenmode computation method for varying cavity geometries. Knowing a set of initial eigenmodes of an unperturbed geometry, the method allows expanding the eigenmodes of any geometry that is part of the unperturbed one as a series of the initial eigenmodes. Thereby the computation effort may be significantly reduced. The method is demonstrated by means of analytically evaluable cavity geometries. 		 
 
MOPPC075 A Generic Data Model for HeadTail: Design and Implementation with Examples electron, simulation, wakefield, collective-effects 307
 
  • K.S.B. Li, G. Rumolo
    CERN, Geneva, Switzerland
  
  HeadTail has been developed in 2002 for the efficient simulation of instabilities and collective effects in large circular accelerators. Since then, the capabilities of the code have been continuously extended and the output data has become increasingly complex and large-scale ranging from the statistical description of single bunches to the statistical description of all slices within bunches up to the dynamics of the full 6D phase space over several thousands of turns. Processing this data in an effective manner and endowing it with a structure that provides a physical concept calls for new and optimised data formats. To meet state-of-the-art standards, the hierarchical data format (HDF5) has been selected as native output data format together with H5Part and XDMF as native data structures. We describe the implementation of the H5Part and the XDMF data structures into HeadTail and show some illustrative examples for data processing.  
 
MOPPC096 Multiphysics Applications of ACE3P simulation, vacuum, cavity, SRF 361
 
  • K.H. Lee, C. Ko, Z. Li, C.-K. Ng, L. Xiao
    SLAC, Menlo Park, California, USA
  • G. Cheng, H. Wang
    JLAB, Newport News, Virginia, USA
  
  Funding: Work supported by US DOE Offices of HEP, ASCR and BES under contract AC02-76SF00515.
The TEM3P module of ACE3P, a parallel finite-element electromagnetic code suite from SLAC, focuses on the multiphysics simulation capabilities, including thermal and mechanical analysis for accelerator applications. In this pa- per, thermal analysis of coupler feedthroughs to supercon- ducting rf (SRF) cavities will be presented. For the realistic simulation, internal boundary condition is implemented to capture RF heating effects on the surface shared by a di- electric and a conductor. The multiphysics simulation with TEM3P matched the measurement within 0.4%. 		 
 
MOPPD061 LHC@home: a Volunteer Computing System for Massive Numerical Simulations of Beam Dynamics and High Energy Physics Events simulation, collider, controls, superconducting-magnet 505
 
  • M. Giovannozzi, F. Grey, A. Harutyunyan, N. Hoimyr, P.L. Jones, A. Karneyeu, M.A. Marquina, E. McIntosh, B. Segal, P. Skands
    CERN, Geneva, Switzerland
  • D. Lombraña González
    CCC, 1211Geneva 23, Switzerland
  • L. Rivkin, I. Zacharov
    EPFL, Lausanne, Switzerland
  
  Recently, the LHC@home system has been revived at CERN. It is a volunteer computing system based on BOINC which allows boosting the available CPU-power in institutional computer centers by the help of individuals that donate the CPU-time of their PCs. Currently two projects are hosted on the system, namely SixTrack and Test4Theory. The first is aimed at performing beam dynamics simulations, while the latter deals with the simulation of high-energy events. In this paper the details of the global system, as well a discussion of the capabilities of either project will be presented. Milestones of progress of the projects will also be discussed.  
 
MOPPP026 Cryogenic Distribution System for the Proposed Cornell ERL Main Linac cryomodule, linac, cavity, vacuum 619
 
  • E.N. Smith
    Cornell University, Ithaca, New York, USA
  • Y. He, G.H. Hoffstaetter, M. Liepe, M. Tigner
    CLASSE, Ithaca, New York, USA
  
  Funding: This material is based upon work supported by the National Science Foundation under Grant No. DMR-0807731.
The proposed Cornell ERL main linac requires a total cooling power of nearly 8kW at 1.8K, 5kW at 5K and over 100kW at 80K. This is distributed over approximately 65 cryomodules, each containing 6 rf cavities and associated input couplers and higher order mode absorbers. situated in two underground tunnels. While the total heat load is comparable to that for each of the 8 individual LHC cryoplants, the very high ratio of dynamic heat load to static heat load, combined with the high power density at various sites produces interesting challenges for the cryogenic distribution system. A schematic view of the design choices selected, some of which are different from existing large cryogenic systems, and the basis for these decisions, is presented in this paper. 		 
 
MOPPR069 Use of Waveguide and Beam Pipe Probes as Beam Position and Tilt Monitoring Diagnostics with Superconducting Deflecting Cavities cavity, dipole, monitoring, simulation 945
 
  • X. Sun, T.G. Berenc, G. Decker, G.J. Waldschmidt, G. Wu
    ANL, Argonne, USA
  
  Funding: Work supported by U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under contract No. DE-AC02-06CH11357.
Waveguide and beam pipe field probes associated with a superconducting deflecting cavity are explored as beam position and tilt monitoring diagnostics. The superconducting deflecting cavity will be used for the Short-pulse X-rays (SPX) in the Advanced Photon Source (APS) upgrade project. Microwave Studio will be used to simulate the techniques of detecting the fields excited by the beam passing through the cavity and determining how close the beam is on electrical center. 		 
 
TUEPPB005 Novel Technique of Suppressing TBBU in High-energy ERLs linac, SRF, lattice, electron 1122
 
  • V. Litvinenko
    BNL, Upton, Long Island, New York, USA
  
  Energy recovery linacs (ERLs) is emerging generation of accelerators promising revolutionize the fields of high-energy physics and photon sciences. One potential weakness of these devices is transverse beam-breakup instability, which may severely limit available beam current. In this paper I am presenting novel idea of using natural chromaticity in ERL arcs to suppressing TBBU instabilities. I present the theory of the process and two exact cases demonstrating that the threshold of TBBU instability could be raised by my orders of magnitude using this method.
* V.N. Litvinenko, Chromaticity of the lattice and beam stability in energy recovery linacs, submitted to PR ST-AB 		 
 
TUPPD063 Interpretation of Dark Current Experimental Results in HZB SC RF Gun cavity, simulation, accelerating-gradient, gun 1545
 
  • V. Volkov
    BINP SB RAS, Novosibirsk, Russia
  • R. Barday, T. Kamps, J. Knobloch, A.N. Matveenko, A. Neumann
    HZB, Berlin, Germany
  
  Funding: Work supported by Bundesministerium für Bildung und Forschung, Land Berlin, and grants of Helmholtz Association VH-NG-636 and HRJRG-214.
The experimental dark current measurement results are obtained on HZB SC RF gun. The field emitters are considered to be random defects on the back wall of the cavity. Conducting wires with 1 micron length, blobs of 200 micron diameter and ”tip on tip” combination of them are taken as dark current emitters in the cavity. RF fields were calculated with CLANS program. The dynamic simulation of dark currents from these emitters fit experimental data. The emitter heating power by RF induced current is four orders of magnitude larger than by the field emitted dark current. The RF induced emitter temperature is proportional to ω1/2 which explains the accelerating gradient limit of a cavity like Kilpatrik law. The RF processing by high order modes seems to be promising. 		 
 
