Most of the published theoretical works on plasma instabilities driven by energetic (superthermal) ions are relevant to tokamaks. However, these instabilities play an important role not only in tokamaks but also in stellarators. That is why it is of importance to analyse the limits of applicability of theoretical results obtained for tokamaks and understand in which cases using these results for the description of similar phenomena in stellarators is justified and, if so, to what extent. On the other hand, stellarator theory incorporating effects of 3D geometry in some cases can be useful for understanding instabilities in tokamaks. Therefore, comparative analysis of instabilities in various types of toroidal systems is of interest for both stellarator and tokamak communities. Such an analysis based on an overview of energetic-ion-driven instabilities in tokamaks and stellarators is carried out in this paper. Instabilities in wide frequency range, from the ion/electron diamagnetic frequency to high frequencies of specific stellarator modes, are considered. Effects of the instabilities on the confinement of both the energetic ions and the bulk plasma are described. Numerical tools available for simulation of instabilities driven by the energetic ions are reviewed.
Physics at the stellarator--tokamak interface