Discharge in dielectric liquid is an active field of research involved in many technological applications. Such multiple discharges are often applied during an experiment and that the electrode and liquid are altered by these stochastically behaving discharges. Therefore, it is important to address the variation of discharge characteristics as a function of discharge occurrence. In this study we analyze the electrical characteristics of multiple discharges run at low repetition rate (5 Hz) in a liquid of known initial composition using an electrode with a specific geometry. The discharges are run continuously until they fail to occur due to the increase in gap distance, and the recorded voltage and current waveforms are processed using an algorithm in order to determine the probability of discharge occurrence, breakdown voltage, discharge current, and discharge delay. The injected charge and energy of each discharge are also calculated. Furthermore, the effects of applied voltage, pulse width, electrode configuration, and liquid composition on the characteristics of the discharge are investigated. The obtained results demonstrate that the highest and lowest numbers of occurred discharges are achieved using the plate-to-plate and pin-to-pin configurations, respectively. Moreover, the composition of the liquid has an appreciable effect on the discharge current, as well as on electrode erosion. For discharges in water and cyclohexane, we measured the lowest and highest current, respectively. As for the erosion rate, it was comparable for the three liquid hydrocarbons but relatively smaller than that in water. The plot of breakdown voltage as a function of discharge current varies depending on the discharge parameters and displays regions that may be linked to the ignition mechanisms. The original data reported herein is of great significance for various applications that utilize repetitive discharges in liquid.

Dye-based water pollution is a subject of great concern as it has been linked to many health hazards. Considering their stable structures, some dyes, such as methylene blue (MB), cannot be easily removed from water. However, recent studies show that plasma-assisted processing has great potential for eliminating these dyes from water bodies. Among the different configurations of plasmas, discharges in gaseous bubbles in water are particularly promising in terms of water processing. The bubble-liquid discontinuity in such plasmas significantly facilitates the occurrence of discharge, and the modification of gas composition allows for controlling induced chemical reactions. In this study, we investigate the degradation of MB using pulsed discharges (amplitude of 20 kV, pulse duration of 500 ns, and repetition rate of 1 kHz) in Ar, O2, and N2 gaseous bubbles dispersed in water. The degradation of MB is evaluated in the direct mode, i.e., MB is present in the water during discharge as well as in the postprocessing mode, i.e., MB is added to water after plasma processing. Based on the obtained results, the most and least efficient degradation rates measured in the direct mode are achieved with O2 and N2 bubbles, respectively. Meanwhile, in the case of the postprocessing mode, degradation with N2 bubbles is initially more efficient than that with O2 or Ar. However, after hundreds of hours, higher degradation efficiency (up to 100%) is observed with O2 and Ar gas bubbles and not with N2. The findings reported herein are of great importance, particularly considering that plasma processing is complementary to the conventional techniques used in water depollution applications.

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