Observations of Centrally Peaked Impurity Profiles Following Pellet Injection in the Alcator-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>C</mml:mi></mml:math>Tokamak

Highly peaked carbon and molybdenum profiles occurred after hydrogen pellet injection. 40 ms after injection, carbon was well fitted by ${[\frac{{T}_{e}}{{T}_{e}(0)}]}^{1.5{Z}_{\mathrm{C}}}$ for $r\ensuremath{\lesssim}6.5$ cm (${Z}_{\mathrm{C}}=6$). Experimental values of the inward convective velocity and diffusivity were $\ensuremath{\sim}{10}^{3}(\frac{r}{a})$ cm/s and \ensuremath{\sim} 300 ${\mathrm{cm}}^{2}$/s, respectively, which are of the order of neoclassical predictions. An internal disruption then occurred, which reduced on-axis impurities by frac23; and ended neoclassical-like transport. Carbon is also found to affect sawtooth dynamics dramatically by altering the central resistivity. The implications of these observations for ignited plasmas are discussed.