Manufacture and installation of JET MKII divertor support structure

The water cooled support structure, comprising twenty-four modules is the main component of the JET MKII divertor system. It is to be installed in the vacuum vessel with high accuracy with respect to the magnetic centre and the other in-vessel components. The paper describes the design and manufacturing cycle including the required tolerances, the assembly and installation method and the material production process required to ensure the accuracy and reliability of the MKII support structure system. The water cooling holes, machined into the support structure require the procurement of special material to prevent risks of leaks inside the vacuum vessel. The design of the support system had to be such that minimal modifications to the existing in-vessel structures were required. A detailed tolerance analysis identified the accuracy required at each stage and helped in establishing a suitable manufacturing and assembly process. Major attention was given to the design and manufacturing of the joints between the modules which, due to access restrictions in the vessel, can only be assembled from one side. A tight tolerance of the joint components to ensure mechanical integrity and stiffness of the module joints is opposed by the necessity to have a realistic assembly tolerance. The pre assembly of the whole ring of modules at the manufacturers' works, which is a rehearsal of the final installation procedure, aims to test the achievement of the design requirements and to ensure the feasibility of the in-vessel installation.