Synergy effects between energetic ion and energetic electron on the stability of beta-induced Alfvén eigenmode

It has been widely observed in experiments that beta-induced Alfvén eigenmodes (BAEs) can be destabilized by both energetic ions (EIs) and energetic electrons (EEs), which are termed as i-BAE and e-BAE propagating along each diamagnetic drift direction. In this work, we focus on the synergy effects of co-existing EIs and EEs on BAE stability, which are investigated numerically using the MAS code based on a Landau fluid–gyrokinetic hybrid model incorporating the kinetic effects of bulk plasma and energetic particle (EP) in a non-perturbative manner. It is found that for the center-peaked EI and EE pressure profiles that effectively drive i-BAE and e-BAE unstable, the synergy effects between EI and EE can lead to the stabilization for both i-BAE and e-BAE branches, which is attributed to the EP fluid convection and kinetic particle compression (KPC) responses that modify the magnetohydrodynamic (MHD) interchange and wave-particle resonances. The EP fluid convection response can enhance MHD interchange with center-peaked pressure profiles, which generally decreases the BAE frequency closer to ion acoustic wave and thus enhances the bulk plasma Landau damping. The passing EIs can resonate with both i-BAE and e-BAE through transit motion resonance, for which the KPC response provides drive for i-BAE with ωp*/ω>0 and damping for e-BAE with ωp*/ω<0 (where ωp* is the EI diamagnetic drift frequency). A stabilizing regime due to EE and EI synergy effects is then demonstrated for BAE, which is helpful for explaining experimental observations and control of Alfvén eigenmode activities through multiple auxiliary heating.