Thermal conductivity and Kapitza resistance of epoxy resin fiberglass tape at superfluid helium temperature

The system of materials composed of fiberglass epoxy resin impregnated tape constitutes in many cases the electrical insulation for 'dry'-type superconducting accelerator magnet such as Nb3Sn magnets. Nb3Sn magnet technology is still under development in a few programs to reach higher magnetic fields than what NbTi magnets can produce. The European program, Next European Dipole (NED), is one of such programs and it aims to develop and construct a 15 T class Nb3Sn magnet mainly for upgrading the Large Hadron Collider. Superfluid helium is considered as one possible coolant and since the magnet has been designed with a 'dry' insulation, the thermal conductivity and the Kapitza resistance of the electrical insulation are the key properties that must be know for the thermal design of such a magnet. Accordingly, property measurements of the epoxy resin fiberglass tape insulation system developed for the NED project was carried out in superfluid helium. Four sheets with thicknesses varying from 40 to 300 pm have been tested in a steady-state condition. The determined thermal conductivity, k, is [(25.8 ± 2.8) - T - (12.2 ± 4.9)] x 10-3 W m-1 K-1 and the Kapitza resistance is given by RK = (1462 ± 345) - T(-1.86±0.41) * 10-6 Km2 W-1 in the temperature range of 1.55-2.05 K. (authors)