Diffusive impurity transport driven by trapped particle turbulence in tokamak plasmas

Abstract

The diffusive impurity transport as a function of charge and mass numbers is investigated in ion driven or electron driven turbulence, in the limit of zero impurity temperature gradient. It is found that the impurity transport decreases slightly with increasing mass number and depends much more strongly on the charge number. Moreover, this transport depends on the nature of the instability that drives turbulence. The impurity flux due to Trapped Electron Mode (TEM) turbulence increases with the charge number Z. In contrast, it is found to decrease with Z when the Trapped Ion Mode (TIM) dominated. In order to explain these observations, the quasilinear flux is derived and is compared with the results obtained from the nonlinear simulations. Quasilinear theory qualitatively reproduces the gyrokinetic numerical observations.