Surface Wave Sustained Discharges

Abstract

A selfconsistent modeling of discharges obviously aims at a full description without requiring prior knowledge or diagnostic determination of any parameter beyond those actually chosen by an operator in the laboratory, i.e. beyond gas type and pressure, geometry and material of discharge tube, electric field frequency and voltage setting of power supply (for simplicity assumed to possess negligible internal resistance). This setting of power supply can be considered here in the case of surface wave (SW) sustained discharges as equivalent to the knowledge of electric field strength right at the beginning of the discharge column. The electric field strength and its spatial structure throughout the discharge is expected to be provided by the model as well as value and spatial structure of electron density. Actually simultaneous determination and (nonlinear) interdependence of electron density and electric field strength is a particular feature of truly selfconsistent modeling. This implies to go beyond the well known Schottky approximation for the electric field strength which may provide simple estimates, but is degenerate in the electron density and requires prior knowledge of its value. A model on the basis of ion and electron fluid equations can be condensed to two equations: the electron energy and the electron particle balance equation. The former connects electron temperature and electric field intensity (nonlocally in case of sufficient heat conductivity). The latter, balancing diffusion losses and ionization, should contain nonlinear contributions such as stepwise ionization or at high density recombination in order to avoid the above mentioned degeneracy in electron density. For selfconsistency these two equations of discharge physics have to be augmented by two equations of electrodynamical character: by the proper SW dispersion relation and wave power equation connecting Poynting flux with power transfer to the plasma. Here SW sustained discharges are chosen, which possess well defined electrodynamic boundary