Present status of JT-60 upgrade

In the JT-60 tokamak, the original outer single-null plasma containment vacuum vessel and poloidal field coils, will be exchanged with those of large D-shaped cross sections. The basic dimensions of the new vessel will allow plasmas of 6-MA current, 70 to 100 m³ volume, and vertical elongations of 1.4 to 1.7. Installation of a large vessel is made possible at the cost of high toroidal ripple volume in the space occupied by the plasma and at the cost of high electromagnetic force acting on the coils and the vessel. A prime requirement for the modification is maximizing the plasma performance with minimum expense, while ensuring access to the plasma for heating and diagnostics. The plasma configuration is designed to allow the largest D-shape discharge with a lower single null, within the boundary of the original toroidal field coils. The D-shaped vessel is designed according to a new concept of Inconel 625 all-welded continuous chamber in a double skin construction. Rectangular tubes are sandwiched by three-dimensionally curved skins to form a totally everywhere rounded vacuum vessel. The gas is being changed to deuterium from hydrogen, which will allow neutral beams of 40 MW. The lower hybrid and ion-cyclotron systems will be provided with larger antennas