Calculation of the gas flow and its effect on the plasma characteristics for a modified Grimm-type glow discharge cell

Abstract

Based on a computational fluid dynamics model, the argon gas flow in a Grimm-type glow discharge cell was calculated. Its effect on the plasma characteristics was investigated by adding convection as an additional transport mechanism of the plasma species as well as diffusion and migration. The Ar gas convection velocity, at an inlet gas flow rate of 100 sccm, was calculated to be of the order of a few tens to a hundred m s−1, increasing to a few hundred m s−1 at the gas inlet and outlet positions. The Ar gas atom density was found to be distributed slightly non-uniformly in the plasma. The calculated Ar gas flow appeared to have only a minor effect on the density distributions of the plasma species, but their fluxes were significantly affected. It appears that, under the conditions investigated, convection is the dominant transport mechanism in the negative glow for all plasma species, except for the electrons. Therefore, the calculated ion fluxes at the exit towards the mass spectrometer appear to increase with gas flow rate, which is in accordance with experimental observations.