A New Paradigm for Fast and Repetitive Chirping of Alfv\'en Eigenmodes

TL;DR

This paper introduces a new 2D nonlinear dynamical framework to explain the rapid and repetitive frequency chirping and amplitude oscillations of Alfvén eigenmodes driven by energetic particles in fusion plasmas, aligning with simulation observations.

Contribution

It develops a non-perturbative, 2D phase-space dynamical paradigm that captures the continuous twisting and folding of wave-particle resonant structures causing mode repetition.

Findings

Repetitive excitation and decay of Alfvén eigenmodes explained by phase-space dynamics.

Radial dependence and particle precession are key to mode behavior.

Simulation results support the new 2D dynamical interpretation.

Abstract

A novel 2D nonlinear dynamical paradigm is constructed to interpret the fast and repetitive frequency chirping and amplitude oscillation of Alfv\'en eigenmodes excited by energetic particles in fusion plasmas as observed in global gyrokinetic simulations. In this non-perturbative paradigm of the collisionless phase-space dynamics, wave-particle resonant interactions cause the phase-space structure to continuously twist and fold, leading to the repetitive excitation and decay of the Alfv\'en eigenmode. The radial (perpendicular to the dominant wave-particle interaction) dependence of the mode amplitude and toroidal precessional drifts of the energetic particles leads to the 2D dynamics of wave-particle interactions, which is found to be responsible for the repetitive process of formation and destruction of the mode structure.