The full comprehension of the dynamics of magnetic islands is a critical point in order to predict and to improve the performance of a tokamak reactor, since their appearance can lead to a substantial deterioration of the radial confinement of both particles and energy. The presence of an island in the plasma generates a parallel current perturbation, through several physical mechanisms. This current affects in turn the stability of the island itself [1]. In this paper, we focus on the current connected with the rotation of the island with respect to the surrounding plasma. In particular,the rotation frequency range is extended beyond the standard assumption that, for ions, the island frequency is larger than the parallel streaming along the island itself for passing particles and than the magnetic precession frequency for trapped particles. In this case, the standard polarization current contribution becomes smaller, and other electric and magnetic effects play a role [2]. An analytical approach is employed, which consists in a two-parameter series expansion of the drift-kinetic equation [3, 4]. When the island propagation frequency drops below the parallel streaming of the ions, the main current contribution is shown to be linked to the interaction of the toroidal electric field generated by the island and the magnetic toroidal precession of trapped particles. A resonance mechanism between preceeding trapped particles and the island is also identified and discussed. The contribution of passing particles is on the other hand shown to be secondary. Numerical calculations performed with the drift-kinetic Hamiltonian code HAGIS [5] support the analytical results.
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