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The nonlinear co-existence of β–induced Alfvén eigenmode (BAE) and β–induced Alfvén-acoustic eigenmode (BAAE) is found in simulations using the gyrokinetic toroidal code, which provides a new mechanism responsible for BAAE excitation in tokamaks. In this work, the normalized pressure β is the ratio between plasma thermal pressure and magnetic pressure. The nonlinear simulation findings show that the BAAE branch emerges after the BAE branch is saturated. The mode structure's evolution shows that existence of BAAE will change the original BAE mode structure. The perturbed distribution functions in the velocity phase space show that a new resonance region manifesting the wave-particlemore » resonance in the BAAE branch appears during the nonlinear co-existence stage.« less

The fast-electron driven beta-induced Alfvén eigenmode (e-BAE) in toroidal plasmas is investigated for the first time using global gyrokinetic particle simulations, where the fast electron is described by the drift kinetic equation. Here, the simulation shows that the e-BAE propagates in the fast electron diamagnetic direction and its polarization is close to an ideal MHD mode. The phase space structure shows that only the fast electron processional resonance is responsible for the e-BAE excitations while fast-ion driven BAE can be excited through all the channels, including transit, bounce, and processional resonance.