Development of Manufacturing Technologies for the ITER Toroidal Field Coil: Insertion Processes of Conductors

Abstract

Series productions of the toroidal field (TF) coils for the ITER have been launched since Oct. 2013. Prior to manufacturing of the TF coils, preliminary tests and mock-up tests were conducted in order to clarify and confirm the conditions of the welding and machining processes. The ITER TF coil has dimensions of 16.5m height and 9.0m width, and the TF coil weight is more than 300 ton. The tolerance requirements for the manufacture of the TF coils are very strict from a view point of stable plasma confinement. The double pancakes, which are layered up to seven and then contained into the TF Coil case, are formed by inserting winding conductor into a radial plate (RP), grooves of which are machined from the special forging. The RP consists of 10 small segments, and each segment is machined and welded to each other to form sectors, and finally, a D-shaped RP is formed. Therefore, the minimization of deformation during welding and machining processes is a key issue to manufacture the D-shaped RP. As for the preliminary tests for the RP, the requirement of flatness within 1mm was achieved by turning segment several times for balancing machining deformation. As for the RP welding, a laser beam welding (LBW) using a 30kW fiber laser was applied to about a half of the plate thickness of 120mm from both sides to minimize the welding deformation and remained portions are welded by TIG welding from both sides. In the process of winding conductor insertion, length of RP grooves is adjusted by final machining since winding conductors are elongated due to heat treatment before insertion. To minimize the error of length between RP grooves and winding conductors, length of winding conductor after heat treatment is measured and length of RP grooves has to be designed according to results of measurement so that winding conductor can be inserted smoothly and Cover plates (CP), which are used for cover of the winding conductor after insertion, do not interfere with winding conductor. From the above, the manufacturing of TF coils has been realized coping with the challenges by the high technique and kinds of tests.