Ramp-Rate Sensitivity of SSC Dipole Magnet Prototypes

Abstract

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.