Impact of ICRH-driven beta-induced Alfvén eigenmode on fast-ion redistribution and ion heating in EAST plasmas

In magnetically confined plasmas, energetic-particle (EP)-driven instabilities can induce redistribution and losses of energetic ions, thereby affecting plasma heating and confinement. In this work, fast-ion-driven beta-induced Alfvén eigenmode (BAE) excited by ion cyclotron resonance heating (ICRH) was investigated in low-density EAST plasmas using experimentally reconstructed equilibria and profiles. Experimentally, strong ICRH led to a significant increase in ion temperature and plasma stored energy, accompanied by the excitation of an Alfvén eigenmode at 64kHz under 1.6 MW heating power, while no such mode was observed at reduced power. Continuum analysis identified this mode as a core-localized BAE. To interpret these observations, integrated simulations combining TORIC, ASCOT, and GTC were performed. A modified fast-ion distribution function was implemented to capture the strong velocity-space anisotropy of ICRH-generated fast ions. Linear gyrokinetic simulations reproduced the observed BAE frequency and identified a threshold in fast-ion pressure for mode excitation. Orbit-following simulations with realistic wall geometry demonstrated that the BAE induces significant phase-space redistribution and enhances the loss of high-energy fast ions (energy >600keV). Separately, the ASCOT power-deposition analysis shows that the strong BAE reduces the collisional power transferred from fast ions to thermal ions, thereby suppressing the fast-ion contribution to ion heating and limiting the increase in ion temperature. As the measured BAE activity decreases in Phase B, recovery of this ion-heating channel explains the subsequent rise in ion temperature. These results clarify the interplay between ICRH-generated fast ions, BAE activity, and ion heating, and provide insights into optimizing fast-ion confinement and heating efficiency in future burning plasma devices.