Pronounced reilluminations can be observed for discharges that are generated in water by submicrosecond high-voltage pulses. This phenomenon can appear during the decrease of the applied voltage, depending on the pulse characteristics, especially fall times. The respective processes are expected to be crucial for optical investigations of discharge characteristics and also for applications. Accordingly, the development of individual corona-like discharges in water was investigated in a needle-to-plate geometry for their ignition by single rectangular high-voltage pulses with a duration of 100 ns. The pulse amplitudes of about 50 kV and adjusted pulse fall times of 20 ns, 26 ns, and 43 ns were used. Voltages, currents and light emissions were synchronized with subsequent images of individual discharge events. Two distinct stages, a propagation phase and a reillumination phase, were identified. The individual discharges expanded for all investigated fall times with the same velocity of (29±2) km/s. No significant differences of streamer morphologies and electrical characteristics were observed for the propagation phase. As the voltage began to decrease, light emissions first went through a minimum before increasing again. The following maxima were strongly dependent on fall times. Corresponding images showed that discharge channels were reilluminated within 6 ns. However, not all of the previously observed filaments reignited at once for longer fall times and instead single channels reilluminated subsequently. The development of reillumination can be explained from the external electric field in the electrode gap during the streamer propagation, which determines the head charge distributions at the discharge channel ends. This space charges generate an internal electrical field in the filaments resulting in the reillumination during the falling edge of the applied high-voltage pulse.

中文翻译：

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水中亚微秒脉冲类电晕放电的再照明

对于亚微秒高压脉冲在水中产生的放电，可以观察到明显的重新照明。这种现象会在外加电压降低期间出现，这取决于脉冲特性，尤其是下降时间。预计相应的过程对于放电特性的光学研究和应用至关重要。因此，在针对板几何形状中研究了水中单个电晕状放电的发展，以通过持续时间为 100 ns 的单个矩形高压脉冲点燃它们。使用了大约 50 kV 的脉冲幅度和 20 ns、26 ns 和 43 ns 的调整脉冲下降时间。电压、电流和光发射与各个放电事件的后续图像同步。两个不同的阶段，确定了传播阶段和重新照明阶段。对于所有调查的坠落时间，单个排放量以 (29±2) 公里/秒的相同速度扩大。对于传播阶段，没有观察到拖缆形态和电特性的显着差异。随着电压开始降低，光发射首先经过最小值，然后再次增加。以下最大值强烈依赖于下降时间。相应的图像显示放电通道在 6 ns 内重新点亮。然而，并非所有先前观察到的灯丝都在较长的下降时间内立即重新点燃，而是随后单个通道重新点亮。重新照明的发展可以从流光传播过程中电极间隙中的外部电场来解释，这决定了放电通道末端的头部电荷分布。该空间电荷在灯丝中产生内部电场，导致在施加的高压脉冲的下降沿期间重新照明。