Simulation of runaway electron inception and breakdown in nanosecond pulse gas discharges

Abstract

Nanosecond pulse discharges can provide high reduced electric field for exciting high-energy electrons, and the ultrafast rising time of the applied pulse can effectively suppress the generation of spark streamer and produce homogeneous discharges preionized by runaway electrons in atmospheric-pressure air. In this paper, the electrostatic field in a tube-plate electrodes gap is calculated using a calculation software. Furthermore, a simple physical model of nanosecond pulse discharges is established to investigate the behavior of the runaway electrons during the nanosecond pulse discharges with a rise time of 1.6 ns and a full-width at half-maximum of 3–5 ns in air. The physical model is coded by a numerical software, and then the runaway electrons and electron avalanche are investigated under different conditions. The simulated results show that the applied voltage, voltage polarity, and gas pressure can significantly affect the formation of the avalanche and the behavior of the runaway electrons. The inception time of runaway breakdown decreases when the applied voltage increases. In addition, the threshold voltage of runaway breakdown has a minimum value (10 kPa) with the variation of gas pressure.PACS: 52.80.-s

Runaway electrons during subnanosecond breakdowns in high‐pressure gases

“…A detailed description of spatial discharge forms and their sequence is presented below. From the data reported here and in other studies [3, 7, 8, 19–22, 25, 28, 30, 48, 49] it follows that it is the runaway electrons which provide preionisation of the discharge gap and formation of a REP DD.…”

“…As has been shown in many papers, diffuse discharges in an inhomogeneous electric field can be formed in different gases at atmospheric and higher pressure whatever the polarity of an electrode with a small curvature radius, see books [3, 40], reviews [7, 8] and papers [19–21, 25–30, 48–54]. In this paper, we consider data on diffuse discharges which occur with SAEB generation.…”

“…Back in the last century, it was shown that this type of discharge develops with the participation of X‐rays and runaway electrons which arise early in the discharge and provide gas preionisation [4–6]. In recent years, interest in the phenomenon of runaway electrons has greatly increased, see collection book [3], reviews [7, 8], and papers [9–30]. There are four main groups of discharges in gases, with exception of those used in plants for controlled thermonuclear fusion, in which runaway electrons and/or X‐rays were registered.…”

Generators of Atmospheric Pressure Diffuse Discharge Plasma and Their Use for Surface Modification

“…Currently, diffuse gas discharges initiated by runaway electrons (runaway electron preionized diffuse discharge-REP DD) are intensively investigated [1][2][3][4]. As it was shown in [5], it is possible to form a diffuse discharge in a gap with an inhomogeneous electric field strength distribution filled with atmospheric-pressure air by applying nanosecond voltage pulses with an amplitude up to several tens of kilovolts to the cathode with a small radius of curvature.…”

Influence of electrode spacing and gas pressure on parameters of a runaway electron beam generating during the nanosecond breakdown in SF 6 and nitrogen

“…It was found that the amplitude of a runway electron beam current realised in SF 6 with a tubular cathode of 6 mm in diameter at the voltage rise time of ∼2 ns increased considerably as the gap width was decreased from 12 to 8 mm [32]. Reasoning that the beam amplitude is determined by the voltage across the gap, all other things being equal, at the instant of generation of runaway electrons [1–27], it can be assumed that a decrease in the electrode spacing increased the gap voltage [32]. The assumption is indirectly supported by research data on a runaway electron beam produced in nitrogen with the gap of 12 mm and tubular cathode with the diameter of 6 mm at the voltage rise time of 0.3 ns [33], showing a considerable increase in the voltage across the gap and the beam current amplitude with a decrease in the pressure.…”