Nonlinear mode couplings between geodesic acoustic mode and toroidal Alfvén eigenmodes in the EAST tokamak

Abstract

Multiple toroidal Alfvén eigenmodes (TAEs) driven unstable by energetic electrons and a geodesic acoustic mode (GAM) have been successively observed in the Experimental Advanced Superconducting Tokamak (EAST) low-density Ohmic discharges. Nonlinear mode couplings among these modes are conclusively identified. Theoretical analysis suggests that the coupling of simultaneously driven TAEs is the mechanism for GAM excitation. These results experimentally show the potential role of nonlinear mode coupling to the saturation of energetic-particle driven TAE instability, which may nonlinearly transfer energy of energetic particles to bulk plasma and heat fuel ions via low frequency mode such as GAM.