Axial neutral gas transport in the low-pressure direct current positive column including the radial variation of the electron temperature

Abstract

A one-dimensional steady state three-gas model for compressible media is used to formulate a boundary value problem for the axial neutral gas transport in the low-pressure positive column. A by-pass tube configuration is considered. The electron temperature and the axial neutral gas drift velocity, both the values on the axis, and the axial component of electric field occur as eigenvalues. The radial profiles of the number densities, of the radial and axial drift velocities of electrons, ions and neutral atoms, of the electric potential and of the electron temperature are calculated. It is shown that the axial gas flow is caused by the difference in the axial momentum transfer between elastic and inelastic collisions from ions to atoms and from electrons to atoms. The direction of the axial neutral gas drift depends on the density of charge carriers. The ion collisions dominate and drive the neutral gas to the cathode if the density of charged particles is very low and, therefore, the positive boundary layer with ion excess is thick. The electron collisions dominate and drive the neutral gas to the anode if the density of charged particles exceeds a threshold depending on the gas density. The electron temperature varies only slightly across the column.