Achievement of precise assembly of the JT-60SA superconducting tokamak

•We have achieved important mile stone for this project at the end of March 2020 taking about seven years since 2013. Namely, the tokamak main assembly has been successfully completed. In this assembly, high accuracy of millimeter order was realized with respect to huge and heavy components.•Vacuum vessel final sector: The welding contraction was predicted and compensated to achieve the required high precision (typically ±10 mm and ±20 mm at the inboard and outboard walls, respectively).•Central solenoid: The CS insertion was successfully done even with a minimum clearance between the TF coils in-bore and the CS outer surfaces of 14 mm by using the laser tracker measurement in real time. Finally, a precise centring of the magnetic axis within ±1.4 mm with a vertical tilt of 1.6 mm was achieved.•Top-CTS and CTL: In order to accelerate these pre-assemblies keeping to the schedule, a stage with two levels was introduced for up-down works. Finally, this made one month acceleration.•In-vessel components: For precise assembly aiming to avoid unacceptable local heat load, its interface facing to the wavy VV surface were precisely machined based on the VV surface measured by the laser tracker with the T-probe. An accuracy of the graphite tile surface alignment within ±1 mm has been achieved. The JT-60 Super Advanced (JT-60SA) tokamak was constructed with very tight tolerances for assembly and handling of heavy components in an enclosed space. Millimetre-order precision was required for the tokamak assembly, not only to avoid mechanical interference, but also to obtain good plasma performance by keeping the magnetic error field low. This effort entailed the development of numerous unique procedures. This paper reports on these procedures, focusing on assembly and testing of the final sector of the vacuum vessel, the central solenoid, top parts of the tokamak, and the in-vessel components.