TUPPD064 Cathode Insert Design for SC RF Guns cathode, gun, cavity, multipactoring 1548
 
  • V. Volkov
    BINP SB RAS, Novosibirsk, Russia
  • R. Barday, T. Kamps, J. Knobloch, A.N. Matveenko
    HZB, Berlin, Germany
  
  Funding: Work supported by Bundesministerium für Bildung und Forschung, Land Berlin, and grants of Helmholtz Assiciation VH-NG-636 and HRJRG-214.
The cathode inserts in superconducting (SC) RF guns are normal conducting devices attached to a SC RF gun cavity. They enable the photocathode replacement and, at the same time, preserve high quality factor and high fields in the RF guns. However, the insert may also limit the gun performance because of multipacting etc. The experience gathered in early designs at Wuppertal [1], and, more recently at BNL [2] and HZDR [3] is taken into account. We consider the design structure of the cathode insert worked out by BINP for 1 cell prototype of SC HZDR RF gun [4]. The detailed electric, mechanic, and thermal calculations of the initial [4] and the upgraded design are presented in this paper.
* A. Michalke et al., EPAC'92, p. 1014 (1992).
** A. Burrill et al., PAC07, p. 2544 (2007).
*** D. Janssen et al., NIM A507, 314 (2003).
**** D. Janssen et al., NIM A445, 408 (2000). 		 
 
TUPPP043 Analysis of Coupled Bunch Instabilities in the NSLS-II Storage Ring with a 7-cell PETRA-III RF Structure impedance, cavity, damping, simulation 1704
 
  • G. Bassi, A. Blednykh, S. Krinsky, J. Rose
    BNL, Upton, New York, USA
  
  Funding: Work supported by DOE contract No: DE-AC02-98CH10886.
A 7-cell PETRA-III cavity is considered to be installed for the commissioning Phase 1 in the NSLS-II storage ring at an average current of 25mA. In this contribution we study transverse and longitudinal coupled-bunch instabilities that may be driven by the higher order modes of the 7-cell PETRA-III cavity. The instability thresholds are calculated with the OASIS tracking code, with parameters of the bare lattice (no damping wigglers and Landau cavities). We study multibunch configurations with arbitrary fill-patterns and discuss the slow head-tail effect at positive chromaticity to increase the transverse instability thresholds. 		 
 
TUPPR025 Higher-Order Modes and Beam Loading Compensation in CLIC Main Linac impedance, coupling, beam-loading, higher-order-mode 1867
 
  • O. Kononenko, A. Grudiev
    CERN, Geneva, Switzerland
  
  Compensation of transient beam loading is one of the major performance issues of the future compact linear collider (CLIC). Recent calculations, which consider only the most important fundamental mode, have shown that the 0.03% limit on the rms relative bunch-to-bunch energy spread in the main beam can be reached by optimizing the RF power pulse shape for the TD26, the CLIC baseline accelerating structure. Here, using HFSS and massively parallel ACE3P codes developed at SLAC, we perform an additional dedicated study of the influence of higher-order modes on the energy spread compensation scheme. It is shown that taking these modes into account in the accelerating structure does not increase the rms energy spread in the main beam above the CLIC specification level. Results of the HFSS and ACE3P simulations are also in a good agreement.  
 
TUPPR037 Simulations of Higher Order Modes in the ACC39 Module of FLASH cavity, dipole, higher-order-mode, simulation 1900
 
  • I.R.R. Shinton, R.M. Jones, P. Zhang
    UMAN, Manchester, United Kingdom
  • Z. Li
    SLAC, Menlo Park, California, USA
  
  This study is primarily focused on the dipole component of the multiband expansion of the wakefield, with the emphasis being on the development of a HOM-based BPM system for ACC39 currently installed and in operation at FLASH and due to be installed at XFEL . Coupled inter-cavity modes are simulated together with a limited band of trapped modes. A suite of finite element computer codes (including HFSS and ACE3P) and globalised scattering matrix calculations (GSM) are used to investigate the modes in these cavities. In this way the nature of the multi-cavity nature of these modules is investigated with implications for a HOM-based BPM system and direct comparison to experimental results.  
 
TUPPR070 High-Gradient Photonic Band-gap (PBG) Structure Breakdown Testing at Ku-Band diagnostics, lattice, damping, coupling 1984
 
  • B.J. Munroe, A.M. Cook, M.A. Shapiro, R.J. Temkin
    MIT/PSFC, Cambridge, Massachusetts, USA
  
  Photonic Band-gap (PBG) structures continue to be a promising area of research forfuture accelerator structures. Previous experiments at X-Band have demonstrated that PBG structures can operate at high gradient and low breakdown probability, provided that pulsed heating is controlled. Two single-cell standing-wave structures have been constructed at MIT to investigate breakdown performance of PBG structures. A metallic structure with small rods will be used to test performance with very high surface temperature rise, while an over-moded structure with dielectric rods will investigate alternative solutions to the issue of surface temperature rise. Both structures are expected to reach gradients of at least 100 MV/m and will utilize novel diagnostics, including fast camera imaging and optical spectroscopy of breakdowns.  
 
TUPPR071 Experimental High-Gradient Testing of an Elliptical-Rod Photonic Band-Gap (PBG) Structure at X-Band damping, wakefield, klystron, lattice 1987
 
  • B.J. Munroe, M.A. Shapiro, R.J. Temkin
    MIT/PSFC, Cambridge, Massachusetts, USA
  • V.A. Dolgashev, S.G. Tantawi, A.D. Yeremian
    SLAC, Menlo Park, California, USA
  • R.A. Marsh
    LLNL, Livermore, California, USA
  
  An 11.4 GHz Photonic Band-gap (PBG) structure where the rods in the inner row have an elliptical cross-section has been designed at MIT and tested at high power and high repetition rate at SLAC. This structure exhibits lower surface magnetic fields on the rods relative to previous round-rod PBG structures tested at SLAC, which reduces the ohmic heating of the rod surface in an effort to reduce pulsed heating damage. This improved PBG structure was tested experimentally such as to avoid excessively high breakdown rates and surface temperature rise. The structure demonstrated performance comparable to disc-loaded waveguide (DLWG) structures with the same iris geometry, achieving greater than 100 MV/m gradient at a breakdown probability of less than 10-3 per pulse per m for 150 ns pulses. This level of performance demonstrates that elliptical-rod PBG structures could be candidates for future accelerator applications.  
 
TUPPR084 HOM Damping and Multipacting Analysis of the Quarter-wave Crab Cavity cavity, damping, simulation, electron 2020
 
  • Q. Wu, S.A. Belomestnykh, I. Ben-Zvi
    BNL, Upton, Long Island, New York, USA
  • R. Calaga
    CERN, Geneva, Switzerland
  
  The Quarter-Wave Crab Cavity design has been analyzed further to accommodate LHC requirements. The goal for the design is to provide strong deflecting voltage to the proton bunches at the IP, while keeping the effective length as short as possible. We will evaluate the Higher Order Mode damping with two magnetic coupling dampers of 90 degrees apart. In this paper, we also show possible multipacting locations which are simulated by 3D code.  
 
