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-Alfvén 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 [Phys. Plasmas 2, 2874 (1995)] and is found to vary poloidally. An approximate relationship between pinch velocity and turbulent diffusion is suggested.
Naulin
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Association EURATOM-Risø National Laboratory, OPL-128 Risø, DK-4000 Roskilde, Denmark.