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Li, Z.

Paper Title Page
TPPE058 Dual Feed RF Gun Design for the LCLS 3432
 
  • L. Xiao, R.F. Boyce, D. Dowell, Z. Li, C. Limborg-Deprey, J.F. Schmerge
    SLAC, Menlo Park, California
 
  Funding: Work supported by the U.S. DOE under contract DE-AC03-76SF00515.

In order to remove the dipole field introduced by the coupler in existing S-band BNL/SLAC/UCLA 1.6 cell rf gun, a dual feed design for the LCLS RF gun is proposed together with several significant changes. The improvements include adopting Z-coupling instead of ?-coupling for easier machining and reducing heating, increasing the 0-and ?-mode separation from 3.4 to 15 MHz to reduce the amplitude of the 0 mode, incorporating race-track cavity shape to minimize the quadruple fields, increased cooling for operation at 120Hz and other small changes to improve performance and diagnostic capabilities. The new design has been modeled with the parallel finite element eigenmode solver Omega3P to provide the desired RF parameters and to generate the gun cavity dimensions needed for fabrication.

 
TPPT031 Coupler Design for the LCLS Injector S-Band Structures 2176
 
  • Z. Li, L.D. Bentson, J. Chan, D. Dowell, C. Limborg-Deprey, J.F. Schmerge, D.C. Schultz, L. Xiao
    SLAC, Menlo Park, California
 
  Funding: Work supported by the U.S. DOE Contract No. DE-AC03-76SF00515.

The LCLS injector is required to provide a 1-nC, 10-ps bunch with a normalized rms transverse projected emittance of less than 1.0-μm. The LCLS beam is generated and accelerated in a 1.6-cell S-band RF gun to 6-MeV followed by two SLAC 3-m S-band accelerator structures to further accelerate the beam to 135 MeV to move it out of the space-charge dominated regime. In the SLAC S-band structures, the RF power feed is through a single coupling-hole (single-feed coupler) which results in a field asymmetry. The time dependent multipole fields in the coupler induce a transverse kick along the bunch and cause the emittance to increase above the LCLS specification. To meet the stringent emittance requirements for the injector, the single-feed couplers will be replaced by a dual-feed racetrack design to minimize the multipole field effects. We will present detailed studies of the multipole fields in the S-band coupler and the improvements with the dual-feed racktrack design using the parallel finite element eigenmode solver Omega3P.

 
TPPT032 Modifications on RF Components in the LCLS Injector 2233
 
  • C. Limborg-Deprey, D. Dowell, Z. Li, J.F. Schmerge, L. Xiao
    SLAC, Menlo Park, California
 
  Funding: This work was supported by U.S. Department of Energy, contract No. DE-AC03-76SF00515A06.

Design of the first generation LCLS injector has now been completed. Components are currently under fabrication and their installation is planned for 2006. We discuss the last modifications made on both the 1.6 cell S-Band RF gun and the SLAC S-Band accelerating structures to minimize the beam emittance. We present results from PARMELA computations which justify those modifications, in particular the suppression of the time dependent dipole and quadrupole kicks. Geometry changes to increase the mode separation between the 0 and PI modes are also presented. For the initial geometry with a mode separation of 3.5MHz, the emittance can increase if the appropriate injection time along the klystron pulse is not chosen. For a mode separation of 15MHz, this problem is minimized and the beam dynamics are improved leading to a substantial reduction of total projected emittance.

 
TPPT044 Beam Position Monitoring Using the HOM-Signals from a Damped and Detuned Accelerating Structure 2804
 
  • S. Doebert, C. Adolphsen, R.M. Jones, J.R. Lewandowski, Z. Li, M.T.F. Pivi, J.W. Wang
    SLAC, Menlo Park, California
  • T. Higo
    KEK, Ibaraki
 
  Funding: Work Supported by DOE Contract DE-AC02-76F00515.

The Next Linear Collider (NLC) and Global Linear Collider (GLC) designs require precision beam-to-accelerator-structure alignment to reduce the effect of short range wakefields. For this purpose, the HOM signals from the structure dipole mode damping ports would be used to determine the beam position in the structure, and then the structures would be moved remotely to center them about the beam (a 5 micron rms alignment is required). In 2000, a test of a 1.8 m prototype structure in the ASSET facility at SLAC achieved 11 micron rms centering accuracy, which was limited by systematic effects caused by beam jitter. This year, such measurements were repeated for a pair of shorter structures (60 cm) that were developed to improve high gradient performance. In addition, the beam position resolution was determined by measuring simultaneously three signal frequencies (14.3, 15, 15.7 GHz) corresponding to modes localized at the beginning, the middle and the end of the structures. In this paper, we present results from the beam centering and position resolution measurements.

