Nonlinear coupling of reversed shear Alfven eigenmode and toroidal Alfven eigenmode during current ramp

TL;DR

This paper investigates two nonlinear mode coupling processes involving reversed shear Alfven eigenmodes during current ramp, revealing mechanisms that saturate instabilities and transfer energy in fusion plasmas.

Contribution

It proposes and analyzes two novel nonlinear coupling processes between RSAE and TAE modes during current ramp, enhancing understanding of mode saturation in fusion plasmas.

Findings

RSAE couples to TAE and generates GAM.

RSAE couples to counter-propagating TAE and generates IAW.

Both processes effectively saturate Alfvenic instabilities.

Abstract

Two novel nonlinear mode coupling processes for reversed shear Alfven eigenmode (RSAE) nonlinear saturation are proposed and investigated. In the first process, RSAE nonlinearly couples to a co-propagating toroidal Alfven eigenmode (TAE) with the same toroidal and poloidal mode numbers, and generates a geodesic acoustic mode (GAM). In the second process, RSAE couples to a counter-propagating TAE and generates an ion acoustic wave quasi-mode (IAW). The condition for the two processes to occur is favored during current ramp. Both processes contribute to effectively saturate the Alfvenic instabilities, as well as nonlinearly transfer of energy from energetic fusion alpha particles to fuel ions in burning plasmas.