JT-60U high performance regimes

摘要

High performance regimes of JT-60U plasmas are presented with an emphasis upon the results from the use of a semiclosed pumped divertor with a W shaped geometry. Plasma perfor- mance in transient and quasi-steady states has been significantly improved in reversed shear and high β_p regimes. The reversed shear regime elevated an equivalent Q_DT~eq transiently up to 1.25 (nD(0)τ_E T_i(0) = 8.6 × 10~20 m~(-3)·s· keV) in a reactor relevant thermonuclear dominant regime. Long sustainment of enhanced confinement with internal transport barriers (ITBs) with fully non-inductive current drive in a reversed shear discharge was successfully demonstrated with LH wave injection. Per- formance sustainment has been extended in the high β_p regime with high triangularity, achieving a long sustainment of plasma conditions equivalent to Q_DT~eq ≈ 0.16 (n_D (0)T_ET_i(0)≈ 1.4 × 10~20 m~(-3)·s· keV) for ～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 the ITB, resulting in a strong E_r shear in the ITB region. The W shaped divertor is effective for helium ash exhaust, demonstrating a steady exhaust capability of τ_He~*/τ_E ≈ 3-10, which is favourable for ITER. Suppression of neutral backflow and chemical sputtering effects has been observed, while MARFE onset density is rather decreased. Negative ion based neutral beam injection (N-NBI) exper- iments have created a clear H mode transition. An enhanced ionization cross-section due to multistep ionization processes was confirmed as theoretically predicted. A current density profile driven by N-NBI is measured in good agreement with the theoretical prediction. N-NBI induced TAEs charac- terized as persistent and bursting oscillations have been observed from a low hot β of (β_h) ≈ 0.1-0.2% without a significant loss of fast ions.