Prediction of Alfvén eigenmode dampings in the Joint European Torus

Predictions from a gyrokinetic toroidal plasma model reproduce for the first time the evolution of Alfvén eigenmode (AE) dampings over a range of discharges. The coupling between shear-and kinetic-Alfvén waves is responsible for the main source of damping through Landau interactions and can be an order of magnitude larger than fluid predictions neglecting global kinetic effects. Strong stabilization occurs when the wave field gets localized radially by a rise in the edge magnetic shear, explaining why global AEs have never been detected in the Joint European Torus [Rebut, Bickerton, and Keen, Nucl. Fusion 25, 1011 (1985)] in the presence of an X point and suggesting how global Alfvén instabilities could be avoided in future reactors.