Effect of photoionisation on initial discharge in air under nanosecond pulse voltage

Effects of photoionisation on the development and electron runaway of the initial discharge in atmospheric air under nanosecond pulse voltage were studied via two‐dimensional particle‐in‐cell/Monte Carlo collision simulations. It was found that photoionisation has little effect at the beginning of the initial discharge. However, as the discharge channel gradually develops towards the anode, photoionisation shows greater impacts on the morphology of discharge but has little influence on the velocity of discharge development. Photoionisation does not appear to have a decisive effect on the growth trend of the highest energy of runaway electrons, but it does affect the change rate of the highest energy and overall distribution of electron energy, resulting in a higher proportion of energetic electrons. The difference in the distributions of the electron energy between the two cases, with and without considering photoionisation, can be attributed to the impact of photoionisation on the discharge morphology, which in turn distorted the electric field. The spatial density distributions of the electrons produced by photoionisation further explained the differences. The authors’ results explicitly demonstrate the influence of photoionisation on the development and the electron runaway of the initial discharge under nanosecond pulse voltage, which provides more comprehensive knowledge for the atmospheric air gap nanosecond pulse discharge physics.