Objectives of the JT-60 research are to establish the physics basis for a steady-state tokamak fusion reactor and to contribute to the ITER physics R&D. Significant progress in key issues such as improved confinement, radiative divertor and non-inductive current drive (CD) was achieved on JT-60U in the recent years.

In 1996, improved confinement regimes with reversed shear and high-b_p H-mode were developed, through deliberate discharge optimization including the current profile control. Efficient steady-state operation is possible with high bootstrap current fraction in high-b_p regime. Therefore, confinement studies in JT-60U are focused on the improved confinement in high-b_p regime. This effort produced the high-b_p H-mode with the highest fusion triple product of 1.5 x 10²¹ m^-3 s keV with the world record of ion temperature, 45 keV.

The reversed shear configuration is one of the leading scenarios for a steady-state tokamak operation. An advanced steady-state operation scenario relies on a large fraction of the bootstrap current being driven by the steep pressure gradient in the middle of the plasma minor radius. In the high performance experiment with the reversed shear configuration, equivalent conditions for break-even in thermonuclear fusion regime were achieved with the JT-60U record of stored energy, 10.9 MJ at I_p=2.8 MA; the calculated fusion amplification factor QDT_eq reached 1.05 in an assumed deuterium-tritium fuel. In the most of the reversed shear discharges, the b_p collapse occurs and the b-value is limited. To clarify the feature of the MHD stability is an important issue to achieve higher plasma performance and the quasi-steady-state operation.

To establish steady-state tokamak operation, experimental efforts are placed on non-inductive current drive with the negative-ion based NB (N-NB) current drive and bootstrap current utilization. The N-NBI system with a beam energy of 0.5 MeV and total beam power of 10 MW was installed in 1996. Current drive by N-NBI (350 keV, 2.5 MW) was initially examined by injecting N-NB into partially current-driven discharges by the positive-ion based NB at I_p=1.0 MA. The NB driven current of 0.28 MA and the CD efficiency of ~0.8 x 10¹⁹ m^-2A/W was predicted by ACCOME code. This result indicates an effectiveness of N-NBI as a core heating and current drive method in reactor relevant plasma. NBCD and current profile control by N-NBI will be applied to sustain the quasi-steady-state operation with the reversed shear configuration.

The divertor was modified from the open divertor to the W-shaped pumped divertor in May, 1997. The inclined target divertor with a dome was adopted because of its effectiveness in achieving dense and cold divertor plasmas, and baffling the back flow of neutral particles. The neutral particles will be exhausted through the inner gap between the divertor plates and the dome. In the open divertor, it was demonstrated that the improved core plasma confinement in the reversed shear plasmas was compatible with the high recycling and radiative boundary plasma by hydrogen and neon gas puffing for the first time in JT-60U. In the new pumped divertor, radiative divetor with high recycling is promising to be compatible with the improved confinement in the reversed shear and ELMy H-mode plasmas by baffling neutral particles (deuterium and neon).