On stability of collisional coupling between relativistic electrons and ions in hot plasmas

The collisional coupling of relativistic electrons and non-relativistic ions in hot plasmas has been analysed. It is found that relativistic effects produce a new feature: while the condition T_e<3T_i guarantees a stable collisional coupling between electrons and ions in low-temperature plasmas, relativistic effects shift the upper T_e/T_i boundary of stability to higher values. Moreover, for sufficiently high temperatures, T_{e,i} > 75 keV, collisional decoupling between relativistic electrons and ions becomes impossible

Relativistic neoclassical radial fluxes in the 1/nu regime

The radial neoclassical fluxes of electrons in the 1/nu regime are calculated with relativistic effects taken into account and compared with those in the non-relativistic approach. The treatment is based on the relativistic drift-kinetic equation with the thermodynamic equilibrium given by the relativistic Maxwell-J\"uttner distribution function. It is found that for the range of fusion temperatures, T_e<100 keV, the relativistic effects produce a reduction of the radial fluxes which does not exceed 10%. This rather small effect is a consequence of the non-monotonic temperature dependence of the relativistic correction caused by two counteracting factors: a reduction of the contribution from the bulk and a significant broadening with the temperature growth of the energy range of electrons contributing to transport. The relativistic formulation for the radial fluxes given in this paper is expressed in terms of a set of relativistic thermodynamic forces which is not identical to the canonical set since it contains an additional relativistic correction term dependent on the temperature. At the same time, this formulation allows application of the non-relativistic solvers currently used for calculation of mono-energetic transport coefficients.Comment: 10 pages, 2 figure