Hybrid model of a plane-parallel hollow-cathode discharge

The development of the hollow-cathode effect in a plane-parallel hollow cathode de argon glow discharge was investigated experimentally and by means of a two-dimensional self-consistent hybrid model, combining the fluid description of positive ions and slow electrons with a particle simulation of fast electrons. In the experiments the discharge was formed between two flat disc copper electrodes (of 3.14 cm diameter and separated by a L = 2 cm gap) serving as cathodes and a metal tube surrounding these electrodes which served as the anode. The electrical characteristics of the discharge and the spatial intensity distribution of selected spectral lines (Ar I 750.3 nm, 811.5 nm and Ar II 476.5 nm) were recorded at current densities 0.1 mA cm(-2) less than or equal to j less than or equal to 0.5 mA cm(-2) and for gas pressures 0.2 mbar less than or equal to p less than or equal to 1 mbar. While at pressures of similar to 1 mbar the cathode regions are developed separately for both cathodes, the light intensity distribution measurements demonstrated the gradual merging of the negative glows with decreasing pressure. At pL less than or equal to 0.8 mbar cm, a common negative glow is formed in the discharge. Complementing the experimental observations, the simulations made it possible to determine various discharge characteristics (e.g. spatial distribution of electric potential, ionization source, and ion density). At low pL values the simulations also indicated the existence of oscillating electrons. The spatial distribution of light intensity calculated for different pressures shows good qualitative agreement with the experimentally observed distributions.