Characterization of Bonded Glass/Polyimide Tapes for the ITER TF Coil Insulation

The insulation of the ITER TF coils consists of multiple wrapped layers of glass fiber polyimide sandwich tapes. In order to simplify the fabrication process, the polyimide tape can be bonded to the glass fiber tape, mainly to avoid misalignments of the polyimide tape. However, due to the intense neutron and γ-radiation exposure, bonding agents have to be radiation resistant, otherwise the composite will be severely damaged, as was observed for the ITER TF model coil insulation. Two bonded glass fiber polyimide tapes (40 mm wide, ~0.175 mm thick) were supplied by Arisawa, Japan, and Advanced Composites Group, United Kingdom. Test materials were fabricated based on the build-up of the ITER TF turn insulation and vacuum pressure impregnated with a 40:60 cyanate ester/epoxy blend supplied by Huntsman, Switzerland. The mechanical properties of these materials were characterized prior to and after reactor irradiation to a fast neutron fluence of 2 × 10²² m^-2 (E >; 0.1 MeV), i.e. twice the ITER design fluence. Static and dynamic tensile tests were carried out at RT and 77 K. The Arisawa tape showed excellent mechanical properties.