A Method for Measuring the Propagation Speed of Streamer Discharge in Water Using its Shockwave Pattern

As a streamer discharge develops in the water, it releases spherical shockwaves from the head of a streamer filament, leaving a chain of discrete shockwaves around the filament. The position of the center of each shock wave is a good indicator of the position of the filament head at a certain moment. The velocity of shockwaves released from the filament head decays to the acoustic velocity (1450 m/s) in water after spreading for ~0.5 mm. Based on these characteristics of shockwaves, we developed a method for measuring the propagation speed of a streamer discharges in water, enabling to investigate the difference in propagation behavior of many filaments generated in a single discharge pulse. Based on this method, we investigated the difference in propagation behavior of many filaments generated in a single discharge pulse at water conductivity of 20~\mu \text{S} /cm and 26 kV. We found that the filaments generated in the same discharge pulse have significantly different propagation speeds, and confirmed that the propagation speed of a filament will significantly slow down after a longtime pause.