Transport properties of a tokamak plasma with impurities in the collision-dominated regime

Abstract

The transport properties of an axisymmetric toroidal plasma containing an arbitrary number of impurity species are considered for the case that all species are in the collision-dominated regime. Energy transfer between the different species, and in particular between electrons and ions, is taken into account. This yields expressions for the particle and heat fluxes applicable to a wide range of parameters.

Nonlinear neoclassical transport in toroidal edge plasmas

“…2 The observed asymmetry is however larger than the analytical prediction, which may have to do with the extreme steepness of the gradients in the experiments. Finally, the energy exchange between the bulk ions and electrons, which is known to significantly affect the ion heat flux in a pure plasma, 10 does not strongly influence the impurity dynamics.…”

“…10 Starting from the ion drift kinetic equation and expanding in the usual way in the smallness of the mean-free path, we can include the ion-electron energy transfer by treating C ie /C ii as O(⌬). Then, to lowest order we have…”

“…As the radial scale length decreases, poloidal asymmetries arise in the plasma. [10][11][12] In an impure plasma, typically the first plasma parameter to develop a poloidal variation is the impurity density, n z , 6 whose poloidal modulation is of the order ñ z /n z ϳ␦ z ϵ␦ ii z 2 , where ii ϵL ʈ / ii is the collisionality, with ii the mean-free path for the bulk ions and L ʈ the connection length. In conventional neoclassical theory ␦ z is assumed to be small.…”

Nonlinear Neoclassical Transport in Toroidal Edge Plasmas

“…If the collisionality is high, ion-electron energy transfer may influence the ion dynamics, as pointed out by Engelmann and Nocentini. 10 Starting from the ion drift kinetic equation and expanding in the usual way in the smallness of the mean-free path, we can include the ion-electron energy transfer by treating C ie /C ii as O(⌬). Then, to lowest order we have…”

“…As the radial scale length decreases, poloidal asymmetries arise in the plasma. [10][11][12] In an impure plasma, typically the first plasma parameter to develop a poloidal variation is the impurity density, n z , 6 whose poloidal modulation is of the order n ˜z /n z ϳ␦ z ϵ␦ ˆii z 2 , where ˆii ϵL ʈ / ii is the collisionality, with ii the mean-free path for the bulk ions and L ʈ the connection length. In conventional neoclassical theory ␦ z is assumed to be small.…”