Keyword: HOM
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MOOCA01 Production and Testing Experience with the SRF Cavities for the CEBAF 12 GeV Upgrade cavity, cryomodule, SRF, higher-order-mode 26
 
  • A. Burrill, G.K. Davis, F. Marhauser, 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 recirculating CW electron linear accelerator at Jefferson Lab is presently undergoing a major upgrade to 12 GeV. This project includes the fabrication, preparation, and testing of 80 new 7-cell SRF cavities, followed by their incorporation into ten new cryomodules for subsequent testing and installation. In order to maximize the cavity Q over the full operable dynamic range in CEBAF (as high as 25 MV/m), the decision was taken to apply a streamlined preparation process that includes a final light temperature-controlled electropolish of the rf surface over the vendor-provided bulk BCP etch. Cavity processing work began at JLab in September 2010 and will continue through December 2011. The excellent performance results are exceeding project requirements and indicate a fabrication and preparation process that is stable and well controlled. The cavity production and performance experience to date will be summarized and lessons learned reported to the community. 		 
slides icon Slides MOOCA01 [4.376 MB]  
 
MOODA01 Experience with the Cornell ERL Injector SRF Cryomodule during High Beam Current Operation cavity, SRF, cryomodule, damping 35
 
  • M. Liepe, D.L. Hartill, G.H. Hoffstaetter, S. Posen, P. Quigley, V. Veshcherevich
    CLASSE, Ithaca, New York, USA
  
  Funding: Supported by NSF award DMR-0807731
Cornell University has developed and fabricated a SCRF injector cryomodule for the acceleration of high current, low emittance CW beams. This cryomodule is based on superconducting RF technology with five 2-cell SRF cavities operated in CW mode. Strong Higher-Order-Mode (HOM) damping and high power RF input couplers support accelerating beam currents of tens of mA. The cryomodule is currently under extensive testing in the Cornell ERL injector prototype with CW beam currents exceeding 25 mA. This paper gives an overview of the experience gained during the high beam current operation of the cryomodule, with a focus on the intrinsic cavity quality factors, input coupler performance, and HOM damping. 		 
 
MOODB02 RF Modeling Plans for the European Spallation Source cavity, electron, beam-losses, linac 56
 
  • S. Molloy, M. Lindroos, S. Peggs
    ESS, Lund, Sweden
  • R. Ainsworth
    Royal Holloway, University of London, Surrey, United Kingdom
  • R.J.M.Y. Ruber
    Uppsala University, Uppsala, Sweden
  
  The European Spallation Source (ESS) will be the world's most powerful next generation neutron source. The ESS linac is designed to accelerate highly charged bunches of protons to a final energy of 2.5 GeV, with a design beam power of 5 MW, for collision with a target used to produce the high neutron flux. In order to achieve this several stages of RF acceleration are required, each using a different technology. The high beam current and power require a high degree of control of the accelerating RF, and the specification that no more than 1 W/m of losses will be experienced means that the excitation and decay of the HOMs must be very well understood. Experience at other high power machines also implies that an understanding of the generation and subsequent trajectories of any field-emitted electrons should be understood. Thermal detuning of the HOM couplers due to multipacting is a serious concern here. This paper will outline the RF modeling plans - including the construction of mathematical models, simulations of HOMs, and multipacting - during the current Accelerator Design Update phase, and will discuss several of the more important issues for ESS.  
slides icon Slides MOODB02 [48.641 MB]  
 
MOPC004 352.2 MHz HOM Damped Normal Conducting ESRF Cavity: Design and Fabrication cavity, coupling, vacuum, storage-ring 68
 
  • V. Serrière, A.K. Bandyopadhyay, D. Boilot, L. Goirand, J. Jacob, B. Ogier, A. Triantafyllou
    ESRF, Grenoble, France
  
  Funding: This work, carried out within the framework of the ESRFUP project, has received research funding from the EU Seventh Framework Programme, FP7.
The ongoing ESRF upgrade included an option for an increase of the storage ring current from 200 to 300 mA, which has been tested successfully with the existing RF system. At this current level the HOM tuning of the existing five-cell copper cavities becomes extremely delicate and in view of a future reliable operation in user mode, new HOM free normal conducting cavities were developed at the ESRF. The design is based on the existing BESSY/ALBA cavity. However, several substantial modifications have been implemented and different fabrication processes elaborated to improve the design. Three operational prototypes will be delivered by three manufacturers in the coming months and will be fully tested on the ring. Although the 300 mA option has finally not been retained for the first phase of the ESRF upgrade, the aim is now to validate the new cavity design for a possible later increase in current. 		 
 
MOPC005 352.2 MHz – 150 kW Solid State Amplifiers at the ESRF cavity, booster, klystron, power-supply 71
 
  • J. Jacob, G. Gautier, M.L. Langlois, J.M. Mercier
    ESRF, Grenoble, France
  
  The ESRF has ordered seven 352.2 MHz – 150 kW Solid State Amplifiers (SSA) from the French company ELTA, with a design derived from the existing SSA developed by SOLEIL. The first four SSA will be commissioned by the end of 2011 and will be connected to the two booster cavities in Winter 2012 providing in total 600 kW in 10 Hz cycles. Thanks to anti-flicker capacitor banks with a total of 3 F in the 280 V DC power supply, up to only 350 kW will be drawn from the mains as compared to 1200 kW for the former klystron transmitter. The three remaining SSA will be received in 2012 and will feed three new single cell HOM damped cavities on the storage ring. The analysis of the market had shown that an alternative to klystrons needed to be investigated to guarantee the long term operation of the ESRF. SSA can be operated with a number of RF modules lost and are therefore intrinsically highly redundant. In parallel to the production by industry of this first batch of SSA, the ESRF is developing its own amplifier modules and proposing an alternative way to combine typically hundred RF modules using a single cavity combiner.  
 
