Particle charge in the bulk of gas discharges

TLDR

An experimental determination of particle charge in a bulk dc discharge plasma over a wide range of neutral gas pressures was recently reported. This paper provides a detailed description of that experiment and presents additional results with particles of different sizes. The measurements are compared with molecular dynamics simulations, other experimental data, and a simple analytical model that includes ion‑neutral collisions. The measured charges are several times smaller than collisionless orbital‑motion‑limited theory predicts, a discrepancy attributed to ion‑neutral collisions that significantly reduce particle charge under typical discharge conditions. Reference: Phys.

Abstract

An experimental determination of particle charge in a bulk dc discharge plasma covering a wide range of neutral gas pressures, was recently reported [S. Ratynskaia, Phys. Rev. Lett. 93, 085001 (2004)]. The charges obtained were several times smaller than the predictions of collisionless orbital motion limited theory. This discrepancy was attributed to the effect of ion-neutral collisions. In the present paper a more detailed description of this experiment is provided and additional experimental results obtained with particles of different sizes are reported. The measurements are compared with molecular dynamics simulations of particle charging for conditions similar to those of the experiment, with other available experimental data on particle charge in the bulk of gas discharges, and with a simple analytical model accounting for ion-neutral collisions. All the considered evidence indicates that ion-neutral collisions represent a very important factor, which significantly affects (reduces) the particle charge under typical discharge conditions.