Filamentary plasma discharge inside water : initiation and propagation of a plasma in a dense medium
Filamentary plasma discharge inside water : initiation and propagation of a plasma in a dense medium
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水中丝状等离子体放电：致密介质中等离子体的引发和传播
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发表时间：
2009
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通讯作者：
P. Ceccato
中科院分区：
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作者：
P. Ceccato
本文对液态水中的丝状微等离子体放电进行了实验研究。这种等离子体被用于液体电绝缘测试和水的污染控制。与气体中的放电相比，人们对稠密介质中的等离子体了解得更少。本论文的目的是了解放电产生和传播的物理机制。构建了一种浸入水中的点面电极结构，并将其置于高压脉冲下。用电学测量和时间分辨纳秒成像表征了细丝的起始和传播以及几种放电模式。用2个ICCD进行了阴影诊断，研究了放电气体含量和冲击波发射。考察了外加电压、极性和导水率对膜性能的影响。对氢原子发射谱带和氢发射谱线进行了光谱测量。在正高压下，放电的生长始于针电极上微秒内的微气泡形核，在外加电压为40KV时，在100 ns内以3 km/S的速度生长出半球形的树状丝状结构，随后第二种丝状结构的生长速度加快了10倍。这种在纳秒时间尺度上的连续传播之后，在蒸馏水的情况下是逐步传播的。当灯丝到达相反的电极时，就会发生电击穿。在负极性时，放电速度要慢得多，600m/S。气腔的形态是由界面不稳定驱动的。奇怪的是，水的导电性在正电压下没有影响，甚至在负电压下抑制了等离子体细丝的生长。这篇论文使得更好地理解水中电放电的详细现象成为可能。
This thesis presents an experimental study of a filamentary microplasma discharge inside liquid water. Such plasmas are used for liquid electrical insulations tests and for pollution control of water. Plasmas inside dense media are less understood than discharge inside gases. The purpose of the present thesis is to understand the physical mechanisms responsible for initiation and propagation of the discharge. A point to plane electrode configuration submerged in water has been constructed and was submitted to a high voltage pulse. Filaments inception and propagation and several discharges modes have been characterized with electrical measurements and time resolved nanosecond imaging. A Shadow diagnostic using 2 iCCDs was implemented to study the gas content and the shock wave emission from the discharge. The influence of the applied voltage polarity and the water conductivity was investigated. Spectroscopic measurements were performed on the OH emission band and the hydrogen emission lines. At positive high voltage the growth of the discharge begins by the nucleation of a microbubble at the needle electrode within a few microseconds at an applied voltage of 40kV, a hemispheric tree like filamentary structure grows at 3km/s during 100ns and is followed by the propagation of second filamentary structure ten time faster. This continuous propagation on a nanosecond time scale is followed by a stepwise propagation in case of distilled water. When the filaments reach the opposite electrode electrical breakdown occurs. At negative polarity the discharge is much slower 600m/s. The morphology of the gas cavity is driven by interface instability. Curiously, water conductivity has no influence at positive voltage polarity and even inhibits the propagation of the plasma filaments at negative voltage polarity. This thesis made possible to achieve a better understanding of the detailed phenomenology of electrical discharges in water.