Electron energy distributions and excitation rates in high-frequency argon discharges

Abstract

The electron energy distribution functions and rate coefficients for excitation and ionisation in argon under the action of an uniform high-frequency electric field were calculated by numerically solving the homogeneous Boltzmann equation. The treatment is restricted to situations in which the electrons do not lose appreciable energy during a cycle of field oscillation. Apart from this restriction the calculations cover the whole range of angular frequencies of the HF field from omega << nu c to omega >> nu c, where nu c is the electron-neutral collision frequency for momentum transfer. Typical values of the ratios of the electric field to the gas density and to the angular frequency considered in this work are in the ranges of 10-16<E/N<10-15V cm2 and 10-10<E/ omega <10-8V cm-1s, respectively. Analytic calculations in the limiting cases of omega >> nu c and omega << nu c are also presented and shown to be in very good agreement with the numerical computations. The results reported here are relevant for the modelling of HF discharges in argon and, in particular, for improving recent theoretical descriptions of a plasma column sustained by surface microwaves.