Major minority: energetic particles in fusion plasmas

This paper describes advances made in the field of energetic-particle physics since the topical review of Alfvén eigenmode observations in toroidal plasmas (Wong 1999 Plasma Phys. Control. Fusion 41 R1–R56). The development of plasma confinement scenarios with reversed magnetic shear and significant population of energetic particles, and the development of novel energetic-particle diagnostics were the main milestones in the past decade, and these are the main experimental subjects of this review. The theory of Alfvén cascade eigenmodes in reversed-shear tokamaks and its use in magnetohydrodynamic spectroscopy are presented. Based on experimental observations and nonlinear theory of energetic-particle instabilities in the near-threshold regime, the frequency-sweeping events for spontaneously formed phase-space holes and clumps and the evolution of the fishbone oscillations are described. The multi-mode scenarios of enhanced particle transport are discussed and a brief summary is given of several engaging research topics that are beyond the authors' direct involvement.