Diffusion in two-temperature thermal plasmas

Combined diffusion coefficients, which allow species to be grouped into their parent gases, are derived in a thermal plasma in which the kinetic temperature of the electrons is different from that of the heavy species. As in previous calculations of combined diffusion coefficients for a one-temperature plasma, chemical equilibrium is assumed, and a plasma in a mixture of two homonuclear nonreacting gases is treated. Expressions for ambipolar diffusion in a two-temperature plasma are derived. Coupling between the electrons and the heavy species is retained in the calculations. It is confirmed that the values of the diffusion coefficients are consistent with mass conservation, in contrast to previous calculations that were based on a theory in which the electrons and heavy species were decoupled. Illustrative results are presented for a thermal plasma in different mixtures of argon and hydrogen at 1 bar, for temperatures up to 25 000 K and different ratios of electron to heavy species temperature.