Importance of collisions with the main plasma components for impurity anomalous transport

Abstract

The problem of impurity transport in fusion plasmas is of extraordinary importance and has been intensively studied for a long time. Nevertheless the experimentally found behaviour of impurity transport characteristics, such as diffusivity and pinch-velocity and, in particular, their dependence on the impurity ion charge, Z, has not been completely understood yet. In this paper the model for the impurity anomalous transport is developed further by taking into account the effects of impurity ion collisions with the main plasma components which become more and more important with increasing impurity charge. In linearized transport equations these effects are included as friction, thermal forces and collision energy exchange, affecting the perturbations of impurity ion parallel velocity and temperature, correspondingly. New terms can provide significant Z-dependence of the impurity anomalous convection and the density peaking factor. A numerical assessment is done for plasma parameters typical in the tokamak JET, with anomalous transport due to the ion temperature gradient/trapped electron unstable modes.