Design and manufacturing of thermal shield for JT-60SA

The thermal shield (TS) of JT-60SA which is a superconducting tokamak, is installed to reduce radiation heat load from a vacuum vessel (VV), a cryostat vessel and ports at ambient temperature to superconducting coils at 4 K. The TS is double walled structure with He cooling pipe at 80 K, and is divided electrically in toroidal direction and poloidal direction to suppress eddy currents flowing through the TS during disruption. The TS is required to be installed in a narrow space which is between the VV, the ports, and the superconducting coils. Manufacturing and assembly accuracy of the TS are required to ensure the sufficient space for the relative displacement caused by thermal displacement and seismic load. Customization of mechanical joints in the divided section of the TS is effective process for keeping the required accuracy. Assembly of 340 ° sector of the vacuum vessel thermal shield has been completed

Manufacturing and welding assembly of the vacuum vessel on JT-60SA

The JT-60SA Vacuum Vessel (VV) was manufactured as the 10 sectors split in the factory and these sectors were weld-assembled as the 360-degree torus with the design offset value of the weld shrinkage. The dimensions as the 10 m scale torus were well controlled regardless of the thin wall thickness of 18 mm and a large amount of welding line due to the double wall structure and 72 port penetrations. The final VV 20-degree sector was installed into the 340-degree sector of the tokamak with the TF coil and the VV Thermal Shield, and the VV was weld-jointed as a torus. This paper reports the design concept to reduce the safety factor and welding amount to achieve the dimension specified, and the result of the VV manufacturing

JT-60SA TF magnet assembly

JT-60SA will be the world’s largest superconducting tokamak when it is assembled in 2020 in Naka, Japan(R = 3 m, a = 1.2 m). It is being constructed jointly by institutions in the EU and Japan under the BroaderApproach agreement. The assembly of its 400-tonne toroidalfield (TF) magnet, designed for an on-axisfield of2.25 T, was completed in July 2018. Consideration of its assembly throughout the design process, with asso-ciated consultation and testing, allowed high positional accuracy and hence respect for magneticfield tolerancesto be achieve