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(OV1/1) JT-60U High Performance Regimes

S. Ishida and the JT-60 Team (see Appendix of the paper)

Japan Atomic Energy Research Institute, Naka Fusion Research Establishment, Naka-machi, Naka-gun, Ibaraki-ken, Japan

Abstract.  High performance regimes of JT-60U plasmas are presented with an emphasis upon the results from the use of a semi-closed pumped divertor with W-shaped geometry. Plasma performance in transient and quasi steady states has been significantly improved in reversed shear and high- $\beta$p regimes. The reversed shear regime elevated an equivalent Q_DT^eq transiently up to 1.25(n_D(0)$\tau_{\mathrm{E}}^{}$T_i(0) = 8.6×10²⁰m^{- 3 .} s ^. keV) in a reactor-relevant thermonuclear dominant regime. Long sustainment of enhanced confinement with internal transport barriers (ITBs) with a fully non-inductive current drive in a reversed shear discharge was successfully demonstrated with LH wave injection. Performance sustainment has been extended in the high- $\beta$p regime with a high triangularity achieving a long sustainment of plasma conditions equivalent to Q_DT^eq $\sim$ 0.16(n_D(0)$\tau_{\mathrm{E}}^{}$T_i(0) $\sim$ 1.4×10²⁰m^{- 3 .} s ^. keV) for $\sim$ 4.5 s with a large non-inductive current drive fraction of 60-70% of the plasma current. Thermal and particle transport analyses show significant reduction of thermal and particle diffusivities around ITB resulting in a strong Er shear in the ITB region. The W-shaped divertor is effective for He ash exhaust demonstrating steady exhaust capability of $\tau_{\mathrm{He}^*}^{}$/$\tau_{\mathrm{E}}^{}$ $\sim$ 3 - 10 in support of ITER. Suppression of neutral back flow and chemical sputtering effect have been observed while MARFE onset density is rather decreased. Negative-ion based neutral beam injection (N-NBI) experiments have created a clear H-mode transition. Enhanced ionization cross-section due to multi-step ionization processes was confirmed as theoretically predicted. A current density profile driven by N-NBI is measured in a good agreement with theoretical prediction. N-NBI induced TAE modes characterized as persistent and bursting oscillations have been observed from a low hot beta of < $\beta_{\mathrm{h}}^{}$ > $\sim$ 0.1 - 0.2% without a significant loss of fast ions.

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