A MODEL FOR PARTICULATE CONTAMINATED GLOW-DISCHARGES

Glow discharges are often contaminated by particulates resulting from gas phase nucleation or sputtering of surfaces in contact with the plasma. If these particulates are sufficiently large, they will negatively charge and act as Coulomb-like scattering centers for electrons. In doing so, rate coefficients for high-threshold processes such as ionization may be reduced compared to those in pristine plasmas. If the contamination is nonuniform, then the resulting spatial irregularities in the rates of excitation may lead to plasma properties which are also nonuniform. In this paper, we report on the results of a model for argon glow discharges contaminated by dust. Rate coefficients for this model are generated by a separate Monte Carlo simulation of electron swarms in dusty plasmas. We find that under quasi-steady-state conditions, current flow and subsequent excitation of the gas are channeled into regions of lower dust density, and that these effects depend on the density, size, and distribution of the dust. In low pressure (< 10 Torr) glow discharges having similar dimensions, comparable perturbation in plasma properties due to contamination is obtained when N(D)P is approximately constant (N(D) is the dust density, P is the gas pressure). The onset of perturbations may occur when N(D)P > 10(5) cm-3 Torr.