Indirect nonlinear interaction between toroidal Alfv\'en eigenmode and ion temperature gradient mode mediated by zonal structures

TL;DR

This paper investigates the indirect nonlinear interaction between toroidal Alfvén eigenmodes and ion temperature gradient modes, revealing that zonal structure beat-driven by TAE has a weak destabilizing effect on ITG, challenging previous assumptions.

Contribution

The study develops a nonlinear gyrokinetic theory framework to analyze the indirect interactions between TAE and ITG modes, incorporating zonal structures and providing both analytical and numerical solutions.

Findings

Zonal structure beat-driven by TAE weakly destabilizes ITG.

Contradicts previous assumptions of strong destabilization.

Provides a new theoretical approach to mode interactions.

Abstract

The indirect nonlinear interactions between toroidal Alfv\'en eigenmode (TAE) and ion temperature gradient mode (ITG) are investigated using nonlinear gyrokinetic theory and ballooning mode formalism. 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 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 zonal structure beat-driven by TAE has only weakly destabilizing effects on ITG, contrary to usual speculations and existing numerical results.