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Xiao, L.

Paper Title Page
TUPMS047 Results of the SLAC LCLS Gun High-Power RF Tests 1296
  • D. Dowell, E. N. Jongewaard, J. R. Lewandowski, Z. Li, C. Limborg-Deprey, J. F. Schmerge, A. E. Vlieks, J. W. Wang, L. Xiao
    SLAC, Menlo Park, California
  Funding: SLAC is operated by Stanford University for the Department of Energy under contract number DE-AC03-76SF00515.

The beam quality and operational requirements for the Linac Coherent Light Source (LCLS) currently being constructed at SLAC are exceptional, requiring the design of a new RF photocathode gun for the electron source. Based on operational experience at GTF at SLAC, SDL and ATF at BNL and other laboratories, the 1.6cell s-band (2856MHz) gun was chosen to be the best electron source for the LCLS injector, however a significant re-design was necessary to achieve the challenging parameters. Detailed 3-D analysis and design was used to produce nearly-perfect rotationally symmetric rf fields to achieve the emittance requirement. In addition, the thermo-mechanical design allows the gun to operate at 120Hz and a 140MV/m cathode field, or to an average power dissipation of 4kW. Both average and pulsed heating issues are addressed in the LCLS gun design. The first LCLS gun is now fabricated and has been operated with high-power RF. The results and analysis of these high-power tests will be presented.

WEPMS048 Modelling Imperfection Effects on Dipole Modes in TESLA Cavity 2454
  • L. Xiao, C. Adolphsen, V. Akcelik, A. C. Kabel, K. Ko, L. Lee, Z. Li, C.-K. Ng
    SLAC, Menlo Park, California
  Funding: Work supported by DOE contract DE-AC02-76SF00515

The actual cell shape of the TESLA cavities differ from the ideal due to fabrication errors, the addition of stiffening rings and the frequency tuning process. Cavity imperfection shift the dipole mode frequencies and alter the Qext's from those computed for the idea cavity. A Qext increase could be problematic if its value exceeds the limit required for ILC beam stability. To study these effects, a cavity imperfection model was established using a mesh distortion method. The eigensolver Omega3P was then used to find the critical dimensions that contribute to the Qext spread and frequency shift by comparing predictions to TESLA cavity measurement data. Using the imperfection parameters obtained from these studies, artificial imperfection models were generated and the resulting wakefields were used as input to the beam tracking code Lucretia to study the effect on beam emittance. In this paper, we present the results of these studies and suggest tolerances for the cavity dimensions.

WEPMS050 HOM and LOM Coupler Optimizations for the ILC Crab Cavity 2457
  • L. Xiao, K. Ko, Z. Li, C.-K. Ng, G. L. Schussman, A. Seryi, R. Uplenchwar
    SLAC, Menlo Park, California
  • L. Bellantoni
    Fermilab, Batavia, Illinois
  • G. Burt
    Cockcroft Institute, Lancaster University, Lancaster
  • P. Goudket, P. A. McIntosh
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
  Funding: Work supported by DOE contract DE-AC02-76SF00515

The FNAL 9-cell 3.9GHz deflecting cavity designed for the CKM experiment was chosen as the baseline design for the ILC BDS crab cavity. Effective damping is required for the lower-order TM01 modes (LOM), the same-order TM11 modes (SOM) as well as the HOM modes to minimize the beam loading and beam centroid steering due to wakefields. Simulation results of the original CKM design using the eigensolver Omega3P showed that both the notch filters of the HOM/LOM couplers are very sensitive to the notch gap, and the damping of the unwanted modes is suboptimal for the ILC. To meet the ILC requirements, the couplers were redesigned to improve the damping and tuning sensitivity. With the new design, the damping of the LOM/SOM/HOM modes is significantly improved, the sensitivity of the notch filter for the HOM coupler is reduced by one order of magnitude and appears mechanically feasible, and the LOM coupler is simplified by aligning it on the same plane as the SOM coupler and by eliminating the notch filter. In this paper, we will present the coupler optimization and tolerance studies for the crab cavity.

