Numerical study of a medium pressure point-to-plane discharge

A numerical study of an electrical discharge in nitrogen in the medium pressure range (10-50 Torr) in a non-uniform electric field (point-to-plane geometry) is presented. It is obtained by solving numerically the continuity equations for electrons and positive ions coupled with Poisson's equation and concerns space-time evolution of electron and ion densities as well as electric field and potential distributions along the discharge axis for distinct values of the applied voltage. These results show that the transition to glow discharge occurs via distinct streamer-like discharge stages. During each stage a potential ionization wave is formed, propagating with distinct velocities extending from 105 to 107 cm s-1. In the last discharge stage, the ionization potential wave, significantly sustained by the secondary ionization phenomena, contributes to the growth of the discharge current so that the transition to the glow discharge is attained. The comparison with experimental results shows a good qualitative agreement. (author)