Computer simulation of a plasma streaming across a magnetic field

Abstract

A one-dimensional electrostatic particle simulation code has been used to study a plasma streaming across a uniform magnetic field in vacuum. It is found that the plasma may be convected across the magnetic field even if the density is less than the critical density nc necessary to maintain steady propagation. For all densities studied, polarization charge layers are formed, but they do not become steady for plasmas with n/nc<1. For plasma densities at n<nc, the electric field keeps oscillating with the upper hybrid frequency, but for nc<n, the amplitude of the oscillations are damped at later times. The mechanism that produces this damping is associated with a nonlinear wave–particle interaction. For unequal mass species, the simulations show that the heavier particles are convected faster than the lighter ones; thus the positive particles move in front and the negatives move behind creating a virtual cathode. The polarization charge layers are asymmetric, with the thicker layer corresponding to the heavier particles. This paper also includes simulations of plasma streams with different initial widths. The results of these simulations are that the electric field oscillation shows an earlier damping for narrow plasmas, the charge layer thickness decreases for wider plasmas, and the drift velocity is not sensitive to the plasma width.