Study of neoclassical tearing modes based on a reduced MHD model in cylindrical geometry

Neoclassical tearing modes (NTMs) are examined with a reduced MHD model including the bootstrap current as a simple model, JBS ∝ -dP/dr, in cylindrical tokamaks. It is found that linear instabilities due to the perturbation of bootstrap current appear for large JBS cases with large parallel thermal diffusivity, χparallel, under small perpendicular thermal diffusivity, χperpendicular, in the pressure evolution equation. Here, other dissipations such as resistivity and viscosity are also finite. Although the linear growth rate of this unstable mode is small, the growth of magnetic energy of this unstable mode is usually accelerated after the saturation of kinetic energy. Its nonlinear behaviour shown by the evolution of magnetic islands is consistent with the standard nonlinear NTM theory. (author)