Risk Mitigation for Cyanate Ester Insulation of Large Magnets Through Cure Optimization

The toroidal field (TF) coils for the internationally supported ITER nuclear fusion reactor currently being assembled in France will be part of the largest superconducting magnet system ever to be assembled. Due to the relatively high radiation dose expected, the TF coils will utilize a cyanate ester/epoxy blended insulation. It is estimated that this application will represent the single largest use of cyanate ester resins to date. Although magnet coils for the National Spherical Torus Experiment (NSTX) and Wendelstein 7-X have been successfully manufactured using a cyanate ester/epoxy blended insulation, the sheer size of the ITER TF coils create new challenges and concerns with the processing of such large quantities of liquid cyanate ester materials. Handling cyanate ester/epoxy resins can require different equipment and procedures than are required for handling pure epoxies. In particular, cyanate ester/epoxy systems are known for their energetic polymerization, requiring extra care to minimize the risk of an uncontrolled reaction when handled on a large scale. In support of the ITER TF coil manufacturers, LORD Corporation and Composite Technology Development, Inc. (CTD) have qualified two cyanate ester/epoxy resin systems, CTD-425 and CTD-435, and have demonstrated processing robustness and specifically designed cure profiles that will enable coil manufacturers to employ their preferred resin impregnation processes with confidence, even at the very large scale of the ITER project. A description of the cure experiments performed as well as the recommended cure profiles and handling practices for LORD CTD-435 will be presented.