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Sonnad, K. G.

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TUXAB03 Self-consistent 3D Modeling of Electron Cloud Dynamics and Beam Response 764
  • M. A. Furman, C. M. Celata, M. Kireeff Covo, K. G. Sonnad, J.-L. Vay, M. Venturini
    LBNL, Berkeley, California
  • R. H. Cohen, A. Friedman, D. P. Grote, A. W. Molvik
    LLNL, Livermore, California
  • P. Stoltz
    Tech-X, Boulder, Colorado
  Funding: Work supported by the U. S. DOE under Contracts DE-AC02-05CH11231 and W-7405-Eng-48, and by the US-LHC Accelerator Research Project (LARP).

We present recent advances in the modeling of beam-electron-cloud dynamics, including surface effects such as secondary electron emission, gas desorption, etc, and volumetric effects such as ionization of residual gas and charge-exchange reactions. Simulations for the HCX facility with the code WARP/POSINST will be described and their validity demonstrated by benchmarks against measurements. The code models a wide range of physical processes and uses a number of novel techniques, including a large-timestep electron mover that smoothly interpolates between direct orbit calculation and guiding-center drift equations, and a new computational technique, based on a Lorentz transformation to a moving frame, that allows the cost of a fully 3D simulation to be reduced to that of a quasi-static approximation.

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TUOCAB02 Measurements of Compression and Emittance Growth after the First LCLS Bunch Compressor Chicane 807
  • P. Emma, K. L.F. Bane, Y. T. Ding, J. C. Frisch, Z. Huang, H. Loos, G. V. Stupakov, J. Wu
    SLAC, Menlo Park, California
  • E. Prat
    DESY, Hamburg
  • F. Sannibale, K. G. Sonnad, M. S. Zolotorev
    LBNL, Berkeley, California
  Funding: U. S. Depertment of Energy contract #DE-AC02-76SF00515.

The Linac Coherent Light Source (LCLS) is a SASE x-ray free-electron laser project presently under construction at SLAC. The injector section from RF photocathode gun through the first bunch compressor chicane was installed during the Fall of 2006. The first bunch compressor chicane is located at 250 MeV and nominally compresses a 1-nC electron bunch from an rms length of about 1 mm to 0.2 mm. The degree of compression is highly adjustable using RF phasing and also chicane magnetic field variations. Transverse phase space and bunch length diagnostics are located immediately after the chicane. We present measurements and simulations of the longitudinal and transverse phase space after the chicane in various beam conditions, including extreme compression where coherent radiation effects are expected to be striking.

slides icon Slides  
THPMN117 Design of a VHF-band RF Photoinjector with MegaHertz Beam Repetition Rate 2990
  • J. W. Staples, K. M. Baptiste, J. N. Corlett, S. Kwiatkowski, S. M. Lidia, J. Qiang, F. Sannibale, K. G. Sonnad, S. P. Virostek, R. P. Wells
    LBNL, Berkeley, California
  Funding: This work is supported by the Director, Office of Science, High Energy Physics, U. S. Dept. of Energy under Contract no. DE-AC02-05CH1121

New generation accelerator-based X-ray light sources require high quality beams with high average brightness. Normal conducting L- and S-band photoinjectors are limited in repetition rate and D-C (photo)injectors are limited in field strength at the cathode. We propose a low frequency normal-conducting cavity, operating at 50 to 100 MHz CW, to provide beam bunches at a rate of one MegaHertz or more. The photoinjector uses a re-entrant cavity structure, requiring less than 100 kW CW, with a peak wall power density less than 10 W/cm2. The cavity will support a vacuum down to 10 picoTorr, with a load-lock mechanism for easy replacement of photocathodes. The photocathode can be embedded in a magnetic field to provide correlations useful for flat beam generation. Beam dynamics simulations indicate that normalized emittances on the order of 1 mm-mrad are possible with gap voltage of 750 kV, with fields up to 20 MV/m at the photocathode, for 1 nanocoulomb charge per bunch after acceleration and emittance compensation. Long-bunch operation (10's of picosecond) is made possible by the low cavity frequency, permitting low bunch current at the 750 kV gap voltage.

