Thermal conductivity measurements of impregnated Nb₃Sn coil samples in the temperature range of 3.5 K to 100 K

In the framework of the luminosity upgrade of the LHC, high-field magnets are under development. Magnetic flux densities of up to 13 T require the use of Nb₃Sn superconducting coils. Quench protection becomes challenging due to the high stored energy density and the low stabilizer fraction. The thermal conductivity and diffusivity of the combination of insulating layers and Nb₃Sn based cables are an important thermodynamic input parameter for quench protection systems and superfluid helium cooling studies. A two-stage cryocooler based test stand is used to measure the thermal conductance of the coil sample in two different heat flow directions with respect to the coil package geometry. Variable base temperatures of the experimental platform at the cryocooler allow for a steady-state heat flux method up to 100 K. The heat is applied at wedges style copper interfaces of the Rutherford cables. The respective temperature difference represents the absolute value of thermal conductance of the sample arrangement. We report about the measurement methodology applied to this kind of non-uniform sample composition and the evaluation of the used resin composite materials. (paper)