Nonlinear charge and current neutralization of an ion beam pulse in a pre-formed plasma

The propagation of a high-current finite-length ion beam in a cold pre-form ed plasma is investigated. The outcome of the calculation is the quantitati ve prediction of the degree of charge and current neutralization of the ion beam pulse by the background plasma. The electric and magnetic fields gene rated by the ion beam are studied analytically for the nonlinear case where the plasma density is comparable in size with the beam density. Particle-i n-cell simulations and fluid calculations of current and charge neutralizat ion have been performed for parameters relevant to heavy ion fusion assumin g long, dense beams with length l(b) much greater thanV(b)/omega (b), where V-b is the beam velocity, and omega (b) is the electron plasma frequency e valuated with the ion beam density. An important conclusion is that for lon g, nonrelativistic ion beams, charge neutralization is, for all practical p urposes, complete even for very tenuous background plasmas. As a result, th e self-magnetic force dominates the electric force and the beam ions are al ways pinched during beam propagation in a background plasma. (C) 2001 Ameri can Institute of Physics.