High performance and steady-state experiments on JT-60U

Progress of high performance and steady-state experiments on JT-60U during last two years are summarized in this paper. JT-60U research for steady-state with high fusion performance was focused to contribute to ITER physics R and D in the recent years. Experiments of the negative-ion based neutral beam injection (N-NBI) have indicated a high neutralization efficiency of 60% at 370 keV and high current drive efficiency of η CD=8×10¹⁸ m^-2 A/W. The toroidicity-induced Alfven eigenmodes (TAE modes) excited by N-NBI was observed at the first time. The divertor was modified from the open divertor to the W-shaped pumped divertor in Feb.-May, 1997. In the new pumped divertor, the radiative divertor by neon and deuterium injection with high recycling enhanced the divertor radiation during the ELMy H-mode. Efficient He exhaust was demonstrated with helium pumping in ELMy H-mode discharges. The halo current was measured in the new divertor and the new database was added for ITER. A high equivalent Q _DT of 1.05 was achieved in the high performance reversed-magnetic-shear discharge. A quasi-steady reversed shear plasma with an internal transport barrier and H-mode edge was sustained for 4.3 s. High triangularity shaping was effectively for improvement of the giant ELM limit and β_N. Steady-state high performance in the ELMy H-mode was sustained for 9 s with the new divertor