Destabilization of the internal kink by energetic-circulating ions

A stability analysis is carried out for the m=1 internal kink mode, in the presence of energetic circulating particles. It is found that, including the effect of finite radial particle-orbit excursion, the m=1 internal kink mode is strongly destabilized by the resonance interaction with the energetic passing particles. Such an instability could explain the experimental observations of the ``fishbone'' oscillations during tangential neutral beam injection [W. W. Heidbrink et al., Phys. Rev. Lett. 57, 835 (1986)].