Propagation behavior of microsecond pulsed positive streamer discharge in water

Abstract

The propagation behavior of microsecond pulsed positive streamer discharge in low-conductivity water was investigated via photography and shadowgraph imaging. Eight successive images were acquired from a single discharge pulse, allowing for the study of the overall streamer propagation behavior; both the emission and the shadow emission-combined images of the streamer discharge were obtained. The experimental results confirmed that the streamer at the later stage of propagation is weak in illuminance and has a propagation velocity of ∼2 km/s, which is slower than that of the secondary streamer (∼30 km/s) but as fast as that of the primary one (∼2 km/s). The streamer filaments propagated stepwise in water with two different behaviors: (1) a filament head launches a shock wave, quietly moves a short distance (or short time) ahead, and then launches the next shock wave and (2) a filament head pauses for a relatively long time while the filament illuminance decays, then restarts launching shock waves and moving ahead, and the decayed filament illuminates again. These pause and reactivation behaviors randomly alternate among the filaments, resulting in different shock-wave patterns and filament illuminance. The drop of the propagation velocity from ∼30 km/s to ∼2 km/s and the many irregular spikes in the discharge current waveform can be associated with this alternation of pause and reactivation behaviors of the filament heads.