Mechanism of runaway electron generation in nanosecond pulsed plate-plate discharge at atmospheric-pressure air

Classical discharge theory (Townsend theory and streamer theory) has limitations in explaining nanosecond pulsed gas discharge. In recent years, the research on nanosecond pulsed gas discharge theory based on the highenergy runaway electrons has attracted extensive attention. But so far, there have been few studies of the generation mechanism of runaway electrons in atmospheric-pressure-air nanosecond pulsed plate-to-plate discharge, which seriously hinders the application and development of nanosecond pulse discharge plasma. In this paper, a one-dimensional implicit particle-in-cell/Monte Carlo collision (PIC/MCC) model is developed to investigate the mechanism of runaway electron generation and breakdown in a 1 mm-long atmospheric-pressure air gap between the plate electrode and plate electrode driven by a negative nanosecond pulse voltage with an amplitude of 20 kV. The results show that under the influence of space charge dynamic behavior, the electric field enhancement region appears between the plate electrode and plate electrode, so that electrons can satisfy the electron runaway criteria and behaves in the runaway mode. In addition, it is also observed that the pre ionization effect of the runaway electrons in front of the discharge channel can cause the secondary electron avalanches. As the secondary electrons avalanche and the discharge channel continues to converge, the discharge is guided and accelerated, eventually leading to the breakdown of the air gap. This study further reveals the mechanism of nanosecond pulsed plate-plate discharge, expands the basic theory of nanosecond pulsed gas discharge, and opens up new opportunities for the application and development of nanosecond pulsed discharge plasma.