Speaker
Description
Based on the experimental parameters in HL-2A tokamak, the linear stability and nonlinear dynamics of BAE with reversed safety factor $q$ profile are investigated by using kinetic-MHD code M3D-K. It is found that the ($m/n=3/2$) BAE is excited by co-passing energetic ions with $q_{min}=1.5$ in linear simulation, and the mode frequency is consistent with experimental meuasurement. The simulation results show that the energetic ions $\beta_h$, the injection velocity $v_0$ and orbit width parameter $\rho_h$ of energetic ions are important parameters determining the drive on BAE. The effect of $\rho_h$ is determined by the orbital averaging, while the effect of $v_0$ is associated with the fraction of resonant ions. Furthermore, the effect of $q_{min}$ (with fixed shape of $q$ profile) is studied, and it is found that: when $q_{min} \le 1.5$, the excited modes are BAEs, which are located near $q=1.5$ rational surfaces; when $q_{min} > 1.5$, the excited modes are reversed-shear Alfven eigenmodes (RSAEs), which are localized around $q=q_{min}$ surfaces. Nonlinear simulation results show that the nonlinear dynamics of BAE depends on the EP drive. For strongly driven case, firstly, redistribution and transport of engetic ions are trigged by $3/2$ BAE, which raised the radial gradient of energetic ions distribution function near $q=2$ rational surface, and then an EPM ($m/n=4/2$) is driven in nonlinear phase. Finally, these two instabilities triggered significant redistribution of energetic ions, which results in the repetitive and mostly-downward frequency chirping of $3/2$ BAE. For weakly driven case, there are no $4/2$ EPM being driven and repetitive chirping in nonlinear phase, since the radial gradient near $q=2$ rational surface is small and almost unchanged.
| Speaker's Affiliation | University of Science and Technology of China, Hefei |
|---|---|
| Member State or IGO | China, People’s Republic of |
