A critical analysis of ionising wave propagation mechanisms in breakdown

Abstract

The formation and propagation of ionising waves in impulsive overvolted gas discharges for parallel plane electrode geometry is studied. The spatio-temporal evolution of the electronic and ionic densities together with the space-charge distorted field was thoroughly examined for different initial electron distributions. The study elucidates the important role of the electrons present ahead of both the anode and cathode ionising waves and shows particularly how the wavefront profile evolves during its propagation. In all cases, provided that the discharge gap is sufficiently large, the wavefront is transformed into an electron shock wave defined by a shock zone of extremely high electronic density and field gradients. This limits the domain of validity of the gas discharge models that neglect both the thermal diffusion of charge carriers and gas photoionisation of photodetachment.