WEOAB03 An Update on a Superconducting Photonic Band Gap Structure Resonator Experiment SRF, cavity, wakefield, niobium 2140
 
  • E.I. Simakov, W.B. Haynes, M.A. Madrid, F.P. Romero, T. Tajima, W.M. Tuzel
    LANL, Los Alamos, New Mexico, USA
  • C.H. Boulware, T.L. Grimm
    Niowave, Inc., Lansing, Michigan, USA
  
  Funding: This work is supported by the U.S. Department of Energy (DOE) Office of Science Early Career Research Program.
We present an update on the 2.1 GHz superconducting rf (SRF) photonic band gap (PBG) resonator experiment in Los Alamos. The SRF PBG cell was designed to operate at 2.1 GHz. PBG cells have great potential for outcoupling long-range wakefields in SRF accelerator structures without affecting the fundamental accelerating mode. Using PBG structures in superconducting particle accelerators will allow operation at higher frequencies and moving forward to significantly higher beam luminosities thus leading towards a completely new generation of colliders for high energy physics. However, the technology of fabrication of PBG accelerator cells from niobium has not been well developed to date. Here we report the results of our efforts to fabricate a 2.1 GHz PBG cell and to test it at high gradients in a liquid helium bath at the temperature of 2 Kelvin. The high gradient performance of the cell will be evaluated and the results will be compared to simulations with the CST Microwave Studio. 		 
slides icon Slides WEOAB03 [2.061 MB]  
 
WEEPPB008 HOM Coupler Optimisation for the Superconducting RF Cavities in ESS cavity, neutron, target, damping 2182
 
  • R. Ainsworth
    Royal Holloway, University of London, Surrey, United Kingdom
  • R. Calaga
    CERN, Geneva, Switzerland
  • S. Molloy
    ESS, Lund, Sweden
  
  The European Spallation Source (ESS) will be the world’s most powerful next generation neutron source. It consists of a linear accelerator, target, and instruments for neutron experiments. The linac is designed to accelerate protons to a final energy of 2.5 GeV , with an average design beam power of 5 MW, for collision with a target used to produce a high neutron flux. A section of the linac will contain Superconducting RF (SCRF) cavities designed to resonate at 704 MHz. Dangerous beam induced modes in these cavities may make the beam unstable and increase the cryogenic load and so couplers are usually installed to provide damping. Previous studies have shown potential designs are susceptible to multipacting, a resonant process which can absorb RF power and lead to heating effects. This paper will show how a coupler suffering from multipacting has been redesigned to limit this effect.  Optimisation of the RF damping is also discussed.  
 
WEEPPB010 RF Modeling Using Parallel Codes ACE3P for the 400-MHz Parallel-Bar/Ridged-Waveguide Compact Crab Cavity for the LHC HiLumi Upgrade damping, cavity, impedance, dipole 2185
 
  • Z. Li, L. Ge
    SLAC, Menlo Park, California, USA
  • J.R. Delayen, S.D. Silva
    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.
Schemes utilizing crab cavities to achieve head-on beam-beam collisions were proposed for the LHC HiLumi upgrade. These crabbing schemes require that the crab cavities be compact in order to fit into the tight spacing available in the existing LHC beamlines at the location where the crab cavities will be installed. Under the support of US LARP program, Old Dominion University and SLAC have joint efforts to develop a 400-MHz compact superconducting crab cavity to meet the HiLumi upgrade requirements. In this paper, we will present the RF modeling and analysis of a parallel-bar/ridged-waveguide shaped 400-MHz compact cavity design that can be used for both the horizontal and vertical crabbing schemes. We will also present schemes for HOM damping and multipacting analysis for such a design. 		 
 
WEPPC006 CW and LP Operation Test of XFEL-Like Cryomodule cryomodule, cavity, cryogenics, feedback 2215
 
  • J.K. Sekutowicz, V. Ayvazyan, M. Ebert, J. Eschke, A. Gössel, D. Kostin, I.M. Kudla, W. Merz, F. Mittag, R. Onken
    DESY, Hamburg, Germany
  • W. Cichalewski, W. Jałmużna, K.P. Przygoda
    TUL-DMCS, Łódź, Poland
  • K. Czuba, L. Zembala
    Warsaw University of Technology, Institute of Electronic Systems, Warsaw, Poland
  • J. Szewiński
    The Andrzej Soltan Institute for Nuclear Studies, Centre Świerk, Świerk/Otwock, Poland
  
  A continuous improvement in the performance of superconducting TESLA cavities will make possible, from the cryogenic point of view, operation of the XFEL linac in continuous wave (cw) mode at gradients up to 7.5 MV/m and in long pulse (lp) mode up to nominal gradient of 23.4 MV/m. Each of these new operation modes will offer an additional flexibility in time structure of the photon beam, and therefore will allow for more experiments and in some cases less demanding and less expensive equipment. In this contribution we discuss results of the first RF test of these new types of operation with a XFEL-like cryomodule.  
 
WEPPC009 Status of the European XFEL 3.9 GHz system cavity, status, linac, diagnostics 2224
 
  • P. Pierini, A. Bosotti, P. Michelato, L. Monaco, R. Paparella, D. Sertore
    INFN/LASA, Segrate (MI), Italy
  • E.R. Harms
    Fermilab, Batavia, USA
  • C. Pagani
    Università degli Studi di Milano & INFN, Segrate, Italy
  • E. Vogel
    DESY, Hamburg, Germany
  
  The injector of the European XFEL will use a third harmonic RF system at 3.9 GHz to flatten the RF curvature after the first accelerating module before the first bunch compression stage. This paper presents qualification tests of the prototype cavities and the status of the activities for the realization of the third harmonic section of the European XFEL towards its commissioning due in 2014.  
 
WEPPC011 Vertical Test Results for ERL 9-cell Cavities for Compact ERL Project cavity, linac, cryomodule, radiation 2227
 
  • K. Umemori, T. Furuya, H. Sakai, M. Satoh, K. Shinoe
    KEK, Ibaraki, Japan
  • E. Cenni
    Sokendai, Ibaraki, Japan
  • M. Sawamura
    JAEA, Ibaraki-ken, Japan
  
  The Compact ERL project, which is a test facility of ERL, is ongoing in Japan. At the first step of this project, main linac cavities accelerate electron beams by 30 MV. Two 9-cell cavities were fabricated for main linac cryomodule, under High Pressure Gas Safety Code in Japan. A series of surface treatments, such as annealing, pre-tuning, electro-polishing (EP), degreasing, high pressure rinsing by ultra-pure water, cavity assembly and baking, were applied for the cavities. For the final EP, current density was selected to be relatively low. Vertical tests were performed for both cavities. Their field successfully reached to 25 MV/m, without any field limitation. The Q-values were more than 1x1010, even at 20 MV/m. Field emission on-sets were to be 14 and 22 MV/m, for each cavities. Both cavities satisfied requirements for ERL main linac cavity. Details of vertical tests, with X-ray and temperature mapping data, are shown, in this paper. These cavities will be mounted with titanium He jackets, assembled and installed into a cryomodule.  
 
WEPPC013 Progress of High Gradient Performance in STF 9-cell Cavities at KEK cavity, accelerating-gradient, status, laser 2233
 
  • Y. Yamamoto, H. Hayano, E. Kako, S. Noguchi, T. Shishido, K. Watanabe
    KEK, Ibaraki, Japan
  
  Vertical tests for ILC have been carried out since 2008 at KEK-STF. Measured cavities are from MHI#5 to MHI#22 (not yet for MHI#18-#22 at the end of November 2011), and MHI#12, #13 and #17 reached the ILC specification of 0.8x1010 at 35MV/m. The MHI cavity was added into the “qualified vendor” for the cavity yield. These three cavities (#12, #13 and #17) had no defect on every EBW seam of equator, iris and beampipe. On the other hand, the other cavities had a few or several defects on EBW seam. Especially, defect on the EBW seam of the equator is the worst case, and cavity performance is limited “certainly”. MHI#10, #15 and #16 cavities were limited by this kind of defect. As for iris region, MHI#14 had large defect at the iris between cell #8 and #9, and the performance was limited by the heavy field emission with “explosive event”. However, after the locally mechanical grind for this defect, the cavity performance was drastically improved with no field emission at 37MV/m. In this paper, the recent progress of the cavity performance at KEK-STF will be reported with the “detailed” defect analysis.  
 
