Observations of centrally peaked impurity profiles in the Alcator C tokamak following pellet injection

Through use of x-ray arrays, highly peaked carbon (C) and molybdenum (Mo) profiles were observed to occur after pellet injection.Multi-ion neoclassical theory predicts equilibrium profiles close to these observations.Specifically, about 40 ms after pellet injection, C, a plateau impurity, was well fit by (Te/Te(O)) 1 . 5Zo for r~<6.5 cm (Zc=6).An internal disruption then occurred, which reduced on-axis impurities by a factor of 3 and terminated the neoclassical-like transport.Based on these observations, we posit that C, the dominant non-hydrogenic contributor to Zeff, dramatically affects sawtooth dynamics by altering the central resistivity.