BAE dynamics in presence of external magnetic field perturbations in AUG, EAST and JET plasmas

A class of MHD instabilities, named beta-induced Alfvén eigenmodes (BAEs) [1, 2], can be destabilized by energetic particles and can cause the redistribution and loss of such particles. To guarantee in ITER and in future burning plasma reactors good confinement of energetic particles and alpha heating efficiency, investigating the BAEs triggering mechanism and their dynamics in present fusion devices is thus of particular importance. This work presents BAEs behaviour in AUG, EAST and JET Ohmic plasmas, in presence of externally applied magnetic fields. In such a plasma, without an energetic particle population, BAEs are due to the non-linear excitation of Alfvén waves by a locked magnetic island, induced by the external fields. It has been observed that BAEs can disappear from the MHD spectrum, despite the magnetic island being present. Such phenomenon can be explained through a theoretical evaluation of the continuum distortion in the presence of magnetic field perturbations, based on the general fishbone like dispersion relation [3, 4, 5].