Charge dependence of impurity peaking factor

The experimentally found dependence of impurity transport characteristics, such as diffusivity and pinch velocity, on the impurity ion charge $Z$, remains unexplained both by neoclassical and anomalous theoretical predictions. In this contribution the model for the impurity anomalous transport due to the ITG/TE unstable modes has been developed further by taking into account the effects of impurity ion collisions with the main plasma components becoming more and more important with increasing impurity charge. In linearized transport equations these effects are included as friction and thermal forces and collision energy exchange affecting perturbations of impurity ion parallel velocity and temperature, correspondingly. For the plasma conditions examined here, where the magnetic shear is low, the collisional effects are dominant in the pinch velocity and result in a very strong Z dependence of the impurity peaking factor. The sign and magnitude of the pinch-velocity and $p$ depends essentially on the instability mechanism, i.e., ITG or TE drive. The results of calculations are compared with the experimental observations.