MULTICOMPONENT DIFFUSION IN 2-TEMPERATURE MAGNETOHYDRODYNAMICS

A recent hydrodynamic theory of multicomponent diffusion in multitempe rature gas mixtures [J. D. Ramshaw, J. Non-Equilib. Thermodyn. 18, 121 (1993)] is generalized to include the velocity-dependent Lorentz forc e on charged species in a magnetic field B. This generalization is use d to extend a previous treatment of ambipolar diffusion in two-tempera ture multicomponent plasmas [J. D. Ramshaw and C. H. Chang, Plasma Che m. Plasma Process. 13, 489, (1993)] to situations in which B and the e lectrical current density are nonzero. General expressions are thereby derived for the species diffusion fluxes, including thermal diffusion , in both single- and two-temperature multicomponent magnetohydrodynam ics (MHD). It is shown that the usual zero-field form of the Stefan-Ma xwell equations can be preserved in the presence of B by introducing g eneralized binary diffusion tensors dependent on B. A self-consistent effective binary diffusion approximation is presented that provides ex plicit approximate expressions for the diffusion fluxes. Simplificatio ns due to the small electron mass are exploited to obtain an ideal MHD description in which the electron diffusion coefficients drop out, re sistive effects vanish, and the electric field reduces to a particular ly simple form. This description should be well suited for numerical c alculations.