Formation of a volume discharge in air at atmospheric pressure upon application of nanosecond high-voltage pulses

Abstract

Volume self-sustained discharges in gases at high pressure are formed with the use of pre-ionization sources and are widely used for pulsed laser pumping [1,2]. In a pulsed nanosecond discharge [3,4], the conditions can be realized in which the time of discharge channel formation is less than the voltage pulse duration. Then the volume discharge is formed under conditions of multielectron initiation when the initial voltage exceeds the static breakdown voltage.In [5][6][7][8][9], the volume pulsed discharge was initiated in air and other gases at atmospheric pressure without preionization source. To this end, nanosecond high-voltage pulses (~100 kV and more) with a leading pulse edge duration of ~1 ns and less were applied to the gap in [5][6][7][8][9]. The anode was flat, and the cathode had a small radius of curvature. With increase in the interelectrode gap, a pulse corona discharge was observed under these conditions. The main difference between volume and corona pulsed discharges is that in the corona discharge, the gas is ionized only in a part of the gap with the highest electric field strength. In the volume discharge, the gas is ionized in the entire gap, which allows high current densities on the anode (~3 kA/cm 2 ), high specific deposited power (~1 J/cm 3 ), and high specific pump power density (~400 MW/cm 3 ) to be obtained [6][7][8][9]. The diffusion discharge with a brighter central channel was realized in [10] when the voltage pulse duration increased up to 170 ns and the leading edge pulse duration increased up to 10 ns. This means that the discharge constriction is observed with increasing pulse duration. However, in [5-10] much attention was given to the study of the discharge initiated in gaps with the potential cathode having a small radius of curvature, and the influence of voltage pulse polarity and a decrease in the strength of electric field applied to the gap on the formation of the volume discharge was not investigated. Only in [9] the volume discharge was realized in air at atmospheric pressure and near the tip anode (the electrode of a shear discharger). The volume discharges initiated in comparatively short interelectrode gaps or with preionization sources were investigated in [1][2][3][4].The present study investigates the influence of polarity and radius of curvature of the electrodes on the formation of the volume pulsed discharge without pre-ionization source under application of nanosecond voltage pulses of comparatively high amplitude (~100 kV).In our experiments we used the pulse generator of the ARINA x-ray apparatus [4]. The open-circuit gap voltage was about 150 kV and the leading pulse edge duration was less than 1 ns. The voltage pulse polarity could be both positive and negative. The pulse duration at half-maximum was ~2 ns for the volume discharge. Three types of the potential metal electrodes were used, including a sphere 40 mm in diameter (electrode No. 1), a tube 6 mm in diameter fabricated from a foil 50 µm thick (electrode No. 2), and a tip (electrode No. 3). The e...

Runaway-electron-preionized diffuse discharge at atmospheric pressure and its application

“…Figure 3(b) shows a waveform of the discharge current pulse in atmospheric pressure nitrogen with a 16 mm interelectrode gap and RADAN-220 pulser. The reverse of the voltage pulse polarity across the electrode of small curvature radius slightly affects the ignition of the REP DD, which agrees with the results obtained earlier [12][13][14]. A waveform of the discharge current rise for the conditions of figure 3(b) and a waveform of the SAEB current downstream of the AlBe foil are shown in figure 3(c).…”

Runaway electrons during subnanosecond breakdowns in high‐pressure gases

“…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.…”

“…Note that diffuse discharges at atmospheric pressure can also be formed at positive voltage polarity applied to an electrode with a small curvature radius [3, 7, 21, 22, 26–29]. This was demonstrated in [29]. Detection of X‐rays in a REP DD at positive voltage polarity of an electrode with a small curvature radius is much more difficult than at negative polarity, but in some studies this was done [21, 22].…”

“…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.…”

Thin Luminous Tracks of Particles from Electrodes with a Small Radius of Curvature in Pulsed Nanosecond Discharges in Air and Argon

“…A diffuse discharge in air at pressure <460 Torr in a gap with a positive tip using a short voltage pulse was obtained in the last century, see, for example, [8]. A diffuse discharge in atmospheric air in a gap with an anode with a small radius of curvature was first realized in [9].…”