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

   
H. Shirai , M. Kikuchi , T. Takizuka , T. Fujita , Y. Koide , G. Rewoldt ¹, D. Mikkelsen ¹, R. Budny ¹, W. M. Tang ¹, 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 $E_{\mbox{r}}$ 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 $E_{\mbox{r}}$ shear, $dE_r/dr$, is not so strong. The box type ITB has a very strong $E_{\mbox{r}}$ shear at the thin ITB layer and the $\chi$ value decreases to the level of neoclassical transport  there. The estimated $E\times B$ 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 $E_{\mbox{r}}$ shear and the strong $E_{\mbox{r}}$ shear contributes to the reduced thermal diffusivity.

     

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