Including electron-electron collisions in Monte Carlo simulations of swarms in partially ionized plasmas

Abstract

A method is described whereby electron-electron (e-e) collisions can be included in Monte Carlo simulations of electron swarms in low-temperature partially ionized plasmas. The method is based on treating e-e collisions in a manner equivalent to electron-neutral collisions by using the impact approximation (instantaneous momentum exchange). This equivalence permits the direct inclusion of e-e collisions in the selection process used for collisions by the Monte Carlo method and is obtained by having electrons collide with a background electron fluid. Momentum exchange occurs with the fluid, thereby requiring periodic updates of the electron energy distribution function of the background fluid. This method is made computationally feasible by use of a modified null cross section technique. For typical discharge conditions (3 torr N/sub 2/, delta =10/sup -5/, E/N=20*10/sup -17/ V-cm/sup 2/) the method converges in less than tens of nanoseconds, making application to systems operating at greater than or equal to tens of megahertz possible.<>