Influence of trapped energetic ions on low-frequency magnetohydrodynamic instabilities with reversed shear profile

The influence of trapped energetic ions (TEIs) on m / n = 2 / 1 low-frequency magnetohydrodynamic (MHD) instabilities with reversed shear profile is investigated by a global kinetic–MHD hybrid simulation. For low energetic-ion beta, TEIs have a stabilizing effect on the double tearing mode (DTM). When the energetic-ion beta is larger than a threshold, an energetic-particle-driven mode, the fishbone-like mode (FLM), is excited; that is, a mode transition from the DTM to the FLM occurs. The threshold increases with increasing resistivity, and the growth rate of the FLM is reduced by the presence of resistivity. In addition, the dependences on energetic-ion beta, gyroradius, and injection velocity of the effects of TEIs are studied systematically.