TUZBC01 Towards Simulation of Electromagnetics and Beam Physics at the Petascale 889
  • Z. Li, V. Akcelik, A. E. Candel, L. Ge, A. C. Kabel, K. Ko, L. Lee, C.-K. Ng, E. E. Prudencio, G. L. Schussman, R. Uplenchwar, L. Xiao
    SLAC, Menlo Park, California
  Funding: Work supported by DOE contract DE-AC02-76SF00515.

Under the support of the U. S. DOE SciDAC program, SLAC has been developing a suite of 3D parallel finite-element codes aimed at high-accuracy, high-fidelity electromagnetic and beam physics simulations for the design and optimization of next-generation particle accelerators. Running on the latest supercomputers, these codes have made great strides in advancing the state of the art in applied math and computer science at the petascale that enable the integrated modeling of electromagnetics, self-consistent Particle-In-Cell (PIC) particle dynamics as well as thermal, mechanical, and multi-physics effects. This paper will present 3D results of trapped mode calculations in an ILC cryomodule and the modeling of the ILC Sheet Beam klystron, shape determination of superconducting RF (SCRF) cavities and multipacting studies of SCRF HOM couplers, as well as 2D and preliminary 3D PIC simulation results of the LCLS RF gun.

slides icon Slides  
TUPMN021 Status of Nb-Pb Superconducting RF-Gun Cavities 962
  • J. S. Sekutowicz, J. Iversen, D. Klinke, D. Kostin, W.-D. Moller, A. Muhs
    DESY, Hamburg
  • M. Ferrario
    INFN/LNF, Frascati (Roma)
  • P. Kneisel
    Jefferson Lab, Newport News, Virginia
  • K. Ko, Z. Li, L. Xiao
    SLAC, Menlo Park, California
  • R. S. Lefferts, A. R. Lipski
    SBUNSL, Stony Brook, New York
  • T. Rao, J. Smedley
    BNL, Upton, Long Island, New York
  • P. Strzyzewski
    The Andrzej Soltan Institute for Nuclear Studies, Centre Swierk, Swierk/Otwock
  We report on the progress in the status of an electron RF-gun made of two superconductors: niobium and lead. The presented design combines the advantages of the RF performance of bulk niobium superconducting cavities and the reasonably high quantum efficiency of lead. Measured values of quantum efficiency for lead at 2K and the RF-performance of three half-cell niobium cavities with the lead spot exposed to high electric fields are reported in this contribution.  
WEOCAB01 Design of the Beam Delivery System for the International Linear Collider 1985
  • A. Seryi, J. A. Amann, R. Arnold, F. Asiri, K. L.F. Bane, P. Bellomo, E. Doyle, A. F. Fasso, L. Keller, J. Kim, K. Ko, Z. Li, T. W. Markiewicz, T. V.M. Maruyama, K. C. Moffeit, S. Molloy, Y. Nosochkov, N. Phinney, T. O. Raubenheimer, S. Seletskiy, S. Smith, C. M. Spencer, P. Tenenbaum, D. R. Walz, G. R. White, M. Woodley, M. Woods, L. Xiao
    SLAC, Menlo Park, California
  • I. V. Agapov, G. A. Blair, S. T. Boogert, J. Carter
    Royal Holloway, University of London, Surrey
  • M. Alabau, P. Bambade, J. Brossard, O. Dadoun
    LAL, Orsay
  • M. Anerella, A. K. Jain, A. Marone, B. Parker
    BNL, Upton, Long Island, New York
  • D. A.-K. Angal-Kalinin, C. D. Beard, J.-L. Fernandez-Hernando, P. Goudket, F. Jackson, J. K. Jones, A. Kalinin, P. A. McIntosh
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
  • R. Appleby
    UMAN, Manchester
  • J. L. Baldy, D. Schulte
    CERN, Geneva
  • L. Bellantoni, A. I. Drozhdin, V. S. Kashikhin, V. Kuchler, T. Lackowski, N. V. Mokhov, N. Nakao, T. Peterson, M. C. Ross, S. I. Striganov, J. C. Tompkins, M. Wendt, X. Yang
