Wall charge and potential from a microscopic point of view

Abstract

Macroscopic objects floating in an ionized gas (plasma walls) accumulate electrons more efficiently than ions because the influx of electrons outruns the influx of ions. The floating potential acquired by plasma walls is thus negative with respect to the plasma potential. Until now plasma walls are typically treated as perfect absorbers for electrons and ions, irrespective of the microphysics at the surface responsible for charge deposition and extraction. This crude description, sufficient for present day technological plasmas, will run into problems in solid-state based gas discharges where, with continuing miniaturization, the wall becomes an integral part of the plasma device and the charge transfer across it has to be modelled more precisely. The purpose of this paper is to review our work, where we questioned the perfect absorber model and initiated a microscopic description of the charge transfer across plasma walls, put it into perspective, and indicate directions for future research.