MOPC021 Design of a Choke-mode Damped Accelerating Structure for CLIC Main Linac damping, impedance, wakefield, dipole 113
 
  • J. Shi, A. Grudiev, W. Wuensch
    CERN, Geneva, Switzerland
  • H. Chen, W.-H. Huang, C.-X. Tang, H. Zha
    TUB, Beijing, People's Republic of China
  
  Choke-mode damped accelerating structures are being studied as an alternative to the CLIC baseline structure by a CERN-Tsinghua collaboration. Choke-mode structures hold the potential for much lower levels of pulsed surface heating and, since milling is not needed, reduced cost. Structures with radial choke attached are simulated in Gdfidl to investigate the damping of the transverse wake. The first pass-band of the dipole modes is well damped, while the higher order dipole modes are possible to be reflected by the choke. Therefore, the geometry of the choke is tuned to minimize the reflection of these higher order dipoles. Based on this damping scheme, an accelerating structure with the same iris dimensions as the nominal CLIC design but with choke-mode damping has been designed. A prototype structure will be manufactured and high power tested in the near future.  
 
MOPC038 Engineering Design and Fabrication of Tapered Damped X-band Accelerating Structures vacuum, damping, wakefield, alignment 157
 
  • A. Solodko, D. Gudkov, A. Samoshkin
    JINR, Dubna, Moscow Region, Russia
  • S. Atieh, A. Grudiev, G. Riddone, M. Taborelli
    CERN, Geneva, Switzerland
  
  The accelerating structures (AS) are one of the main components of the Compact LInear Collider (CLIC), under study at CERN. Each AS contains about 30 copper disks, which form the accelerating cavity. A fully featured AS is very challenging and requires several technologies. Different damping methods, waveguides, vacuum manifolds, slots and choke, result in various design configurations. In the CLIC multibunch AS, called TDS (Tapered Damped Structure), each cell is damped by its four waveguides, which are extended by channels machined in dedicated external vacuum manifolds. The manifolds combine few functions such as damping, vacuum pumping and cooling. Silicon carbide absorbers, fixed inside of each manifold, are required for effective damping of High Order Modes. CERN is producing X-band RF structures in close collaboration with a large number of laboratories taking advantage of their large expertise and test facilities. The fabrication includes several steps from the machining to the final assembly, including quality controls. This paper describes the engineering design and fabrication procedure of the X-band AS with damping material, by focusing on few technical solutions.  
 
MOPC045 Commissioning of the ALBA Storage Ring RF System cavity, LLRF, storage-ring, pick-up 178
 
  • F. Pérez, B. Bravo, A. Salom, P. Sanchez
    CELLS-ALBA Synchrotron, Cerdanyola del Vallès, Spain
  
  ALBA is a 3 GeV, 400 mA, 3rd generation Synchrotron Light Source that is under commissioning in Cerdanyola, Spain. The RF System has to provide 3.6 MV of accelerating voltage and restore up to 540 kW of power to the electron beam. For that six RF plants, working at 500 MHz, are foreseen. The RF plants include several new developments: DAMPY cavity; the normal conducting HOM damped cavity developed by BESSY and based in the EU design; six are installed. CaCo; a cavity combiner to add the power of two 80 kW IOTs to produce the 160 kW needed for each cavity. WATRAX; a waveguide transition to coaxial, specially designed to feed the DAMPY cavities due to the geometrical and cooling constrains. Digital LLRF; fully designed at ALBA using commercial components. This paper shortly describes these systems and reports their performance during the ALBA commissioning.  
 
MOPC046 CaCo: A Cavity Combiner for IOTs Amplifiers cavity, simulation, storage-ring, high-voltage 181
 
  • B. Bravo, F. Mares, F. Pérez, P. Sanchez
    CELLS-ALBA Synchrotron, Cerdanyola del Vallès, Spain
  • M.L. Langlois
    ESRF, Grenoble, France
  
  The ALBA storage ring uses six room temperature cavities; each one fed by two 80 kW IOTs amplifiers at 499.654 MHz. The power of the pair of transmitters is combined by a cavity combiner, CaCo. One of the design requirements of CaCo was that it continued working safely and with a good efficiency in the case of an IOT failure (asymmetrical mode). During the first asymmetric full power tests, in May 2010, with an active IOT and the other passive, the result was dramatic, the passive IOT broke in two parts after few hours of operation. This paper presents the experimental results and the electromagnetic field simulations of the asymmetrical operation mode of CaCo, i.e. one active IOT and the other passive, and analyze why the ceramic of the output tube of the passive IOT broke during the first performance of this mode. Also, it reports a possible solution to solve this problem.  
 
MOPC050 Multipacting Analysis for the Superconducting RF Cavity HOM Couplers in ESS cavity, electron, simulation, superconducting-RF 190
 
  • S. Molloy
    ESS, Lund, Sweden
  • R. Ainsworth
    Royal Holloway, University of London, Surrey, United Kingdom
  • R.J.M.Y. Ruber
    Uppsala University, Uppsala, Sweden
  
  The European Spallation Source (ESS) linac will consist of three families superconducting RF cavities to accelerate protons to the required 5 MW for collision with the target. If it is determined that HOM damping is required to limit the effect of beam induced modes, it is quite likely that HOM couplers will be installed. Multipacting in these couplers is a concern as thermally induced detuning of the fundamental notch filter has limited the achievable gradient in other high power machines. It is therefore important to avoid potential multipacting conditions during the design phase. Presented here are simulations using the Track3P code developed at SLAC. Multipacting regions are highlighted, electron trajectories are shown, and suitability of the proposed HOM coupler design is discussed.  
 
