One of the major achievements of the magnet R & D program for the Superconducting Super Collider (SSC) is the fabrication and test of a series of twenty 5-cm-aperture, 15-m-long dipole magnet prototypes. The ramp-rate sensitivity of these magnets appear to fall in at least two categories, which can be correlated to the manufacturer and production batch of the strands used for the inner-coil cables. The first category, refered to as type-A, is characterized by a strong quench current degradation at high ramp rates, usually accompanied by large distortions of the multipole fields and large energy losses. The second category, refered to as type-B, is characterized by a sudden drop of quench current at low ramp rates, followed by a much milder degradation at larger rates. The multipole fields of the type-B magnets show little ramp-rate sensitivity, and the energy losses are smaller than for the type-A magnets. The behavior of the type-A magnets can be explained in terms of inter-strand eddy currents arising from low and non-uniform resistances at the crossovers between the strands of the two-layer, Rutherford-type cable. Anomalies in the transport-current repartition among the cable strands are suggested as a possible cause for the type-B behavior. The origins of these anomalies have not yet been clealy identified. The SSC project was canceled by decision of the United States Congress on October 21, 1994.
Introductory explanation on metallic superconductors was described. The focus was placed on popular superconducting wires made of Nb-Ti alloy and Nb3Sn intermetallic compounds. From the actual point of view, the maximum transportable current was discussed considering several factors which had relation to the critical current density and stability such as pinning force, flux jump, stabilizer, disturbance and AC losses. The basic concept of designing a practical multifilamentary composite superconducting wire was exhibited.