Transition From Fishbone Mode To Beta-Induced Alfven Eigenmode On Hl-2a Tokamak

In the presence of energetic particles (EPs) from auxiliary heating and burning plasmas, fishbone instability and Alfven modes can be excited and their transition can take place in certain overlapping regimes. Using the hybrid kinetic-magnetohydrodynamic model in the NIMROD code, we have identified such a transition between the fishbone instability and the beta-induced Alfven eigenmode (BAE) for the NBI heated plasmas on HL-2A. When the safety factor at magnetic axis is well below one, typical kink-fishbone transition occurs as the EP fraction increases. When q(0) is raised to approaching one, the fishbone mode is replaced with BAE for sufficient amount of EPs. When q(0) is slightly above one, the toroidicity-induced Alfven eigenmode dominates at lower EP pressure, whereas BAE dominates at higher EP pressure.