Current Neutralization and Charge Transport of an REB in Low-Pressure Argon

A numerical study of current neutralization and its effect on charge transport of a 0.175-MeV 6-kA 30-ns relativistic electron beam (REB) in argon at low pressure of 10-2-1 torr is presented. Contribution of two-stream instabilities to plasma conductivity is included in the calculations. The calculations show that energy coupled from beam to plasma is about 1-3 percent in the pressure range 0.1-1 torr. Though the two-stream contribution influences the time-dependent electron temperature and density around 0.1 torr, its effect on beam transport has been found to be only marginal. The results indicate that a maximum charge transport of 76 percent occurs around 0.08 torr when current neutralization is negligible. At 1-torr pressure, 75-percent current neutralization occurs and the charge transport is reduced to 40 percent. The numerical results have been compared with experiment and show good agreement in the pressure range 0.2-1 torr.