Impurity and trace tritium transport in tokamak edge turbulence

The turbulent transport of impurity or minority species, as for example tritium, is investigated in drift-Alfven edge turbulence. The full effects of perpendicular and parallel convection are kept for the impurity species. The impurity density develops a granular structure with steep gradients and locally exceeds its initial values due to the compressibility of the flow. An approximate decomposition of the impurity flux into a diffusive part and an effective convective part (characterized by a pinch velocity) is performed and a net inward pinch effect is recovered. The pinch velocity is explained in terms of turbulent equipartition [Nycander and Yan'kov, Phys. Plasmas 2, 2874 (1995)] and is found to vary poloidally. An approximate relationship between pinch velocity and turbulent diffusion is suggested.