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Progress of High-Beta Experiments in Stellarator/Heliotron

Kiyomasa Y. Watanabe, Arthur Weller, Satoru Sakakibara, Yoshiro Narushima, Satoshi Ohdachi, Kazumichi Narihara, Kenji Tanaka, Katsumi Ida, Kazuo Toi, Hiroshi Yamada, Yasuhiro Suzuki, Osamu Kaneko, Large Helical Device Experimental Group, Wendelstein 7-AS Experimental Group

Fusion Science and Technology / Volume 46 / Number 1 / July 2004 / Pages 24-33

Technical Paper / Stellarators /

Recently, dramatic progress has been achieved in the study of helical systems with high-beta experiments. Discharges with more than 3% beta plasmas have been achieved in Large Helical Device (LHD) and Wendelstein 7-AS (W7-AS). Although magnetohydrodynamic (MHD) instabilities affect local pressure gradients, the global transport property does not seem to limit the achieved beta value in either device. We summarize the LHD high-beta properties in MHD stability, equilibrium, and transport, and we show the relationship between the experimentally achieved parameters and theoretical predictions. We contrast the LHD results with the W7-AS high-beta properties. In both devices, stationary discharges in the definitely MHD unstable region have not been observed. We mention the key issue for achievement of the beta values >5%.

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