Basic Information on Processes in Ionized Gases
The ionization process in a strongly ionized plasma differs much from that in a weakly ionized plasma, where molecules are ionized by electrons that have acquired their energy directly from the electric field. In moderate fields, its value is much smaller than the potentials of electronic level excitation and ionization. Like ionization, the attachment of electrons in a constant field is accompanied by their drift. Electrons mostly collide with neutral particles rather than with one another or with ions. At electron energies of tens of electron volts, inelastic energy losses by electrons considerably exceed elastic losses. Elastic collisions are generally of minor importance, and electrons are primarily scattered forward in such collisions. Dissociative recombination or diffusion toward the walls, as in a low pressure glow discharge, are much faster processes than recombination in three-body collisions, which is a reverse process for reaction.