Experimental Electron Temperature Gradient Dependence of Heavy Impurity Transport in Fusion Devices

The turbulent impurity (nickel) transport dependence on the normalized electron temperature gradient has been analyzed in sawtooth-free electron cyclotron wave heated Tore Supra plasmas. In the core, our experimental analysis shows that the lower R/LTe, the lower the nickel diffusion coefficient. The latter decreases until the instability threshold is reached. The experimental threshold is in agreement with the one computed by a gyrokinetic model. Further out, R/LTe plays no role in the impurity diffusion. This set of experimental results is consistent with a quasilinear gyrokinetic analysis.