Magnetohydrodynamic Instabilities in a High Shear Helical System

Abstract

Current driven kink and tearing modes and low m pressure driven modes are investigated by applying the stellarator expansion to the high shear helical system or the heliotron configuration. For the low β current carrying heliotron configuration, the kink modes with m=1 and n≥2 give wide unstable regions and large growth rates. Eigenfunctions of kink modes are fairly localized inside the plasma column even for no resonant surface in the plasma column. For finite β plasmas, the pressure term destabilizes the low m modes and gives larger growth rates and wider unstable regions than the low β case. For currentless finite β plasmas, β limit due to low m pressure driven modes is estimated and β\gtrsim5% may be expected by tailoring the pressure profile according to the shear parameter.