Core localized alpha-channeling via low frequency Alfven mode generation in reversed shear scenarios

TL;DR

This paper proposes a new fuel ion heating method in tokamaks using the decay of reversed shear Alfven eigenmodes into low frequency modes, enhancing core plasma heating in future reactors.

Contribution

It introduces a novel alpha-channeling mechanism via RSAE decay into LFAM, with analysis of conditions, saturation, and heating rates using nonlinear gyrokinetic theory.

Findings

RSAE spontaneous decay conditions identified

Saturation level and heating rate derived

Potential impact on future reversed shear tokamak reactors

Abstract

A novel channel for fuel ions heating in tokamak core plasma is proposed and analyzed using nonlinear gyrokinetic theory. The channel is achieved via spontaneous decay of reversed shear Alfven eigenmode (RSAE) into low frequency Alfven modes (LFAM), which then heat fuel ions via collisionless ion Landau damping. The conditions for RSAE spontaneous decay are investigated, and the saturation level and the consequent fuel ion heating rate are also derived. The channel is expected to be crucial for future reactors operating under reversed shear configurations, where fusion alpha particles are generated in the tokamak core where the magnetic shear is typically reversed, and there is a dense RSAE spectrum due to the small alpha particle characteristic dimensionless orbits.