WEPPC015 Construction of Injector Cryomodule for cERL at KEK cryomodule, cavity, pick-up, linac 2239
 
  • E. Kako, S. Noguchi, T. Shishido, K. Watanabe, Y. Yamamoto
    KEK, Ibaraki, Japan
  
  The cERL injector cryomodule includes three 2-cell cavities, and each cavity has 2 input couplers and 5 HOM couplers. Three 2-cell cavities for cERL has already completed. Vertical test of the three cavities has been going on. The first cavity have achieved Eacc of 30 MV/m. Vertical tests will be carried out twice in each cavity, till the end of December, 2011. Six cw input couplers for cERL has already completed. RF processing at the high-power test stand with a cw 300kW-klystron will be carried out in Jan.-Feb., 2012. After the cavities were covered with a He jacket, assembly of the cERL injector cryomodule will be carried out in March-April, 2012. The first cool-down of the cryomodule is scheduled in June 2012.  
 
WEPPC021 Development of Superconducting Radio Frequency Cavities at SINAP cavity, niobium, superconducting-cavity, electron 2248
 
  • J.F. Liu, H.T. Hou, C.W. Lu, C. Luo, Z.Y. Ma, D.Q. Mao, J. Shi, Zh.G. Zhang, S.J. Zhao, X. Zheng
    SINAP, Shanghai, People's Republic of China
  • Z.Q. Feng, Z. Li, J.F. Liu, Y.L. Wei, K. Xu, Y.B. Zhao
    Shanghai KEY Laboratory of Cryogenics & Superconducting RF Technology, Shanghai, People's Republic of China
  • H. Yu
    Graduate School of the Chinese Academy of Sciences, Beijing, People's Republic of China
  
  This paper presents the development of superconducting radio frequency cavities at Shanghai Institute of Applied Physics (SINAP) mainly focused on the 500MHz band. Firstly, Two KEKB type 500MHz single cell niobium cavities have been fabricated and one of them has been vertical tested successfully in 2010. The highest accelerating gradient of the fabricated cavity higher than 10MV/m was obtained while the quality factor was better than 4·108 at 4.2K. Secondly, a new type of 500MHz single cell cavity has been designed which adopts the fluted beam pipe for higher order modes propagation and a coaxial type high power input coupler. Thirdly, a 500MHz 5-cell superconducting cavity with large aperture, enlarged beam pipe for HOM propagation and high r/Q value has been optimized which can be a candidate cavity for high current FEL and ERL.  
 
WEPPC027 A Quarter Wave Design for Crab Crossing in the LHC cavity, acceleration, high-voltage, higher-order-mode 2260
 
  • R. Calaga
    CERN, Geneva, Switzerland
  • S.A. Belomestnykh, I. Ben-Zvi, Q. Wu
    BNL, Upton, Long Island, New York, USA
  
  Funding: This work partially supported by the US Department of Energy through the US LHC Accelerator Research Program (LARP).
The aperture constraints of the LHC interaction region and the alternating crossing schemes at two collision points calls for a superconducting deflecting cavity with very compact dimensions at low frequencies for the purpose of crab crossing. A new concept of using a superconducting 1/4-wave design, ideally suited to address the LHC constraints at 400 MHz, is proposed. The optimized RF cavity design and associated advantages of using a 1/4 wave resonator are presented. Aspects related to higher order mode damping, multipacting and frequency tuning are also addressed. 		 
 
WEPPC028 Slim Elliptical Cavity at 800 MHz for Local Crab Crossing cavity, coupling, damping, impedance 2263
 
  • L. Ficcadenti, J. Tückmantel
    CERN, Geneva, Switzerland
  
  A slim highly eccentric elliptical Crab cavity with vertical deflection at 800 MHz, compatible to beam line distances everywhere in the LHC ring, was designed. It is a good fall-back solution in case of problems with new compact 400 MHz designs. Simulated RF characteristics of the delfecting mode, HOM spectra and damping, tuning and multipacting effects are presented. First the most simple HOM coupling system was investigated. The rejection of the working mode was not sufficient and a notch filter was added. Results of both cases will be presented.  
 
WEPPC031 Completed Assembly of the Daresbury International ERL Cryomodule and its Implementation on ALICE cryomodule, cavity, cryogenics, controls 2272
 
  • P.A. McIntosh, M.A. Cordwell, P.A. Corlett, P. Davies, E. Frangleton, P. Goudket, K.J. Middleman, S.M. Pattalwar, A.E. Wheelhouse
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  • S.A. Belomestnykh
    BNL, Upton, Long Island, New York, USA
  • A. Büchner, F.G. Gabriel, P. Michel
    HZDR, Dresden, Germany
  • J.N. Corlett, D. Li, S.M. Lidia
    LBNL, Berkeley, California, USA
  • G.H. Hoffstaetter, M. Liepe, H. Padamsee, P. Quigley, J. Sears, V.D. Shemelin, V. Veshcherevich
    CLASSE, Ithaca, New York, USA
  • T.J. Jones, J. Strachan
    STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom
  • R.E. Laxdal
    TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada
  • D. Proch, J.K. Sekutowicz
    DESY, Hamburg, Germany
  • T.I. Smith
    Stanford University, Stanford, California, USA
  
  The completion of an optimised SRF cryomodule for application on ERL accelerators has now culminated with the successful assembly of an integrated cryomodule, following an intensive 5 years of development evolution. The cryomodule, which incorporates 2 x 7-cell 1.3 GHz accelerating structures, 3 separate layers of magnetic shielding, fully adjustable & high power input couplers and fast piezo tuners, has been installed on the ALICE ERL facility at Daresbury Laboratory. It is intended that this will permit operational optimisation for maximised efficiency demonstration, through increased Qext adjustment whilst retaining both effective energy recovery and IR-FEL lasing. The collaborative design processes employed in completing this new cryomodule development are explained, along with the assembly and implementation procedures used to facilitate its successful installation on the ALICE ERL facility.  
 
WEPPC038 Status of the Short-Pulse X-ray Project at the Advanced Photon Source cavity, LLRF, cryomodule, simulation 2292
 
  • A. Nassiri, N.D. Arnold, T.G. Berenc, M. Borland, B. Brajuskovic, D.J. Bromberek, J. Carwardine, G. Decker, L. Emery, J.D. Fuerst, A.E. Grelick, D. Horan, J. Kaluzny, F. Lenkszus, R.M. Lill, J. Liu, H. Ma, V. Sajaev, T.L. Smith, B.K. Stillwell, G.J. Waldschmidt, G. Wu, B.X. Yang, Y. Yang, A. Zholents
    ANL, Argonne, USA
  • J.M. Byrd, L.R. Doolittle, G. Huang
    LBNL, Berkeley, California, USA
  • G. Cheng, G. Ciovati, P. Dhakal, G.V. Eremeev, J.J. Feingold, R.L. Geng, J. Henry, P. Kneisel, K. Macha, J.D. Mammosser, J. Matalevich, A.D. Palczewski, R.A. Rimmer, H. Wang, K.M. Wilson, M. Wiseman
    JLAB, Newport News, Virginia, USA
  • Z. Li, L. Xiao
    SLAC, Menlo Park, California, 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.
The Advanced Photon Source Upgrade (APS-U) Project at Argonne will include generation of short-pulse x-rays based on Zholents’* deflecting cavity scheme. We have chosen superconducting (SC) cavities in order to have a continuous train of crabbed bunches and flexibility of operating modes. In collaboration with Jefferson Laboratory, we are prototyping and testing a number of single-cell deflecting cavities and associated auxiliary systems with promising initial results. In collaboration with Lawrence Berkeley National Laboratory, we are working to develop state-of-the-art timing, synchronization, and differential rf phase stability systems that are required for SPX. Collaboration with Advanced Computations Department at Stanford Linear Accelerator Center is looking into simulations of complex, multi-cavity geometries with lower- and higher-order modes waveguide dampers using ACE3P. This contribution provides the current R&D status of the SPX project.
* A. Zholents et al., NIM A 425, 385 (1999). 		 
 
