Chaotic magnetic field lines in a Tokamak with resonant helical windings

We use a Hamiltonian description for magnetic field lines in a large aspect ratio Tokamak for describing the effect of resonant helical windings in a perturbative way, taking into account the toroidal correction. We consider the formation of chains of primary (main and satellites) and secondary isla nds, analysing their interactions to describe the generation of chaotic mag netic field lines within a portion of the plasma column. This chaotic struc ture is responsible for disruptive instabilities that may spoil plasma conf inement in the Tokamak. Results are compared with numerical integration of magnetic field line equations. (C) 2000 Elsevier Science Ltd. All rights re served.