Electron swarm characteristics in Ar : NF3 mixtures under steady-state Townsend conditions

The effect of small amounts of electronegative NF3 molecules on the electro n swarm characteristics in Ar:NF3 mixtures is studied numerically under ste ady-state Townsend conditions. Two different methods of calculation are use d: the solution of the two-term Boltzmann equation (BE) and the Monte Carlo (MC) simulation. The BE analysis is performed for an established electron energy distribution function. The MC calculations give the distance at whic h the shape of the distribution function approaches that resulting from the BE analysis. It is shown that the losses of electrons in the attachment processes play a significant role in the formation of the electron energy distribution func tion. In a wide range of the reduced electric field strength E/N and NF3 co ncentrations the distribution function with a maximum at finite energy is e stablished. It is also shown that the diffusion-modified drift velocity V-d is a non-monotonous function of E/N and that the so-called field-determine d part of the V-d is negative in a wide range of E/N values. These effects are explained in terms of the specific energy dependence of the cross secti on for electron attachment to the NF3, molecules and the momentum transfer cross section of Ar.