WEPPC053 SSR1 HOM Analysis and Measurements dipole, quadrupole, cavity, higher-order-mode 2333
 
  • M.H. Awida, P. Berrutti, I.V. Gonin, T.N. Khabiboulline, V.P. Yakovlev
    Fermilab, Batavia, USA
  
  Funding: Operated by Fermi Research Alliance, LLC, under Contract DE-AC02-07CH11359 with the U.S. DOE
Single spoke resonators (SSR1, β=0.22) are currently under development for Project X at Fermilab. In this paper, extensive Higher Order Mode (HOM) analysis carried out on SSR1 is reported including the simulated R/Q for monopoles, dipoles, and quadrupoles. HOM measurements carried out on several spoke cavities are also reported including the harmonic response and the bead pull measurements. Comparison between the measured R/Q values and the simulated ones are presented. 		 
 
WEPPC054 Resonance Excitation of Longitudinal High Order Modes in Project X Linac linac, collider, factory, kaon 2336
 
  • A.I. Sukhanov, M.H. Awida, I.V. Gonin, T.N. Khabiboulline, A. Lunin, N. Solyak, V.P. Yakovlev
    Fermilab, Batavia, USA
  
  Results of simulation of power loss due to excitation of longitudinal high order modes (HOMs) in the accelerating superconducting RF system of CW linac of Project X are presented. Beam structures corresponding to the various modes of Project X operation are considered: CW regime for 3 GeV physics program; pulsed mode for neutrino experiments; and pulsed regime, when Project X linac operates as a driver for Neutrino Factory/Muon Collider. Power loss and associated heat load due to resonance excitation of longitudinal HOMs are shown to be small in all modes of operation. Conclusion is made that HOM couplers can be removed from the design of superconducting RF cavities of Project X linac.  
 
WEPPC072 High Current Operation of the Cornell ERL Superconducting RF Injector Cryomodule SRF, cavity, cryomodule, damping 2378
 
  • M. Liepe, G.H. Hoffstaetter, S. Posen, P. Quigley, V. Veshcherevich
    CLASSE, Ithaca, New York, USA
  
  Cornell University has developed a SCRF injector cryomodule for the acceleration of high current, low emittance beams in continuous wave operation. This cryomodule is based on superconducting RF technology, and is currently under extensive testing in the Cornell ERL injector prototype with CW beam currents exceeding 25 mA. Strong damping of Higher-Order-Modes in the cavities is essential for high beam current operation, and is achieved by beamline RF absorber located at cryogenic temperatures in the beam pipe sections between the cavities. This paper gives an overview of the experience gained during the high beam current operation of the cryomodule.  
 
WEPPC073 Progress on Superconducting RF Work for the Cornell ERL cavity, linac, SRF, cryomodule 2381
 
  • M. Liepe, F. Furuta, G.M. Ge, Y. He, G.H. Hoffstaetter, T.I. O'Connell, S. Posen, J. Sears, M. Tigner, N.R.A. Valles, V. Veshcherevich
    CLASSE, Ithaca, New York, USA
  
  Cornell University is developing the superconducting RF technology required for the construction of a 100 mA hard X-ray light source driven by an Energy-Recovery Linac. Prototypes of all beam line components of the 5 GeV cw SRF main linac cryomodule have been fabricated and tested in detail. This work includes an optimized 7-cell SRF cavity, a broadband HOM beamline absorber, a cold frequency tuner, and a 5 kW CW RF input coupler. A one-cavity test cryomodule has been assembled for a first full cryomodule test of the main linac cavity, and is currently under testing. In this paper we give an overview of these extensive R&D activities at Cornell.  
 
WEPPC074 HOM Studies on the Cornell ERL Prototype Cavity in a Horizontal Test Cryomodule cavity, higher-order-mode, linac, simulation 2384
 
  • N.R.A. Valles, M.G. Billing, G.H. Hoffstaetter, M. Liepe, C.E. Mayes
    CLASSE, Ithaca, New York, USA
  
  The main linac 7-cell cavity for Cornell's Energy Recovery Linac was optimized to maximize threshold current through the ERL. This was achieved by designing center and end cells that reduce the strength of dipole higher-order modes. A prototype cavity was fabricated based on the optimized RF design and found to meet fundamental mode specifications in a vertical test. The higher-order-mode spectrum was measured when the cavity was installed in a horizontal test cryomodule and is compared to 2D and 3D EM simulations.  
 
WEPPC075 Testing of the Main-Linac Prototype Cavity in a Horizontal Test Cryomodule for the Cornell ERL cavity, linac, cryomodule, cryogenics 2387
 
  • N.R.A. Valles, F. Furuta, G.M. Ge, Y. He, K.M.V. Ho, G.H. Hoffstaetter, M. Liepe, T.I. O'Connell, S. Posen, P. Quigley, J. Sears, M. Tigner, V. Veshcherevich
    CLASSE, Ithaca, New York, USA
  
  Cornell has recently finished producing and testing the first prototype 7-cell main linac cavity for the Cornell Energy Recovery Linac (ERL). The cavity construction met all necessary fabrication constraints. After a bulk BCP, 650C outgassing, final BCP, and 120C bake the cavity was vertically tested. The cavity met quality factor and gradient specifications (2·1010 at 16.2 MV/m) in the vertical test. Progressing with the ERL linac development, the cavity was installed in a horizontal test cryomodule and the quality factor versus accelerating gradient was again measured. This baseline measurement is the first test in a sequence of tests of the main linac cavity in the test cryomodule. Subsequent tests will be with increased complexity of the beam line, e.g. with HOM beamline loads installed, to study potential sources of reducing the cavity’s quality factor.  
 
WEPPC086 Higher Order Modes Damping Analysis for the SPX Deflecting Cavity Cyromodule cavity, damping, dipole, impedance 2414
 
  • L. Xiao, Z. Li, C.-K. Ng
    SLAC, Menlo Park, California, USA
  • A. Nassiri, G.J. Waldschmidt, G. Wu
    ANL, Argonne, USA
  • R.A. Rimmer, H. Wang
    JLAB, Newport News, Virginia, 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.
A single-cell superconducting deflecting cavity operating at 2.812 GHz has been proposed and designed for the Short Pulse X-ray (SPX) project for the Advanced Photon Source upgrade. A cryomodule of 4 such cavities will be needed to produce the required 2-MV deflecting voltage. Each deflecting cavity is equipped with one fundamental power coupler (FPC), one lower order mode (LOM) coupler, and two higher order mode (HOM) couplers to achieve the stringent damping requirements for the unwanted modes. The damping of the HOM/LOM modes below the beampipe cutoff has been analyzed in the single cavity geometry and shown to meet the design requirements. The HOMs above beam pipe cutoff in the 4-cavity cyromodule, however, may result in cross coupling which may affect the HOM damping and potentially trapped modes between the cavities which could produce RF heating to the beamline bellows and even be detrimental to the beam. We have evaluated the HOM damping and trapped modes in the 4-cavity cryomodule using the parallel finite element EM code ACE3P developed at SLAC. We will present the results of the cryomodule analysis in this paper. 		 
 
WEPPC087 Second Harmonic Cavity Design for Project-X Main Injector cavity, simulation, dipole, impedance 2417
 
  • L. Xiao, C.-K. Ng
    SLAC, Menlo Park, California, USA
  • J.E. Dey, I. Kourbanis
    Fermilab, Batavia, USA
  
  In order to accelerate the proposed beam intensity for Project-X, a new RF system for Main Injector (MI) will be required. A new 53 MHz first harmonic RF cavity that meets the MI requirements for Project-X has been designed. In order to reduce the peak longitudinal beam density a 106 MHz second harmonic RF system is also needed. The first harmonic RF cavity design is a quarter wave coaxial resonator with a single accelerating gap and a perpendicular biased ferrite tuner. The second harmonic RF cavity baseline design is similar to the fundamental one and scaled down from it. RF simulations and shape optimizations on the second harmonic cavity are carried out to obtain the optimal performance which meets Project-X requirements. The results are discussed and presented in this paper.  
 
