Impurity transport studies in the Texas Experimental Tokamak (TEXT)

The results of impurity transport experiments in the Texas Experimental Tokamak (TEXT) [Nucl. Technol./Fusion 1, 479 (1981)] are compared with the predictions of a turbulence-based transport model. In the experiments, Sc was injected into the plasma using laser ablation and the time-resolved profiles of critical Sc ionization stages were measured along with the potential fluctuation profile. The experiment was simulated using a one-dimensional (1-D) radial transport code with the standard transport flux Γ=−D(∂n/∂r)+nV. The diffusion coefficient D and convective velocity V parameters were varied until the time-dependent 1-D simulations reproduce the data. This representation for the empirical impurity transport is compared with the E×B turbulent diffusivities and mobility based on the fluctuation data and the measured radial electric field. The agreement is best with the E×B diffusivity taken in the strong turbulence regime, where D=cD(φ̃/BT), while the comparison with the weak turbulence diffusivity and the collisional (no fluctuations) diffusivity results in qualitative disagreements. The percolation theory diffusivity (φ̃/BT)7/10(Δω/k2⊥)3/10 is also briefly discussed.