Impurity transport and neoclassical predictions

The authors present a brief review of collisional (classical and neoclassical) and anomalous transport. Particular emphasis is devoted to the question of charge independence of the anomalous transport coefficients and the combined action of anomalous and collisional transport. In the light of these results the experimental facts are analysed and interpreted. It is found that impurity accumulation-characterized by peaked z eff -profiles-is caused by the combined effects of improved confinement (i.e. reduction of anomalous transport) and peaking of the electron density profile. For the cases of pellet refuelled plasmas and counter neutral injection heating quantitative comparisons are performed which show good agreement between the experimental measurements and simulations based upon neoclassical theory.