A model of radial variations in the low-pressure mercury–argon positive column

Abstract

The low-pressure Hg–Ar positive column is studied with a model which accounts for radial transport mechanisms. The model calculates, not assumes, the radial density distribution for each of the species and the radial temperature distributions for the electron and the neutral gases. Solutions to the discharge equations are found for specified values of the wall (Hg reservoir) temperature, electric current, Ar pressure, and tube diameter. These solutions compare favorably with available parametric data for 3.6- and 1.4-cm-diam. discharge tubes. The model is used to investigate effects such as radial cataphoresis, the effect of radiation trapping on radial distributions, and deviations from a radially uniform electron temperature. The work supports some of the simplifying assumptions often made in modeling the discharge at the standard fluorescent lamp operating condition, such as a radially invariant electron temperature, the use of a constant escape factor to describe radiation trapping, and negligible radial cataphoresis. Under conditions of high Ar pressure, the assumption of a radially invariant electron temperature is found to be less valid.