A simulation studies of direct current microhollow cathode sustained discharge and comparison with experimental investigation

Abstract

Microdischarges are direct current discharges that operate at a relatively high pressure of about 10-1000 Torr and geometric dimensions in the several hundred micrometer ranges. Microhollow cathode sustained discharge (MCSD) is a particular type of microdischarges configuration that uses microhollow cathode discharge (MHCD) as an electron source for sustaining larger volume plasma. At high gas pressure, microdischarges in these specific geometries possess several unique properties that can be very stable and useful tools for atomic emission spectrometry, surface treatment and reduction of pollutants, fuel reforming and generation of UV and VUV radiation. Limitation of experimental data in conventional diagnostics due to small dimension a detailed study on this microdischarge relies on numerical analysis. In this paper a combined simulation of the MCSD and the MHCD is attempted and the corresponding simulation results of discharge properties such as electrostatic potential, electron density, atomic and molecular ion densities, excited species (metastables) densities, electron temperature, gas temperature etc. are presented. The glow discharge model is based on a self-consistent, multi-species, continuum (fluid) model which describes the microdischarge phenomena by solving conservation equations for plasma species continuity and electron energy, and Poisson's equation for the self-consistent electric field. The expansion of microdischarges in the sustained discharge region does not noticeably alter the characteristics of the MHCD. The influences of gas pressure on sustained discharge properties are also investigated. It is found that ions are responsible for plasma expansion at lower pressure in the sustained discharge with positively biased third electrode. Predictions from numerical simulations are compared with experimental observations.