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Chan, K.C.D.

Paper Title Page
THPCH069 BBU Calculations for Beam Stability Experiments on DARHT-2 2943
 
  • Y. Tang
    ATK-MR, Albuquerque, New Mexico
  • K.C.D. Chan, C. Ekdahl
    LANL, Los Alamos, New Mexico
  • T.P. Hughes
    Voss Scientific, Albuquerque, New Mexico
 
  The DARHT-2 (Dual-Axis Radiographic Hydrodynamics Test) facility is expected to produce a 2-kA, 20-MeV, 2-microsecond flattop electron beam pulse. Normal operation requires that the beam exit the accelerator with a normalized transverse emittance of less than 0.15-cm-rad. The beam break up (BBU) instability is a potentially serious effect for a high current linear accelerator. It arises from the interaction between the beam and the cavity modes of the accelerating cells. In support of the beam stability experiments, simulations of BBU for DARHT-2 using the Lamda code have been carried out. The simulations used experimental data for the transverse impedance of the cells. Lamda was benchmarked against results calculated with the LLNL code BREAKUP. For nominal transport parameters, simulation results showed that the BBU growth was not significant in changing the beam spot. For a magnetic field reduced by a factor of 5, BBU growth was over a factor of 100, and the image displacement effect was significant.  
THPCH070 Long-pulse Beam Stability in the DARHT-II Linear-induction Accelerator 2946
 
  • C. Ekdahl, E.O. Abeyta, P.A. Aragon, R. Archuleta, R. Bartsch, K.C.D. Chan, D. Dalmas, S. Eversole, R.J. Gallegos, J. Harrison, E. Jacquez, J. Johnson, B.T. McCuistian, N. Montoya, S. Nath, D. Oro, L.J. Rowton, M. Sanchez, R.D. Scarpetti, M. Schauer
    LANL, Los Alamos, New Mexico
  • H. Bender, W. Broste, C. Carlson, D. Frayer, D. Johnson, A. Tipton, C.-Y. Tom
    Bechtel Nevada, Los Alamos, New Mexico
  • R.J. Briggs
    SAIC, Alamo, California
  • T.P. Hughes, C. Mostrom, Y. Tang
    ATK-MR, Albuquerque, New Mexico
  • M.E. Schulze
    GA, San Diego, California
 
  The beam breakup instability has long been a problem for linear induction accelerators (LIAs). Although it is predicted to saturate in the strong focus regime relevant to LIAs most, if not all, LIAs have had pulse-widths too short to observe this effect. We recently completed BBU experiments on a 1.2 kA, 6.7-MeV configuration of the DARHT-II LIA having a 1600-ns pulse length much longer than the saturation time. The saturated growth observed in these experiments when we reduced the magnetic guide-field strength was in agreement with theory. We used these results to deduce that BBU growth will be insignificant in the final 2-kA, 17-MeV DARHT-II configuration with the tunes that will be used. Another problematic instability for long-pulse LIAs such as DARHT-II is the ion-hose. We also performed experiments with the 6.7-MeV long-pulse configuration of DARHT-II in which we deliberately induced ion-hose by raising the background pressure far above its normal value. The results of these experiments were used to show that ion-hose will not be a problem for to the final DARHT-II configuration.