Résumé

Global Alfven eigenmodes are studied using fluid and kinetic plasma models to determine how the finite Larmor excursions of the bulk species and the resonant Landau interactions modify the spectrum in the toroidicity Alfven eigenmode (TAE) range of frequencies. A new kinetic Alfven mode conversion mechanism is described taking place away from the resonances through toroidal coupling, when the spatial scales of the fast and the kinetic Alfven waves become comparable. If the Landau damping of the mode converted wave is sufficiently small, groups of kinetic Alfven eigenmodes (KAE) appear inside and above the fluid gap; those induced in the neighborhood of a global fluid mode have a broad radial extension that could lead to substantial a-particle losses. Using an experimental equilibrium, the theoretical Alfven spectrum is directly compared with saddle-coil antenna measurements from the JET tokamak, showing that the multiple peaks observed on the response are KAE induced in the neighborhood of an elongation induced Alfven eigenmode.

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