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(EX/P2-08) Property of Internal Transport Barrier Formation in JT-60U

Y. Sakamoto¹⁾, T. Suzuki¹⁾, S. Ide¹⁾, Y. Koide¹⁾, H. Takenaga¹⁾, Y. Kamada¹⁾, T. Fujita¹⁾, T. Fukuda¹⁾, T. Takizuka¹⁾, H. Shirai¹⁾, N. Oyama¹⁾, Y. Miura¹⁾, K.W. Hill²⁾, G. Rewoldt²⁾, JT-60 Team^1)
 
1) Naka Fusion Research Establishment, Japan Atomic Energy Research Institute, Naka-machi, Ibaraki-ken, Japan
²⁾ Princeton Plasma Physics Laboratory, Princeton, New Jersey, U.S.A

Abstract.  Response of the ion thermal diffusivity ( $\chi_{i}$) to the radial electric field ( E_r) shear has been investigated in JT-60U and the following results were found. (1) In the case of positive magnetic shear (PS) plasma, $\chi_{i}$ in the core region shows L mode state, weak internal transport barrier (ITB), and strong ITB depending upon the heating power. In the case of reversed magnetic shear (RS) plasma, however, no power degradation of $\chi_{i}$ is observed. (2) In the case of weak ITB, $\chi_{i}$ decreases gradually with increasing the E_r shear for both PS and RS plasmas. There exists a threshold of an effective E_r shear to change its state from weak to strong ITBs. (3) The threshold of the effective E_r shear in the case of RS plasma is small compared with that in the case of PS plasma.

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