Modeling the Hg-Ar low-pressure-discharge positive column: A comparative study.

Abstract

For the description of the low-pressure Hg-Ar positive column a self-consistent collisional-radiative model has been used. Calculations of the population densities for the fundamental and the first five excited Hg levels, electron and rare-gas temperature, and densities have been carried out. All these quantities, except electron temperature, have been evaluated as functions of the radial position in the axially uniform positive column; no assumptions on the radial profiles have been made. Macroscopic quantities such as electric-field strength and radiative power output have been also calculated. A diffusion-controlled positive column has been assumed. The most important collisional processes in the plasma have been taken into account (elastic collisions, electron-atom and atom-atom inelastic collisions including excitation, direct and stepwise ionizations, and also superlastic collisions). Argon excitation and stepwise ionization have been included. Radiation trapping has been taken into account, including pressure broadening of resonance lines due to Ar. In our calculations a non-Maxwellian electron-energy distribution function has been used. Diffusion of the charged particles in the presence of ${\mathrm{Hg}}^{+}$ and ${\mathrm{Ar}}^{+}$ has been considered. Diffusion of the metastable Hg levels has been taken into account. The results obtained in this paper have been compared to corresponding values given in the literature and detailed discussion of the validity of several models has been carried out.