Using high-speed photography and shadow photography, the structure of the glow and the microstructure of the spark discharge in a 1.5-mm long “pin(cathode)–plane” gap in air in the pressure range from 300 to 760 Torr has been studied. The presence of a microchannel structure of the discharge in the indicated pressure range was established – the discharge is a aggregation of a large number of micron-diameter channels. It is shown that with decreasing pressure, the evolution of the microstructure and glow of the discharge lags behind the onset of breakdown, however, their morphology retains similarity at different pressures.

Using high-speed shooting and shadow photography, the spatial structure of a pulsed discharge in a 1.5-mm long “pin(cathode)–plane” gap in nitrogen and argon in the pressure range from 0.25 to 2 atm was studied. It has been found that a spark discharge is realized in nitrogen and a diffuse form of discharge is realized in argon. For both cases, the presence of a microstructure of discharges in the studied pressure range was found, when the discharge is an aggregation of a large number of micron-diameter channels. It is shown that for each gas the dynamics of the discharge glow structure remains similar at different pressures. It has been established that the glow and microstructure of the discharge in nitrogen are similar to those in air.