Strategy and experimental progress of the EXL-50U spherical torus in support of the EHL-2 project

• Published in: Plasma science & technology Vol. 27; no. 2; pp. 24003 - 24013
• Main Authors: SHI, Yuejiang, SONG, Xianming, GUO, Dong, JIANG, Xinchen, GU, Xiang, DONG, Lili, WANG, Xueyun, SUN, Tiantian, TAN, Muzhi, CHEN, Zhengyuan, YANG, Guang, YANG, Danke, XIE, Huasheng, ZHAO, Hanyue, LIU, Yong, TAO, Renyi, LI, Jia, LI, Songjian, GAO, Fan, ZHAO, Yihang, ZHANG, Yupeng, ZHANG, Cong, HE, Hongda, YANG, Enwu, YANG, Yuanming, WANG, Yu, SONG, Shaodong, HAN, Lei, XING, Bo, LI, Pengmin, WANG, Zhenxing, ZHOU, Peihai, LUO, Wenwu, WANG, Yumin, LIU, Bing, WU, Chao, ZHAO, Xin, LIANG, Yunfeng, DONG, Jiaqi, YUAN, Baoshan, PENG, Y-K Martin, LIU, Minsheng, Team, the EXL-50U
• Format: Journal Article
• Language: English
• Published: Plasma Science and Technology 01.02.2025
• Subjects: EHL-2; EXL-50U; spherical torus
• ISSN: 1009-0630; 2058-6272
• DOI: 10.1088/2058-6272/ad9e8f

The EXL-50U is China’s first large spherical torus device with a toroidal field reaching 1 T. The major radius of the EXL-50U ranges from 0.6 m to 0.8 m, with an aspect ratio of 1.4−1.8. The goal of plasma current in the first experimental phase is 500 kA, and in the future second phase, the goal of plasma current is 1 MA. On the EXL-50U project, the ENN fusion team expeditiously accomplished a series of comprehensive tasks including physical and engineering design, main component construction installation, and system commissioning, all within a mere eighteen-month timeframe. In the experiments of 2024, the EXL-50U achieved a 500 kA limiter configuration discharge using ECRH (Electron Cyclotron Resonance Heating) for non-inductive current start-up and a current ramp-up with the synergetic effect of ECRH and central solenoid (CS). Preliminary divertor configuration plasmas were also obtained under 200 kA plasma current. The core ion temperature of 1 keV was achieved with low-power NBI heating, and the energy confinement time of 30 ms was reached with Ohmic heating in the flat-top phase. The current and future experiments of EXL-50U will strongly support the physical design and operational scenarios of EHL-2 in the areas of current drive, high ion temperature exploration, energy transport and confinement, and hydrogen-boron physical characteristics. At the same time, the experience in the design, construction, and commissioning of the engineering, heating, and diagnostics systems on EXL-50U is also very beneficial for enhancing the feasibility of the engineering design for EHL-2.