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首页> 外文期刊>Plasma Sources Science & Technology >Investigation of the initial phases of nanosecond discharges in liquid water
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Investigation of the initial phases of nanosecond discharges in liquid water

机译：液态水中纳秒放电初始相的研究

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In this work, we examine initial phases of micro-discharges produced in deionised water by high-voltage (HV) pulses of nanosecond duration.We apply opto-electrical diagnostics with extremely high temporal (down to 30 ps) as well as spatial (down to 1 μm) resolution. Frozen interferometric and shadowgraph images show three distinct events. The first, the subcritical (no-discharge) event, is characterised by periodic perturbations of the index of refraction which depart from the anode surface and are pulled away at the speed of sound as an expanding envelope defined by the shape of the anode tip. One-dimensional hydrodynamicmodelling of the subcritical phase under conditions mimicking curvatures of real anode tips reveals basic characteristics of perturbations caused by dynamic balance between the hydrostatic and electrostrictive pressures consistent with experimental observations. The second, the dark or non-luminous discharge event, is characterised by the onset of a few isolated very tiny tree-like structures growing from the anode tip. Depending on the HV amplitude, the initial structures occur with a delay of ~2-3 ns after onset of the HV pulse and subsequently expand with average velocity of ~1 ×10~5-2 ×10~5 m s~(-1), creating very dense bush-like structures made of thin hair-like filaments in a few nanoseconds. The third, the luminous discharge event, follows (nearly simultaneously) the dark discharge event and unveils much simpler tree-like morphology determined by the extension of non-luminous bush-like structures. Characteristic dimensions of observed events range from about 1 μm (typical diameter of non-luminous filaments) to tens of micrometres (characteristic diameters of luminous filaments). Furthermore, we address a possible role of microbubbles developing in the anode region due to the periodic HV pulses and verify that the UV-vis-NIR spectrometric signatures of the luminous phase notably change when replacing non-degassed deionised water with dega
机译：在这项工作中，我们研究了纳秒级高压脉冲在去离子水中产生的微放电的初始阶段。我们应用光电诊断，具有极高的时间分辨率（低至30ps）和空间分辨率（低至1μm）。冻结的干涉和阴影图像显示了三个不同的事件。第一个是亚临界（无放电）事件，其特征是折射率的周期性扰动，该扰动偏离阳极表面，并以声速被拉开，形成由阳极尖端形状定义的扩展包络。在模拟真实阳极尖端曲率的条件下，亚临界相的一维流体动力学模型揭示了静水压力和电致伸缩压力之间的动态平衡引起的扰动的基本特征，与实验观察结果一致。第二种是暗放电或非发光放电，其特征是从阳极尖端开始生长一些孤立的非常微小的树状结构。根据HV振幅的不同，初始结构在HV脉冲开始后延迟约2-3 ns，随后以约1×10~5-2×10~5 m s~（-1）的平均速度扩展，在几纳秒内形成由细毛状细丝构成的非常密集的灌木状结构。第三个是发光放电事件，紧随（几乎同时）暗放电事件，揭示了由非发光灌木状结构的延伸所决定的更简单的树状形态。观察到的事件的特征尺寸范围从约1μm（非发光灯丝的典型直径）到数十微米（发光灯丝的特征直径）。此外，我们还探讨了由于周期性高压脉冲而在阳极区域形成的微气泡的可能作用，并验证了当用dega替换未脱气去离子水时，发光相的UV-vis-NIR光谱特征显著改变

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