Manufacture and Test of a Prototype Cyanate Ester Coil

In order to demonstrate that cyanate ester resin could be successfully used in an industrial environment to produce a fusion magnet, a test coil has been made as part of the MAST-Upgrade programme. Cyanate ester offers a number of advantages over conventional epoxy-based insulation systems-notably increased high temperature strength, greater radiation resistance and significantly extended pot life. However, industrial experience is extremely limited and its use is not without challenges-for example, the gelling reaction is strongly exothermic and the resin is particularly sensitive to moisture. Cyanate ester is required for the new solenoid (1.7 Vsec) and inboard shaping coils for the proposed MAST-Upgrade Spherical Tokamak, and to reduce the project risk a test coil was considered essential. The coil was manufactured by Danfysik to the Culham Centre for Fusion Energy's specification, with resin and support from Composite Technology Development Inc. The coil was successfully tested at Culham to its design current of 10 kA for 5 s, performing as expected and reaching 95 degrees C. It was then subjected to 10,000 thermal cycles to validate the design of the MAST-Upgrade inboard shaping coils-space restrictions on these dictate that the coolant inlet and outlet be immediately adjacent, causing high thermal stresses between the two layers of the coil.