Nonlinear Charge and Current Neutralization of an Ion Beam Pulse in a Pre-formed Plasma
Authors: Igor D. Kaganovich, Gennady Shvets, Edward Startsev, and Ronald C. Davidson
Date of PPPL Report: January 2001
Published in: Phys. Plasmas 8 (October 2001) 4180-4192.
The propagation of a high-current finite-length ion beam in a cold pre-formed plasma is investigated. The outcome of the calculation is the quantitative prediction of the degree of charge and current neutralization of the ion beam pulse by the background plasma. The electric magnetic fields generated by the ion beam are studied analytically for the nonlinear case where the plasma density is comparable in size with the beam density. Particle-in-cell simulations and fluid calculations of current and charge neutralization have been performed for parameters relevant to heavy ion fusion assuming long, dense beams with l >> Vb/wb, where Vb is the beam velocity and wb is the electron plasma frequency evaluated with the ion beam density. An important conclusion is that for long, nonrelativistic ion beams, charge neutralization is, for all practical purposes, complete even for very tenuous background plasmas. As a result, the self-magnetic force dominates the electric force and the beam ions are always pinched during beam propagation in a background plasma.