THPAN075 Modeling Incoherent Electron Cloud Effects 3393
  • F. Zimmermann, E. Benedetto, G. Rumolo, D. Schulte, R. Tomas
    CERN, Geneva
  • W. Fischer
    BNL, Upton, Long Island, New York
  • G. Franchetti
    GSI, Darmstadt
  • K. Ohmi
    KEK, Ibaraki
  • M. T.F. Pivi, T. O. Raubenheimer
    SLAC, Menlo Park, California
  • K. G. Sonnad, J.-L. Vay
    LBNL, Berkeley, California
  Incoherent effects driven by an electron cloud could seriously limit the beam lifetime in proton storage rings or blow up the vertical emittance in positron ones. Different approaches to modeling these effects each have their own merits and drawbacks. We compare the simulation results and computing time requirements from a number of dedicated codes under development over the last years, and describe the respective approximations for the beam-electron cloud interaction, the accelerator structure, and the optical lattice, made in each of these codes. Examples considered include the LHC, CERN SPS, RHIC, and the ILC damping ring. Tentative conclusions are drawn and a strategy for further codes development is outlined.  
THPAS008 Simulation of the Dynamics of Microwave Transmission Through an Electron Cloud 3525
  • K. G. Sonnad, M. A. Furman
    LBNL, Berkeley, California
  • J. R. Cary
    CIPS, Boulder, Colorado
  • P. Stoltz, S. A. Veitzer
    Tech-X, Boulder, Colorado
  Funding: Work supported by the U. S. DOE under Contract no. DE-AC02-05CH11231

Simulation studies are under way to analyze the dynamics of microwave transmission through a beam channel containing electron clouds. Such an interaction is expected to produce a shift in phase accompanied by attenuation in the amplitude of the microwave radiation. Experimental observation of these phenomena would lead to a useful diagnosis tool for electron clouds. This technique has already been studied* at the CERN SPS. Similar experiments are being proposed at the PEP-II LER at SLAC as well as the Fermilab MI. In this study, simulation results will be presented for a number of cases including those representative of the above mentioned experiments. The code VORPAL is being utilized to perform electromagnetic particle-in-cell (PIC) calculations. The results are expected to provide guidance to the above mentioned experiments as well as lead to a better understanding of the problem.

* T. Kroyer, F. Caspers, E. Mahner , pg 2212 Proc. PAC 2005, Knoxville, TN

FRPMS028 Simulations of Electron Cloud Effects on the Beam Dynamics for the FNAL Main Injector Upgrade 3985
  • K. G. Sonnad, C. M. Celata, M. A. Furman, D. P. Grote, J.-L. Vay, M. Venturini
    LBNL, Berkeley, California
  Funding: Work supported by the U. S. DOE under Contract no. DE-AC02-05CH11231.

The Fermilab main injector (MI) is being considered for an upgrade as part of the high intensity neutrino source (HINS) effort. This upgrade will involve a significant increasing of the bunch intensity relative to its present value. Such an increase will place the MI in a regime in which electron-cloud effects are expected to become important. We have used the electrostatic particle-in-cell code WARP, recently augmented with new modeling capabilities and simulation techniques, to study the dynamics of beam-electron cloud interaction. This study involves a systematic assesment of beam instabilities due to the presence of electron clouds.

FRPMS066 Commissioning the Fast Luminosity Dither for PEP-II 4165
  • A. S. Fisher, S. Ecklund, R. C. Field, S. M. Gierman, P. Grossberg, K. E. Krauter, E. S. Miller, M. Petree, N. Spencer, M. K. Sullivan, K. K. Underwood, U. Wienands
    SLAC, Menlo Park, California
  • K. G. Sonnad
    LBNL, Berkeley, California
  Funding: Supported by US DOE under contract DE-AC03-76SF00515.

To maximize luminosity, a feedback system adjusts the relative transverse (x,y) position and vertical angle (y') of the electron and positron beams at the interaction point (IP) of PEP-II. The original system sequentially moved ("dithered") the electrons in four steps per coordinate. Communication with DC corrector magnets and field penetration through copper vacuum chambers led to a full-cycle time of 10 s. Machine tuning can move the beams at the IP and so had to be slowed to wait for the feedback. A new system installed in 2006 simultaneously applies a small sinusoidal dither to all three coordinates at 73, 87 and 103 Hz. Air-core coils around stainless-steel chambers give rapid field penetration. A lock-in amplifier at each frequency detects the magnitude and phase of the luminosity's response. Then corrections for all coordinates are determined using Newton's method, based on convergence from prior steps, and are applied by the same DC correctors used previously but with only one adjustment per cycle for an expected ten-fold increase in speed. We report on the commissioning of this system and on its performance in maintaining peak luminosity and aiding machine tuning.