Electrical Interconnection of Superconducting Strands by Electrolytic Cu Deposition

The electrical interconnection of Nb₃Sn/Cu strands is a key issue for the construction of superconducting devices such as Nb₃Sn based insertion devices for third generation light sources. As an alternative connection method for brittle superconducting strands like Nb₃Sn/Cu, test joints have been produced by electrolytic deposition of Cu. The resistance of first test joints produced by electrolytic Cu deposition with a strand overlap length of 3 cm at 4.2 K is about 10 nΩ, similar to the resistance measured for joints produced by soft soldering with the same strand overlap length. Interconnection by electrolytic Cu deposition can be done before or after the reaction heat treatment, and it produces a mechanically strong connection. Simulations have been performed with Comsol multiphysics in order to estimate the influence of deposit imperfections on the joint resistance, and to compare the resistance of joints made with different techniques.