Numerical simulations of runaway electron generation in pressurized gases

TL;DR

This paper presents numerical simulations of runaway electron generation in pressurized nitrogen and helium gases, revealing a two-stage process influenced by initial conditions and space charge effects.

Contribution

It introduces a detailed numerical model of runaway electron generation in pressurized gases, highlighting the two-stage process and effects of initial conditions.

Findings

Runaway electrons form in two stages: initial emission and virtual cathode formation.

Runaway electron current is limited by space charge shielding and virtual cathode formation.

Initial conditions like voltage and gas type significantly influence runaway processes.

Abstract

The results of a numerical simulation of the generation of runaway electrons in pressurized nitrogen and helium gases are presented. It was shown that runaway electrons generation occurs in two stages. In the first stage, runaway electrons are composed of the electrons emitted by the cathode and produced in gas ionization in the vicinity of the cathode. This stage is terminated with the formation of the virtual cathode, which becomes the primary source of runaway electrons in the second stage. Also, it was shown that runaway electrons current is limited by both the shielding of the field emission by the space charge of the emitted electrons and the formation of a virtual cathode. In addition, the influence of the initial conditions, such as voltage rise time and amplitude, gas pressure, and the type of gas, on the processes that accompany runaway electrons generation is presented.