Simulation of convective transport during frequency chirping of a TAE using the MEGA code

TL;DR

This paper introduces a simulation method to analyze phase-space dynamics during frequency chirping of TAEs in tokamak plasmas, revealing coherent structures and their impact on particle transport.

Contribution

The study presents a new procedure using the MEGA code to examine phase-space during TAE chirping, demonstrating coherent structures and their effects on particle transport.

Findings

Identification of traveling wave in phase-space

Formation of holes and clumps in phase-space

Frequency chirping rate increases with damping rate

Abstract

We present a procedure to examine energetic particle phase-space during long range frequency chirping phenomena in tokamak plasmas. To apply the proposed method, we have performed self-consistent simulations using the MEGA code and analyzed the simulation data. We demonstrate a travelling wave in phase-space and that there exist specific slices of phase-space on which the resonant particles lie throughout the wave evolution. For non-linear evolution of an n=6 toroidicity-induced Alfven eigenmode (TAE), our results reveal the formation of coherent phase-space structures (holes/clumps) after coarse-graining of the distribution function. These structures cause a convective transport in phase-space which implies a radial drift of the resonant particles. We also demonstrate that the rate of frequency chirping increases with the TAE damping rate. Our observations of the TAE behaviour and the corresponding phase-space dynamics are consistent with the Berk-Breizman (BB) theory.