Investigation of plasma properties in the phase of the radial expansion of a spark channel in the ‘pin-to-plate’ geometry

Abstract

Observations of the early stage of a spark discharge in air at atmospheric pressure in the pin-to-plate geometry under a single high-voltage pulse, including an initial stage of the channel expansion, are presented. It was shown that an interelectrode gap is closed by a large number of microchannels at 20-30 ns. The start of a radial channel expansion begins at the moment when the electron concentration reaches the maximum value of 2 × 10 19 cm −3 . Theoretical analysis based on the proposed model takes the following plasma-channel properties: electric field strength is about several kV cm −1 , electron temperature is close to 2-3 eV, plasma conductivity is in the order of ∼200 Ω −1 •cm −1 , speed of the radial spark channel expansion is ∼5 km s −1 .

The role of excited electronic states in ambient air ionization by a nanosecond discharge

“…For comparison, the electron-neutral thermalization time, τ E en , remains above 200 ns and becomes much longer than τ E ei after t = 13.5 ns, as shown in figure 8. The thermalization by electron-ion collisions has already been discussed in the literature [40,49] and the critical electron number density was found to be around n e = 10 16 -10 17 cm −3 [50,51], which is consistent with the present simulations.…”

“…8. The thermalization by electron-ion collisions has already been discussed in the literature [40,49] and the critical electron number density was found to be around ne = 10 16 -10 17 cm -3 [50,51], which is consistent with the present simulations.…”

“…These later processes are found to have a minor impact under the present conditions. The three-body recombination rate coefficients of N + have been computed in various studies [36][37][38][39][40][41]. These global rate coefficients do not differentiate recombination into different electronic states of the atoms.…”

Jetting axial flow induced by nanosecond repetitively pulsed discharges in quiescent ambient air

“…In LTE sparks, the main mechanism of rapid temperature increase is the elastic collisions between electrons and heavies. Fast thermalization is achieved owing to elastic electron-ion Coulomb collisions [37,46]. Therefore, under our conditions, when LTE plasma is observed near the electrode, hydrodynamic effects are mostly defined by ultrafast thermalization rather than by fast gas heating from chemical reactions.…”

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

“…When the voltage pulse duration was increased up to ≥10 ns, microchannels with an increased electron number density were evident near a cathode with a small radius of curvature on the background of a diffuse discharge, and microcraters were found on a flat anode after spark discharge and at the point of contact of the spots with the electrode surface [10][11][12][13]. It was shown in [11][12][13] that a large number of microdamages with a diameter from 1 to 20 μm are formed on flat metal anodes. The microdamage number and size were determined by the voltage pulse parameters and the discharge gap length.…”