Investigation of sheath phenomena in electronegative glow discharges

Two different methods of analyzing the cathode fall region of low pressure glow discharges were developed and applied to three different electronegative gas mixtures. One method was based on a self-consistent numerical solution to Poisson's equation, the current continuity equations for electrons and negative ions, and the current conservation equation. This method assumes the electrons are always in equilibrium with the electric field. The other method was based on a self-consistent numerical solution of the Boltzmann transport equation for electrons, Poisson's equation, and the current conservation equation. This method allows the electrons not to be in equilibrium with the field. Comparing these two methods revealed that nonequilibrium prevails throughout the cathode fall region. The electronegative gas mixtures investigated were small concentrations (less that 10%) of hydrogen chloride in helium, argon, or xenon. The electric field, Townsend ionization and attachment coefficients, electron and negative ion current densities, and electron, positive ion, and negative ion number densities are plotted as functions of distance through the cathode fall region.