Electron multiplication in nanovoids at the initial stage of nanosecond discharge in liquid water

TL;DR

This study uses Monte Carlo simulations to explore how electrons multiply inside nanovoids in liquid water during nanosecond discharges, revealing mechanisms that could explain energetic electron formation and luminous filament creation.

Contribution

It uncovers two distinct electron multiplication mechanisms inside nanovoids and identifies geometric conditions that favor charge amplification over thermalization.

Findings

Electrons can be accelerated inside nanovoids bouncing off interfaces.

Charge multiplication occurs along the nanovoid, not in bulk water.

Simulation results align with experimental observations of luminous filaments.

Abstract

The process of electron multiplication through the bouncing-like accelerated motion of electrons inside nanovoids formed owing to external electric fields in bulk liquid water is investigated using Monte Carlo simulations in Geant4-DNA. Our results show that the initial charge developed at the metal/liquid interface can be multiplied and expanded along the direction of the external electric field on a picosecond timescale, owing to collision-free interiors of the nanoruptures. Characteristic features of two different electron multiplication mechanisms are revealed and characterized. We find that electrons can be accelerated inside cylindrical nanoruptures while bouncing off the void/water interface. Simulations predict geometric conditions leading to charge multiplication along the void, rather than electron capture or thermalization in bulk liquid. Our results are consistent with the recent verification of the causal relation between electrostriction-induced perturbations in bulk liquid, and the subsequent formation of luminous filaments evidencing the presence of energetic electrons.