Interaction between energetic-ions and internal kink modes in a weak shear tokamak plasma

Based on the conventional tokamak HL-2A-like parameters and profiles, the linear properties and the nonlinear dynamics of non-resonant kink mode (NRK) and non-resonant fishbone instability (NRFB) in reversed shear tokamak plasmas are investigated by using the global hybrid kinetic-magnetohydrodynamic nonlinear code M3D-K. This work mainly focuses on the effect of passing energetic-ions on the NRK and NRFB instabilities, which is different from the previous works. It is demonstrated that the NRFB can be destabilized by the passing energetic-ions when the energetic-ion beta β_h exceeds a critical value. The transition from NRK to NRFB occurs when the energetic-ion beta β_h increases to above a critical value. The resonance condition responsible for the excitation of NRFB is interestingly found to be satisfied at ω_t + ω_p ≈ ω, where ω_t is the toroidal motion frequency, ω_p is the poloidal motion frequency and ω is the mode frequency. The nonlinear evolutions of NRFB's mode structures and Poincaré plots are also analyzed in this work and it is found that the NRFB can induce evident energetic-ion loss/redistribution, which can degrade the performance of the plasmas. These findings are conducive to understanding the mechanisms of NRFB induced energetic-ion loss/redistribution through nonlinear wave-particle interaction.