Lap Joint Resistance of YBCO Coated Conductors

The National High Magnetic Field Laboratory is constructing a 32 T all superconducting magnet. The high field insert coil, which produces about 17 T field, will be made of YBCO coated conductor. Due to the limited available coated conductor piece length, solder splice joints are necessary in the insert coil. In order for the magnet to achieve stable operation with reasonable liquid helium consumption, it is important to minimize the resistance of the joints. In this paper, we prepared 40 mm long lap joints made by 4 mm wide SuperPower coated conductors. Joints made from different conductor batches are soldered with Sn63Pb37 solder at different temperatures using different soldering method. The joint resistivity measurements were performed at both 77 K and 4.2 K in high magnetic fields with different field orientations. We found that the joint resistivity is strongly correlated with conductor batch number. The joint resistivity temperature, magnetic field and field angle dependence is not strong. Therefore the joint resistivity measured at 77 K self field can be used to approximate that at 4.2 K in magnetic field.