Interaction between energetic particles and Alfven eigenmodes in reversed shear plasmas

The interaction between energetic particles and Alfven eigenmodes in reversed shear tokamak plasmas were investigated for different minimum safety-factor values using a hybrid simulation code for magnetohydrodynamics (MHD) and energetic particles. When the energetic particle distribution is isotropic in velocity space, the transition from low-frequency reversed shear Alfven eigenmode (RSAE mode) to toroidal Alfven eigenmode (TAE mode) is demonstrated as the minimum safety-factor value decreases. The frequency rises up from a level above the geodesic acoustic mode frequency to the TAE frequency. It is found that the energetic particles both co- and counter-going to the plasma current are transported by the TAE mode, whereas only the co-going particles are transported by the low-frequency RSAE mode. When only the co-passing particles are retained, the low-frequency RSAE modes are destabilized. On the other hand, the high-frequency RSAE modes are destabilized when only the counter-passing particles are retained. (author)