On the simulation of gas ionization by fast electrons

Impact ionization of a rarefied gas by a high-energy electrons is considered. An approximate hydrodynamic model of the current density of low-energy secondary electrons formed during impact ionization is constructed. Concentration, drift velocity and specific energy are constructed by an approximate solution of the kinetic equation for secondary electrons. Spatial homogeneity, isotropy of the initial distribution of secondary electrons, coincidence of the directions of their drift and the electric field are assumed. Additional approximations are associated with the structure of the distribution function of secondary electrons and averaging of the cross sections. The results of model validation by comparison with direct collision modeling are presented.