Stability Analysis of Alfvén Eigenmodes in the Experimental Advanced Superconducting Tokamak

The stability of Alfvén eigenmodes (AEs) driven by fast ions is investigated in the Experimental Advanced Superconducting Tokamak (EAST). It is demonstrated that all AEs found in toroidal AE gaps are stable and that the least stable mode is a reversed shear Alfvén eigenmode (RSAE) with n=9. The calculation results show that collisional damping is the main damping mechanism for toroidal mode number n<11. The excitation threshold for the RSAE is about βcrit,b = 3.33%, bigger than the value of the central beam ion beta βb = 1.01%. The results show that AEs driven by fast ions are stable in EAST, at least for the parameters shown in this work. The effect of beam ion pressure and energy on AE stability is also presented. The drive coming from fast ions increases with the pressure gradient, and the drive mainly comes from υA/3 resonance.