Surface-wave produced discharges in hydrogen: I. Self-consistent model of diffusion-controlled discharges

A fluid-plasma model of diffusion-controlled hydrogen discharges sustained in the field of propagating surface waves is presented in this study. The self-consistent description of the discharge structure achieved provides results for the inter-related variations of the discharge characteristics: the electron concentration ne, the concentrations of the three ionic species (H+, H2+ and H3+), the concentrations of the two neutral gas components (H and H2), the electron temperature, the power ? absorbed on average by an electron, the gas temperature, the wavenumber and the space damping rate ? of the wave. Wave behaviour in radially inhomogeneous collisional plasmas is taken into account because it provides the proper description of diffusion-controlled discharges. The general mechanism of nonlocal heating of the electrons in the wave field is considered. The model is extended to comparatively low gas pressures (p?0.2?Torr) by introducing effective mobilities of the ions in which, besides the ion?neutral elastic collisions, the production and destruction of ions by collisions are included. Based on these effective mobilities, the ambipolar diffusion coefficients of the charged particles are specified. The most important reactions that contribute?under the gas-discharge conditions considered?to the production of charged particles and hydrogen atoms as well as to the electron-energy and gas-energy balances are involved in the model. It is shown that in hydrogen discharges, the (??ne)-relation, which besides the (??ne)-relation ensures a self-consistent description of the axial structure of surface-wave-sustained plasmas, in general, stems from the dependence of ? on the concentrations of the neutral gas components (H, H2) and their relation to the concentrations of the ions (H+, H2+ and H3+). The results obtained using the model are discussed in the context of experiments showing a peculiar behaviour of the axial structure of hydrogen discharges compared to discharges in other gases.

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