Thermal conductivity and Kapitza resistance of cyanate ester epoxy mix and tri-functional epoxy electrical insulations at superfluid helium temperature

Abstract

In the framework of the European Union FP7 project EuCARD, two composite insulation systems made of cyanate ester epoxy mix and tri-functional epoxy (TGPAP-DETDA) with S-glass fiber have been thermally tested as possible candidates to be the electrical insulation of 13T Nb3Sn high field magnets under development for this program. Since it is expected to be operated in pressurized superfluid helium at 1.9K and 1atm, the thermal conductivity and the Kapitza resistance are the most important input parameters for the thermal design of this type of magnet and have been determined in this study. For determining these thermal properties, three sheets of each material with different thicknesses varying from 245 to 598μm have been tested in steady-state condition in the temperature range of 1.6–2.0K. The thermal conductivity for the tri-functional epoxy (TGPAP-DETDA) epoxy resin insulation is found to be k=[(34.2±5.5)⋅T−(16.4±8.2)]×10−3Wm−1K−1 and for the cyanate ester epoxy k=[(26.8±4.8)⋅T−(9.6±5.2)]×10−3Wm−1K−1. For the Kapitza resistance, Rk, the best curve fitting the experimental data is described by Rk=(3057±593)×10−6⋅T (−1.79±0.34)m2KW−1 for the TGPAP-DETDA insulation and Rk=(4114±971)×10−6⋅T (−1.73±0.41)m2KW−1 for the cyanate ester epoxy insulation. Our results are compared with other epoxy based composite electrical insulation found in the literature.