Electrical resistance of Nb3Sn/Cu splices produced by electromagnetic pulse technology and soft soldering

The electrical interconnection of Nb3Sn/Cu strands is a key issue for the construction of Nb3Sn based damping ring wigglers and insertion devices for third generation light sources. We compare the electrical resistance of Nb3Sn/Cu splices manufactured by solid state welding using electromagnetic pulse technology (EMPT) with that of splices produced by soft soldering with two different solders. The resistance of splices produced by soft soldering depends strongly on the resistivity of the solder alloy at the operating temperature. Using solid state welding, splice resistances below 10 nΩ can be achieved with 1 cm strand overlap length only, which is about four times lower than the resistance of Sn96Ag4 soldered splices with the same overlap length. A comparison of experimental results with finite element simulations shows that the electrical resistance of EMPT welded splices is determined by the resistance of the stabilizing copper between the superconducting filaments, and confirms that welding of the strand matrix is indeed achieved. EMPT allows the ductile, unreacted strands to be interconnected, which reduces the risk of damaging the brittle reacted Nb3Sn strands. (paper)