Breakdown characteristics of a nanosecond-pulsed plasma discharge in supercritical air

We report on an experimental study of the behavior of a nanosecond-pulsed plasma discharge in air near the critical point. The plasma discharge was generated by a voltage pulse of 10 ns duration with amplitude up to 8 kV, applied between two pin electrodes separated by a gap distance of 25 µ m. The breakdown voltage and associated current were measured. The total electrical energy deposited per pulse was about 200 µ J. The results show a non-linearity of the plasma behavior at the critical point of air. An explanation is proposed based on strong density fluctuation characteristics of fluid behavior near the critical point.