Multi-Ion Ambipolar Diffusion
AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH SCHOOL OF ENGINEERING
Pagination or Media Count:
The continuity and momentum equations for electrons and multiple ion species are solved analytically and numerically using a new model for ambipolar diffusion. The general form of the model is valid for any quasi-neutral plasma for which the diffusion approximation is appropriate, including positive or negative ions, arbitrary geometries, and time dependence. The model provides criteria for determining when single ion diffusion theory is appropriate for describing multi-ion discharges, when a multi-ion proportional model is appropriate, and when a multi-ion nonproportional model is necessary. An expression is developed which provides a necessary condition for proportionality and provides the proportionality constant from the net source terms. Proportional analytic solutions are determined for uniform external ionization or single-step ionization by the bulk electrons in planar and cylindrical geometries, and double-exponential external ionization or bulk ionization and nonresonant charge transfer in planar geometries. Numerical comparisons are made to previous experimental and theoretical determinations of electron temperature, particle flux, or particle number densities. Numerical solutions for generic two-ion plasmas with recombination or charge transfer as volume losses and external or electron impact ionization sources provide scaling relationships for the effects of multiple ions on discharge parameters. Diffusion Plasmas physics Diffusion coefficient Electron mobility Gas discharges Glow discharges Ambipolar diffusion.
- Plasma Physics and Magnetohydrodynamics