Simulation of a runaway electron avalanche developing in an atmospheric pressure air discharge

Abstract

To gain a better understanding of the operation of atmospheric pressure air discharges, the formation of a runaway electron beam at an individual emission site on the cathode has been numerically simulated. The model provides a description of the dynamics of the fast electrons emitted into an air gap from the surface of the emission zone by solving numerically two-dimensional equations for the electrons. It is supposed that the electric field at the surface of the emission zone is enhanced, providing conditions for continuous acceleration of the emitted electrons. It is shown that the formation of a runaway electron beam in a highly overvolted discharge is largely associated with avalanche-type processes and that the number of electrons in the avalanche reaches 50% of the total number of runaway electrons.

Wire Explosion in Vacuum

“…However, the initial discharge stage (breakdown), even in gas discharges, having been the subject of investigation for many decades, still remains not fully understood and debatable [134], [135]. At this stage, both the radiation of the plasma and the runaway electrons that occur at the streamer head can play a significant part [134]- [136]. Naturally, the breakdown along the surface of an exploding wire cannot be described in the context of the MHD model, and the theory of this breakdown is to be developed in the future research.…”

Generation of runaway electrons in plasma after a breakdown of a gap with a sharply non-uniform electric field strength distribution

“…They can be used are also generated in tokamak-type setups, including ITER, and damage the internal components of the vacuum chamber [8][9][10][11]. In nanosecond gas discharges, REs are often generated in the prebreakdown stage [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28]. They can be measured directly with a collector or by measuring x-ray radiation [29][30][31][32][33][34].…”

Emission Features and Structure of an Electron Beam versus Gas Pressure and Magnetic Field in a Cold-Cathode Coaxial Diode

“…Regarding the attainable beam current amplitudes, of primary interest is the range of residual gas pressure [48], where the "vacuum" EEE mechanism [49] is transformed and supplemented by the generation of RAEs in the gas (Section 3.3). We assumed that, at the transformation stage, the presence of RAEs and accompanying ionization processes can lead to the "gas amplification" of the current [47,50] already at the leading edge of the formed beam. An interpretation of these effects is provided in Section 3.4.…”