Computational analysis of gas breakdown modes in direct current micro-plasmas at elevated pressures

Abstract

Direct current micro-plasmas in the non-homogeneous electric field are analyzed over a wide pressure range using the self-consistent two-dimensional axisymmetric fluid model. We observe that the breakdown voltage is not the unique function of Pd, where P is the gas pressure and d is the interelectrode spacing, but also depends on the aspect ratio d/r, where r is the anode radius. This result agrees with the data reported in the literature. For fixed d, we find two modes of ionization wave propagation on the right branch of the breakdown curve: an axial streamer mode that is obtained at low pressures and a hollow streamer mode obtained at high pressures. By varying the ballast resistance connected to the anode, we analyze the steady-state parameters of the micro-discharge for the cathode–anode gap of 200 μm. We obtain normal and sub-normal glow modes of the micro-discharge operation. The instability of the latter mode is analyzed.