Abstract
The evolution and the stability property of a helical perturbation for arbitrary magnetic shear configurations are investigated. An analytic stability criterion has been obtained and predicts that nonlocal perturbations exhibit stronger instabilities than local perturbations. A weak positive magnetic shear is favorable to the stability, while a strong negative magnetic shear contributes little to the instability for reversed magnetic shear configurations, which do not show better stabilities than positive shear configurations. Instability is stronger in the decreasing region of the r-direction perturbation amplitude than in the increasing region and perturbations with a steep negative slope produces strong localized instabilities. A larger poloidal or toroidal mode number of the perturbations relates to a stronger instability. Instability is weaker in the core than in other regions.
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