A time scale for electrical screening in pulsed gas discharges

TL;DR

This paper introduces the ionization screening time, a new time scale for electric field screening in gas discharges that accounts for impact ionization growth, aiding understanding of pulsed discharge development.

Contribution

It presents an analytic estimate for the ionization screening time and compares it with numerical simulations, extending the concept of Maxwell time to gas discharges.

Findings

The ionization screening time can be accurately estimated analytically.

Minimum plasma density needed to prevent streamer growth is identified.

Effects of photoionization and electron detachment on screening are discussed.

Abstract

The Maxwell time is a typical time scale for the screening of an electric field in a medium with a given conductivity. We introduce a generalization of the Maxwell time that is valid for gas discharges: the \emph{ionization screening time}, that takes the growth of the conductivity due to impact ionization into account. We present an analytic estimate for this time scale, assuming a planar geometry, and evaluate its accuracy by comparing with numerical simulations in 1D and 3D. We investigate the minimum plasma density required to prevent the growth of streamers with local field enhancement, and we discuss the effects of photoionization and electron detachment on ionization screening. Our results can help to understand the development of pulsed discharges, for example nanosecond pulsed discharges at atmospheric pressure or halo discharges in the lower ionosphere.