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 plasma pressure threshold for the mode is lowered by the particles. The growth rate is near the ideal magnetohydrodynamic value, but the frequency is comparable to the trapped particle precission frequency. A model for the instability cycle gives stability properties, associated particle losses, and neutron emissivity consistent with the fishbone events observed in PDX