 
TPPT056 Design of a Low Loss SRF Cavity for the ILC 3342
 
  • J.S. Sekutowicz
    DESY, Hamburg
  • L. Ge, K. Ko, L. Lee, Z. Li, C.-K. Ng, G.L. Schussman, L. Xiao
    SLAC, Menlo Park, California
  • I.G. Gonin, T.K. Khabiboulline, N. Solyak
    Fermilab, Batavia, Illinois
  • P. Kneisel
    Jefferson Lab, Newport News, Virginia
  • Y. Morozumi, K. Saito
    KEK, Ibaraki
 
  An international team comprising DESY, KEK, JLAB, FNAL and SLAC is collaborating on the design, fabrication and test of a low loss, 1.3 GHz 9-cell SRF structure as a potential improvement for the ILC main linac. The advantages of this structure over the TTF structure include lower cryogenic loss, shorter rise time, and less stored energy. Among the issues to be addressed in this design are HOM damping, Lorentz force detuning and multipacting. We will report on HOM damping calculations using the parallel finite element eigenmode solver Omega3P and the progress made towards an optimized design. Studies on multipacting and estimates of the Lorentz force detuning will also be presented.  
ROAC004 High Gradient Performance of NLC/GLC X-Band Accelerating Structures 372
 
  • S. Doebert, C. Adolphsen, G.B. Bowden, D.L. Burke, J. Chan, V.A. Dolgashev, J.C. Frisch, R.K. Jobe, R.M. Jones, R.E. Kirby, J.R. Lewandowski, Z. Li, D.J. McCormick, R.H. Miller, C.D. Nantista, J. Nelson, C. Pearson, M.C. Ross, D.C. Schultz, T.J. Smith, S.G. Tantawi, J.W. Wang
    SLAC, Menlo Park, California
  • T.T. Arkan, C. Boffo, H. Carter, I.G. Gonin, T.K. Khabiboulline, S.C. Mishra, G. Romanov, N. Solyak
    Fermilab, Batavia, Illinois
  • Y. Funahashi, H. Hayano, N. Higashi, Y. Higashi, T. Higo, H. Kawamata, T. Kume, Y. Morozumi, K. Takata, T. T. Takatomi, N. Toge, K. Ueno, Y. Watanabe
    KEK, Ibaraki
 
  Funding: Work Supported by DOE Contract DE-AC02-76F00515.

During the past five years, there has been an concerted effort at FNAL, KEK and SLAC to develop accelerator structures that meet the high gradient performance requirements for the Next Linear Collider (NLC) and Global Linear Collider (GLC) initiatives. The structure that resulted is a 60-cm-long, traveling-wave design with low group velocity (< 4% c) and a 150 degree phase advance per cell. It has an average iris size that produces an acceptable short-range wakefield in the linacs, and dipole mode damping and detuning that adequately suppresses the long-range wakefield. More than eight such structures have operated over 1000 hours at a 60 Hz pulse rate at the design gradient (65 MV/m) and pulse length (400 ns), and have reached breakdown rate levels below the limit for the linear collider. Moreover, the structures are robust in that the breakdown rates continue to decrease over time, and if the structures are briefly exposed to air, the rates recover to their low values within a few days. This paper presents a final summary of the results from this program, which effectively ended last August with the selection of ‘cold’ technology for a next generation linear collider.

 
RPPP044 Studies of Room Temperature Accelerator Structures for the ILC Positron Source 2827
 
  • J.W. Wang, C. Adolphsen, V. Bharadwaj, G.B. Bowden, V.A. Dolgashev, R.M. Jones, E.N. Jongewaard, J.R. Lewandowski, Z. Li, R.H. Miller
    SLAC, Menlo Park, California
 
  Funding: Work supported by U.S. Department of Energy, contract DE-AC02-76F00515.

There are many challenges in the design of the normal-conducting portion of ILC positron injector system such as achieving adequate cooling with the high rf and particle loss heating, and sustaining high accelerator gradients during millisecond-long pulses in a strong magnetic field. The proposed design for the positron injector contains both standing-wave and traveling-wave L-band accelerator structures for high RF efficiency, low cost and ease of fabrication. This paper presents results from studies of particle energy deposition for both undulator based and conventional positron sources, cooling system design, accelerator structure optimization, RF pulse heating, cavity frequency stabilization, and RF feed system design.