Epoxy Resins for Vacuum Impregnating Superconducting Magnets: A Review and Tests of Key Properties

Epoxy impregnated superconducting magnets often have a long quench training and an uncertain performance. This is particularly an issue for Nb
₃
Sn accelerator magnets planned for future high-energy proton colliders, which need thousands of such magnets. This paper reviews epoxies used in major Nb
₃
Sn superconducting magnet systems, sorts them into three groups, and examines differences of their resistances to cracking when subjected to repeated thermal shocks and other key properties. The first group, including CTD-101K using which nearly all Nb
₃
Sn accelerator magnets have been potted, is found to be brittle and prone to cracking. A second epoxy group is shown to have a much higher toughness. Their mechanical properties, potting characteristics, and glass transition temperatures were measured, compared, and discussed in terms of the potential uses of the second epoxy group for impregnating Nb
₃
Sn accelerator magnets with a minimized training.