Kinetic coefficients for a heavy impurity in a multispecies plasma
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A KINETICS
Kinetic Coefficients for a Heavy Impurity in a Multispecies Plasma N. A. Bobrova, A. É. Kocharyan, and P. V. Sasorov Institute of Theoretical and Experimental Physics, Bol’shaya Cheremushkinskaya ul. 25, Moscow, 117259 Russia Received December 22, 2006
Abstract—A model of a plasma consisting of electrons and two ion species with markedly different masses is considered. All the required kinetic coefficients for heavy ions are obtained for an arbitrary ratio between the densities of the ion species. The resulting complete system of equations in two-temperature magnetohydrodynamics coincides with that derived by Bobrova, Lazzaro, and Sasorov (Phys. Plasmas 12, 022102 (2005)), who, in particular, presented a full set of kinetic coefficients for electrons and light ions. The exact form of the equations and coefficients is found to be independent of the details of the description of heavy ions. On the other hand, in the cited paper, the kinetic coefficients for heavy ions were obtained for the case in which their density is not too low. In the present paper, the kinetic coefficients are obtained for heavy ions having an arbitrary density. PACS numbers: 52.27.Cm DOI: 10.1134/S1063780X07090024
1. INTRODUCTION Natural and laboratory plasmas often have a complex chemical composition. Along with electrons, they contain ions of different charge and/or mass. One of the plasma species will be regarded as impurity (which does not imply, however, that its effect is small). The nature of impurity diffusion relative to the main plasma often governs the workability of plasma devices, e.g., tokamaks and those operating with capillary discharges. In order to describe the plasma dynamics in such devices and to interpret the experimental data, it is necessary to develop adequate theoretical models. However, realistic and reliable physical models that would provide a theoretical description of the evolution of the plasma chemical composition are still lacking. A system of two-temperature MHD equations that account for the unsteady nature of the nonuniform plasma chemical composition was obtained in [1] by solving the kinetic equations for electrons and two ion species in the MHD approximation in which the plasma collisionality was assumed to be sufficiently high. The ion plasma component consisting of two ion species was treated as a single fluid with the same temperature and the same mass velocity, but the diffusion of one ion species relative to the other was taken into account. In the zeroth approximation, the ion and electron plasma components were assumed to be in local thermodynamic equilibrium. The system of equations for a plasma consisting of electrons and two ion species contains one more equation in comparison to that for a plasma consisting of electrons and one ion species. This additional equation describes the dynamics of the relative density of, say, heavier ions. The right-hand side of
the equation is the divergence of the diffusive flux of impurity ions in terms of the gradients of the partial pressures of al
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