Ionization in a dusty gas

Abstract

Summary form only given, as follows. Dust grains (solid particles of micron to sub-micron sizes) can be charged positively by electron emission processes such as photoemission, thermionic emission, or secondary electron emission. Recently a theoretical scheme for forming a Coulomb lattice of positively charged dust grains in a high-pressure gas has been discussed. In that scheme, the grains are charged positively by the emission of photo-electrons in the presence of a flux of ultraviolet (UV) photons with energy larger than the work function of the grain, but lower than the ionization potential of the gas. We extend that theoretical analysis to explore grain charging processes such as photoemission or thermionic emission as a source of ionization (electrons) in a gas. In the simplest case of an inert gas, the electron density generated may be determined by balancing the electron emission from the grains with the electron loss processes involving recombination onto the grains. Some example regimes of dust, gas, and photon flux parameters are investigated. Aspects of basic physics issues relevant to these dust ionization processes are also explored, including the effect of grain size and background gas parameters on the electron emission process, and the heating and cooling of small grains via radiation or conduction.