Solenoid-free current drive via ECRH in EXL-50 spherical torus plasmas. (1st August 2022)

• Record Type: Journal Article
• Authors: Shi, Yuejiang; Liu, Bing; Song, Shaodong; Song, Yunyang; Song, Xianming; Tong, Bowei; Cheng, Shikui; Liu, Wenjun; Wang, Mingyuan; Sun, Tiantian; Guo, Dong; Li, Songjian; Li, Yingying; Chen, Bin; Gu, Xiang; Cai, Jianqing; Luo, Di; Banerjee, Debabrata; Zhao, Xin; Yang, Yuanming; Luo, Wenwu; Zhou, Peihai; Wang, Yu; Ishida, Akio; Maekawa, Takashi; Liu, Minsheng; Yuan, Baoshan; Martin Peng, Y.-K.; the EXL-50 Team,
• Is Part Of: Nuclear fusion. Volume 62:Number 8(2022)
• Publication Date: 2022-08-01
• Subjects: spherical torus -- solenoid-free current drive -- ECRH; Nuclear fusion -- Periodicals; 621.48405
• DOI: 10.1088/1741-4326/ac71b6
• Languages: English
• ISSNs: 0029-5515

Abstract

Abstract: As a new spherical tokamak designed to simplify the engineering requirements of a possible future fusion power source, the EXL-50 experiment features a low aspect ratio vacuum vessel (VV), encircling a central post assembly containing the toroidal field coil conductors without a central solenoid. Multiple electron cyclotron resonance heating (ECRH) resonances are located within the VV to improve current drive effectiveness. Copious energetic electrons are produced and measured with hard x-ray detectors, carry the bulk of the plasma current ranging from 50–150 kA, which is maintained for more than 1 s duration. It is observed that over one ampere current can be sustained per watt of ECRH power issued from the 28 GHz gyrotrons. The plasma current reaches I p > 80 kA for high density (>5 × 10 18 m −2 ) discharge with 150 kW ECRH. An analysis was carried out combining reconstructed multi-fluid equilibrium, guiding-center orbits of energetic electrons, and resonant heating mechanisms. It is verified that in EXL-50 a broadly distributed current of energetic electrons creates a smaller closed magnetic-flux surface of low aspect ratio that in turn confines the thermal plasma electrons and ions and participate in maintaining the equilibrium force balance.