Kinetic simulation of positive column instabilities

Summary form only given. Striations are a class of ionization instability that affects the positive column of direct current discharges in many gases over a wide range of pressure and current density. The origin of this effect was for long a mystery, which was substantially resolved during the course of the nineteen-sixties when the observed phenomena where shown to be qualitatively explained in terms of hydrodynamic theories of ionization waves. A kinetic theory has been given subsequently. These works are mainly analytic. In this paper, we discuss the application of a modern kinetic simulation technique-namely particle in cell simulation with Monte Carlo collisions-to instabilities of positive columns. We use a simplified one dimensional treatment. Where the axial direction is explicitly represented while plasma loss to the walls in the radial direction is modelled by removing electron-ion pairs at a given rate, which is determined a priori as a function of the pressure-radius product. When a pair of particles is removed in this way, both are selected from within a single simulation cell, so that the noise level in the simulation is not appreciably increased. This procedure may be used either with periodic boundary conditions to simulate a finite section of the positive column, or with finite boundary conditions to simulate a complete positive column including the structure at the anode and the cathode. We will present examples of both cases.