空气中正流光的重联与合并
Reconnection and merging of positive streamers in air
摘要：
图片显示，从同一电极出现的流光或子流光放电通道有时似乎重新连接或合并，尽管它们的头部携带相同极性的电荷;因此，人们可能会怀疑重新连接是图片中二维投影的伪影。在这里，我们使用立体摄影来研究这些事件的完整三维结构。我们分析重新连接，可能是一个静电效应，其中一个较晚的薄流光重新连接到一个较早的厚流光通道，合并，建议的光电离效应，其中两个同时传播的流光头合并成一个新的流光。我们使用四种不同的阳极几何形状（一个尖端、两个尖端、板中的两个不对称突起和一根线），在环境空气中放置在平坦阴极板上方40 mm处。正高压脉冲施加到阳极，产生正电晕放电。这种放电是研究与快速ICCD相机，在许多情况下，结合光学，使立体成像。我们发现上面定义的重连经常发生。另一方面，仅在25毫巴的压力和2 mm的尖端间隔下观察到合并，即，对于p*d=50微米 * 巴的减小的尖端距离。在这种情况下，拖缆通道的半峰全宽大于尖端间距的10倍。在较高的压力下或使用金属丝阳极时，没有观察到合并。
英文摘要：
Pictures show that streamer or sprite discharge channels emerging from the same electrode sometimes seem to reconnect or merge though their heads carry electric charge of the same polarity; one might therefore suspect that reconnections are an artifact of the two-dimensional projection in the pictures. Here we use stereo-photography to investigate the full three-dimensional structure of such events. We analyze reconnection, possibly an electrostatic effect in which a late thin streamer reconnects to an earlier thick streamer channel, and merging, a suggested photoionization effect in which two simultaneously propagating streamer heads merge into one new streamer. We use four different anode geometries (one tip, two tips, two asymmetric protrusions in a plate, and a wire), placed 40 mm above a flat cathode plate in ambient air. A positive high voltage pulse is applied to the anode, creating a positive corona discharge. This discharge is studied with a fast ICCD camera, in many cases combined with optics to enable stereoscopic imaging. We find that reconnections as defined above occur frequently. Merging on the other hand was only observed at a pressure of 25 mbar and a tip separation of 2 mm, i.e., for a reduced tip distance of p*d=50 micrometer*bar. In this case the full width at half maximum of the streamer channel is more than 10 times as large as the tip separation. At higher pressures or with a wire anode, merging was not observed.
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