Experimental Observation of Bifurcation Nature of Radial Electric Field in CHS Heliotron/Torsatron

• Published in: Journal of Plasma and Fusion Research Vol. 75; no. 5; pp. 604 - 613
• Main Authors: FUJISAWA, Akihide, IGUCHI, Harukazu, YOSHIMURA, Yasuo, MINAMI, Takashi, TANAKA, Kenji, OKAMURA, Shoichi, MATSUOKA, Keisuke, FUJIWARA, Masami
• Format: Journal Article
• Language: English
• Published: Nagoya The Japan Society of Plasma Science and Nuclear Fusion Research 1999; Japan Society of Plasma Science and Nuclear Fusion Research
• Subjects: CHS; electric field bifurcation; flip-flop behavior; HIBP; neoclassical theory; power threshold; protuberance potential profile; repetitive transition oscillatory steady state; toroidal helical plasma
• ISSN: 0918-7928
• DOI: 10.1585/jspf.75.604

Several interesting phenomena, such as the formation of a particular potential profile with a protuberance around the core and oscillatory stationary states termed electric pulsation, have been discovered using a heavy ion beam probe in the electron cyclotron heated plasmas of the CHS. This paper presents experimental observations which indicate that bifurcation of the radial electric field is responsible for such phenomena; existence of an ECH power threshold to obtain the profile with a protuberance, and its striking sensitivity to density. In particular, flip-flop behavior of the potential near the power threshold clearly demonstrates bifurcation characteristics. Bifurcation of radial electric field in neoclassical theory is presented, and its qualitative expectation is discussed in the bifurcation phenomena. The neoclassical transition time scale between two bifurcative states is compared with the experimental observations during the electric pulsation. It is confirmed that the neoclassical transition time is not contradictory with the experimental one.