High Frequency Mode Generation By Toroidal Alfven Eigenmodes

Nonlinear generation of high frequency modes (HFMs) by the toroidal Alfven eigenmode (TAE) observed in the HL-2A tokamak is analyzed using nonlinear gyrokinetic theory. It is found that the HFM can be dominated by nq-m=1 perturbations with predominantly ideal magnetohydrodynamic polarization if the two primary TAEs are copropagating, while the HFM can be characterized by nq - m=0 electrostatic perturbations if the two primary TAEs are counter-propagating. Here, n and m are the toroidal and poloidal mode numbers, respectively, and q is the safety factor. The nonlinear process is sensitive to the equilibrium magnetic geometry of the device.