Field and temperature dependencies of critical current on industrial Nb3Sn strands

The increasing need for high field magnetic devices has focused attention on filamentary Nb3Sn conductors, whose critical data are superior to NbTi conductors. To choose the suitable operating parameters and to determine the stability margin of magnet systems, it is very important to know the effect of temperature and magnetic field on the superconducting properties, especially on the critical current. Up to now, for design calculation, the so-called "Summers model" was assessed theoretically on experimental data obtained by Spencer et al., (The temperature and magnetic field dependence of superconducting critical current densities of multiinflammatory Nb3Sn and NbTi composite wires. IEEE Trans Mag, Mag-15 (1979) 76 and Suenaga et al., Superconducting critical-current densities of commercial multifilamentary Nb3Sn(Ti) wires made by the bronze process. Cryogenics (1985) 25, 123). Apart these very useful preliminary experimental data, very little has been done on the very different industrial strands which are now produced in the industry. Industrial Nb,Sn strands are generally tested and checked only at 4.2 K and their operating design temperature is often very different, sometimes around 6 K. It is now urgent to validate the model and to confirm that the data taken up to now in the design calculations are conservative. (C) 1998 Elsevier Science Ltd. All rights reserved.