Investigation of the prebreakdown stage of the self-sustained subnanosecond discharge in high pressure nitrogen

Abstract

The results of the investigations of the prebreakdown stage of the self-sustained subnanosecond discharge in nitrogen at pressures between 5 and 40 atm are presented. A high voltage pulse with a front of approximately 250 ps at the level of 0.1–0.9 in amplitude (full duration of the pulse front was 500 ps) was applied to the studied gas gap. In this case, the voltage rise rate in the discharge gap at the prebreakdown stage reached up to 7 × 1014 V/s. Breakdown occurs at the front of the voltage pulse. During these experiments, the parameters of the voltage pulse at the output of the pulse generator were not modified. In this study, it was discovered that increasing of the pressure from 5 atm to 40 atm leads to a significant decrease in the overvoltage in the discharge gap. It is shown that at pressures above 10 atm, the delay time of breakdown is less than the time of growth for electron avalanches to reach a critical size. The critical length of avalanche is approximately one order of magnitude less than the length of the discharge gap. Hence, the avalanche-streamer model is inapplicable in this situation. A mechanism of subnanosecond breakdown initiation with a help of runaway electrons at pressures above 10 atm has been suggested.