FIELD AND TEMPERATURE DEPENDENCIES OF CRITICAL-CURRENT ON INDUSTRIAL NB3SN STRANDS

The increasing need for high field magnetic devices has focused attent ion 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 importan t to know the effect of temperature and magnetic field on the supercon ducting properties, especially on the critical current. Up to now, for design calculation, the so-called ''Summers model'' was assessed theo retically on experimental data obtained by Spencer et al., (The temper ature and magnetic field dependence of superconducting critical curren t densities of multiinflammatory Nb3Sn and NbTi composite wires. IEEE Trans Mag, Mag-15 (1979) 76 and Suenaga et al., Superconducting critic al-current densities of commercial multifilamentary Nb3Sn(Ti) wires ma de by the bronze process. Cryogenics (1985) 25, 123). Apart these very useful preliminary experimental data, very little has been done on th e very different industrial strands which are now produced in the indu stry. Industrial Nb,Sn strands are generally tested and checked only a t 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 c onservative. (C) 1998 Elsevier Science Ltd. All rights reserved.