Effects of transition particles on plasma instabilities in a quasi-isodynamic stellarator

Abstract

We consider the impact of transition particles on the Alfvén waves and electrostatic trapped ion modes in a stellarator with closed contours of the second adiabatic invariant, which do not perfectly coincide with magnetic surfaces (a so-called quasi-isodynamic (QI) stellarator). Due to orbit transitions, the damping rate of Alfvén eigenmodes on localized electrons becomes independent of the collision frequency in the broad range of low-collision rates. Dissipative trapped ion modes (Kadomtsev–Pogutse (KP) modes) induced by the ion temperature gradient (ITG) are strongly stabilized by collisionless orbit transitions.