Development of insulation technology with Cyanate Ester resins for ITER TF coils

Some technical issues still remain in the manufacturing process of the ITER Toroidal Field (TF) coil. Since the impregnation and curing of its insulation system is one of the issues, the authors performed trial impregnation using Cyanate Ester (CE) resin, which is a new candidate among resins because of its excellent resistance to radiation. The authors also studied the feasibility of curing the Winding Pack (WP). A previous study by the authors showed that a void, which may degrade insulation performance, may be generated as a result of an excessively brief impregnation, which was determined by pot life, namely the time required for viscosity to reach 100 mPas. Since the pot life of the improved CE resin was measured to be 200 h, the insulation system is allowed to be impregnated more slowly. Therefore, in an impregnation test, a 0.6 m sample was impregnated more slowly using CE resin than in previous studies, resulting in no voids in the insulation layers. In addition, calculations by the authors indicate that the required curing temperature tolerance of ±5 °C is difficult to achieve through the conventional method of using external heaters because of the heavy mass of the WP. However, it is shown that this demanding tolerance margin is achievable using the conductor as an additional heater. These results suggest that it is time for full qualification testing of the impregnation and curing process in a dummy double-pancake trial.