MHD instabilities in current carrying heliotron plasmas

Instabilities in low beta l = 2 heliotron plasmas with peaked toroidal current density profiles are investigated using resistive reduced magnetohydrodynamic equations. Such heliotron plasmas can have a nonmonotonic rotational transform ι-bar profile with two ι-bar = 2/3 rational surfaces. When the distance between the resonant surfaces is large, resistive instabilities can be found. Current-driven ideal modes with larger growth rates appear when the minimum of the rotational transform becomes just above the rational number 2/3 and there is no resonant surface. The existence of this non-resonant mode is explained by the expression for the current-driven term of the plasma potential energy. (author)