# High frequency mode generation by toroidal Alfven eigenmodes

## TL;DR

This paper investigates the nonlinear generation of high frequency modes by toroidal Alfven eigenmodes in a tokamak, revealing how mode propagation directions influence the mode characteristics and their dependence on magnetic geometry.

## Contribution

It provides a theoretical analysis of high frequency mode generation by TAEs using nonlinear gyrokinetic theory, highlighting the role of mode propagation and magnetic geometry.

## Key findings

- HFM dominated by |nq-m|=1 perturbations when TAEs co-propagate
- HFM characterized by nq-m=0 electrostatic perturbations when TAEs counter-propagate
- Nonlinear process sensitive to magnetic equilibrium geometry

## Abstract

Nonlinear generation of high frequency mode (HFM) by toroidal Alfven eigenmode (TAE) observed in 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 if the two primary TAEs are co-propagating; 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 respectively the toroidal and poloidal mode numbers, and $q$ is the safety factor. The nonlinear process is sensitive to the equilibrium magnetic geometry of the device.