MOPC051 The 100 MHz RF System for the MAX IV Storage Rings cavity, LLRF, storage-ring, impedance 193
 
  • Å. Andersson, E. Elafifi, M. Eriksson, D. Kumbaro, P. Lilja, L. Malmgren, R. Nilsson, H. Svensson, P.F. Tavares
    MAX-lab, Lund, Sweden
  • J.H. Hottenbacher
    RI Research Instruments GmbH, Bergisch Gladbach, Germany
  • A. Milan
    CELLS-ALBA Synchrotron, Cerdanyola del Vallès, Spain
  • A. Salom
    ELETTRA, Basovizza, Italy
  
  The construction of the MAX IV facility has started and user operation is scheduled to commence 2015. The facility is comprised of two storage rings optimized for different wavelength ranges, and a linac-based short pulse facility. In this paper the RF systems for the two storage rings are described. The RF systems will be based on either tetrode or solid state amplifiers working at 100 MHz. Circulators will be used to give isolation between cavity and power amplifier. The main cavities are of normal conducting, entire copper, capacity loaded type, where the present cavities at MAX-lab has served as prototypes. For the MAX IV ring operation it is essential to elongate bunches, in order to minimize the influence of intra beam scattering on beam transverse emittances. For this, 3rd harmonic passive (Landau-) cavities are employed. These are of similar type as the main cavities, mainly because the capacity loaded type has the advantage of pushing higher order modes to relatively high frequencies compared to pill-box cavities. Digital low level RF systems will be used, bearing in mind the possibility of post mortem analysis.  
 
MOPC078 Operation of Superconducting Cavities in a Fast Ramping Electron Storage Ring cavity, impedance, acceleration, storage-ring 253
 
  • A. Roth, W. Hillert
    ELSA, Bonn, Germany
  
  Funding: Supported by German Research Foundation through SFB/TR 16.
The achievable maximum energy of a medium-sized electron accelerator is mainly limited by the accelerating voltage. Using superconducting (sc) cavities, the energy limitation can be shifted considerably. However, the operation of sc multi-cell cavities in a fast ramping storage ring causes additional problems which were investigated at the 3.5 GeV Electron Stretcher Accelerator ELSA. We studied the use of two 500 MHz sc cavities providing the necessary resonator voltage of up to 14 MV and replacing the normal conducting cavities of PETRA type. A large cavity coupling factor is required, so that using the existing 250 kW klystron, an internal beam of 50 mA can be accelerated up to 5 GeV. In addition, a fast detuning of the resonance frequency of the cavities must be implemented during beam injection and the energy ramp of 4 GeV/s. An appropriate 500 MHz structure is given by a five-cell cavity constructed for the JAERI-FEL-LINAC. Based on this geometry, HOM have been calculated from a numerical simulation. Since all monopole and a larger number of dipole HOM are well above the multibunch instabilities threshold, further studies about beam instabilities damping are essential. 		 
 
MOPC080 First Considerations Concerning an Optimized Cavity Design for the Main Linac of BERLinPro cavity, linac, coupling, impedance 259
 
  • B. Riemann, T. Weis
    DELTA, Dortmund, Germany
  • W. Anders, J. Knobloch, A. Neumann
    HZB, Berlin, Germany
  • H.-W. Glock, C. Potratz, U. van Rienen
    Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
  • F. Marhauser
    JLAB, Newport News, Virginia, USA
  
  Funding: work supported by BMBF under contracts 05K10PEA and 05K10HRC
The Berlin Energy Recovery Linac Project (BERLinPro) is designed to develop and demonstrate CW linac technology and expertise required to drive next-generation Energy Recovery Linacs. Strongly HOM-damped multicell 1.3 GHz cavities are required for the main linac. The optimization of the cavities presented here is primarily based on the CEBAF 1.5 GHz 5-cell high-current cavity design, including HOM waveguide couplers. The cavity was scaled to 1.3 GHz and extended to 7 cells. Modifications to the end group design have also been studied. An effort was also made to reduce the ratio Epk/Eacc while still permitting HOMs to propagate. 		 
 
MOPC086 Description and First Experience with the RF Measurement Procedure for the European XFEL SC Cavity Production cavity, SRF, cryomodule, superconducting-cavity 277
 
  • A.A. Sulimov, Th. Buettner, A. Gössel, D. Kostin, G. Kreps, W.-D. Möller, D. Reschke, J.H. Thie, K. Twarowski
    DESY, Hamburg, Germany
  
  Cavity production for the European XFEL was recently started with first Nb sheets arriving. From this stage to the accelerating module being ready for the linac installation, many critical RF measurements are necessary. During the mechanical cavity fabrication the cavity half-cells, dumb-bells and end-groups are measured and sorted. The cavity spectrum and field profiles are measured and tuned. The HOM (Higher Oder Modes) couplers filter tuning, vertical cavity RF tests, cavity checks during the string assembly and final cavity performance measurements in the module as well as the fundamental mode and HOM RF spectra measurements complete the sequence. We present the procedures of the RF measurements and discuss the first results for the XFEL prototype modules with special attention for the cavity tuning.  
poster icon Poster MOPC086 [0.515 MB]  
 
MOPC095 Superconducting Cavity R&D for ILC at MHI cavity, superconducting-cavity, linac, status 298
 
  • H. Hitomi, H. Hara, F. Inoue, K. Kanaoka, K. Sennyu, T. Yanagisawa
    MHI, Kobe, Japan
  
  We have developed and manufactured some superconducting RF cavity for STF project in KEK. In recent vertical test in KEK, the MHI-#12 cavity which is one of cavities for STF phase 2 project reached ILC specification(max Eacc was about 40MV/m). So techniques for manufacturing cavity is making steady progress in MHI. To be realized ILC project, we also try to decrease the manufacturing cost by using some new techniques, for example Laser Beam Welding, deep drawing, seamless dumbbell, etc. In this meeting, we will report recent MHI's activities for ILC.  
 
