Electron swarms in two-phase plasmas

Abstract

Commercial and research devices using electric discharges (low-temperature, partially ionized plasmas) are inevitably contaminated by solid particulate matter. The plasma is therefore composed of two phases: solid and gas. If the size of the particulate matter is comparable to or larger than the Debye length, a sheath will develop at the surface of the dust in a manner similar to that at the surface of a macroscopic object in contact with the plasma. The sheath around the particulate matter occludes current flow and perturbs the electron energy distribution function (EEDF). The former process can lead to discharge instabilities; the latter can detrimentally effect the electron impact rate coefficients. To assess the impact of charged particulate matter on electron transport coefficients, a hybrid molecular-dynamics-Monte-Carlo simulation has been developed. The EEDF is obtained by integrating the trajectory of electrons in the sheath regions of the dust while simultaneously applying Monte Carlo techniques for collisions with gas atoms or molecules. A self-consistent value is obtained for the sheath potential at the surface of the dust by requiring that equal fluxes of electrons and ions flow to the surface. Electrons striking the dust are removed from the simulation, thereby effectively cutting off the EEDF at the sheath potential.<>