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.
This paper summarizes the results of the first critical current intercomparison implemented in the framework of VAMAS (Versailles Project on Materials and Standards) and discusses on the origins of data scatters reported by the participants. Three different Nb3Sn conductors were used and participants made measurements using their own techniques. As a result, variation coefficients for these samples were 8.0% to 29.9% at 12T. A major source of these variations was found to be strain sensitivity of the Nb3Sn conductors. Effects of factors in the critical current measurement, such as magnetic field, temperature, current bypassing through mandrel, current transfer voltage, etc. were also examined on the basis of the results of the intercomparison.
Typical forced flow cooled superconductor has a lot of strands in a conduit. It is pointed out, however, that there could be a non uniform current distribution in those strands because of the difference of inductance of each strand and/or the difference of contact resistance at terminals. This non uniform current distribution affects and greatly reduces the conductor's stability margin. We discuss the stability degradation and quench characteristics of a forced flow cooled superconducting coil that we have made. The conductor has 54 strands. Each strand has formvar insulation layer and electrically insulated each other. We have measured the stability margin of the test coil and characteristics of normal zone propagation and pressure rise during quench. We analyze these characteristics using numerical simulation code. It can simulate stability degradation, if we take non uniform current distribution into account. An additionl heat input, however, has to be taken into account to simulate quench characteristics in the simulations. This additional heat input is thought to be the heating caused by the heat diffusion between turns through the bobbin.
The evaluation of unoccupied space in epoxies has been evaluated in terms of positron annihilation method. Based on the evaluated unoccupied space the cohesive condition of the epoxy molecular was modeled. The model suggested that the epoxies were classified into two types that is the epoxy could be explain by the free volume and that by free space. The former was understood as the epoxy of which molecular network was destroyed by the plasticizer and the latter as that of which molecular weight between crosslinks was changed. In this work the former mechanism was confirmed experimentally. The addition of plasticizer was confirmed not to be effective to improve the cryogenic mechanical properties as expected by the model.