MOPC096 Design and Fabrication of a 5-Cell High Current Superconducting Cavity cavity, simulation, dipole, quadrupole 301
 
  • Y.M. Li, K.X. Liu, S.W. Quan, F. Zhu
    PKU/IHIP, Beijing, People's Republic of China
  • R. Nassiri
    ANL, Argonne, USA
  
  Funding: National High Technology Research and Development program 863 (2009AA03Z206)
Energy recovery linacs (ERL) is promising to achieve high average current with superior beam quality. The key component for accelerating such high current beams is the superconducting radio frequency (SRF) cavity. The design of a 1.3 GHz 5-cell high current superconducting cavity has been carried out under the cooperation between Peking University (PKU) and Argonne National Laboratory (ANL). RF properties, damping of the HOMs, multipacting and mechanical features of this cavity have been discussed and the final design is presented. 		 
 
MOPC106 Study of the Variation of Transverse Voltage in the 4 Rod Crab Cavity for LHC cavity, luminosity, simulation, dipole 322
 
  • B.D.S. Hall, P.K. Ambattu, G. Burt, C. Lingwood
    Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
  • P. Goudket, C. Hill
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  
  The planned high luminosity upgrade to LHC will utilise crab cavities to rotate the beam in order to increase the luminosity in the presence of a finite crossing angle. A compact design is required in order for the cavities to fit between opposing beam-lines. In this paper we discuss we discuss one option for the LHC crab cavity based on a 4 rod TEM deflecting cavity. Due to the large transverse size of the LHC beam the cavity is required to have a large aperture while maintaining a constant transverse voltage across the aperture. The cavity has been optimised to minimise the variation of the transverse voltage while keeping the peak surface electric and magnetic fields low for a given kick. This is achieved while fitting within the strict design space of the LHC. The variation of deflecting voltage across the aperture has been studied numerically and compared with numerical and analytical estimates of other deflecting cavity types. Performance measurements an aluminium prototype of this cavity are presented and compared to the simulated design.  
 
MOPC107 HOM and FP Coupler Design for the NLSF High Gradient SC Cavity cavity, simulation, SRF, damping 325
 
  • R.M. Jones, N. Juntong
    UMAN, Manchester, United Kingdom
  
  The design of both higher order mode (HOM) and fundamental power (FP) couplers for the New Low Surface Field (NLSF) cavity* is presented. Here we study using the ILC baseline couplers for this new superconducting cavity. A Balleyguier method** of calculating external quality factor is used and the results validated using both Microwave studio and HFSS.
* N. Juntong and R.M. Jones, SRF2009, THPPO024, 2009.
** P. Balleyguier, LINAC98, MO4037, 1998
 		 
 
MOPC112 Fabrication and Testing Status of CEBAF 12 GeV Upgrade Cavities cavity, cryomodule, electron, status 337
 
  • F. Marhauser, A. Burrill, G.K. Davis, D. Forehand, C. Grenoble, J. Hogan, R.B. Overton, A.V. Reilly, R.A. Rimmer, M. Stirbet
    JLAB, Newport News, Virginia, USA
  
  Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
The 12 GeV upgrade of the Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Laboratory (JLab) is under way. All cavities have been built by industry and are presently undergoing post-processing and final low and high power qualification before cryomodule assembly. The status is reported including fabrication-related experiences, observations and issues throughout production, post-processing and qualification. 		 
 
MOPC113 Results of Cavity Series Fabrication at Jefferson Laboratory for the Cryomodule “R100” cavity, cryomodule, target, damping 340
 
  • F. Marhauser, W.A. Clemens, M.A. Drury, D. Forehand, J. Henry, S. Manning, R.B. Overton, R.S. Williams
    JLAB, Newport News, Virginia, USA
  
  Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
A series production of eight superconducting RF cavities for the cryomodule R100 was conducted at JLab in 2010. The cavities underwent chemical post-processing prior to vertical high power testing and routinely exceeded the envisaged performance specifications. After cryomodule assembly, cavities were successfully high power acceptance tested. In this paper, we present the achievements paving the way for the first demonstration of 100 MV (and beyond) in a single cryomodule to be operated at CEBAF. 		 
 
MOPC118 Effects of the Thickness of Niobium Surface Oxide Layers on Field Emission* controls, cavity, SRF, niobium 355
 
  • A.T. Wu, S. Jin, J.D. Mammosser, R.A. Rimmer
    JLAB, Newport News, Virginia, USA
  • X.Y. Lu, K. Zhao
    PKU/IHIP, Beijing, People's Republic of China
  
  Funding: 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.
Field emission on the inner surfaces of niobium superconducting radio frequency cavities is still one of the major obstacles for reaching high accelerating gradients for SRF community. Our previous experimental results* seemed to imply that the threshold of field emission was related to the thickness of Nb surface oxide layers. In this contribution, a more detailed study on the influences of the surface oxide layers on the field emission on Nb surfaces will be reported. By anodization technique, the thickness of the surface pentoxide layer was artificially fabricated from 3 nm up to 460 nm. A home-made scanning field emission microscope was employed to perform the scans on the surfaces. Emitters were characterized using a scanning electron microscope together with an energy dispersive x-ray analyzer. The SFEM experimental results were analyzed in terms of surface morphology and oxide thickness of Nb samples and chemical composition and geographic shape of the emitters. A model based on the classic electromagnetic theory was developed trying to understand the experimental results. Possibly implications for Nb SRF cavity applications from this study will be discussed.
* A.T. Wu et al., Proc. of IPAC 2010, Kyoto, Japan, WEPEC081, p. 3067 (2010).
Authored by The Southeastern Universities Research Association, Inc. under U.S. DOE Contract No. DE-AC05-84ER40150.
 
