ICAP 2002 Abstracts and Posters

PIC Simulation of Space-Charge-Dominated Sources

Abstract

For the highly space-charge-dominated beams found in some experiments, such as the HCX transport system at LBNL and the UMER ring at the University of Maryland, details of the beam distribution as it emerges from the source region can determine the beam behavior well downstream. This occurs because collective space-charge modes excited as the beam is born remain undamped for many focusing periods. In some cases these modes can also seed an instability, which is driven by the accelerative cooling of the beam that occurs only the longitudinal direction. Traditional studies of the source region in particle beam systems have emphasized the behavior of averaged beam characteristics, such as total current, rms beam size, or emittance, rather than the details of the full beam distribution function that are necessary to predict the excitation of the collective modes.

Simulations of the beam in the source region using the particle-in-cell WARP code and comparisons to experimental measurements at LBNL and the University of Maryland will be presented. This work illustrates some of the complexity in beam characteristics that has been uncovered as increased attention has been devoted to developing a detailed understanding of the source region. In addition, direct measurement of the beam characteristics can be limited by lack of access to the source region or by difficulties in obtaining enough data to completely characterize the distribution function. Methods will therefore be discussed for using the simulation to infer characteristics of the beam distribution from the data that can be obtained.

(a)I. Haber,S. Bernal, R. A. Kishek, P. G. O’Shea, M. Reiser Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, MD 20742-3511 (b)F. M. Bieniosek, C. M. Celata, A. Friedman,D. P. Grote, E. Henestroza, J. -L. Vay Heavy Ion Fusion – Virtual National Laboratory, Berkeley CA 97420 USA (c)W. B. Herrmannsfeldt Stanford Linear Accelerator Center, Stanford University, Stanford, CA 94305

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