Kinetics of the fast ionization waves with runaway electrons

Abstract

In nanosecond gas breakdown, runaway electrons are responsible for the interelectrode space pre-ionization, which supports the propagation of fast ionization waves or streamers. However, a detailed understanding of mechanisms of how this happens is still elusive because of the wide range of energies of runaway electrons, from the hundreds of eV to the hundreds of keV. While the low-energy part of the runaway electron population can only ionize the background gas, the high-energy part can produce x-rays that can also ionize the gas. The objective of this paper is to understand the influence of different electron groups on the fast ionization wave dynamics for the conditions typical for runaway electrons generation. We find that there are two main groups, one having energies below 100 eV and another having energies above 1 keV. The first group defines the establishment of the fast ionization waves and their plasma parameters, while the second group defines the speed of the ionization front propagation.