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(EX4/1) Sustainment of High Confinement in JT-60U Reversed Shear Plasmas

T. Fujita¹⁾, Y. Kamada¹⁾, S. Ide¹⁾, S. Takeji¹⁾, Y. Sakamoto¹⁾, A. Isayama¹⁾, T. Suzuki¹⁾, T. Oikawa¹⁾, T. Fukuda^1)
 
1) Japan Atomic Energy Research Institute, Naka Fusion Research Establishment, Naka-machi, Ibaraki-ken, Japan

Abstract.  Experimental results towards long sustainment of JT-60U reversed shear plasmas, where high confinement is achieved owing to strong internal transport barriers (ITBs), are reported. In a high current plasma with an L-mode edge, deuterium-tritium-equivalent fusion power gain, Q_DT^eq = 0.5 was sustained for 0.8 s ($\sim$ energy confinement time) by adjusting plasma beta precisely using feedback control of stored energy. In a high triangularity plasma with an ELMy H-mode edge, the shrinkage of reversed shear region was suppressed and quasi steady sustainment of high confinement was achieved by raising the poloidal beta and enhancing the bootstrap current peaked at the ITB layer. High bootstrap current fraction ($\sim$ 80%) was obtained in a high q regime ( q₉₅ $\sim$ 9), which leaded to full non-inductive current drive condition. The normalized beta ( $\beta_{\mathrm{N}}^{}$) of $\sim$ 2 and H-factor of H₈₉ $\sim$ 3.5 ( HH_98y2 $\sim$ 2.2) were sustained for 2.7 s ($\sim$ 6 times energy confinement time).

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