Symmetry breaking and self-consistent rotation of magnetic islands in neoclassical viscous regimes

Classical or neoclassical tearing modes (NTMs) perturb the ideal axisymmetry of tokamaks. As a consequence of symmetry breaking a neoclassical toroidal viscosity (NTV) appears, that depends on the island amplitude. This work shows that in the low collisionality regimes NTV has a key role in determining self-consistently the magnetic island velocity and at the same time modifies significantly the ion polarization current effects on NTM instability. This finding can provide a better understanding of the mechanism of onset of NTMs, observed experimentally, and improve the concepts for their control or avoidance. (C) 2009 American Institute of Physics. [doi:10.1063/1.3216546]