Numerical investigation of neoclassical tearing mode in toroidal plasma

The neoclassical tearing mode (NTM) is numerically investigated with the three-dimensional toroidal magnetohydrodynamic model. Both the linear and nonlinear behaviors are simulated and compared with the theory. It is found that in the large aspect ratio condition, the growth rate for a small island limit and the saturated island width for 2/1 NTMs are in good agreement with the MRE theory. However, in the toroidal geometry, the toroidal effect will alter the NTM behaviors. In the small island region, the island growth rate is significantly reduced due to the GGJ effect, because the poloidal asymmetry of the perturbed bootstrap current and the perturbed Pfirsch–Schlüter current are resulted from the Grad–Shafranov shift. As the magnetic island grows, the poloidal asymmetry is substantially reduced, and the growth rate increases significantly.