Experimental observations and interpretations of bubble-induced discharges under microsecond pulsed voltages in water

This paper presents experimental investigations on the formation, propagation and termination of bubble-induced discharges in deionized water. Time-resolved visualization and electrical measurements are performed to investigate bubble deformation behaviour and ionization development. The distribution of delay in bubble formation indicates that bubble formation can be categorized into two classes, explained by pre-existing microbubbles and Joule heating, respectively. The weak luminance in bubbles suggests the initiation of ionization, which is verified by calculation of the ionization coefficient. The influence of the charges deposited on the bubble surface on the evolution of bubble morphology and luminance is investigated with time-resolved imaging methods. Observations of strong light emission at the falling edge of voltage as well as termination of the discharges are reported, and the underlying mechanisms are discussed.