An avalanche of runaway electrons formed in an air discharge

Abstract

Numerical simulation and analysis of energy loss in a nanosecond spark gap switch I V Lavrinovich and V I Oreshkin-Effect of electron extraction from a grid plasma cathode on the generation of emission plasma V N Devyatkov and N N Koval-Optimization of the vacuum insulator stack of the MIG pulsed power generator G Khamzakhan and S A Chaikovsky-Recent citations Simulation of a runaway electron avalanche developing in an atmospheric pressure air discharge E. V. Oreshkin et al-Runaway electron beam in atmospheric pressure discharges E V Oreshkin et al-This content was downloaded from IP address 54.149.104.195 on 09/05 Abstract. A numerical simulation of a beam of runaway electrons formed from an individual emission zone on a cathode has been performed for discharges in air of atmospheric pressure. The model is based on solving numerically two-dimensional equations of motion for the electrons and allows one to describe the dynamics of the fast electrons injected from the surface of the emission zone. In calculations it was supposed that the electric field at the surface of the emission zone is enhanced due to which conditions are realized for the electrons injected from the surface to switch into the mode of continuous acceleration. 1. Introduction Runaway electrons (RE) were discovered in atmospheric pressure discharges in the late 1960th [1]. An RE beam passing through a gas initiates, due to avalanche multiplication of fast electrons, breakdown, which has been termed runaway electron breakdown (REB) [2, 3]. It is supposed that REBs take place in lightning discharges. The possibility of existence of REBs gave impetus to both theoretical [2-4] and experimental research [5,6] of RE avalanches. An RE avalanche was observed in an atmospheric pressure air discharge when the average electric field in the gap, E av , was much greater than the dc breakdown electric field, E br [6]. These experiments have shown that the pulsed RE current in discharges with E av >> E br has the following structure. Its first portion of duration some tens of picoseconds, showing a strongly pronounced current peak, consists of high-energy runaway electrons. These are the electrons emitted from the cathode region where the field is enhanced due to the cathode geometry. Subsequently, with some delay, a second peak of RE current or a section of slowly decreasing current arises. This was accounted for by the formation of an avalanche of runaway electrons. The duration of the secondary electron beam was of the order of 100 ps and its current could be an order of magnitude greater than the current of the primary runaway electron beam. This took place if it was possible to avoid the decrease in electric field in the gap caused by the passage of the primary beam. Laboratory investigations of REs in high pressure gas discharges are carried out both at microsecond rise times of the gap voltage [1,7,8] for E av < E br and at subnanosecond rise times (that is, in overvolted electrode gaps) [5,6,9] for E av >> E br. In the latter case, the mechanism of fo...