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Chan, K.-C.D.

Paper Title Page
ROAB001 DARHT-II Long-Pulse Beam-Dynamics Experiments 19
  • C. Ekdahl, E.O. Abeyta, R. Bartsch, L. Caudill, K.-C.D. Chan, D. Dalmas, S. Eversole, R.J. Gallegos, J. Harrison, M. Holzscheiter, E. Jacquez, J. Johnson, B.T. McCuistian, N. Montoya, S. Nath, K. Nielsen, D. Oro, L. Rodriguez, P. Rodriguez, L.J. Rowton, M. Sanchez, R. Scarpetti, M. Schauer, D. Simmons, H.V. Smith, J. Studebaker, G. Sullivan, C. Swinney, R. Temple
    LANL, Los Alamos, New Mexico
  • H. Bender, W. Broste, C. Carlson, G. Durtschi, D. Frayer, D. Johnson, K. Jones, A. Meidinger, K.J. Moy, R. Sturgess, A. Tipton, C.-Y. Tom
    Bechtel Nevada, Los Alamos, New Mexico
  • R.J. Briggs
    SAIC, Alamo, California
  • Y.-J. Chen, T.L. Houck
    LLNL, Livermore, California
  • S. Eylon, W.M. Fawley, E. Henestroza, S. Yu
    LBNL, Berkeley, California
  • T.P. Hughes, C. Mostrom, Y. Tang
    ATK-MR, Albuquerque, New Mexico
  • M.E. Schulze
    GA, San Diego, California
  Funding: This work was supported by the U.S. National Nuclear Security Agency and the U.S. Department of Energy under contract W-7405-ENG-36.

When completed, the DARHT-II linear induction accelerator (LIA) will produce a 2-kA, 18-MeV electron beam with more than 1500-ns current/energy "flat-top." In initial tests DARHT-II has already accelerated beams with current pulse lengths from 500-ns to 1200-ns full-width at half maximum (FWHM) with more than1.2-kA, 12.5-MeV peak current and energy. Experiments are now underway with a ~2000-ns pulse length, but reduced current and energy. These pulse lengths are all significantly longer than any other multi-MeV LIA, and they define a novel regime for high-current beam dynamics, especially with regard to beam stability. Although the initial tests demonstrated absence of BBU, the pulse lengths were too short to test the predicted protection against ion-hose instability. The present experiments are designed to resolve these and other beam-dynamics issues with a ~2000-ns pulse length beam.

ROAB004 Ion Effects in the DARHT-II Downstream Transport 375
  • K.-C.D. Chan, H. Davis, C. Ekdahl
    LANL, Los Alamos, New Mexico
  • T.C. Genoni, T.P. Hughes
    ATK-MR, Albuquerque, New Mexico
  • M.E. Schulze
    GA, San Diego, California
  Funding: Work supported by US NNSA/DOE.

The DARHT-II accelerator produces an 18-MeV, 2-kA, 2-μs electron beam pulse. After the accelerator, the pulse is delivered to the final focus on an x-ray producing target via a beam transport section called the Downstream Transport. Ions produced due to beam ionization of residual gases in the Downstream Transport can affect the beam dynamics. Ions generated by the head of the pulse will cause modification of space-charge forces at the tail of the pulse so that the beam head and tail will have different beam envelopes. They may also induce ion-hose instability at the tail of the pulse. If these effects are significant, the focusing requirements of beam head and tail at the final focus will become very different. The focusing of the complete beam pulse will be time dependent and difficult to achieve, leading to less efficient x-ray production. In this paper, we will describe the results of our calculations of these ion effects at different residual-gas pressure levels. Our goal is to determine the maximum residual-gas pressure allowable in DARHT-II Downstream Transport such that the required final beam focus is achievable over the entire beam pulse under these deleterious ion effects.