RADIAL AND POLOIDAL IMPURITY TRANSPORT IN THE H-MODE EDGE PEDESTAL OF ALCATOR C-MOD

Radial impurity density profiles of highly charged fluorine in the H-mode edge pedestal region of Alcator C-Mod have been quantitatively derived from very high-resolution (dR ∼ 1 − 2 mm) measurements of ne(r), Te(r), and x-ray emissivity of fluorine at two poloidal locations (outboard midplane and top). At the midplane, a distinct inward shift of the fluorine x-ray profile with respect to the ne pedestal is ob-served (∼10 mm for typical plasma parameters), as can be seen in Fig. 1. This inward impurity shift at the midplane suggests the existence of an inward pinch velocity. In order to investigate this further, the MIST impurity transport code[1] has been used to calculate the steady-state density profiles of highly charged fluorine, nF, using as inputs the measured ne and Te profiles at the outboard midplane, the self-consistent neoclassical pinch velocity, VNC, which is shown in Fig. 2, and a diffusion coefficient, DI, consistent with empirically determined values (0.01-0.05 m 2/s) from previous inde-pendent measurements. Due to its strong dependence on gradients, VNC is significant only in the edge pedestal region. The calculated profile of nF clearly exhibits an inwar