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(EXP5/32) Measurement of Impurity Transport Coefficients in the Confined Plasma of ASDEX Upgrade

R. Dux¹⁾, A. G. Peeters¹⁾, A. Gude¹⁾, A. Kallenbach¹⁾, R. Neu¹⁾, ASDEX Upgrade Team^1)
 
1) Max-Planck-Institut für Plasmaphysik, EURATOM Assoziation, Garching, Germany

Abstract.  For ASDEX Upgrade H-Mode discharges, the core plasma impurity transport has been investigated in the quiet phase between sawtooth crashes. For the elements Ne, Ar, Kr and Xe the diffusion coefficient in the center is D$\le$6×10^-2m²/s and rises with the radial distance from the center. With increasing Z number the transport becomes strongly convective with inwardly directed drift velocities that produce very peaked impurity densities for high Z. The calculated neoclassical diffusion coefficient and drift velocity are close to the experimental values for the lower Z elements Ne and Ar. The calculated drift velocity is too small by a factor of 10 for Kr and Xe. For these elements, toroidal rotation of the plasma leads to an increased impurity density on the outboard side of the flux surfaces which is not taken into account by the neoclassical calculations. The outboard/inboard ratio for Kr is $\approx$ 1.5 and the toroidal Mach number M_tor $\approx$ 2. Investigations of Si and Ne transport in the edge region, i.e. the region of the temperature pedestal and the steep temperature gradient zone, yield an inwardly directed drift velocity in the quiet phase between ELMs. The inward pinch is observed in the radial range of the steep temperature gradient. The transport induced by an ELM is best described by a very high radial diffusion coefficient rather than by an outwardly directed drift velocity.

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