A review on impurity transport in divertors

Abstract

Power exhaust is one of the most crucial requirements for future fusion reactors, like ITER. It is widely recognized that impurity injection is needed to significantly reduce the heat load to the divertor plates. By controlled injection of light impurities, the compatibility of high confinement core plasma with strong radiative divertor has been successfully demonstrated in many tokamaks. However, the core impurity contamination was high ( Z eff ∼ 3) compared to the value required for ITER ( Z eff < 1.6). Therefore, a scheme for impurity retention in the divertor region should be established for fusion research. This paper reviews the recent progress in experiments and simulations which have been made for the purpose of understanding impurity transport in divertors. The issues contained in the paper are impurity generation, shielding and cross field diffusion. As for the impurity generation, chemical sputtering and wall source are discussed with emphasis on the characteristics of their transport and shielding. Impurity control with plasma flow induced by gas puffing and divertor pumping, and adequately designed divertor geometry is also presented.