Gas Heating Effects in the Constriction of a High-Pressure Glow Discharge Column

Abstract

Numerical calculations have been made to examine effects of rapid gas heating and subsequent gas density changes on the current density distribution in a high-pressure positive column. Radial profiles of gas temperature, radial expansion velocity, density, and pressure and of electron current density are calculated as functions of time for a simplified model of a glow discharge column. Initially, the glow is diffuse and the background gas is uniform. Considered specifically is a hydrogen discharge with an initial pressure of 500 Torr, an initial current of 6.0 A, a constant axial electric field of 10 kV/cm, and a radius of ∼0.75 mm. The gas dynamics are described by conservation equations for mass, momentum, and energy in a viscous, thermally conductive, compressible fluid and by the equation of state for a perfect gas. The dependence of the ionization rate on the electric field to gas density ratio makes the electron current density a sensitive function of the gas density. At 60 nsec the gas temperature near the axis is sufficiently high for the onset of rapid thermal dissociation in an axial core, and effects of gas transport are significant. The axial gas density is decreased ∼10%; the axial current density is twice its initial value; and the column is partially constricted. Calculated results are consistent with properties of a similar discharge studied experimentally by Cavenor and Meyer, particularly at the time of the formation of a filamentary channel, observed experimentally after the first stage of the glow-to-arc transition.