The inception of pulsed discharges in air: simulations in background fields above and below breakdown

TL;DR

This study uses 3D particle simulations to explore how electrical discharges initiate in air under various background electric fields, revealing differences in streamer formation above and below breakdown thresholds.

Contribution

It provides detailed particle-based insights into discharge inception, highlighting the role of background ionization and electron detachment in streamer development.

Findings

Discharges above breakdown form large avalanches rather than double-headed streamers.

Below breakdown, positive streamers can develop from a strongly ionized seed.

Electron detachment has minimal impact on discharge development below breakdown.

Abstract

We investigate discharge inception in air, in uniform background electric fields above and below the breakdown threshold. We perform 3D particle simulations that include a natural level of background ionization in the form of positive and O$_{2}^-$ ions. When the electric field rises above the breakdown and the detachment threshold, which are similar in air, electrons can detach from O$_{2}^-$ and start ionization avalanches. These avalanches together create one large discharge, in contrast to the `double-headed' streamers found in many fluid simulations. On the other hand, in background fields below breakdown, something must enhance the field sufficiently for a streamer to form. We use a strongly ionized seed of electrons and positive ions for this, with which we observe the growth of positive streamers. Negative streamers were not observed. Below breakdown, the inclusion of electron detachment does not change the results much, and we observe similar discharge development as in fluid simulations.