Evaluation of ECCD power requirement for neoclassical tearing modes suppression in the CFETR hybrid scenario

Abstract

The optimal minimum ECCD power is evaluated numerically for completely suppressing the 3/2 and 2/1 NTMs in the CFETR hybrid scenario. For two typical frequencies of ECCD sources launching from two upper launcher (UL) ports, fec = 210 GHz and 240 GHz with O1-mode, UL1: (Ri, Zi) = (8.47, 5.7) m and UL2: (Ri, Zi) = (8.2, 4.5) m, higher frequency of ECCD source launching from the UL2 port is better than that low frequency counterpart from the UL1 port. Using 240 GHz ECCD source launching from the UL2 port, the minimum power required to fully suppress the two NTMs with precise ECCD alignment is 12.4 MW and 16.7 MW, respectively. When good alignment cannot be achieved, the results suggest that the misalignment should not exceed 0.02a, preferably 0.015a, corresponding to 4.4 cm and 3.3 cm. Considering engineering difficulty of high-frequency gyrotron sources, the optimal minimum ECCD power with the 210 GHz source launching from the UL2 port is 17.9 MW and 20.6 MW for completely suppressing the 3/2 and 2/1 NTMs, respectively. In view of this, it is a good choice to select the 210 GHz ECCD source launching from the UL2 port in the short and medium term.