Indirect nonlinear interaction between toroidal Alfvén eigenmode and ion temperature gradient mode mediated by zonal structures

The indirect nonlinear interactions between toroidal Alfvén eigenmode (TAE) and ion temperature gradient mode (ITG) are investigated utilizing nonlinear gyrokinetic theory and ballooning mode decomposition. More specifically, the local nonlinear ITG mode equation is derived adopting the fluid-ion approximation, with the contributions of zonal field structure and phase space zonal structure (ZS) beat-driven by finite amplitude TAE accounted for on the same footing. The obtained nonlinear ITG mode equation is solved both analytically and numerically, and it is found that the ZS beat-driven by TAE only has a weak destabilizing effect on ITG, contrary to usual speculations and existing numerical results.