Gyrokinetic simulation of eigenmode GAM in EAST H-mode plasma

Abstract Gyrokinetic simulations based on the Gyrokinetic Toroidal Code are conducted to investigate the geodesic acoustic mode (GAM) physics in the pedestal of EAST H-mode discharge <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mi mathvariant="normal">#</mml:mi> </mml:mrow> </mml:math> 74036 (Zhou et al 2018 Nucl. Fusion 58 106009). Linear simulations reveal that the instabilities are dominated by the collisionless trapped electron mode (CTEM) in the absence of collisions, and transit to the dissipative trapped electron mode (DTEM) when the collisions are considered. The frequency and propagation direction of DTEM align with those of the edge coherent mode (ECM) observed in the experiments after considering the Doppler shift correction due to the radial electric field on the frequency, indicating DTEM is the dominant component of ECM. In the nonlinear simulations, it is found that CTEM turbulence drives the continuum GAM, whose frequency increases with the ion temperature, aligning with the theoretical predictions. In comparison, DTEM turbulence excites the eigenmode GAM, whose frequency almost does not change with the ion temperature, consistent with the experimental observations. The properties of eigenmode GAM are further confirmed through antenna excitation. Both the continuum and eigenmode GAMs are found to strongly modulate the turbulent transport.