Excitation of Internal Kink Modes by Trapped Energetic Beam Ions

Energetic trapped particles are shown to have a destabilizing effect on the internal kink mode in tokamaks. The growth rate is near the ideal magnetohydrodynamic value, but the frequency is comparable to the trapped-particle precession frequency. A model for the instability cycle gives stability properties, associated particle losses, and neutron emissivity consistent with the "fishbone" events observed in poloidal divertor experiments.