Fine Structure Zonal Flow Excitation by Beta-induced Alfven Eigenmode

TL;DR

This paper investigates how beta-induced Alfven eigenmodes nonlinearly excite low frequency zonal structures, revealing the preferential excitation of electrostatic zonal flows with fine radial structures due to BAE localization.

Contribution

It demonstrates that electrostatic zonal flows are preferentially excited by BAE and uncovers the fine radial structure of ZF caused by BAE localization.

Findings

Electrostatic zonal flow is preferentially excited by BAE.

ZF exhibits fine radial structure due to BAE localization.

Zonal electric field has an even mode structure at the rational surface.

Abstract

Nonlinear excitation of low frequency zonal structure (LFZS) by beta-induced Alfven eigenmode (BAE) is investigated using nonlinear gyrokinetic theory. It is found that electrostatic zonal flow (ZF), rather than zonal current, is preferentially excited by finite amplitude BAE. In addition to the well-known meso-scale radial envelope structure, ZF is also found to exhibit fine radial structure due to the localization of BAE with respect to mode rational surfaces. Specifically, the zonal electric field has an even mode structure at the rational surface where radial envelope peaks.