Re-illumination and pause behavior of streamer filament of streamer discharge in water

The streamer discharge in water is a main object for studying the basic physical and chemical processes of an electric discharge in water. In this paper, the re-illuminations and the pause behaviors of a streamer filament of the microsecond pulsed streamer discharge in water with different conductivities (20 to 800 µS/cm) are studied by adopting a needle-plate electrode system and an ultra-high-speed camera system. The cause why the re-illumination of the streamer filament is difficult to detect by using the camera system as the water conductivity gets higher is discussed. It is found that the re-illumination alternately occurs among different streamer filaments, and two modes of the re-illumination are identified: one is that the whole filament quenches and then illuminates again; the other is that only the tip part of the filament quenches and then resumes the illumination. The appearance rate of the re-illumination of the streamer filament decreases rapidly as the water conductivity increases, and then drops to zero as the water conductivity exceeds 540 µS/cm. Within a water conductivity range of 20–800 µS/cm, the appearance rate of segmentation in shockwave pattern of the streamer filament is larger than 65%, indicating that the pause is a common behavior of the streamer filament. By measuring the difference in radius between two adjacent shockwave segments, the average pause period of the streamer filament is estimated at 157 ns, which is almost not affected by the water conductivity. As the water conductivity increases, the light intensity of the streamer filament increases rapidly. The light intensity of the streamer filament cannot decay to the noise level of the camera system during the pause period of the streamer filament as the water conductivity exceeds 350 µS/cm. The streamer filament produces glow on the light emission image, which makes it difficult to distinguish the “extinction and illumination” process by the camera system.