Low Temperature Thermal and Thermo-Mechanical Properties of Soft Solders for Superconducting Applications

Abstract

High temperature superconducting (HTS) systems require electrical connection of the superconductors with each other or with a parallel shunt metal. Soft soldering is commonly used for the electrical interconnection of superconducting strands. However, soldering of these electrical interconnections should be carried out at possible low temperatures to prevent degradation of the superconducting material and avoid reduction of oxygen within superconductor. Therefore, solders with low melting temperatures are of special interest for superconducting applications. For the design of these electrical joints, along with electrical properties, it is important to know the thermal and thermo-mechanical properties at low temperatures of the solder to be used. For example, a large mismatch between thermal expansion of the superconductors and the solder cause stresses during cool down. This may lead to a degradation of the superconducting properties. Thermal conductivity, thermal expansion and mechanical properties of the solder at low temperatures influence the quench propagation and life time of joints, and, therefore, the performance of the superconducting device. In this report we present low temperature thermal and thermo-mechanical properties of several soft solders, which are commonly used for cryogenic applications.