Observation of a beam-driven low-frequency mode in Heliotron J. (14th March 2019)

• Record Type: Journal Article
• Authors: Zang, L.G.; Yamamoto, S.; Spong, D.A.; Nagasaki, K.; Ohshima, S.; Kobayashi, S.; Minami, T.; Lu, X.X.; Nishino, N.; Kado, S.; Adulsiriswad, P.; Okada, H.; Kenmochi, N.; Inagaki, S.; Zhu, J.X.; Weir, G.M.; Mizuuchi, T.; Konoshima, S.; Ishizawa, A.; Yu, D.L.; Shi, Z.B.; Liu, Yi; Yan, L.W.; Li, J.Q.; Yang, Q.W.; Xu, M.; Duan, X.R.; Liu, Yong
• Is Part Of: Nuclear fusion. Volume 59:Number 5(2019:May)
• Publication Date: 2019-03-14
• Subjects: Heliotron J -- STELLGAP -- stellarator/heliotron -- gas puff imaging -- BAE -- GAE; Nuclear fusion -- Periodicals; 621.48405
• DOI: 10.1088/1741-4326/ab0197
• Languages: English
• ISSNs: 0029-5515

Abstract

Abstract: A low-frequency electromagnetic mode (LF-mode) has been observed in a stellarator/heliotron device, Heliotron J. The LF-mode is observed only in neutral beam heated plasmas with a co-current, which increases the rotational transform. The observed LF-mode peaks at rho = 0.86–0.91, where rho = r / a is the normalized minor radius. The LF-mode propagates in the ion diamagnetic drift direction, and the poloidal mode number is m ~ 6–8, determined with a combination of Mirnov coil arrays and 2D fast camera measurement. A high m number induces significant Doppler shift from the background ion flow. The frequency is corrected with both E × B rotation and the ion diamagnetic flow. The corrected frequency is almost consistent with the beta-induced Alfvén eigenmode gap evaluated with the STELLGAP code, although very close to the accumulation point. The mode could also be a global Alfvén eigenmode.