Assembly of the ITER tokamak

Significant issues for assembly of ITER are derived from the large size and mass of components, and associated tight installation tolerances. Critical tolerances are driven by; minimization of non-axisymmetric error fields of the magnet system, and alignment of the plasma facing components with the toroidal magnetic field. Error fields resulting from magnet shape and location tolerances must be <~10^-4 of the toroidal field to allow the correction coil system to adequately compensate. Installation tolerances on the limiter, divertor, and blanket first wall are driven by a requirement to distribute heat loads to acceptable values during off-normal plasma events. Specialized tooling is designed for installation of large subassemblies. The largest consists of a toroidal field (TF) coil, a thermal shield segment, and a vacuum vessel (VV) segment. These components are pre-assembled on a subassembly tool and installed with the 1500 tonne dual-crane system. Position tolerances of ±2 mm at the TF coil inboard leg are held using customized shims and adjustable guides. The most severe requirement for assembly is controlling and compensating for weld distortion in field joints of the VV and the blanket backplate (BP). Blanket modules must be aligned with the toroidal field lines to tolerances of ±3 mm in the most critical locations. These modules are installed after completion of the final BP welds to allow a post-weld survey of mounting points using the optical metrology system (OMS)