Enhanced central fuelling and m=1 island formation after pellet ablation in the Frascati Tokamak Upgrade

Injection of frozen deuterium pellets from the magnetic low field side into discharges of the Frascati Tokamak Upgrade with high current and broad temperature profile gives rise to strong central fuelling, whereas pellet ablation calculations predict that pellets should be almost completely sublimated outside the q = 1 magnetic surface. Enhanced central fuelling has been observed in many tokamaks; in these experiments, strong temperature asymmetries are observed inside the q = 1 surface in addition to anomalous central fuelling. Both phenomena are explained by the rapid growth of an m = 1 magnetic island. Detailed simulations of temperature evolution have been performed by means of a modified version of he MITEV code in which the density evolution has been added.