Pulse-By-Pulse Streamer-To-Leader Transition In N2-SF6 Mixtures Under Repetitive Sub-Microsecond Pulses

Low-temperature plasma applications driven by high-voltage repetitive pulses, such as flow control, combustion, etc., urgently require the development of high-voltage high-repetitive-frequency pulse generator. The gas-gap insulation capability dramatically and nonlinearly decreased with increasing the pulse repetition frequency (PRF). However, fundamental breakdown mechanisms under repetitive pulses, especially the progressive pulse-by-pulse discharge channel evolution from a localized partial discharge into a destructive spark event, are largely unclear yet. A unique streamer-to-leader transition tendency under repetitive pulses in high-pressure N 2 with the addition of SF 6 (a typical strong electronegative gas in the field of high-voltage insulation area) was observed. A saturation trend of the number of applied pulses before spark breakdown appeared with increasing PRF. Evolutions of the discharge channel under repetitive pulses were compared between pure N 2 and N 2 -1% SF 6 scenarios. In pure N 2 , the discharge channel development remained as the streamer mechanism. However, in N 2 -1% SF 6 , the discharge channel transited into the precursor section under positive pulses, and followed the stem mechanism under negative pulses, respectively. Effects of residual space charges on the progressive streamer-to-leader transition were discussed. Observations of streamer-to-leader transition and discussions of effects of residual space charges may provide in-depth understanding of repetitively pulsed discharge physics.