Search

The evolution of a microsecond pulsed barrier discharge initiated in atmospheric pressure air in the point–plane electrode geometry has been investigated using streak camera photorecording and shadow photography with micrometer resolution and nanosecond exposure. It has been shown that the discharge develops in series and its structure evolves both within a series and from series to series. It has been found that, irrespective of the polarity of a feed voltage pulse, the discharge develops from the point electrode, having the form of a set of many micrometer-diameter channels. At the late stage, the discharge consists of a number of glowing microstructured channels, which occupy the space between the point and barrier and deviate from the point axis, and many faint channels radially propagating over the surface of the barrier. Numerical parameters of the structured have been obtained.

A spark discharge in a 1.5-mm-long tip (cathode)-plane gap in the time interval from the breakdown onset to 200 ns has been studied. Тhe discharge has been found to arise in the form of a bundle of microchannels. The dynamics of the discharge spatial structure, the electron concentration, the gas temperature in the channel, and the velocity of its radial expansion have been determined.

The results of studies of the dynamics of near-electrode processes in the initial phase of a spark discharge in atmospheric-pressure air in the point-plane geometry are presented. After breakdown, regions of about 50 μm or more in size with an increased electron concentration of (3–8) × 1019 cm–3 near the surface of the flat cathode have been observed. With allowance for the experimental data on erosion effect of the discharge on the surface of a flat electrode and the associated gas-dynamic effects, a physical model of near-electrode processes has been proposed, based on which the gas-dynamic parameters are estimated.

A microchannel structure of a spark discharge initiated in atmospheric-pressure air in a point–plane gap has been discovered by shadow photography. The structure has been observed since the onset of the discharge glow. The evolution of the microstructure over times from several nanoseconds to several tens of nanoseconds has been traced. Specifically, the development of microchannels from the point into the discharge gap, expansion of the microchannels, and their interaction have been observed. A correlation has been found between the microstructure of the spark channel in the discharge gap and its autograph on the surface of the plane electrode.

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 of a large number of microchannels at 20-30 ns. Start of a radial channel expansion is beginning at the moment when the electron concentration reaches the maximum value of 2*10^19 cm-3. Theoretical analysis based on proposed model takes the following plasma-channel properties: electric field strength is about several kV/cm, 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 about ~5 km/s.

The microchannel structure of a spark discharge in a 1.5-mm-long point–plane gap has been studied by the method of shadow photography. The discharge dynamics (propagation of microchannels from the point into the discharge gap, branching and expansion of the microchannels, formation of a joint front of the spark’s shock wave and its motion) has been observed over a time from several nanoseconds to several hundred nanoseconds. Objects of a half-ring shape have been discovered. They have been identified as semispherical shock waves resulting from the formation of microcraters near sites where the microchannels touch the plane electrode.

The results of studies of the microstructure in the initial phase of the discharge in air in the gap between the pin and a plane 1.5 mm long are presented. Measurements show that within 15 ns after breakdown, the channel is a bundle of a large number of microchannels, the current in the channel grows almost linearly up to 1 kA, and the electron concentration reaches 2 × 1019 cm−3. Taking into account the experimental data, the electron temperature dynamics in a separate microchannel was calculated. It was found that the average electron temperature is from 4 to 8 eV, the electric field strength is ∼300 kV/cm, and the electrical conductivity is ∼10 Ω−1 cm−1. The obtained results indicate that it is the microstructure of the discharge that determines the relatively high values of the average temperature of electrons in combination with a sufficiently high degree of ionization.