Computer Simulation of an Electron Swarm at low E/p in Helium

Abstract

A computer simulated electron swarm at E/P293 = 1�0 V cm -1 tore 1 in a model gas has been used to examine the validity of a recent theory of electron drift and diffusion. The computed results are in agreement with well-established theories for the electron energy distribution function, drift velocity and transverse diffusion coefficient, and confirm that, for a constant momentum transfer cross section, the longitudinal diffusion coefficient is approximately half the transverse coefficient. However, significant differences have been found between the computed swarm and the predictions of the theory of Huxley (1972). In particular, over the time scale considered, the electron swarm is not symmetric about its centroid but is spatially anisotropic in such a way that it could appropriately be described as 'pear shaped'.