Neoclassical transport of heavy impurities with poloidally asymmetric density distribution in tokamaks

Abstract

Heavy impurity ions in tokamaks are not always evenly distributed over flux surfaces. For instance, toroidal plasma rotation can give rise to a centrifugal force large enough to push impurities to the outboard side of the torus, or ion-cyclotron resonance heating of minority ions can cause inboard impurity localization. It is shown that such poloidally uneven distribution of the impurity ions can enhance or reduce their neoclassical transport by one to two orders of magnitude, or even reverse the direction of the neoclassical impurity convection, depending on the level of poloidal asymmetry of the impurity density distribution and on the ratio of the logarithmic ion temperature gradient to the logarithmic density gradient.