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(EXP1/01) Impurity Transport Studies on the FTU Tokamak

   
D. Pacella , F. Romanelli , B. C. Gregory ¹, M. Leigheb , G. Mazzitelli , L. Gabellieri , R. de Angelis , M. Finkenthal ², M. May ², K. Fournier ³, W. H. Goldstein ³
Associazione EURATOM-ENEA sulla Fusione, CR Frascati, 00044 Frascati, Rome, Italy
¹ Institut National de la Recherche Scientifique (INRS), Montreal, Canada
² The John Hopkins University, Baltimore, MD 21218
³ Lawrence Livermore National Laboratories, Livermore, CA 9450

Abstract
In this work, the radial profile of the diffusion coefficient  D and the convective velocity V in the plasma core (0 $<$ r/a $<$ 0.7) are obtained directly by the measurements of the absolute fluxes of a few molybdenum charge states (intrinsic impurity). The fluxes are derived from the measured ion density profiles and application of the continuity equation in stationary conditions. The peak values of these coefficients in the intermediate region of the plasma are $\rm D \approx 10 m^2/s$ and $V \approx 100 m/s$. A model for the anomalous transport  induced by electrostatic turbulence is developed. With a typical fluctuation spectrum ( $\omega = 10^5-2\times10^5$ Hz), calculations can reproduce very well the experimental results. To inestigate the impurity behaviour in a non-stationary phase, Kr gas was injected into the plasma. It is found that the total flux of Kr gas flowing into the core is also driven by diffusion but the magnitude is much lower than the single ion fluxes derived for Mo ions. The effect of the turbulence on the single ion is very strong but it is reduced when averaged over many charge states.

 

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