Numerical simulations of positively-biased probes and dielectric-conductor disks in a plasma

Abstract

A cylindrical particle-in-cell (PIC) plasma simulation code applicable to plasma densities encountered in low earth orbit has been refined. The basic configuration simulated consists of a conductor, partially covered with dielectric material, placed upon a conducting ground plate. The plasma is Maxwellian for both ions and electrons at large distances. Current-versus-voltage curves have been computed by following in time a randomly loaded initial system in which the conductor was held at a specific voltage. The resulting time stationary state is identified as the solution of the boundary value problem. These results have been compared to experimental values showing quantitatively correct behavior. Techniques allowing the simulation of dielectric charging using PIC time scales are discussed. A method of simulating large ion-to-electron mass ratios by moving the ions once every n time steps, where n is the square root of the desired mass ratio, has been developed. Enhanced diagnostics have allowed a more detailed study of the plasma behavior near the conductor (hole) and dielectric.