Simulation on Sawtooth Period Control in Tokamak Plasma

Abstract

The sawtooth period control is important in inductive operation of tokamak plasma because the sawteeth with long periods trigger the neoclassical tearing modes (NTMs) which reduce the plasma confinement capability significantly. We studied the effect of the sawtooth period control by the electron cyclotron current drive (ECCD) in ITER using the 1.5-dimensional transport code TOTAL. There is the optimum condition (CD direction and radial position) of ECCD for minimizing the sawtooth period. In addition, it was found that the optimum condition hardly depends on the total external heating power from 50 MW to 110 MW and the driven current from 0.5 MA to 1.0 MA. The effect of the sawtooth period control on the critical normalized beta for triggering NTMs was investigated, and it was found that the critical normalized beta increases according to increase in the driven current and ECCD can increase the margin of the normalized beta.