Prediction of Nonlinear Evolution Character of Energetic-Particle-Driven Instabilities

TL;DR

This paper introduces a comprehensive criterion for predicting nonlinear evolution, specifically chirping oscillations, of energetic-particle-driven instabilities in tokamak plasmas, incorporating realistic models and phase-space effects.

Contribution

It presents a new predictive model that includes detailed phase-space dependences, stochastic scattering, and Coulomb drag to accurately forecast instability behaviors.

Findings

Successfully predicts emergence of chirping oscillations in experiments.

Highlights importance of micro-turbulence in mode behavior transition.

Resolves discrepancies between spherical and conventional tokamak observations.

Abstract

A general criterion is proposed and found to successfully predict the emergence of chirping oscillations of unstable Alfv\'enic eigenmodes in tokamak plasma experiments. The model includes realistic eigenfunction structure, detailed phase-space dependences of the instability drive, stochastic scattering and the Coulomb drag. The stochastic scattering combines the effects of collisional pitch angle scattering and micro-turbulence spatial diffusion. The latter mechanism is essential to accurately identify the transition between the fixed-frequency mode behavior and rapid chirping in tokamaks and to resolve the disparity with respect to chirping observation in spherical and conventional tokamaks.