Advances in physics understanding of high poloidal beta regime toward steady-state operation of CFETR

• Published in: Physics of plasmas 2021-04, Vol.28 (4)
• Main Authors: Qian, J. P., Garofalo, A. M., Gong, X. Z., Huang, J., Ding, S. Y., Holcomb, C. T., Hyatt, A., Ferron, J., McClenaghan, J., McKee, G., Kotschenreuther, M., Wu, M. Q., Shi, S. Y., Li, M. H., Zhu, X., Sun, Y. W., Xu, G. S., Wang, L., Chen, J. L., Zang, Q., Zhang, B., Zhang, L., Liu, H. Q., Lyu, B., Guo, W. F., Pan, C. K., Ren, Q., Li, G. Q., Wang, H. Q., Zhang, X. J., Pinsker, R. I., Staebler, G. M., Lao, L. L.
• Format: Article
• Language: English
• Subjects: 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; Plasma confinement; Plasma transport properties; Tokamaks
• ISSN: 1070-664X; 1089-7674

Experimental and modeling investigations of the high βp scenarios on the DIII-D and EAST tokamaks show advantages in high energy confinement, avoidance of n = 1 MHD, and core-edge integration with reduced heat flux, making this scenario an attractive option for CFETR steady-state operation. Experiments show that plasmas with high confinement and high density can be achieved with neutral beam injection on DIII-D (βp ~ 2.2, βN ~ 3.5, fBS ~ 50%, fGw ~ 1.0, H98y2 ~ 1.5) and pure RF power on EAST (βP ~ 2.0, βN ~ 1.6, fBS ~ 50%, fGw ~ 0.8, H98y2 > 1.3). By tailoring the current density profile, a q-profile with local (off-axis) negative shear is achieved that yields improved confinement and MHD stability. Transport analysis and simulation suggest that the combination of high density gradient and high Shafranov shift allows turbulence stabilization and higher confinement. Using on-axis ECH injection, tungsten accumulation is avoided on EAST, and this is reproduced in modeling. Reduced heat flux (by >40%) and maintenance of high core confinement is achieved with active feedback control of the radiated divertor, an important result for long pulse operation in tokamaks. In conclusion, the improved physics understanding and validated modeling tools are used to design a 1GW steady-state scenario for CFETR.