Impulse breakdown mechanism based on discharge propagation process under non-uniform electric field in air

In this paper, we aim to clarify the discharge mechanism leading to breakdown under non-uniform electric field in air, especially on the propagation process of discharge current channel. The discharge measurement was performed in a needle (φ1 mm)-plane electrode system with gap length g=15-100 mm in 0.1 MPa dry air under applying a positive impulse voltage. We observed discharge current waveform and fast-framing images of light emission with image intensifier controlled by a nanosecond pulse. We found out two types of breakdown mechanisms from streamer initiation to breakdown (BD); secondary streamer progress and leader progress. In addition, we investigated the transition region between both types of BD mechanism, focusing on the case of gap length (g=30 mm). Finally, we found that the secondary streamer propagation would dominate the formation process of the discharge channel and the mechanism leading to BD. Also, we found the criterion of impulse breakdown mechanism in air.