The modelling of Alfvénic instabilities is discussed from the pointof view of mode-conversion, showing how the development of the theoryaffects the predictions as the limitations of the models are graduallyrelaxed. Conventional tokamak plasmas are relatively well understood andare used for the case of a kinetic Alfvén eigenmode (AE) to assessthe resonant wave-particle interactions along the magnetic field. Thelarge safety factor in the core of deeply reversed shear plasmas and thelow magnetic field of spherical tokamaks, however, bring the AEs downinto the drift-frequency range; modifications of the spectrum throughtoroidal mode-conversion then creates a new class of drift-kinetic AEsthat could affect the fast particle confinement.Experiments have beencarried out to verify these predictions in JET. They confirm thepresence of weakly damped modes, which do not follow the usual AEsscaling.
Active control of Alfvén eigenmodes in magnetically confined toroidal plasmas