Investigation of double frequency fishbone in EAST with neutral beam injection

作者：Wei Shen, Liqing Xu, Zhiyong Qiu, Yan Chao, Yifeng Wang, Yuqi Chu, Jianwen Liu, Baolong Hao, M. Xu, Yifei Jin, Guoqiang Zhong, Zhihong Kuang, Shengfa Wu, the EAST Team · 发表于：Nuclear Fusion · 年份：2025 · DOI：10.1088/1741-4326/add359 · 被引用次数：5 · 研究领域：Non-Destructive Testing Techniques、Particle accelerators and beam dynamics

Abstract In the EAST experiments with neutral beam injection and at a low electron density, fishbone instabilities characterized by mode numbers m / n = 1/1, 2/2 have been observed. The simultaneous growth of these modes, particularly m / n = 1/1 and m / n = 2/2, results in a decrease in neutron emission at the plasma core. As the electron density continues to decrease, the beta-induced Alfvén eigenmode (BAE) emerges, replacing the m / n = 2/2 fishbone just before a more severe sawtooth crash occurs. Numerical simulations with the global kinetic-magnetohydrodynamic (MHD) code M3D-K show that the m / n = 2/2 high frequency fishbone branch is linearly stable, but nonlinearly grows due to the coupling with the m / n = 1/1 low frequency fishbone branch. The m / n = 2/2 fishbone frequency is almost twice of the m / n = 1/1 fishbone, and both fishbone frequencies chirp down together. The mode frequencies and structures of the simulated fishbones are consistent with the experimental measurements. In addition, a BAE with m / n = 2/2 is observed in the late nonlinear stage of the simulation. Energetic particle nonlinearity is dominant for the m / n = 2/2 fishbone saturation and transition to BAE. In particular, the transition from m / n = 2/2 fishbone to BAE is found to be the consequence of fast ion redistribution due to the fishbone instability.