Thermo-mechanical characterization of insulated and epoxy-impregnated Nb3Sn composites

Nb₃Sn is, at present, the best superconductor for high field accelerator magnets. Several models using Nb₃Sn are under development in many laboratories. Knowledge of the thermo-mechanical properties of the impregnated coils is of crucial importance for the design of these magnets. In fact, the performance of epoxy-impregnated coils is sensitive to the thermal conductivity value, especially in case of heating caused by hysteretic losses, which are usually relevant in Nb₃Sn magnets, and in the case of continuous heat deposition, such as in magnets near the interaction region of a collider. Thermal contraction measurements are necessary to estimate the stresses during the magnet thermal cycle. Different insulation materials have been studied at Fermilab utilizing various design approaches and fabrication methods. Thermal conductivity and thermal contraction measurements, at cryogenic temperatures, have been performed respectively at INFN-LASA and Fermilab. The results are reported and discussed in this paper.