Simplified models of electron excitation and ionization at very highE/n

Models of electron excitation and ionization at very high electric-field–to–gas-density ratios E/n are compared under conditions appropriate to discharge experiments at low gas densities, such as those in ${\mathrm{N}}_2$ described in the preceding paper. The models considered use the monoenergetic beam approximation in a velocity moment technique for solution of the electron Boltzmann equation. They differ in the treatment of the electrons produced by ionization and in the use of either the momentum balance or the energy balance to obtain the effective frictional effect. A simplified single-beam model is found to agree reasonably well with multiple-beam models, with the few published Monte Carlo results, and with experimentally measured spatial ionization coefficients.