Lap joint resistance of Nb3Sn cable terminations for the ICCS-HFTF 12 tesla coil program

Lap joint resistance as a function of current and magnetic field has been measured across 12 Tesla Coil conductor cable terminations. The terminations were at the ends of a 2.2 m Nb3Sn hairpin of internally cooled and cabled superconductor (ICCS), and were soft soldered to NbTi bus bars. The resulting lap joints were each 15 cm long with a contact area of 19.8 cm². The maximum measured lap joint voltage drop was 75 μV at 21 kA and 4.2 K, with the cable center at zero magnetic field. This represents an upper bound on all measured voltage drops, including those with the cable center at 10 and 12 T, and corresponds to a maximum heat flux of 0.01 w/ cm²to pool boiling helium. The results imply that the 12 Tesla Coil, with four lap joints, would dissipate less than 7 watts in the steady-state at 21 kA. The zero field results and results at cross fields of 10 and 12 T are discussed. Manufacturing and experimental parameters relevant to this study are also considered.