Coupling between the Alfvén eigenmode and edge-coherent mode on the experimental advanced superconducting tokamak

Abstract

High-frequency electromagnetic fluctuations and edge-coherent modes (ECMs) have been detected by Doppler reflectometry (DR) in the pedestal region of the Experimental Advanced Superconducting Tokamak (EAST). The frequency of the electromagnetic fluctuations was proportional to the Alfvén velocity and localized in the ellipticity-induced Alfvén eigenmodes (EAE) gap in the Alfvén continuum. Therefore, the fluctuations are presumed to be EAE.
The DR measurements of poloidal flow fluctuations show that EAEs and ECMs have amplitude envelopes that are localized near the bottom of the radial electric field well.
Simultaneous EAE and ECM activity generates sidebands at $f_{EAE} \pm f_{ECM}$, the strengths of the upper and lower sidebands are unequal, with the upper sideband being stronger. This is consistent with the theoretical prediction of Chen et al.
Compared with ECM-only discharges, the inclusion of EAEs leads to an increase in $D\alpha$ intensity, thus indicating enhanced outward particle transport.