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(EX5/4) Reduced Transport and E_R Shearing in Improved Confinement Regimes in JT-60U

H. Shirai, M. Kikuchi, T. Takizuka, T. Fujita, Y. Koide, G. Rewoldt¹, D. Mikkelsen¹, R. Budny¹, W. M. Tang¹, Y. Kishimoto, Y. Kamada, T. Oikawa, O. Naito, T. Fukuda, N. Isei, Y. Kawano, M. Azumi and the JT-60 Team

Japan Atomic Energy Research Institute Naka-machi, Naka-gun, Ibaraki-ken, 311-0193 Japan
¹ Princeton Plasma Physics Laboratory, Princeton, New Jersey, 08543 USA

Abstract.  The global confinement and the local transport properties of improved core confinement plasmas in JT-60U have been studied in connection with E_r shear formation. The improved core confinement mode with ITB, the internal transport barrier, is roughly classified into ``parabolic'' type ITBs and ``box'' type ITBs. The parabolic type ITB has the reduced thermal diffusivity, $\chi$, in the core region; however, the E_r shear, dE_r/dr, is not so strong. The box type ITB has a very strong E_r shear at the thin ITB layer and the $\chi$ value decreases to the level of neoclassical transport there. The estimated E×B shearing rate, $\omega_{E\times B}^{}$, becomes almost the same as the linear growth rate of the drift microinstability, $\gamma_{L}^{}$, at the ITB layer in the box type ITB. Experiments of hot ion mode plasmas during the repetitive L-H-L transition shows that the thermal di usivity clearly depends on the E_r shear and the strong E_r shear contributes to the reduced thermal diffusivity.

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