Neoclassical tearing modes (NTMs) with different mode numbers havebeen observed in tokamak plasmas. These NTMs, however, never occursimultaneously in ASDEX Upgrade. As a mode with a different helicity starts togrow, this usually leads to suppression of the first NTM. Bothanalytical and numerical modelling have been carried out to investigatethe interaction between NTMs of different helicities. It is found thatonce the two magnetic islands are close, the more unstable magneticisland survives and suppresses the less unstable one, in agreement withthe experimental results. The mechanism responsible for thissuppression is the decreased fundamental harmonic pressureperturbations of the NTM in the presence of magnetic perturbations of different helicities.
Investigation of neoclassical tearing mode detection by ECE radiometry in an ITER-like tokamak via asymptotic matching techniques