Observation and Simulation of $n=1$ Reversed Shear Alfvén Eigenmode on the HL-2A Tokamak
P. W. Shi1, Y. R. Yang2, W. Chen1, Z. B. Shi1*, Z. C. Yang1, L. M. Yu1, T. B. Wang1, X. X. He1, X. Q. Ji1, W. L. Zhong1, M. Xu1, and X. R. Duan1
1Southwestern Institute of Physics, Chengdu 610041, China 2State Key Laboratory of Intense Pulsed Radiation Simulation and Effect, Northwest Institute of Nuclear Technology, Xi'an 710024, China
Abstract:A branch of high-frequency Alfvénic modes is observed on the HL-2A tokamak. The electromagnetic mode can be driven unstably in the plasma with an off-axis neutral beam heating. Its mode frequency keeps almost unchanged or presents a slow-sweeping behavior, depending on the detail current evolution. The poloidal and toroidal mode numbers are $m/n=1/1$. The mode has a quite short duration ($\leq$20 ms) and usually appears 5–10 ms after the neutral beam being injected into the plasma. Hybrid simulations based on M3D-K have also been carried out. The result suggests that co-passing energetic particles are responsible for the mode excitation. The simulated mode structures are localized nearby location of minimum safety factor ($q_{\rm min}$) and agree with the structures obtained through tomography of soft x-ray arrays. Further, the modes are localized in the continuum gap and their frequencies increase with variation of $q_{\rm min}$ in a wide range. Last but not least, the characteristic of unchanged frequency on experiment is also reproduced by the nonlinear simulation with a fixed safety factor. All those evidences indicate that the $n=1$ high-frequency mode may belong to a reversed shear Alfvén eigenmode.
. [J]. 中国物理快报, 2022, 39(10): 105201-.
P. W. Shi, Y. R. Yang, W. Chen, Z. B. Shi, Z. C. Yang, L. M. Yu, T. B. Wang, X. X. He, X. Q. Ji, W. L. Zhong, M. Xu, and X. R. Duan. Observation and Simulation of $n=1$ Reversed Shear Alfvén Eigenmode on the HL-2A Tokamak. Chin. Phys. Lett., 2022, 39(10): 105201-.