Development of Superconducting Joints for TWC High-J_c Nb₃Sn Wires for NMR Superconducting Magnet Applications

Abstract

For a persistent mode high-field NMR magnet involving several Nb₃Sn coils, Nb₃Sn-Nb₃Sn joints with extremely small resistance values are required to maintain an acceptable field-decay rate. We have successfully developed a very reliable superconducting joining technique for Teledyne Wah Chang (TWC) high critical current-density (high-J _c), niobium diffusion barrier modified jelly roll (MJR) Nb₃Sn wires. In this paper, the joint fabrication and test results are presented. The range of the electric resistance of the Nb₃Sn-Nb₃Sn joints fabricated is about 10^-14 Ohms (Ω) for currents up to 500 A and less than 6 × 10^-14 Ω for currents up to 1000 A in a field of about 0.03 Tesla generated by the test coil. Both the standard four-terminal and field-decay methods were used for the measurements of joint resistance. Four joints have been tested and the success rate of the tested joints is 100%.