Breakdown voltage fluctuation and channel shift under high-repetition-frequency pulses in a gas gap

The repetitive breakdown voltage and breakdown channel of a 6 mm atmospheric air gap were investigated using repetitive pulses up to 100 kHz. The results show that below 10 kHz, the breakdown voltage and channel basically remain unchanged over time. Above 20 kHz, however, the breakdown voltage fluctuates quasi-periodically in milliseconds: first gradually increasing, then abruptly dropping, and repeating this cycle. Correspondingly, the breakdown channel first gradually shifts outward and then returns to the axis. This phenomenon could not be observed in the previous relatively low-frequency experiments. The maximum breakdown voltage at 20 kHz exceeds that at 10 kHz, which differs from the conventional recovery curve of breakdown voltage obtained by the double-pulse method. Schlieren imaging and numerical simulations demonstrate that at high frequencies, the dynamic process of heated gas following spark extinguishing leads to the low-density region deviating from the axis, which in turn changes the subsequent breakdown channel length and thus the breakdown voltage. The present work advances the understanding of pulse breakdown and gas recovery under higher repetition frequency.