On the applicability of local asymptotic stability criteria to stellaratorstability

An intrinsic consequence of the three-dimensional nature of the stellarator equilibrium may be the existence of local flattening of the pressure profi le at the resonant surfaces. This local flattening of the pressure profile significantly changes the stability properties. The localized interchange m odes are stabilized, and a new instability branch controls the critical bet a. This instability is strongly stabilized by shear at high poloidal mode n umbers. As a consequence, the plasma stability properties change, and the a symptotically derived local stability criteria often used in stellarator de sign are no longer applicable. (C) 2001 American Institute of Physics.