Observations of centrally peaked impurity profiles following pellet injection in the Alcator-C tokamak.
Highly peaked carbon and molybdenum profiles occured after hydrogen pellet injection. 40 ms after injection, carbon was well fit by (T-italic/sub e-italic//T/sub e/(0))/sup =/ for r-italicapprox. <6.5 cm (Z-italic/sub C-italic/ = 6). Experimental values of the inward convective velocity and diffusivity were --10/sup 3/(r/a) cm/s and --300 cm/sup 2//s, respectively, which are of the order of neoclassical predictions. An internal disruption then occurred, which reduced on-axis impurities by (2/3) and ended neoclassical-like transport. Carbon is also found to affect sawtooth dynamics dramatically by altering the central resistivity. The implications of these observations to ignited plasmas are discussed.