PREDICTION OF ALFVEN EIGENMODE DAMPINGS IN THE JOINT EUROPEAN TORUS

Predictions from a gyrokinetic toroidal plasma model reproduce for the first time the evolution of Alfven eigenmode (AE) dampings over a ran ge of discharges. The coupling between shear-and kinetic-Alfven waves is responsible for the main source of damping through Landau interacti ons and can be an order of magnitude larger than fluid predictions neg lecting global kinetic effects. Strong stabilization occurs when the w ave field gets localized radially by a rise in the edge magnetic shear , explaining why global AEs have never been detected in the Joint Euro pean Torus [Rebut, Bickerton, and Keen, Nucl. Fusion 25, 1011 (1985)] in the presence of an X point and suggesting how global Alfven instabi lities could be avoided in future reactors. (C) 1998 American Institut e of Physics.