Magnetic island structures and their rotation after pellet injection in FTU

Pellet injection gives rise to a rich variety of observations on m = 1 island dynamics. Pellet ablation near the q = 1 surface triggers fast growth of an island; as the island reaches a large amplitude, magnetic reconnection mixes the plasma centre with the q = 1 pellet fuelled region, so enhancing the effective pellet deposition depth. Long-lived m = 1 islands that coexist with sawtooth crashes are accompanied by higher harmonics (m/n = 1 with m > 1, where m is the poloidal mode number and n is the toroidal one) near the q = 1 surface; progressive phase shifts observed in the phase of such harmonics indicate island deformation by sheared viscous flow. Coupling between m = 1 and m = 2 islands is observed in sawtooth-free plasmas. Reconnection at the q = 2 surface is driven by a toroidal sideband of the m = 1 island; coupling is associated with strong braking of the m = 1 island.