Nonlinear dynamics of phase space zonal structures and energetic particle physics in fusion plasmas

TL;DR

This paper develops a theoretical framework to understand the nonlinear behavior of phase space zonal structures and energetic particles in fusion plasmas, highlighting phenomena like frequency chirping and phase locking that influence particle transport.

Contribution

It introduces a comprehensive theoretical model for nonlinear phase space dynamics and applies it to analyze mode-resonant particle interactions in fusion plasmas.

Findings

Non-adiabatic frequency chirping can cause secular particle transport.

Mode-resonant interactions are crucial for understanding Alfvén wave instabilities.

The framework connects nonlinear plasma physics with concepts like autoresonance and superradiance.

Abstract

A general theoretical framework for investigating nonlinear dynamics of phase space zonal structures is presented in this work. It is then, more specifically, applied to the limit where the nonlinear evolution time scale is smaller or comparable to the wave-particle trapping period. In this limit, both theoretical and numerical simulation studies show that non-adiabatic frequency chirping and phase locking could lead to secular resonant particle transport on meso- or macro-scales. The interplay between mode structures and resonant particles then provides the crucial ingredient to properly understand and analyze the nonlinear dynamics of Alfv\'en wave instabilities excited by non-perturbative energetic particles in burning fusion plasmas. Analogies with autoresonance in nonlinear dynamics and with superradiance in free electron lasers are also briefly discussed.