Response of MHD stability to resonant magnetic perturbation in the Large Helical Device

Penetration of m/n = 1/1 resonant magnetic perturbation (RMP) in different magnetic configurations was investigated in the Large Helical Device (LHD). In the experiments with constant plasma parameters and heating condition, it was found that the mode penetration threshold increased linearly with increase in the magnetic shear. Also the threshold of penetration was increased by mitigating the magnetic hill. The amplitude of the perturbation field after the penetration was larger than that given by the RMP field. When the magnetic shear was further reduced by the plasma current and the plasma entered the ideal unstable regime, m/n = 1/1 minor collapse occurred after the mode rotation was decelerated and stopped. The occurrence of the collapse was independent of the existence of the error field.