Modeling of back diffusion of electrons in argon

Abstract

Back-diffusion of electrons to cathode is studied by Monte Carlo simulation for realistic argon cross sections. In particular we study the influence of different aspects of back-diffusion modeling with an aim to simplify the models used in modeling of plasma displays, low pressure gas breakdown and detectors of high energy particles. It was found that the initial electron energy distribution is one of the critical parameters and affects the calculated escape factors very much. The same is true for reflection while angular distribution of initial electrons has a very small influence on the escape factors. The model of cross sections combined with the selection of realistic initial conditions was shown to represent the back-diffusion in argon very well giving good agreement with the available experimental data. Most importantly it was found that the range of electrons returning to the cathode exceeds by far a mean free path and that the number of collisions that they make before returning is quite large. Thus it was found that for a relatively high pressure of around 10 torr the range exceeds d= 1 cm (at E/N=12 Td, 1 Td= and therefore application of the escape ratios below that value of p d (where p is the pressure) is questionable, i.e. under those conditions calculations should be performed for the actual geometry.