Towards an improved understanding of nanosecond-pulse discharge initiation in water: From cavitation to electron multiplication

Underwater nanosecond-pulse discharges have been widely utilized in numerous industrial applications. However, the physical processes before nanosecond discharge ignition are still not well understood. In this paper, we investigate the full processes incorporating cavitation, nanopores expansion and subsequent electron multiplication based on an electrostriction mechanism. We modify the energy barrier of cavitation to avoid the overestimation of nucleation rate at highly negative pressure. A varying hydrostatic pressure instead of a fixed pressure adopted by previous models is considered to restrain the unlimited expansion of nanopores. We estimate the electron generation rate by the product of the generation rate of incident electrons and the number density of nanopores. The simulation results using real experimental conditions are in accordance with the experimental data. It is inferred that the electrostriction can be responsible for the underlying mechanism of underwater nanosecond discharge. This work provides a quantitative solution to calculating electron generation rate in liquid water under fast-pulse voltages (nanosecond or even picosecond), and can be referred in future 2D and 3D modelling.