Diffusion of collisional plasma by the example of a high-current arc in $\rm He$: Binary and trinary ionized mixtures

In this study the applicability of the binary mixture model utilizing the first-order gas-kinetic Chapman–Enskog theory is substantiated for describing diffusion processes at different degrees of ionization of a single-temperature simple gas plasma consisting of three components: atoms, ions and electrons. On the same bases, the obtained expressions for a trinary mixture are applicable to a plasma with a fourth component that is difficult to ionize. The thermal diffusion relations of a trinary mixture are derived, whose peculiarity is the electronic component, which does not affect the diffusion flows of atoms and ions. It is shown that in a highly ionized He arc plasma with developed diffusion and ionization nonequilibrium, thermal diffusion is insignificant. It is noted that when thermodynamic equilibrium is violated, the diffusion coefficients may not change at all or decrease by half at most.