 
MOPC121 Design of Low-frequency Superconducting Spoke Cavities for High-velocity Applications cavity, impedance, superconductivity, linac 364
 
  • J.R. Delayen, C.S. Hopper
    ODU, Norfolk, Virginia, USA
  • R.G. Olave
    Old Dominion University, Norfolk, Virginia, USA
  
  Superconducting single- and multi-spoke cavities have been designed to-date for particle velocities from β~0.15 to β~0.65. Superconducting spoke cavities may also be of interest for higher-velocity, low-frequency applications, either for hadrons or electrons. We present the design of 325 and 352 MHz spoke cavities optimized for β=0.8 and β=1.  
 
MOPO011 The First 1 1/2 Years of TOTEM Roman Pot Operation at LHC alignment, controls, scattering, beam-losses 502
 
  • M. Deile, G.H. Antchev, R.W. Assmann, I. Atanassov, V. Avati, J. Baechler, R. Bruce, M. Dupont, K. Eggert, B. Farnham, J. Kaspar, F. Lucas Rodríguez, J. Morant, H. Niewiadomski, X. Pons, E. Radermacher, S. Ravat, F. Ravotti, S. Redaelli, G. Ruggiero, H. Sabba, M. Sapinski, W. Snoeys, G. Valentino, D. Wollmann
    CERN, Geneva, Switzerland
  • R. Appleby
    UMAN, Manchester, United Kingdom
  
  Since the LHC running season 2010, the TOTEM Roman Pots (RPs) are fully operational and serve for collecting elastic and diffractive proton-proton scattering data. Like for other moveable devices approaching the high intensity LHC beams, a reliable and precise control of the RP position is critical to machine protection. After a review of the RP movement control and position interlock system, the crucial task of alignment will be discussed.  
 
MOPS040 Intra-Bunch Energy Spread of Electrons in Powerful RF Linacs for Nuclear Physics Research* linac, target, electron, simulation 691
 
  • V.V. Mytrochenko, M.I. Ayzatskiy, V.A. Kushnir, A. Opanasenko, S.A. Perezhogin, V.L. Uvarov
    NSC/KIPT, Kharkov, Ukraine
  
  Funding: Ukrainian State program of fundamental and applied studies on the use of nuclear materials, nuclear and radiation technologies in the fields of economics (YaMRT project No. 826/35)
There are some particles in RF electron linacs with energy that may be significantly different from that of particles within a core of the bunch. Loss of these particles at average beam power of tens of kilowatts can cause radiation and thermal problems. Filtration of such particles during the initial stage of acceleration, at energies below the threshold of photonuclear reactions, is important. The paper analyzes several ways to perform such type of filtration in the injector part of a powerful electron linac using a RF chopper or magnetic systems. 		 
 
MOPS047 Studies of Transverse Single-pass Beam Breakup in E-Linac cavity, linac, dipole, emittance 706
 
  • D. Kaltchev, R.A. Baartman, Y.-C. Chao, P. Kolb, S.R. Koscielniak, L. Merminga, A.K. Mitra, V. Zvyagintsev
    TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, Vancouver, Canada
  
  Time-domain simulations of single-pass transverse beam-breakup (BBU) effects in E-linac are described. We use dipole-HOM parameters for the 9-cell cavity obtained with Particle Studio to evaluate the rms bunch orbit offsets at linac exit. Finding the multi-bunch orbit contribution to machine emittance as a function of the average beam current allows to evaluate the performance of two cavity models for two different modes of machine operation.  
 
MOPS051 Modeling of the Beam Break Up Instability for BERLinPro* cavity, linac, optics, solenoid 718
 
  • Y. Petenev, A.V. Bondarenko, A.N. Matveenko
    HZB, Berlin, Germany
  
  Following funding approval late 2010, Helmholtz-Zentrum Berlin officially started Jan. 2011 the design and construction of the Berlin Energy Recovery Linac Project BERLinPro. The initial goal of this compact ERL is to develop the ERL accelerator physics and technology required to accelerate a high-current low emittance beam. In this work the threshold current of the Beam Break Up (BBU) instability was calculated for the BERLinPro. The comparison of two 100 MeV linacs based on different type of superconducting cavities is made. Different methods of BBU suppression are investigated (e.g. the influence of solenoid, pseudo-reflector and quadruple triplets in the linac structure on the BBU threshold).  
 
MOPS076 Long Range Wakefields in the SwissFEL C-band Linac wakefield, linac, simulation, impedance 781
 
  • A. Citterio, M. Aiba, R. Zennaro
    PSI, Villigen, Switzerland
  
  The SwissFEL main linac consists of more than hundred constant gradient C-band accelerating structures which boost the beam energy from 410 MeV at the injector to the final nominal energy of 5.8 GeV. With a repetition rate of 100 Hz, two bunches per pulse can be accelerated with a spacing of 28 ns to feed simultaneously two different FEL arms*. Rising of the long range wakefields, both longitudinal and transverse, could affect this multibunch operation, causing degenerative effects on the quality of the second bunch. A direct computation of the longitudinal and transverse wakes by means of time domain simulations is compared with a model based on the computation of the dispersion curves of the wake modes by frequency domain simulations. A good agreement is obtained for both the synchronous frequency and impedance of all the main modes contributing to the wakefields. Moreover, the total longitudinal wake at 28 ns is below the thighter tolerances required by the beam dynamics, so that neither Higher Order Modes (HOMs) either beam loading require compensation. The effects on the beam of the long range transverse wakefields are also negligeable.
*R. Ganter et al, SwissFEL CDR, PSI report n. 10-04; http://www.psi.ch/swissfel/CurrentSwissFELPublicationsEN/SwissFELCDR_v1903.03.11-small.pdf 		 
 