WEPPC088 Standardization of CEBAF 12 GeV Upgrade Cavity Testing cavity, radiation, survey, LabView 2420
 
  • T. Bass, G.K. Davis, C. Grenoble, M. Stirbet
    JLAB, Newport News, Virginia, USA
  
  Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
CEBAF 12GeV upgrade project includes 80 new 7-cell cavities to form 10 cryomodules. Each cavity underwent RF qualification at 2 Kelvin using a high power accelerating gradient test and an HOM survey in JLab’s Vertical Testing Area (VTA) before cavity string assembly. In order to ensure consistently high quality data, updated cavity testing procedures and analysis were implemented and used by a group of 10 VTA operators. For high power tests, a cavity testing procedure was developed and used in conjunction with a LabVIEW program to collect the test data. Additionally while the cavity was at 2K, an HOM survey was performed using a network analyzer and a combination of Excel and Mathematica programs. Data analysis was standardized and an online logbook, Pansophy, was used for data storage and mining. The Pansophy system allowed test results to be easily summarized and searchable across all cavity tests. In this presentation, the CEBAF 12GeV upgrade cavity testing procedure, method for data analysis, and results reporting results will be discussed. 		 
 
WEPPC089 SRF Cavity Performance Overview for the 12 GeV Upgrade cavity, cryomodule, SRF, radiation 2423
 
  • A. Burrill, G.K. Davis, C.E. Reece, A.V. Reilly, M. Stirbet
    JLAB, Newport News, Virginia, USA
  
  Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
The CEBAF accelerator, a recirculating CW electron accelerator that is currently operating at Jefferson Laboratory, is in the process of having 10 new cryomodules installed to allow for the maximum beam energy to be increased from 6 GeV to 12 GeV. This upgrade required the fabrication, processing and RF qualification of 80, seven cell elliptical SRF cavities, a process that was completed in February 2012. The RF performance achieve in the vertical testing dewars has exceeded the design specification by ~25% and is a testament to the cavity design and processing cycle that has been implemented. This paper will provide a summary of the cavity RF performance in the vertical tests, as well as review the overall cavity processing cycle and duration for the project. 		 
 
WEPPC092 12 GeV Upgrade Project - Cryomodule Production cryomodule, cavity, SRF, controls 2429
 
  • J. Hogan, A. Burrill, G.K. Davis, M.A. Drury, M. Wiseman
    JLAB, Newport News, Virginia, USA
  
  Funding: This manuscript has been authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
The Thomas Jefferson National Accelerator Facility (Jefferson Lab) is producing ten 100+MV SRF cryomodules (C100) as part of the CEBAF 12 GeV Upgrade Project. Once installed, these cryomodules will become part of an integrated accelerator system upgrade that will result in doubling the energy of the CEBAF machine from 6 to 12 GeV. This paper will present a complete overview of the C100 cryomodule production process. The C100 cryomodule was designed to have the major components procured from private industry and assembled together at Jefferson Lab. In addition to measuring the integrated component performance, the performance of the individual components is verified prior to being released for production and assembly into a cryomodule. Following a comprehensive cold acceptance test of all subsystems, the completed C100 cryomodules are installed and commissioned in the CEBAF machine in preparation of accelerator operations. This overview of the cryomodule production process will include all principal performance measurements, acceptance criterion and up to date status of current activities.
The U.S. Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce this manuscript for U.S. Government purposes. 		 
 
WEPPC100 Design of Electron and Ion Crabbing Cavities for an Electron-Ion Collider cavity, electron, ion, damping 2447
 
  • A. Castilla, J.R. Delayen, G.A. Krafft
    ODU, Norfolk, Virginia, USA
  • A. Castilla
    JLAB, Newport News, Virginia, USA
  
  Beyond the 12 GeV upgrade at the Jefferson Lab a Medium Energy Electron-Ion Collider (MEIC) has been considered. In order to achieve the desired high luminosities at the Interaction Points (IP), the use of crabbing cavities is under study. In this work, we will present to-date designs of superconducting cavities, considered for crabbing both ion and electron bunches. A discussion of properties such as peak surface fields and higher-order mode separation will be presented.  
 
WEPPC102 Design and Development of Superconducting Parallel-bar Deflecting/Crabbing Cavities cavity, luminosity, pick-up, damping 2453
 
  • S.U. De Silva, J.R. Delayen
    ODU, Norfolk, Virginia, USA
  • S.U. De Silva
    JLAB, Newport News, Virginia, USA
  
  The superconducting parallel-bar cavity is a deflecting/crabbing cavity with attractive properties that is being considered for a number of applications. We present the designs of a 499 MHz deflecting cavity developed for the Jefferson Lab 12 GeV Upgrade and a 400 MHz crabbing cavity for the LHC High Luminosity Upgrade. Prototypes of these two cavities are now under development and fabrication.  
 
WEPPC110 3D Simulations of Multipacting in the 56 MHz SRF Cavity simulation, cavity, electron, higher-order-mode 2477
 
  • Q. Wu, S.A. Belomestnykh
    BNL, Upton, Long Island, New York, USA
  • L. Ge, C. Ko, Z. Li, C.-K. Ng, L. Xiao
    SLAC, Menlo Park, California, USA
  
  Funding: This work was supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. DOE.
The 56 MHz SRF Quarter-Wave Resonator (QWR) is designed for RHIC as a storage cavity to improve the collider performance. 2D multipacting simulation has been done for the cavity alone. Ripples were added to the outer body of the cavity for multipacting suppression based on the simulation findings. During operation, there will be four higher order mode (HOM) couplers and a fundamental power coupler (FPC) inserted through the end ports of the cavity and a fundamental mode damper (FD) inserted through a special port on the outer body. All of these components will be exposed to high RF fields. In this presentation we compare 2D and 3D codes simulation results for multipacting in the cavity. We also report 3D simulation results for multipacting simulation at the couplers. 		 
 
WEPPC113 Progress on the High-Current 704 MHz Superconducting RF Cavity at BNL cavity, damping, higher-order-mode, impedance 2486
 
  • W. Xu, S.A. Belomestnykh, I. Ben-Zvi, H. Hahn, P. Jain
    BNL, Upton, Long Island, New York, USA
  • C.M. Astefanous, M.D. Cole, J.P. Deacutis, D. Holmes
    AES, Medford, NY, USA
  
  Funding: This work was supported by Sotny Brook under contract No. DE-SC0002496 and Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. DOE.
The 704 MHz high current superconducting cavity has been designed with consideration of both performance of fundamental mode and damping of higher order modes. A copper prototype cavity was fabricated by AES and delivered to BNL. RF measurements were carried out on this prototype cavity, including fundamental pass-band and HOM spectrum measurements, HOM studies using bead-pull setup, prototyping of antenna-type HOM couplers. The measurements show that the cavity has very good damping for the higher-order modes, which was one of the main goals for the high current cavity design. 3D cavity models were simulated with Omega3P code developed by SLAC to compare with the measurements. The paper describes the cavity design, RF measurement setups for the copper prototype, and presents comparison of the experimental results with computer simulations. The progress with the niobium cavity fabrication will also be described. 		 
 
