Solenoid-free current drive via ECRH in EXL-50 spherical torus plasmas
Abstract
As a new spherical tokamak (ST) designed to simplify engineering requirements of a possible future fusion power source, the EXL-50 experiment features a low aspect ratio (A) 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 50kA to 150kA, which is maintained for more than 1s duration. It is observed that over one Ampere current can be maintained per Watt of ECRH power issued from the 28-GHz gyrotrons. The plasma current reaches Ip>80kA for high density (>5e18me-2) discharge with 150kW ECHR heating. 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 smaller closed magnetic-flux surfaces of low aspect ratio that in turn confine the thermal plasma electrons and ions and participate in maintaining the equilibrium force-balance.
Keywords
Cite
@article{arxiv.2104.14844,
title = {Solenoid-free current drive via ECRH in EXL-50 spherical torus plasmas},
author = {Yuejiang Shi and Bing Liu and Shaodong Song and Yunyang Song and Xianming Song and Bowei Tong and Shikui Cheng and Wenjun Liu and Minyuan Wang and Tiantian Sun and Dong Guo and Songjian Li and Yingying Li and Bin Chen and Xiang Gu and Jianqing Cai and Di Luo and Debabrata Banerjee and Xin Zhao and Yuanming Yang and Wenwu Luo and Peihai Zhou and Yu Wang and A. Ishida and T. Maekawa and Minsheng Liu and Baoshan Yuan and Y-K Martin Peng},
journal= {arXiv preprint arXiv:2104.14844},
year = {2025}
}