Advances in JT-60U facilities and its operation

Recent advances in the JT-60 upgrade (JT-60U) facilities are described which have been made for supporting various physics programs aiming at obtaining reactor-grade plasmas with higher performance in quasi-steady state. It has been proved that B₄C-converted (0.3 mm thick) carbon fiber composite (CFC) graphite divertor tiles and decaborane-based boronization using a mixture of deuterium and helium as working gas of a glow discharge are effective for wall conditioning. For improving the confinement and edge plasma characteristics, the operation of divertor plasmas with a shape of high triangularity in excess of 0.4 has been started. Feedback control of neutron production by NBI injection has been demonstrated for establishment of advanced plasma control in steady state operation. With regard to the heating systems, the increase in the NBI beam power up to 36 MW has accelerated the progress in the JT-60U plasma performance and the increase in the ICRF power up to 6.4 MW has progressed the studies on fast ion behavior, especially the TAE mode since 1994. Although ten years passed since the first plasma of the JT-60, the integrity of its main facilities has been kept by good maintenance activities. Moreover, the JT-60U operational efficiency has been much improved by the above advances of the facilities, which has given rise to remarkable progress in the JT-60U plasma performance has been successfully obtained. Two important developments of a negative-ion-based NBI system with beam energy of 500 keV and injection power of 10 MW and an advanced closed pumped divertor are now in progress towards steady-state operation with high performance