MOPS082 Some Considerations on the Choice of Frequency and Geometrical Beta in High Power Proton Linacs in the Context of Higher Order Modes cavity, linac, simulation, proton 793
 
  • M. Schuh, F. Gerigk
    CERN, Geneva, Switzerland
  • M. Schuh
    MPI-K, Heidelberg, Germany
  • C.P. Welsch
    Cockcroft Institute, Warrington, Cheshire, United Kingdom
  
  Several high power superconducting (SC) proton linear accelerators are currently in the design stage around the world, such as for example the European Spallation Source (ESS) in Lund, Project X at Fermilab, the European ADS demonstrator MYRRAH in Mol and the Superconducting Proton linac (SPL) at CERN. In this contribution, the influence of Higher Order Modes (HOMs) in elliptical SC cavities is discussed as a function of the operation frequency, the number of cells and the geometrical beta of the cavity. Based on cavity design data beam dynamics simulations are executed for different linac layouts to quantify the influence of HOMs.  
 
MOPS085 Wakefield Calculations for the LCLS in Multibunch Operation* linac, dipole, injection, FEL 802
 
  • K.L.F. Bane
    SLAC, Menlo Park, California, USA
  
  Funding: Work supported by the U.S. Department of Energy under contract DE-AC02-76SF00515.
Normally the Linac Coherent Light Source (LCLS) operates in single-bunch mode, sending a bunch of up to 250 pC charge at 120 Hz through the linac and the undulator, and the resulting FEL radiation into one of the experimental hutches. With two bunches per rf pulse, each pulse could feed either two experiments or one experiment in a pump-probe type configuration. Two-bunch FEL operation has already been briefly tested at the LCLS, and works reasonably well*, although not yet routinely. In this report we study the longitudinal and transverse long-range (bunch-to-bunch) wakefields of the linacs and their effects on LCLS performance in two-bunch mode. The longitudinal wake changes the average energy and chirp at the second bunch, and the transverse wake misaligns the second bunch (in transverse phase space) in the presence of e.g. transverse injection jitter or quad misalignments. Finally, we extend the study to consider the LCLS with trains of up to 20 bunches per rf pulse.
* F.-J. Decker et al, "A demonstration of multi-bunch operation in the LCLS," Proceedings of FEL2010, Malmoe, Sweden, p. 467. 		 
 
MOPS086 Beam Breakup Simulation for the PEP-X ERL cavity, emittance, simulation, recirculation 805
 
  • Y. Jiao, Y. Cai, A. Chao
    SLAC, Menlo Park, California, USA
  
  Funding: The work is supported by the U.S. Department of Energy under contract No. DE-AC02-76SF00515.
The transverse beam breakup (BBU) is one of the dominant factors in ERL for the available beam current. A tracking code built in Matlab is developed and benchmarked by comparing with the analytical solutions with the simple model. Study on the threshold current and emittance growth due to the transverse BBU for PEP-X ERL are presented in this paper. 		 
 
MOPZ010 An Accelerator Design Tool for the International Design Study for the Neutrino Factory factory, lattice, simulation, solenoid 841
 
  • A. Kurup
    Imperial College of Science and Technology, Department of Physics, London, United Kingdom
  • P. Bonnal, B. Daudin, J. De Jonghe, M. Dutour
    CERN, Geneva, Switzerland
  
  A tool has been developed to simplify the accelerator design process from the lattice design, through tracking simulations with engineering features, to costing the facility. The aim of this tool is to facilitate going through the design loop efficiently and thus allow engineering features to be included early on in the design process without hindering the development of the lattice design. The tool uses a spreadsheet to store information about the accelerator and can generate MADX input files, G4beamline input files and interfaces with the costing tool developed by CERN. Having one source for the information simplifies going between lattice simulations, tracking simulations and costing calculations and eliminates the possibility of introducing discrepancies in the design. The application of this tool to cost the Neutrino Factory, which is part of the IDS-NF and EUROnu studies for delivering the Reference Design Report, will be presented.  
 
TUPC054 LHeC ERL Design and Beam-dynamics Issues linac, optics, emittance, cavity 1120
 
  • S.A. Bogacz, I. Shin
    JLAB, Newport News, Virginia, USA
  • D. Schulte, F. Zimmermann
    CERN, Geneva, Switzerland
  
  We discuss machine and beam parameter choices for a Linac-Ring option of the Large Hadron electron Collider (LHeC) based on the LHC. With the total wall-plug power limited to 100 MW and a target current of about 6 mA the desired luminosity of 1033 cm-2 s-1 can be reached, providing one exploits unique features of the Energy Recovery Linac (ERL). Here, we describe the overall layout of such ERL complex located on the LHC site. We present an optimized multi-pass linac optics enabling operation of the proposed 3-pass Recirculating Linear Accelerator (RLA) in the Energy Recovery mode. We also describe emittance preserving return arc optics architecture; including layout and optics of the arc switch-yard. Furthermore, we discuss importance of collective effects such as: beam breakup in the RLA, as well as ion accumulation, with design-integrated mitigation measures, and the electron-beam disruption in collision. Finally, a few open questions are highlighted.  
 
