Why isolated streamer discharges hardly exist above the breakdown field in atmospheric air

TL;DR

This study uses advanced 3D particle simulations to show that in atmospheric air with electric fields above breakdown, isolated streamer discharges are unlikely due to collective screening effects caused by background ionization.

Contribution

The paper introduces a detailed 3D particle simulation model that incorporates background ionization, revealing the collective screening mechanism prevents isolated streamers at high fields.

Findings

Many electron avalanches start at different locations.

Discharges eventually screen the electric field internally.

Isolated streamers are unlikely to exist above breakdown fields.

Abstract

We investigate streamer formation in the troposphere, in electric fields above the breakdown threshold. With fully three-dimensional particle simulations, we study the combined effect of natural background ionization and of photoionization on the discharge morphology. In previous investigations based on deterministic fluid models without background ionization, so-called double-headed streamers emerged. But in our improved model, many electron avalanches start to grow at different locations. Eventually the avalanches collectively screen the electric field in the interior of the discharge. This happens after what we call the `ionization screening time', for which we give an analytical estimate. As this time is comparable to the streamer formation time, we conclude that isolated streamers are unlikely to exist in fields well above breakdown in atmospheric air.