DIMERIZED ISLAND CHAINS IN TOKAMAKS

Magnetic surfaces are studied on MHD equilibrium plasmas with non-mono tonic safety factor radial profiles, confined on large aspect-ratio to kamaks. Perturbing helical windings lead to twin Poincare-Bhirkhoff ch ains and reconnection phenomenon, giving rise to dimerized island chai ns. Evolution of radial rotation number profiles, together with the ra dial progression of equilibrium points clarify the reconnection proces s. Toroidal perturbation leads to reconnection for values of the param eter I-h, much lower than those in the integrable case. Then, for high er I-h, we have overlap of secondary islands and the onset of chaotic regions from the edge region to the center.