Parametric Dependences of Impurity Transport in Tokamaks
The neoclassical and turbulent models for impurity transport are reviewed. Analytical expressions of the neoclassical terms and the role of the impurity collisionality are summarised. A global presentation of the turbulence models for impurity transport is made. An quasi-linear fluid expression of the turbulent impurity flux is discussed. Theoretical and experimental aspects of the relative contributions of the neoclassical effects and of the turbulent effects are presented. The convective term of the flux is shown to depend largely on the main ion density and temperature gradients and on the dominant turbulent modes. Finally the dependence of the impurity flux on the impurity charge is reviewed. It is shown that both neoclassical and turbulent diffusion coefficients are predicted to decrease with increasing charge, while the neoclassical temperature screening effect increases with Z.