Batch testing of BSCCO 2212 cable in subcooled liquid nitrogen

A technique has been developed for testing long lengths of superconducting cable made from BSCCO 2212 wires in liquid nitrogen. The cable is tested as a large diameter spiral with removable voltage taps so that the conductor can be recovered for use in fabricating developmental magnets. Since the transition temperature of BSCCO 2212 conductors is often lower than 77 K the nitrogen bath must be pumped to reduce its temperature. As the pressure is slowly reduced the transition temperature can be determined and the current carrying capabilities measured as a function of temperature. 55 K can be easily achieved with the same equipment used for superfluid testing in liquid helium. Four cables have been tested ranging in length from 30 m to 0.6 m. A steady improvement in the superconducting properties of these cables was observed, reflecting the experience gained in strand fabrication and heat treatment by the manufacturer. For some of these cables, measurements were also made at 4.2 K to establish a correlation between the transition temperature and the expected current carrying capabilities in liquid helium.