Modelling of macroscopic magnetic islands in tokamaks

The article presents experimental and theoretical investigations on the dyn amics of saw-teeth and neoclassical tearing modes in tokamak plasmas. The m ain findings of these investigations are: (1) The experimental validation, on the basis of FTU and TCV data, of a model for the prediction of the sawt ooth period and amplitude; (2) the importance of diamagnetic effects in det ermining the threshold for sawtooth crashes and the rotation of non-linear tearing modes; (3) a clarification of collisionless reconnection processes, in particular the role of phase mixing in association with magnetic island growth and saturation in dissipationless regimes. The interplay between EC RH and macroscopic island dynamics is also discussed.