WEPPD075 A Novel Planar Balun Structure for Continuous Wave 1 kW, 500 MHz Solid-state Amplifier Design simulation, synchrotron, impedance, coupling 2699
 
  • T.-C. Yu, L.-H. Chang, M.H. Chang, L.J. Chen, F.-T. Chung, M.-C. Lin, Y.-H. Lin, C.H. Lo, M.H. Tsai, Ch. Wang, T.-T. Yang, M.-S. Yeh
    NSRRC, Hsinchu, Taiwan
  
  In general, the coaxial type balun plays key role in push-pull amplifier design in the increasing high power solid-state technique transmitter design for accelerator application. However, the coaxial baluns not only increase the complexity in manufacturing procedure but also introduce additional tolerance variation between modules. The variation between parallel power modules would decreases combining efficiency and thus increase the operation cost. Here, a novel planar balun has been proposed and successfully implemented on 1kW solid-state amplifier design for continuous operation with newly designed water cooling plates. The long-term CW test has demonstrated the feasibility of the newly designed planar is quite suitable for CW operation with its excellent low loss, balance property and also low tolerance between modules in mass production.  
 
WEPPP026 Dielectric-plate-implanted Higher Order Mode (HOM) Waveguide for High Intensity Multi-beam Device Application simulation, wakefield, lattice, electron 2781
 
  • Y.-M. Shin
    Fermilab, Batavia, USA
  
  A mode-selective oversized RF-beam channel has been investigated for high intensity multi-beam devices. Implanting the equi-spaced dielectric plates at the transverse positions where longitudinal electric fields of a HOM are minimal in the micro-metallic structure strongly suppresses all lower energy modes and other wakefield modes. The dielectric lattice captures only a single HOM of the wavelengths that correspond to the plate spacing. Electromagnetic simulations have shown that the lower energy modes, TE10 and TE20 modes, are suppressed down to < ~ -60 dB by two plate loads, while TE310-mode prominently propagates through the 2 mm long waveguide only with –4 dB (= -2dB/mm) at 1 THz. The numerical calculation indicated that the TE30 mode has ~ a few times higher Q than the lower energy modes. The strong single mode selectivity has been extensively looked into with a more highly overmoded structure. Feasibility analysis of the HOM structure for multi-beam device application is under investigation. Particle-in-cell (PIC) simulation has shown coherent beam bunching and energy gain from THz driving signal.  
 
WEPPP027 PBG-slab Embedded Traveling Wave Structure for Planar Beam Accelerator Application electron, acceleration, photon, lattice 2784
 
  • Y.-M. Shin
    Fermilab, Batavia, USA
  
  The oversized traveling wave (TE10-mode) channel integrated with the photonic-band-gap (PBG) slab arrays have been investigated for planar beam accelerator application. Simulation analysis showed that the slab arrays allow only the PBG-modes (5-6 GHz) to propagate with ~ 2 dB of insertion loss, corresponding to ~ 1.14 dB/cm attenuation, which thereby effectively suppresses trapped non-PBG modes down to ~ -14.3 dB/cm. It will enable monochromatic propagation of fundamental acceleration modes along the heavily over-moded planar waveguide without anomalous excitation of unstable trapped HOMs. The saturated maximum field gradients of the accelerating structure have been analyzed with respect to operational frequency bands corresponding to structural sizes. The field gradient of the guided PBG-mode has been investigated with finite-integral-method (FIM) simulations at W-band. This mode-filter could be utilized for HOM dampers in high aspect ratio (HAR) planar beam accelerators. An experimental test is currently under consideration.  
 
WEPPP033 Design of a Wakefield Experiment in a Traveling-wave Photonic Band Gap Accelerating Structure wakefield, electron, higher-order-mode, target 2798
 
  • E.I. Simakov, R.L. Edwards
    LANL, Los Alamos, New Mexico, USA
  
  Funding: This work is supported by the U.S. Department of Energy (DOE) Office of Science Early Career Research Program.
We designed an experiment to conduct a thorough 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. We present the design of the accelerating structure that will be tested at AWA in the near future. The structure will consist of sixteen 2pi/3 PBG cells, including two coupler cells. We will also present the results of the initial cold-testing of the few sample cells and a plan for the beam test. 		 
 
WEPPP035 Pushing the Gradient Limitations of Superconducting Photonic Band Gap Structure Cells SRF, wakefield, electron, higher-order-mode 2801
 
  • E.I. Simakov, W.B. Haynes, S.S. Kurennoy, J.F. O'Hara, E.R. Olivas, D.Y. Shchegolkov
    LANL, Los Alamos, New Mexico, USA
  
  Funding: This work is supported by the Department of Defense High Energy Laser Joint Technology Office through the Office of Naval Research.
We present a design of a superconducting photonic band gap (PBG) accelerator cell operating at 2.1 GHz. The cell is designed with the PBG rods that are specially shaped to reduce the peak magnetic fields and at the same time to preserve its effectiveness for suppression of the higher order modes (HOMs). It has been long recognized that PBG structures have great potential in reducing and even completely eliminating HOMs in accelerators. This is especially beneficial for superconducting electron accelerators for high power free-electron lasers (FELs), which are intended to provide high current continuous duty electron beams. Using PBG structures to reduce the prominent beam-breakup phenomena due to HOMs will allow significantly increased beam-breakup thresholds, and consequently will allow the increase of the frequency of SRF accelerators and the development of novel compact high-current accelerator modules for FELs. High gradient limitations of PBG resonators and the optimal arrangement of the wakefield couplers will be discussed in details in this presentation. 		 
 
WEPPR029 Alternative Cavity for H E Part of the Project X linac cavity, linac, cryomodule, emittance 2997
 
  • A. Lunin, A. Saini, N. Solyak, A.I. Sukhanov, V.P. Yakovlev
    Fermilab, Batavia, USA
  
  An alternative superconducting elliptical cavity is suggested for High Energy (HE) part of the Project X linac. The cavity is suitable to operate at CW regime with high beam current (10 mA), which is critical for Accelerator-Driven Subcritical (ADS) systems and for intense muon source for future Neutrino Factory or Muon Collider. We present the algorithm of the cavity shape optimization, comprehensive tolerances analysis and the solution for monopole High Order Modes (HOM) damping. Based on these results we estimated the probabilities of cryogenic losses per cryomodule and a growth of the beam longitudinal emittance due to the resonance excitation of monopole HOMs in the HE linac for Project X.  
 
WEPPR051 Issues for a Multi-bunch Operation with SPARC C-band Cavities wakefield, linac, betatron, dipole 3042
 
  • A. Mostacci, M. Migliorati, L. Palumbo
    URLS, Rome, Italy
  • D. Alesini, B. Spataro, C. Vaccarezza
    INFN/LNF, Frascati (Roma), Italy
  
  SPARC C-band traveling wave cavities were originally designed for the SPARC energy upgrade in the single bunch operation mode. In the context of a gamma source based on Compton backscattering and based on the SPARC C-band technology, we investigated the issues related to the use of these structures in the multi-bunch operation mode. Several beam configurations have been considered and the effects of transverse and longitudinal long range wakefields on beam dynamics have been studied. In the paper we present the results of these studies and, in particular, the issues related to transverse beam break-up that could prevent the multi-bunch operation. Possible HOM damped structures are also proposed.  
 
