Impulsive discharges in water: acoustic and hydrodynamic parameters

Underwater spark discharges are used in multiple practical applications including plasma closing switches, water treatment, plasma channel drilling and mineral processing, waste recycling, treatment of metals and medical lithotripsy. Spark discharges in water have been studied for several decades, however, despite significant research efforts and progress in this area, further investigation into the efficiency of plasma-acoustic sources and their optimisation is required in order to expand their practical applications. This paper is aimed at investigation of the electrical and hydrodynamic parameters of underwater plasma-generated cavities, including plasma resistance, energy delivered into the plasma cavity, period of cavity oscillations and characteristics of pressure impulses. Different energy levels, breakdown voltages and gap distances were used in the present study to allow systematic analysis of these electrical and hydrodynamic parameters. Empirical scaling laws which link the maximum acoustic pressure and the period of cavity oscillations with the energisation parameters and the resistance of plasma have been obtained. These empirical functions can be used for optimisation of the plasma-acoustic sources and for tailoring their parameters for specific practical applications