Effect of Neoclassical Tearing Mode on Confinement Degradation
N. HAYASHI, T. OZEKI, H. SHIRAI, T. TAKIZUKA, K. SHIMIZU
Naka Fusion Research Establishment, Japan Atomic Energy Research Institute
Abstract.
The effect of the neoclassical tearing mode (NTM) on the confinement degradation in tokamak plasmas is studied by using a 1.5D time-dependent tokamak simulation code TOPICS. NTM limits the plasma beta and degrades the plasma confinement in long-pulse tokamak discharges. > From this point of view, time evolutions of NTM island and the confinement degradation are investigated. The following models are additionally developed for simulating the NTM effect.NTM island width is calculated according to the modified Rutherford's equation which includes the effect of a perturbed bootstrap current. In order to simulate a flattening effect on the plasma pressure profile due to the magnetic island, particle and heat diffusivities for the plasma transport are assumed to be enhanced within the island width. We will perform transport simulations of JT-60U plasmas with TOPICS and will study the effect of NTM on the confinement degradation. The process for growing and saturating the magnetic island will be investigated as well.