Progress in confinement and stability with plasma shape and profile control for steady-state operation in the Japan Atomic Energy Research Institute Tokamak-60 Upgrade

This paper describes the latest achievements of the Japan Atomic Energy Research Institute Tokamak-60 Upgrade (JT-60U) [H. Kimura and the JT-60 Team, Phys. Plasmas 3, 1943 (1996)] for the establishment of the physics and technology basis for steady-state, fully noninductive current-drive plasmas with high fusion performance. Recent results are highlighted by (1) high performance reversed-magnetic-shear discharges [an idealized equivalent $Q_{\mathrm{DT}}$ of 1.05, a confinement-enhancement factor ($H$ factor) of 3.23, and a normalized beta value ${\mathrm{(\beta }}_N)$ of 1.88 at $I_p\text{=2.8\hspace{0.17em}}\mathrm{MA}{\mathrm{/P}}_{\mathrm{abs}}\text{=17\hspace{0.17em}}\mathrm{MW}$ ]; the first observation of thermal transport barriers both for electrons and ions, (2) the first injection of negative-ion-based neutral deuterium beams in the world for studies of current drive, heating, and high-energy particle behavior (achieved so far: 2.5 MW/400 keV, design values: 10 MW/500 keV); high neutralization efficiency of 60% at 370 keV; high current drive efficiency of ${\mathrm{\eta }}_{\mathrm{CD}}{\mathrm{=8\times 10}}^{\mathrm{18}}{\mathrm{\hspace{0.17em}m}}^{\mathrm{-2}}\mathrm{\hspace{0.17em}A/W},$ (3) improved giant edge-localized-mode (ELM) limit and normalized beta limit by high triangularity (δ) shaping; the quasi-steady-state ELMy plasmas with integrated high performance were sustained for 8 times the energy confinement time ($\text{δ=0.35,}$ $\text{H=2.5,}$ ${\beta }_N\text{=2.5}$ at $I_p\text{=1.5\hspace{0.17em}}\mathrm{MA}$ and $B_t\text{=3.6\hspace{0.17em}}\mathrm{T}$ ), and (4) enhanced divertor radiation and detached divertor in reversed-shear discharges with neon puffing, while the internal transport barrier was sustained.