Statistical analysis of pulsed spark discharges in water: Effects of gap distance, electrode material, and voltage polarity on discharge characteristics

Repetitive discharges in dielectric liquid are involved in many technological applications. The relatively poor reproducibility of such discharges, induced by significant modification of experimental conditions (electrode and liquid), hinders the understanding of their fundamental dynamics and optimizing processes. In this paper, we study the electrical characteristics of multiple discharges run in de-ionized water, at low frequency (3 Hz), using pin-to-plate electrode geometry, under varying conditions of gap distance (50–500 μm), electrode composition (Cu and W), and voltage polarity (amplitude of ±20 kV and pulse width of 500 ns). The voltage and current waveforms of each occurring discharge are recorded and then processed to determine the probability of discharge occurrence, breakdown voltage, discharge current, discharge delay, injected charge, and injected energy. The results show that the highest numbers of occurring discharges are achieved at shortest distance, using the Cu electrode, and negative polarity. The data points comprising the electrical characteristics waveforms (e.g., breakdown voltage) are more or less dispersed, depending on the electrode composition and voltage polarity. Moreover, in negative polarity, a reflected positive pulse of ∼5 kV is observed when discharges do not occur in the first pulse. Considering that these pulses may induce discharges, their characteristics are also provided. Finally, the voltage-current plots show appreciable dependence on discharge conditions, and the data are well fitted by linear profiles with slopes, i.e., resistances, that may reflect the ignition conditions of the discharge.