WEPPR077 Analysis of Long-range Wakefields in CLIC Main Linac Accelerating Structures with Damping Loads wakefield, simulation, damping, resonance 3111
 
  • G. De Michele
    Paul Scherrer Institut, Villigen, Switzerland
  • G. De Michele
    EPFL, Lausanne, Switzerland
  • A. Grudiev
    CERN, Geneva, Switzerland
  
  The baseline design of the CLIC accelerating structure foresees a moderate detuning and heavy damping of high order modes (HOMs), which are the source of long-range transverse wakefields. Such unwanted fields produce bunch-to-bunch instabilities so the HOMs must be suppressed. In order to damp these modes, the CLIC RF structure is equipped with lossy material inserted into four rectangular waveguides coupled to each accelerating cell. The lossy material absorbs EM (electromagnetic) wave energy with little reflection back to the accelerating cells. In the past, computations of the long-range wake of CLIC accelerating modes have been done using perfectly absorbing boundaries to terminate the damping waveguides. In this paper, 3D EM simulations of CLIC baseline accelerating structure with HOMs damping loads will be presented. A comparison between different EM codes (GdfidL, CST PARTICLE STUDIO®) will be discussed as well as the analysis of different types of absorbing materials with respect to the wakefields damping.  
 
WEPPR083 New Sector 37 Chamber Design and Installation for High-Current Operation of the APS Storage Ring impedance, vacuum, cavity, storage-ring 3123
 
  • Y.-C. Chae, R. Bechtold, W. Berg, L. Erwin, M. Givens, J.E. Hoyt, L.H. Morrison, K.M. Schroeder, R. Soliday, J.B. Stevens, G.J. Waldschmidt
    ANL, Argonne, USA
  
  Funding: Work supported by U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under contract No. DE-AC02-06CH11357.
The Advanced Photon Source is a 7-GeV hard x-ray synchrotron light source consisting of 40 sectors. Sector 37 accommodates four radio-frequency cavities followed by a short straight section, which is set aside for the future installation of a diagnostic device. The 60-cm-long section of spool pieces can be isolated by two gate valves and has an independent vacuum pump. The spool pieces are normally under high vacuum condition when the total current is below 100 mA. However, at the higher current required for the APS Upgrade, rf heating causes an unacceptable rise in temperature. We analyzed this situation by wakefield simulation, which led to a new chamber design. Proper fabrication and careful installation with twelve thermocouples ensured a temperature rise under 40-50 degrees Celsius at 100 mA. A brief thermal analysis shows that the present observed temperature rise in the new chamber is mainly due to the resistive wall. 		 
 
WEPPR096 Recirculating Beam Breakup Study for the 12 GeV Upgrade at Jefferson Lab cryomodule, linac, cavity, simulation 3162
 
  • I. Shin, S. Ahmed, R.M. Bodenstein, S.A. Bogacz, T. Satogata, M. Stirbet, H. Wang, Y. Wang, B.C. Yunn
    JLAB, Newport News, Virginia, USA
  • I. Shin
    University of Connecticut, Storrs, Connecticut, USA
  
  Two new high gradient C100 cryostats with a total of 16 new cavities were installed at the end of the CEBAF south linac during the 2011 summer shutdown as part of the 12 GeV upgrade project at Jefferson Lab. We ran recirculating beam breakup (BBU) study in November 2011 to evaluate CEBAF low energy performance, measure transport optics, and evaluate BBU thresholds due to higher order modes (HOMs) in these cavities. This paper discusses the experiment setup, cavity measurements, machine setup, optics measurements, and lower bounds on existing CEBAF C100 BBU thresholds established by this experiment.  
 
THPPC029 High-power Waveguide Dampers for the Short-Pulse X-Ray Project at the Advanced Photon Source cavity, damping, vacuum, cryomodule 3344
 
  • G.J. Waldschmidt, B. Brajuskovic, J. Liu, M.E. Middendorf, A. Nassiri, T.L. Smith, G. Wu
    ANL, Argonne, USA
  • J. Henry, J.D. Mammosser, R.A. Rimmer, M. Wiseman
    JLAB, Newport News, Virginia, USA
  
  Funding: Work supported by U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
High-power waveguide dampers have been designed and prototyped for the Short-Pulse X-ray (SPX) cavities at the Advanced Photon Source. The cavities will operate at 2.815 GHz and utilize the TM110 dipole mode. As a result, higher-order (HOM) and lower-order mode (LOM) in-vacuum dampers have been designed to satisfy the demanding broadband damping requirements in the APS storage ring. The SPX single-cell cavity consists of two WR284 waveguides for damping the HOMs and one WR284 waveguide for primarily damping the LOM where up to 2kW will be dissipated in the damping material. The damper designs and high-power experimental results will be discussed in this paper. 		 
 
THPPC069 Design, Test and Implementation of New 201.25 MHz Power Amplifier for the LANSCE Linac cathode, DTL, electron, cavity 3446
 
  • J.T.M. Lyles, Z. Chen, J. Davis, A.C. Naranjo, D. Rees, G. M. Sandoval, Jr.
    LANL, Los Alamos, New Mexico, USA
  • D. Baca, R.E. Bratton, R.D. Summers
    Compa Industries, Inc., Los Alamos, New Mexico, USA
  • N.W. Brennan
    Texas A&M University, College Station, Texas, USA
  
  Funding: Work supported by the United States Department of Energy, National Nuclear Security Agency, under contract DE-AC52-06NA25396
A new 201.25 MHz final power amplifier (FPA) has been designed, fabricated, and tested at Los Alamos Neutron Science Center (LANSCE). The prototype FPA has produced 3 MW peak and 250 kW of mean power with 15 dB of power gain and over 60% efficiency. It has been tested for several thousand hours with a load. A Thales TH628 Diacrode® electron tube is key to the performance of the new amplifier. It is configured with a full wavelength output circuit, having the lower main tuner situated ¾λ from the central electron beam region in the tube and the upper slave tuner ¼λ from the same point. The FPA is designed with input and output transmission line cavity circuits, grid decoupling circuits, an adjustable output coupler, DC blocking and RF bypassing capacitors, HOM suppressors, and a cooling system. A pair of production amplifiers are planned to be power-combined for up to 3.6 MW peak power at high duty factor. Three of these combined amplifiers will be installed in place of the original 1968-vintage amplifiers to return LANSCE operation to 12% beam duty factor with higher peak current than presently possible. 		 
 
THPPP037 Status of the 325 MHz 4-ROD RFQ simulation, rfq, dipole, linac 3815
 
  • B. Koubek, A. Schempp, J.S. Schmidt
    IAP, Frankfurt am Main, Germany
  • L. Groening
    GSI, Darmstadt, Germany
  
  For the FAIR project of GSI as part of the proton linac, a 325 MHz 4-ROD RFQ with an output energy of 3 MeV is planned. Due to the simulations regarding the RF design, a prototype of this RFQ was built. Measurements with this prototype to verify the simulation results have been done. In addition, simulations with increasing cell numbers and simulations concerning the boundary fields of the electrodes are presented in this paper.  
 
THPPP068 Investigation of a Multi-cell Cavity Structure Proposed for Improved Hydroforming cavity, focusing, coupling, SRF 3895
 
  • K.R. Shin
    ORNL RAD, Oak Ridge, Tennessee, USA
  • A.E. Fathy
    University of Tennessee, Knoxville, Tennessee, USA
  • J.A. Holmes, Y.W. Kang
    ORNL, Oak Ridge, Tennessee, USA
  
  A multi-cell cavity structure with rectangular coupling aperture between cavity cells is proposed. This investigation is to study the RF properties of such structure that may provide high yield in hydroforming. In mechanical point of view, the rectangular aperture iris may provide much improved structure quality in hydroforming since it can help to reduce the stress incurring within the sheet metal with improved structural malleability. The necking procedure can be easier because of greater perimeter in the iris geometry. Peak electric and magnetic fields per accelerating gradient may increase however, compared to traditional TESLA type elliptical cavity structure. The rectangular iris shape provides asymmetric transverse focusing per half RF period. If the horizontal and vertical rectangular irises are interleaved, the net transverse focusing may be achieved. 3D simulations with CST MWS have been carried out to analyze EM field properties and the cavity parameters.