Energetic‐Particle‐Driven Instabilities in General Toroidal Configurations

Abstract

Energetic-particle driven instabilities have been extensively observed in both tokamaks and stellarators. In order for such devices to ultimately succeed as D-T fusion reactors, the super-Alfvénic 3.5 Mev fusion-produced alpha particles must be sufficiently well confined. This requires the evaluation of losses from classical collisional transport processes as well as from energetic particle-driven instabilities. An important group of instabilities in this context are the discrete shear Alfvén modes, which can readily be destabilized by energetic particles (with velocities of the order of v Alfvén ) through wave-particle resonances. While these modes in three-dimensional systems have many similarities to those in tokamaks, the detailed implementation of modeling tools has required development of new methods. Recent efforts in this direction will be described here, with an emphasis on reduced models.

Energetic particle physics in fusion research in preparation for burning plasma experiments

“…Nevertheless, BAAEs were identified in NSTX, JET [206,371], DIII-D [372], HL-2A [373] and reported from AUG [370] when electrons had a temperature comparable with ions. The Alfvén acoustic gaps are much more complex [9] in helical devices such as stellarators and have only begun to be studied experimentally [367,374].…”

“…From the relevance for BPs in ITER, recently, BAEs are again studied theoretically and experimentally in tokamaks and stellarator/helical devices [297,312,366,367,369,376,380,381]. In AUG, BAEs destabilized by energetic ions are clearly detected during the sawtooth phase and the plasma current ramp-up phase.…”

Toroidal Alfvén eigenmodes with nonlinear gyrokinetic and fluid hybrid models

“…These hybrid approaches have been extensively exploited. Other examples of self-consistent fluid-electron, gyrokinetic ion codes include GEM, GTC, and XHMGC [17][18][19], while other examples of perturbative hybrid codes include NOVA-K, CAS3D-K, AE3D-K and VENUS-K [20][21][22][23]. These codes differ in the completeness of their MHD treatment of the bulk plasma, which can result in differing mode structure.…”

Energetic-Ion-Driven Global Instabilities Observed in the Large Helical Device and Their Effects on Energetic Ion Confinement

“…Important research areas that have not yet been intensively explored in the LHD are the following: (i) Characterization of low-frequency energetic-ion-driven modes of which the gaps are generated by acoustic Alfvén wave coupling, for instance, beta-induced Alfvén eigenmodes (BAEs) [64], (ii) Excitation of low-frequency energetic-ion-driven modes such as fishbone instabilities by trapped energetic ions, (iii) MHD spectroscopy, which is aimed at extracting accurate information on MHD equilibrium, such as the rotational transform profile and electron/ion temperature, based on the linear and nonlinear characteristics of various energetic-ion-driven AEs (TAEs, RSAEs, BAEs, HAEs, and so on) and GAM [3], (iv) Improvement in bulk plasma confinement and energy channeling to the bulk plasma by energetic-ion-driven modes such as AEs and GAM [3,50], (v) Study of energetic ion transport by various energeticion-driven modes in the regime where energetic ions have a small gyro-radius and near isotropic velocity distribution toward a fusion reactor, and (vi) Effects of micro-turbulence on slowed-down energetic ions. …”