Recent progress in high performance and steady-state experiments on the Japan Atomic Energy Research Institute Tokamak-60 Upgrade with W-shaped divertor

In the Japan Atomic Energy Research Institute (JAERI) Tokamak-60 Upgrade [H. Shirai and the JT-60 Team, Phys. Plasmas 5, 1712 (1998)], high performance and steady-state experiments have been conducted in the W-shaped divertor. The equivalent deuterium-tritium (D-T) fusion multiplication factor, $Q_{\mathrm{DT}}^{\mathrm{eq}},$ was enhanced transiently up to 1.25 in the reversed shear plasma. The reduction in particle diffusivity in the internal transport barriers (ITB) region of the reversed shear plasma was confirmed as well as the thermal diffusivity. It was also confirmed that the correlation length of density fluctuations is reduced inside the ITB of density. The performance with a confinement-enhancement factor (H-factor, $H_{89})$ of 2.2 and $Q_{\mathrm{DT}}^{\mathrm{eq}}$ of 0.16 was sustained in a quasi-steady-state in the high-poloidal-beta ${\mathrm{(\beta }}_p)$ and high confinement mode (H-mode) regime. The reversed shear configuration with ITBs was sustained by injecting the lower-hybrid waves combined with neutral beam injection and fully noninductive current drive in the reversed shear plasmas was realized for the first time. The driven current by the negative-ion-based neutral beam (NNB) injection increased up to 0.6 MA. The H-mode transition was triggered with the NNB injection and the H-mode with $H_{89}\text{∼1.6–1.8}$ was sustained. The toroidicity-induced Alfvén eigenmode was excited for a volume-averaged fast ion beta, ${\mathrm{〈\beta }}_h\mathrm{〉,}$ as low as ∼0.1%.