TUPC108 Beam Diagnostics Based on Higher Order Mode for High Repetition Beam cavity, simulation, diagnostics, single-bunch 1269
 
  • X. Luo, X.Y. Lu, F. Wang
    PKU/IHIP, Beijing, People's Republic of China
  • F.S. He
    JLAB, Newport News, Virginia, USA
  
  The signals from the HOM ports on superconducting cavities can be used as beam position monitors. The HOM amplitude of dipole mode is proportional to the beam offset. For high repetition bunches operation, the spectrum is consist of the HOMs peaks and the peaks which is integer times of the bunch repetition. The HOMs amplitudes should be separated from the two kinds of peaks. Based on the simulation from a TESLA 2-cell cavity, the transform matrix between the HOMs amplitudes and beam offsets has been found, as well as the cavity axis. The simulation results have demonstrated that beam diagnostics based on HOMs is feasible while high repetition bunches operation.  
 
TUPO026 Developments towards a Full Energy Recovery Linac cavity, gun, cathode, SRF 1494
 
  • P. vom Stein, J.H. Hottenbacher, A. Metz
    RI Research Instruments GmbH, Bergisch Gladbach, Germany
  
  Energy Recovery Linacs (ERLs) are high potential candidates for driving light sources based on laser Compton scattering with high brilliance photon beams and sub pico second time structure. We report on developments for an advanced ERL design, which allows the recovery of nearly full electron beam energy up to the limits set by the energy width of the beam. This “Full” Energy Recovery Linac (FERL) allows a substantial reduction of the complexity of the accelerator systems resulting into a very compact light source design suitable for industrial and medical applications.  
 
TUPS096 ESS Parameter List Database and Web Interface Tools linac, lattice, neutron, cavity 1762
 
  • K. Rathsman, S. Peggs, P. Reinerfelt, G. Trahern
    ESS, Lund, Sweden
  • J. Bobnar
    Cosylab, Ljubljana, Slovenia
  
  The European Spallation Source is an intergovernmental project building a multidisciplinary research laboratory based upon the world's most powerful neutron source. The main facility will be built in Lund, Sweden. Construction is expected to start around 2013 and the first neutrons will be produced in 2019. The ESS linac delivers 5 MW of power to the target at 2.5 GeV, with a nominal current of 50 mA. The Accelerator Design Update (ADU) collaboration of mainly European institutions will deliver a Technical Design Report at the end of 2012. To ensure consistency of the information being used amongst all subgroups throughout the period of accelerator design and construction, a parameter list database and web interface have been proposed. The main objective is to provide tools to identify inconsistencies among parameters and to enforce groups as well as individuals to work towards the same solution. Another goal is to make the Parameter Lists a live and credible endeavor so that the data and supporting information shall be useful to a wider audience such as external reviewers as well as being easily accessible.  
 
TUPS106 Absorber Materials at Room and Cryogenic Temperatures* cavity, cryogenics, damping, electron 1792
 
  • F. Marhauser, T.S. Elliott, A.T. Wu
    JLAB, Newport News, Virginia, USA
  • E.P. Chojnacki
    CLASSE, Ithaca, New York, USA
  • E. Savrun
    Sienna Technologies Inc., Woodinville, USA
  
  Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
We recently reported on investigations of RF absorber materials at cryogenic temperatures conducted at Jefferson Laboratory (JLab). The work was initiated to find a replacement material for the 2 Kelvin low power waveguide Higher Order Mode (HOM) absorbers employed within the original cavity cryomodules of the Continuous Electron Beam Accelerator Facility (CEBAF). This effort eventually led to suitable candidates as reported in this paper. Furthermore, though constrained by small funds for labor and resources, we have analyzed a variety of lossy ceramic materials, several of which could be usable as HOM absorbers for both normal conducting and superconducting RF structures, e.g. as loads in cavity waveguides and beam tubes either at room or cryogenic temperatures and, depending on cooling measures, low to high operational power levels. 		 
 
WEPC093 Various Approaches to Electromagnetic Field Simulations for RF Cavities simulation, cavity, impedance, higher-order-mode 2226
 
  • C. Liu, W. Ackermann, W.F.O. Müller, T. Weiland
    TEMF, TU Darmstadt, Darmstadt, Germany
  
  Funding: Work supported by BMBF under contract 05H09RD5
In the Superconducting Proton Linac (SPL) cavity, there is not only the fundamental mode for the particle acceleration but also many higher order modes (HOMs), which can lead to particle beam instabilities. This is very dangerous for SPL cavity. Therefore it is necessary to simulate the electromagnetic field in the SPL cavity, so that the field distribution and the shunt impedance for every higher order mode can be precisely calculated. At TEMF this research work can be done in three different ways: 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. Finally the HOM coupler will be considered for the effective damping of higher order modes in the SPL cavity. 		 
 
WEPC097 A Concatenation Scheme for the Computation of Beam Excited Higher Order Mode Port Signals cavity, wakefield, coupling, higher-order-mode 2238
 
  • T. Flisgen, H.-W. Glock, U. van Rienen
    Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
  
  Ongoing studies investigate in how far higher order mode (HOM) port signals of superconducting RF cavities can be used for machine and beam diagnostics. Apart from experiments e.g. at the FLASH facility at DESY in Hamburg, numerical modelling is needed for the prediction of HOM coupler signals. For this purpose, the RF properties of the entire accelerating module have to be taken into account, since higher order modes can propagate along the cavity chain. A discretization of the full chain, followed by a wake field simulation is only feasible with powerful and expensive cluster computers. Instead, an element wise wake field simulation of sub-sections of the chain, followed by a suitable concatenation scheme can be performed on standard hardware assuming the beam to be sufficiently stiff. In this paper a concatenation scheme for the computation of beam excited HOM port signals is derived as a generalization of the Coupled S-Parameter scheme CSC. Furthermore, the validity of the method is shown for a sample structure.  
 
