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 beta (h) exceeds a critical value. The transition from NRK to NRFB occurs when the energetic-ion beta beta (h) increases to above a critical value. The resonance condition responsible for the excitation of NRFB is interestingly found to be satisfied at omega (t) + omega (p) approximate to omega, where omega (t) is the toroidal motion frequency, omega (p) is the poloidal motion frequency and omega is the mode frequency. The nonlinear evolutions of NRFB's mode structures and Poincare 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.

Automated summary

Based on the M3D-K code, the linear and nonlinear properties of non-resonant kink mode (NRK) and non-resonant fishbone instability (NRFB) in reversed shear tokamak plasmas are investigated. It is found that passing energetic ions can destabilize NRFB, and the NRK transitions to NRFB when the energetic-ion beta exceeds a critical value.