水中流光放电流光丝的再发光和暂停行为

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

水中流光放电是研究水中放电基本物理、化学过程的主要研究对象.本文利用四分幅超高速相机、采用针-板电极结构、在20—800μS/cm水电导率范围内研究了水中微秒脉冲流光放电流光丝的再发光和暂停行为,探讨了高水电导率下观测不到流光丝的再发光的原因.结果发现:再发光在不同的流光丝之间交替发生并存在两种模式:一种为整根丝熄灭后再发光;一种为只有先端部分发光熄灭随后恢复发光.随着水电导率的增大,观测到流光丝的再发光现象的频度急剧减小, 540μS/cm水电导率时降到零;在20—800μS/cm水电导率条件下都可观测到流光丝伴生冲击波串分段现象,冲击波串分段现象的出现频度在65%以上,表明在20—800μS/cm水电导率条件下流光丝的暂停是一种普遍行为.通过测量两段冲击波的半径差得到流光的暂停时间平均为157 ns,几乎不受水电导率的影响;随着水电导率的增大,流光丝的发光强度显著增大,水电导率大于350μS/cm时,流光丝暂停期间内流光丝的光强度无法衰减到相机分辨水平以下,在相机获得的发光图像上看上去是持续发光的,难以分辨出流光丝"熄灭-再发光"过程.

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.