Stability of Alfven eigenmodes in optimized tokamaks

Alfven eigenmodes (AEs) with intermediate toroidal mode numbers are modelle d using the global gyrokinetic PENN code to determine the stability of high performance tokamak discharges in the presence of energetic particles. A l arge plasma pressure and a weak magnetic shear in the core give rise to rad ially extended kinetic AEs, which are stabilized by the high shear at the e dge of a divertor (X point) configuration. Large values for the safety fact or and the ion Larmor radius in reversed shear operation may however trigge r drift kinetic Alfven eigenmode instabilities that could affect the alpha particle confinement in a reactor.