Experimental study of non-inductive current start-up using electron cyclotron wave on EXL-50 spherical torus

• Published in: Plasma physics and controlled fusion 2022-07, Vol.64 (7), p.75006
• Main Authors: Wang, Mingyuan, Guo, Dong, Shi, Yuejiang, Chen, Bo, Liu, Bing, Song, Shaodong, Zhao, Xin, Song, Yunyang, Liu, Wenjun, Guan, Yupeng, Banerjee, Debabrata, Li, Songjian, Sun, Tiantian, Li, Yingying, Tian, Xiaomin, Zhu, Yubao, Song, Xianming, Dong, Jiaqi, Yuan, Baoshan, Martin Peng, Y-K
• Format: Article
• Language: English
• Subjects: electron-cyclotron-wave; EXL-50; non-inductive current start-up; preferential confinement of collisionless tail electron currents
• ISSN: 0741-3335; 1361-6587
• DOI: 10.1088/1361-6587/ac70fb

Although experiments have demonstrated a feasibility of the electron-cyclotron-wave (ECW) non-inductive current start-up, the physical mechanism of the current start-up remains unclear, particularly the role of the preferential confinement of collisionless tail electron currents ( j TPC ) and vertical charge-separation currents ( j VTF ) . Therefore, j TPC and j VTF were observed using limiter probes during the ECW non-inductive current start-up on an ENN XunLong-50 (EXL-50) spherical torus to understand the significance of these values. It was found that j TPC increased and j VTF decreased during start-up, indicating a dominant role played by j TPC in this process. Furthermore, it was found that the product of the gas pressure and vertical magnetic field has a limit for the ECW non-inductive current start-up. Finally, we found that the ECW non-inductive current start-up can be realized only for sufficiently low vertical fields and gas pressures in EXL-50.