Applicability of global phase locking beyond chorus waves

Investigate whether global phase locking operates in other slowly evolving resonant systems, including free-electron lasers.

Background

The paper develops global phase locking as a mechanism governing superradiant amplification in whistler-mode chorus waves. In this framework, the stable resonant phase remains approximately fixed while the resonance detuning evolves, requiring the wave amplitude to track the detuning and producing linear amplitude growth with distance.

The authors state that the mechanism may extend beyond magnetospheric plasma physics because pendulum-like nonlinear phase-space structures occur broadly in resonant wave–particle interactions. However, they do not establish whether the same phase-locking mechanism operates in other slowly evolving resonant systems, specifically mentioning free-electron lasers as a subject for future investigation.