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(PD/3) Interactions between Neoclassical Tearing Modes and their Stabilization by an Externally Applied Helical Field

Q. Yu¹⁾, S. Günter¹⁾, K. Lackner^1)
 
1) Max-Planck Institute of Plasma Physics, EURATOM Association, D-85748, Garching, Germany

Abstract.  The interaction between the neoclassical tearing modes (NTMs) of different helicities is investigated theoretically. It is found that once two magnetic islands are close, the more unstable island survives and suppresses the less unstable one, in agreement with the experimental results. The mechanism responsible for this suppression is the decreased fundamental harmonic pressure perturbation of the NTM in the presence of magnetic perturbations of different helicity. Based on the mechanism found, the effect of static helical magnetic fields on the nonlinear growth of neoclassical tearing modes (NTM) is investigated, and the NTM is found to be stabilized by an externally applied helical field of a different helicity if the field magnitude is sufficiently large, suggesting a very simple method for stabilizing the NTM.

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