Screening efficiency of the magnetically mixed layer generated in the boundary region of the TEXTOR tokamak by a localized high multipolar conductor configuration

Abstract

The impurity transport in, a magnetically mixed layer is investigated on the basis of the average ion model and a two-dimensional model for the neutral impurity atoms. The magnetic field structure is globally described by the mean inclination angle of the field lines against the toroidal direction. The radial dependence of this angle is computed from the data of the specific perturbation coil which is foreseen for the TEXTOR tokamak. The particle and energy flux densities in the magnetically mixed layer are essentially derived from the inclination angle, the partial pressures of the different species, and the friction between the hydrogen ions and the impurity ions. The calculations show that the impurity density profiles become hollow in the boundary layer. The central iron density is decreased by a factor of 4 and the neutral oxygen concentration is increased by a factor of 30.