Stimulated emission of fast Alfv\'en waves within magnetically confined fusion plasmas

TL;DR

This paper demonstrates that fast Alfvén waves can be stimulated to grow via a natural population inversion of fusion-born ions in magnetically confined fusion plasmas, potentially enabling new energy transfer mechanisms.

Contribution

It introduces a novel stimulated emission process for fast Alfvén waves in fusion plasmas, supported by fully nonlinear simulations showing alpha-particle channelling.

Findings

Stimulated emission of Alfvén waves occurs during inward propagation.

Population inversion of fusion-born ions is naturally formed.

Simulations confirm the alpha-particle channelling mechanism.

Abstract

A fast Alfv\'en wave with finite amplitude is shown to grow by a stimulated emission process that we propose for exploitation in toroidal magnetically confined fusion plasmas. Stimulated emission occurs while the wave propagates inward through the outer mid-plane plasma, where a population inversion of the energy distribution of fusion-born ions is observed to arise naturally. Fully nonlinear first principles simulations, which self-consistently evolve particles and fields under the Maxwell-Lorentz system, demonstrate this novel "alpha-particle channelling" scenario for the first time.