Ultra high-current superconducting cables for a 2.2-tesla, 300-kilojoule energy storage magnet

We have built and tested two types of superconducting cables to be used in pulsed energy storage magnets for the LASL Magnetic Energy Transfer and Storage (METS) program. These 2.2-T, 300-kJ magnets are to operate at 10 to 12 kA with a safety factor in critical current of about 50% at 10 kA. The conductor must exhibit low losses in addition to being stable. Magnetic Corporation of America (MCA) designed a flat conductor using 1224 copper-matrix, monofilament wires combined in two stages of cabling followed by two stages of flat braiding. Two of these conductors were constructed, one with wire already on hand and the second using wire made specifically for this application. Intermagnetics General Corporation (IGC) designed two rectangular conductors using 315 and 319 mixed-matrix multifilament wires combined in three stages of cabling followed by compaction in a Turk's head. The maximum transport current capabilities (I
t
) of these cables were measured in hairpin shaped samples with the straight section under test in perpendicularly applied fields. The measured results at 2.5 T for the two MCA cables were 11.7 kA and 15.4 kA, and for the IGC cables were 18.2 kA and 19.3 kA (extrapolated). In addition, samples of the compacted and uncompacted major strands from the IGC cables were tested. The results of these measurements are compared with values of I
t
calculated from the single-wire critical currents taking into account the adjacent conductor fields and the cable self-fields. Several causes of degradation of I
t
in the compacted cable are discussed including those due to experimental factors.