Suppression of non-axisymmetric field-induced α-particle loss channels in a quasi-axisymmetric stellarator

• Published in: AIP advances 2022-05, Vol.12 (5), p.055214-055214-10
• Main Authors: Zhang, Yichao, Liu, Haifeng, Huang, Jie, Xu, Yuhong, Zhang, Jian, Shimizu, Akihiro, Satake, Shinsuke, Isobe, Mitsutaka, Wang, Xianqu, Cheng, Jun, Liu, Hai, Zhang, Xin, Tang, Changjian
• Format: Article
• Language: English
• Subjects: Channels; Configurations; Confinement; Drift; Energetic particles; Fusion reactors; Mathematical analysis; Multiple objective analysis; Optimization; Position (location); Stellarators
• ISSN: 2158-3226; 2158-3226
• DOI: 10.1063/5.0079827

In future fusion reactors, the confinement of α-particles is a crucial issue. The perfect omnigenity may be difficult to achieve in the quasi-isodynamic and quasi-symmetric stellarators when a multi-objective optimization is considered. Non-axisymmetric field can result in collisionless particles’ transport via localized trapping by ripples. Specific loss channels have been revealed to essentially exist in quasi-axisymmetric stellarators [Yang et al., Europhys. Lett. 129, 35001 (2020)] and W7-X [J. M. Faustin et al., Nucl. Fusion 56, 092006 (2016)]. It indicates a drastic loss of collisionless ions through these channels. This paper is devoted to investigate the effects of axisymmetry-breaking magnetic fields on collisionless α-particle transport in the CFQS (Chinese First Quasi-axisymmetric Stellarator) -like reactor configuration. A semi-analytic representation of radial and poloidal drifts in Boozer coordinates is given, by which we found an effective route to mitigate α-particle losses, i.e., adjusting the location of the quasi-axisymmetric radial position. Such a route enables the enhancement of the poloidal drift and decrease of radial drift in peripheral regions of the identified loss channels. The particles launched inside the quasi-axisymmetric radial surface can be well confined because localized particles that may fall in loss channels can transit into blocked particles near the quasi-axisymmetric surface, escaping from loss channels, which is beneficial for the improvement of the particle confinement. Moreover, this paper may provide a set of proxy functions for suppression of energetic particle losses to optimize stellarator configurations.