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 × 1019 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.