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(EX6/6) Observation of Bifurcation Property of Radial Electric Field Using a Heavy Ion Beam Probe in CHS

A. Fujisawa¹⁾, H. Iguchi¹⁾, T. Minami¹⁾, Y. Yoshimura¹⁾, H. Sanuki¹⁾, K. Itoh¹⁾, M. Isobe¹⁾, C. Suzuki¹⁾, S. Nishimura¹⁾, K. Tanaka¹⁾, M. Osakabe¹⁾, I. Nomura¹⁾, K. Ida¹⁾, S. Okamura¹⁾, K. Toi¹⁾, S. Kado¹⁾, R. Akiyama¹⁾, A. Shimizu¹⁾, C. Takahashi¹⁾, M. Kojima¹⁾, K. Matsuoka¹⁾, Y. Hamada¹⁾, M. Fujiwara^1)
 
1) National Institute for Fusion Science, Oroshi-cho, Toki, Japan 509-5292

Abstract.  Bifurcation nature of potential profile of a toroidal helical plasma is investigated in the Compact Helical System (CHS), using a heavy ion beam probe. The measurements reveal that there exist three main branches of potential profiles in electron cyclotron resonance (ECR) heated plasmas with low density of n_e $\sim$ 0.5×10¹³cm^{- 3}. The branches with higher central potential exhibit a rather strong radial electric field shear that should result in fluctuation reduction and formation of transport barrier. Lissajous expression is useful to extract the bifurcation characteristics of potential structure.

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