[en] Pellet fueling experiments on Alcator C focused on the regime of improved energy and particle confinement, where it was observed that transport for the ionic species was reasonably well described by neo-classical theory. Ion energy transport dropped and particle confinement, particularly for impurity species increased dramatically. These effects have been ascribed to the suppression of ion temperature gradient driven modes (/eta//sub i/) by the peaked density profile set up by pellet injection. Although radiation by high Z ions was unimportant in these discharges, the accumulation of low Z impurities, principally carbon, had a profound effect on the discharge by peaking the resistivity profile and reducing the current density near the plasma center. One result of this was a modification of sawtooth activity; a lengthening of the period between sawteeth and ultimately their complete suppression. After suppression of the sawteeth, very large amplitude m = 1, n = 1 oscillations were often observed. The appearance of this mode was often correlated with saturation of impurity confinement. We speculate that this mode is a form of the m = 1 ideal mode that has been held responsible for the sawtooth crash. 14 refs., 5 figs