Wave of ionization in streamer breakdown of gas. Kinetic effects

A wave of ionization is modelled numerically on the basis of the hydrodynamic approximation. It is found that the velocity of the streamer is virtually the same and the conductivity of the channel is higher than in the case when the diffusion-drift approximation is used to describe the motion of the electrons. The distribution function of the electrons in the ionization wave is found by the Monte Carlo method. It is shown that the electron runaway effect for the anode-directed streamer results in the appearance of electrons which overtake the wave of ionization in the case of high current densities. As a result of this the velocity of the wave of ionization increases rapidly and the channel conductivity drops. In the case of a cathode-directed streamer the runaway electrons do not qualitatively change the mechanism of streamer motion.