Repetitively pulsed positive streamer discharge in electronegative gas mixtures at high pressure

Electronegative gas components and gas pressure are two important influential factors of the evolutions of repetitively pulsed positive streamer discharge. Discharge memory effect agents may significantly change with increasing the electronegative gas components. Meanwhile, the decay and diffusion processes are dependent on the gas pressure. We experimentally investigated evolutions of repetitively pulsed positive streamer discharge in typical weak electronegative (O2) and strong electronegative (SF6) gas mixtures. Propagation features in N2 and N2-O2 mixtures are similar. The secondary streamer is accelerated under following voltage pulses than under the first voltage pulse, probably due to the effect of residual pre-ionization density on the conductivity of the primary streamer stage. Interestingly, discharge evolutions and discharge memory effects are more pronounced in N2-SF6 mixtures. A large radial deviation of the following discharge channel from the central axis could be observed. It is possibly induced by the high-density residual charges. It is preliminarily observed that the leader formation is possible under following pulses in a pulse train. It implies that the gas gap breakdown mechanism no longer follows the streamer mechanism but the leader mechanism, where the thermal process plays a decisive role.