Enhanced adhesive shear strength of cyanate ester electrical insulation for fusion magnets

In many Next-Step Option (NSO) fusion magnet designs the shear strength of the electrical insulation and its adhesion to the conductor is a performance limiting factor, especially during high temperature excursions. Significant design compromises, such as the need for large compressive loads or increased part cross-sections, must be made in order to accommodate the low shear strength of the insulation. Improving the shear strength of the insulation/conductor system will reduce the negative impact on system design and allow for higher temperature operation. Typical adhesive shear strength of conventional epoxy-based insulation systems on clean copper ranges from 76 MPa in liquid nitrogen to only 17 MPa at 100 °C. These values are insufficient for the planned applications. On the other hand, cyanate ester based insulation has been shown to exhibit enhanced properties that will allow for magnet operation at 100 °C and possibly even higher. A new cyanate ester resin has been developed by Composite Technology Development exhibiting improved adhesive strength to copper, especially at elevated temperatures. It is expected that the high temperature value can be further increased with optimization. In addition, the enhanced radiation resistance of cyanate ester resins implies that the new insulation systems will out-perform traditional epoxy-based insulations and lead to reduced costs for future fusion energy devices.