Comprehensive Gyrokinetic Study of Eigenstate Transitions in Fast Ion-Driven Electrostatic Drift Instabilities

TL;DR

This paper develops a comprehensive gyrokinetic theory for fast ion-driven drift instabilities, revealing how passing fast ions influence eigenstate transitions and plasma transport, with validation from simulations relevant to fusion heating.

Contribution

It extends existing theory by including resonant passing fast ions and demonstrates their impact on eigenstates and transport in plasma, verified through gyrokinetic simulations.

Findings

Passing fast ions significantly influence instability behavior.

Eigenstate transitions are more likely in weak shear and high safety factor plasmas.

Net energy flux can be inward, affecting plasma heating and confinement.

Abstract

This study comprehensively investigates fast ion-driven drift instability, extending the theory in [B. J. Kang and T. S. Hahm, Phys. Plasmas 26, 042501 (2019)]. The eigenmode equation, including the resonant contribution of passing fast ions, is derived and solved using the shooting method. Passing fast ions significantly affect the instability in weak negative shear or moderate positive shear plasmas. Eigenstate transitions to non-ground states occur more readily in weak magnetic shear, high safety factor, and long wavelength perturbations. Linear gyrokinetic simulations using the GKV code verify the theory, showing good agreement with shooting method results. The estimated quasilinear transport indicates that the net energy flux can be inward, without contradicting the second law of thermodynamics. These findings have important implications for heating efficiency and plasma confinement in the heating process, such as Ion Cyclotron Resonance Heating (ICRH) in future fusion devices.