Comparison between Double-Resonant and Non-Resonant Mode Driven Convections in a Stellarator with a Non-Monotonic Rotational Transform

Abstract

For a stellarator (or tokamak) with a non-monotonic rotational transform, both the double-resonant and non-resonant interchange type modes become unstable, when the magnetic curvature is unfavorable in a finite region including the zero magnetic shear surface r = r s . These modes generate convective motions and poloidal shear flows. The non-resonant mode driven convection affects the r ≃ r s region significantly, although a decrease of central density is seen. On the other hand, the double-resonant mode driven convection affects the central region for a peaked density profile and a stair-like decrease of the central density is seen. The evolution of the density profile is also correlated with the behavior of the nonlinearly generated poloidal flow.