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 GAMMA = -D(partial derivative n/partial derivative 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 EXB turbulent diffusivities and mobility based on the fluctuation data and the measured radial electric field. The agreement is best with the EXB diffusivity taken in the strong turbulence regime, where D=c(D)(phi/B(T)), while the comparison with the weak turbulence diffusivity and the collisional (no fluctuations) diffusivity results in qualitative disagreements. The percolation theory diffusivity (phi/B(T))7/10(DELTAomega/k(perpendicular-to)2)3/10 is also briefly discussed.