Influence of Water Vapor on the Spatial Oscillations of the Average Electron Energy in Helium in a Constant Electric Field

The characteristics of spatial relaxation of the average electron energy in pure helium and in helium containing an admixture of water vapor in a constant electric field have been investigated by Monte Carlo simulation. The conditions under which the spatial relaxation in helium has a form of damped oscillations are considered. It is shown that even a small (0.1%) additive of water vapor leads to a significant decrease in the relaxation length, and the spatial oscillations almost disappear at 3% H2O. Calculations were also performed for a mixture He : (H2O : H-2 : O-2 : H), where the composition of atoms and molecules in the parentheses correspond to the composition formed from the initial water vapor in discharge plasma due to the dissociation of water molecules and subsequent plasma-chemical reactions.