Divertor impurity seeding with a new feedback control scheme for maintaining good core confinement in grassy-ELM H-mode regime with tungsten monoblock divertor in EAST

作者：Guosheng Xu, Qiping Yuan, Kedong Li, Liang Wang, J.C. Xu, Qingquan Yang, Yanmin Duan, L.Y. Meng, Zengyin Yang, F. Ding, J.B. Liu, Huan Guo, H.Q. Wang, D. Eldon, Y.Q. Tao, Kai Wu, N. Yan, Rui Ding, Yifeng Wang, Y. Ye, Ling Zhang, Tao Zhang, Qing Zang, Yingying Li, Haiqing Liu, Guozhang Jia, Xiaoju Liu, Hang Si, Erzhong Li, Long Zeng, J.P. Qian, S. Y. Lin, Liqing Xu, Huihui Wang, Xianzu Gong, Baonian Wan · 发表于：Nuclear Fusion · 年份：2020 · DOI：10.1088/1741-4326/ab91fa · 被引用次数：62 · 研究领域：Magnetic confinement fusion research、Fusion materials and technologies、Laser-Plasma Interactions and Diagnostics

Abstract Small perturbations and strong impurity exhaust capability associated with the small grassy ELMs render the grassy-ELM regime a suitable candidate for achieving steady-state H-mode operation with a radiative divertor, especially in a metal-wall device, such as the Experimental Advanced Superconducting Tokamak (EAST). As the degradation of pedestal performance with excessive divertor impurity seeding or accumulation tends to be accompanied with significantly increased radiation near the divertor X point, feedback control of the absolute extreme ultraviolet (AXUV) radiation near the X point has been employed to maintain the confinement property in EAST. However, the absolute value of the AXUV radiation at the outer target varies with plasma conditions as during the divertor detachment process. Thus, a new feedback-control scheme has been recently developed and applied to grassy-ELM H-mode plasmas in EAST to achieve stationary partial detachment while maintaining good global energy confinement with H 98,y2 >1. In this scheme, electron temperatures ( T et ) measured by divertor Langmuir probes are used to identify the onset of detachment, and then the plasma control system (PCS) switches to the feedback control of one channel of AXUV radiation near the X point, where a steep gradient in the radiation profile is present. The feedback is performed through pulse-width-modulated duty cycle of a piezo valve to seed impurities with mixed gas (50% Ne and 50% D 2 ) from the o...