    Fermilab, Batavia, Illinois
  • K. Buesser
    DESY, Hamburg
  • P. Burrows, G. B. Christian, C. I. Clarke, A. F. Hartin
    OXFORDphysics, Oxford, Oxon
  • G. Burt, A. C. Dexter
    Cockcroft Institute, Warrington, Cheshire
  • J. Carwardine, C. W. Saunders
    ANL, Argonne, Illinois
  • B. Constance, H. Dabiri Khah, C. Perry, C. Swinson
    JAI, Oxford
  • O. Delferriere, O. Napoly, J. Payet, D. Uriot
    CEA, Gif-sur-Yvette
  • C. J. Densham, R. J.S. Greenhalgh
    STFC/RAL, Chilton, Didcot, Oxon
  • A. Enomoto, S. Kuroda, T. Okugi, T. Sanami, Y. Suetsugu, T. Tauchi
    KEK, Ibaraki
  • A. Ferrari
    UU/ISV, Uppsala
  • J. Gronberg
    LLNL, Livermore, California
  • Y. Iwashita
    Kyoto ICR, Uji, Kyoto
  • W. Lohmann
    DESY Zeuthen, Zeuthen
  • L. Ma
    STFC/DL, Daresbury, Warrington, Cheshire
  • T. M. Mattison
    UBC, Vancouver, B. C.
  • T. S. Sanuki
    University of Tokyo, Tokyo
  • V. I. Telnov
    BINP SB RAS, Novosibirsk
  • E. T. Torrence
    University of Oregon, Eugene, Oregon
  • D. Warner
    Colorado University at Boulder, Boulder, Colorado
  • N. K. Watson
    Birmingham University, Birmingham
  • H. Y. Yamamoto
    Tohoku University, Sendai
  The beam delivery system for the linear collider focuses beams to nanometer sizes at the interaction point, collimates the beam halo to provide acceptable background in the detector and has a provision for state-of-the art beam instrumentation in order to reach the physics goals. The beam delivery system of the International Linear Collider has undergone several configuration changes recently. This paper describes the design details and status of the baseline configuration considered for the reference design.  
slides icon Slides  
WEPMS042 Optimization of the Low-Loss SRF Cavity for the ILC 2439
  • Z. Li, L. Ge, K. Ko, L. Lee, C.-K. Ng, G. L. Schussman, L. Xiao
    SLAC, Menlo Park, California
  • T. Higo, Y. Morozumi, K. Saito
    KEK, Ibaraki
  • P. Kneisel
    Jefferson Lab, Newport News, Virginia
  • J. S. Sekutowicz
    DESY, Hamburg
  Funding: Work supported by DOE contract DE-AC02-76SF00515.

The Low-Loss shape cavity design has been proposed as a possible alternative to the baseline TESLA cavity design for the ILC. The advantages of this design over the TESLA cavity are its lower cryogenic loss, and higher achievable gradient due to lower surface fields. High gradient prototypes for such designs have been tested at KEK (ICHIRO) and JLab (LL). However, issues related to HOM damping and multipacting (MP) still need to be addressed. Preliminary numerical studies of the prototype cavities have shown unacceptable damping for some higher-order dipole modes if the typical TESLA HOM couplers are directly adapted to the design. The resulting wakefield will dilute the beam emittance thus reduces the machine luminosity. Furthermore, high gradient tests on a 9-cell prototype at KEK have experienced MP barriers although a single LL cell had achieved a high gradient. From simulations, MP activities are found to occur in the end-groups of the cavity. In this paper, we will present the optimization results of the end-groups for the Low-Loss shape for effective HOM damping and alleviation of multipacting. Comparisons of simulation results with measurements will also be presented.