Abstract
This article is a tutorial review of the interaction between energetic particles and Alfvén eigenmodes (AEs) which is one of the important research issues for fusion burning plasmas. The destabilization mechanism of AEs is a kind of inverse Landau damping through the resonant interaction with energetic particles. The important properties of the AE instability, such as resonance condition, conserved variable during the interaction, and particle trapping by the AE, are explained. The time evolution of AEs is classified into various types, steady state, frequency splitting, frequency chirping, and recurrent bursts. Berk and Breizman presented both a one-dimensional weakly nonlinear theory for marginal stability and a reduced simulation model that qualitatively explain the various types of time evolution. Berk–Breizman’s theory and reduced simulation model are introduced, and their limitations and the future works are discussed in this article. In addition, energetic particle transport by AEs is illustrated with surface-of-section plots. The particle trapping by the AE creates phase space islands and leads to the local flattening of the energetic particle spatial profile. The resonance overlap of multiple AEs and the overlap of higher-order resonances of a single AE lead to the emergence of stochasticity in phase space and the global transport of energetic particles.
Highlights
Three types of wave exist in MHD, namely, shear Alfvén wave, slow magnetosonic wave, and fast magnetosonic wave
Global Alfvén eigenmode (GAE) (Appert et al 1982) and reversed shear Alfvén eigenmode (RSAE) (Fukuyama and Akutsu 2002) are located at the extrema of the safety factor which is an index of the torsion of the magnetic field, and toroidal Alfvén eigenmode (TAE) (Cheng et al 1985; Cheng and Chance 1986) and beta-induced Alfvén eigenmode (BAE) (Heidbrink et al 1993) appear at the gaps of the Alfvén continuous spectra, which are created by toroidicity and finite plasma pressure, respectively
We have explained the basics of the interaction between energetic particles and Alfvén eigenmodes (AEs), which is an important research issue for burning plasmas
Summary
Alpha particles born from the deuterium–tritium (D–T) reaction with energy 3.5 MeV are expected to heat the fusion burning plasmas to maintain the high temperature that is needed for the D–T reaction. Magnetohydrodynamics (MHD) is a theoretical framework of plasmas that combines the fluid equations, the induction
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