Localized Residual Heat and Formation of Nonbranched Positive Streamer With Highly Repetitive Streamer Discharge

The mechanism of a mode change from a branch-type to a nonbranch positive streamer with increase in pulse repetition rate was investigated from the point of view of background gas heating. In this experiment, a repetitive streamer was generated between a needle and a plane electrode. The repetition rate of impulse positive streamer discharge was changed from 500 to 10 500 pulse/s. The branching of a streamer decreased with the increase in pulse repetition rate and the streamer shape completely changed to a nonbranched type at 10 000 pulse/s. The gas temperature in the repetitive streamer was quantitatively measured at different pulse repetition rates by a spectroscopic method using N2 second positive system band (0, 0). In addition, the gas density change between the electrodes due to gas heating caused by the repetitive streamers was observed using the laser schlieren method. As a result, it was confirmed that the gas temperature in repetitive streamers increased with the increase in pulse repetition rate. The gas temperature in a streamer increased up to 420 K by the accumulation of background gas heating at 10 000 pulse/s. Furthermore, residual gas heat in the shape of a single filament due to a highly repetitive streamer and its dissipation process were clearly visualized.