Thermal and Mechanical Design of Error Field Correction Coil for JT-60SA

The inhomogeneous poloidal magnetic field of tokamak device, which is called error field, has to be reduced because the error field degrades the plasma performance. There are 18 sets of EFC coils installed inside the vacuum vessel for JT-60SA to compensate the error field. The conceptual design of EFC coils has been completed. The water-cooled hollow copper conductor was selected to reduce the conductor size since the available space for EFC coils is small. The outer size of the conductor and the diameter of the cooling channel were optimized in considering hydraulic and thermal characteristics. The design of the conductor was validated by the testing of a mock-up coil. The bar springs are used for the structure of EFC coils. The structural analysis was performed to optimize the parameters of bar springs. The results of structural analysis suggest that the structure of EFC coils can be used for both the conditions of plasma operation and baking operation with the use of Inconel625 for bar springs. In this paper, the specification of the JT-60SA EFC coils, the test results of mock-up coils, and the structural analysis results of the EFC coil structure are described. The manufacture of EFC coils has started based on these designs.