WEPC099 Coupler Design and Optimization by GPU-Accelerated DG-FEM simulation, scattering, higher-order-mode, linac 2244
 
  • C. Potratz, H.-W. Glock, U. van Rienen
    Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
  
  The numerical optimization of rf-components like couplers is a common task during the design phase of particle accelerators. Typically, these optimizations involve the simulation of a multitude of very similar structures with minor geometric variations. Nevertheless, this process is in its entire extend rather demanding on both the invested time and hardware budget. With recent advancements in the field of numerical electromagnetic field simulation and consumer graphic processors, an interesting alternative for the time-consuming simulation part of the optimization is available. In this contribution we show, how the Discontinuous Galerkin FEM method in conjunction with consumer graphic cards can be used to build moderately prized cluster solutions for the parallel simulation of rf-components. The contribution will mainly focus on, but is not limited to, Higher Order Mode couplers as a typical application example, where the DG-FEM method accelerated by a graphic processor might be used to significantly reduce the overall time necessary for the optimization.  
 
WEPC125 Higher Order Modes in Coupled Cavities of the FLASH Module ACC39 cavity, simulation, diagnostics, dipole 2301
 
  • R.M. Jones, I.R.R. Shinton
    UMAN, Manchester, United Kingdom
  • Z. Li
    SLAC, Menlo Park, California, USA
  
  We analyse the higher order modes (HOMs) in the 3.9GHz bunch shaping cavities installed in the FLASH facility at DESY. A suite of finite element computer codes (including HFSS and ACE3P) and globalised scattering matrix calculations are used to investigate the modes in these cavities. 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. Coupled inter-cavity modes are simulated together with a limited band of trapped modes.  
 
THPPA00 Study of Beam Diagnostics with Trapped Modes in Third Harmonic Superconducting Cavities at FLASH cavity, dipole, simulation, electron 2891
 
  • P. Zhang
    DESY, Hamburg, Germany
  • P. Zhang
    UMAN, Manchester, United Kingdom
  
  Contribution selected for EPS-AG Prize d). Off-axis beams passing through an accelerating cavity excite dipole modes among other higher order modes (HOMs). These modes have linear dependence on the transverse beam offset from the cavity axis. Therefore they can be used to monitor the beam position within the cavity. The fifth dipole passband of the third harmonic superconducting cavities at FLASH has modes trapped within each cavity and do not propagate through the adjacent beam pipes, while most other cavity modes do. This could enable the beam position measurement in individual cavities. This paper investigates the possibility to use the fifth dipole band for beam alignment in the third harmonic cavity module. Simulations and measurements both with and without beam-excitations are presented. Various analysis methods are used and compared. A good correlation of HOM signals to the beam position is observed.  
slides icon Slides THPPA00 [2.740 MB]  
 
THPO007 Operation Status of SSRF Power Supplies and Interlocks for Top-up Operation power-supply, controls, storage-ring, quadrupole 3349
 
  • R. Li, C.L. Guo, M.M. Huang, T.J. Shen
    SINAP, Shanghai, People's Republic of China
  
  Digital switching mode magnet power supplies are used in SSRF accelerators which have been operating since 2008. Summary of the operation and maintenance of these power supplies will be shared over here. The availability of the power supplies is increased steadily over the past 4 years. And the power supplies interlocks for the SSRF top-up operation will be also introduced in this paper.  
 
THPO015 External Energy Dump for Superconducting Magnet of the Uni-polar Power System power-supply, controls, superconductivity, simulation 3367
 
  • Y.S. Wong, K.-B. Liu, W.S. Wen
    NSRRC, Hsinchu, Taiwan
  
  This thesis focuses on the design of superconducting discharge energy circuit structure in Uni-polar power supply [1]~[3]. Superconductivity is an electrical resistance of exactly zero which occurs in certain materials below a characteristic temperature [4]. It’s operation at the steady state in constant temperature area. When Rise up resistance and temperature of superconductivity will have been dissipates function. Uni-polar power supply has needed to design discharge energy circuit when superconductor reduces the current. To make use release the energy transfers to external circuit keep the constant temperature with the superconductivity. The superconducting coil wingding has a total length magnetic period of 56.56cm, total magnet length of 478.9cm and vertical (horizontal) magnetic field of 18.7T.  
 
THPO017 Improvement of Output Current Characteristics for Bira MCOR30 Correction Magnet Power Supply controls, power-supply, feedback, storage-ring 3373
 
  • J.C. Huang, K.-B. Liu, Y.S. Wong
    NSRRC, Hsinchu, Taiwan
  
  The correction magnet power supplies installed at the Taiwan light source (TLS) are Bira Systems’ MCRO 30 power modules, a full-bridge configuration power stage converting the unregulated DC bulk power into a bi-polar current source. The MCOR 30 is theoretically regulated under a very fine control method, with this control method the Bira MCOR 30 should overcome the zero crossover distortion of a standard H-Bridge PWM schemes is used and result in a low frequency noise signature on the output when the magnet current is close to zero. The PWM control circuitry embedded in MCOR 30 theoretically but not really fulfills the purpose what the MCOR 30 want to achieve. With a home-made PWM control circuitry installed into MCOR 30, the width of real pulses can smoothly drop to zero, the MCOR 30 could output current not only with a low frequency noise signature but also much with higher bandwidth of frequency response and much lower Total Harmonic Distortion no matter what output current is demanded.  
 
FRYBA01 The European Spallation Source cavity, linac, target, proton 3789
 
  • S. Peggs
    ESS, Lund, Sweden
  
  The principles of the design, and the technical and beam dynamics challenges of the ESS are presented, as well as possible future upgrade options.  
slides icon Slides FRYBA01 [5.122 MB]