Nonlinear coupling of rotating magnetic island triplets

The role and mechanism of nonlinear coupling of finite size rotating magnetic islands in a tokamak are analyzed in a finite dimensional model obtained from the continuum Reduced Magnetohydrodynamic (RMHD) description of resistive tearing modes. General properties of the electrodynamic interaction of modes of different helicities are found and a phase space analysis of the effects of inertia and eddy currents in the tokamak wall is presented. The results obtained are relevant for the definition of strategies of feedback control of resistive instabilities and a possible help for the interpretation of tokamak performances linked to the onset of a spectrum of magnetic perturbations. (C) 1999 American Institute of Physics. [S1070-664X(99)02704-4].