Research on Manufacture and Enclosure Welding of ITER Correction Coils Cases

Extensive research and analysis has illustrated that there are field errors existed on ITER magnet system due to the misalignment of the coils and winding deviations from the nominal shape. To compensate the errors, correction coils (CCs) are developed and employed on ITER. The CCs consist of 6 top CCs (TCC), 6 bottom CCs (BCC) and 6 side CCs (SCC), arranged toroidally around the machine inside the PF coils and mounted on the TF coils. The CC case provides structural reinforcement to the winding packs. It is made of 316LN stainless steel and has a thickness of 20 mm. The main characteristics of the case are small section (~240 mm × 147 mm), large dimensions (~7 m) over wide angle (~60°) and large bending radius (~8 m). During the manufacture, the SCC case is divided into two L-shaped parts and the B/TCC case is a U-shaped part and a flat cover plate. Both the L-shaped part and the U-shaped part are obtained by respectively welding L-shaped sub-parts and U-shaped sub-parts which are manufactured by extrusion. During the final enclosure welding of the case, the fiber laser multi-pass welding technique with filler wire is proposed as a manufacture route due to its little deformation and narrow heat affected zone. The configuration of the enclosure welding machine, the tests for welding process parameters and the welding procedures are discussed in the paper.