Numerical Analysis of Neoclassical Tearing Mode Stabilization by Electron Cyclotron Current Drive

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Neoclassical tearing mode (NTM) stabilization by an electron cyclotron current drive (ECCD) has been studied by using the numerical model on the basis of the modified Rutherford equation coupled with the 1.5 D transport code and the EC code. The transport code solves the current diffusion equation, including the EC current profile. The background current modification and the resultant movement of rational surface by ECCD are taken into account. The EC code consists of the ray tracing method and the Fokker-Planck calculation. Undetermined parameters in themodified Rutherford equation are estimated from a comparison with the JT-60U experiments. Sensitivity of stabilization to the EC current location is investigated by simulation. The low EC current and peaked EC current profile mitigatesthe sensitivity, whereas the high EC current and peaked EC current profile moves the rational surface more largely via background current modification by the EC current and intensifies the sensitivity. The high EC current and broad EC current profile mitigates the sensitivity. The EC current necessary for the full stabilization is studied for ITER parameters. The necessary EC current strongly depends on the parameters of bootstrap current and ECCD terms in the modified Rutherford equation. Necessary ECCD power on ITER is evaluated on the basis of parameters estimated from comparisons with JT-60U experiments.


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