Generation of magnetic fields over 21T in a 61mm clear bore using low copper ratio (Nb,Ti)(3)Sn conductors

A 21 T superconducting magnet system has been developed and improved at the National Research Institute for Metals in Japan, qs the steady progress of high-Tc superconducting coils required a larger bore for testing their performance, a new innermost coil has been det eloped. We increased the available bore from 50 mm to 61 mm. The new coil employed three kinds of rectangular (Nb,Ti)(3)Su conductors. External copper stabilized these conductors, with a Cu:SC ratio df only 0.25. The new coil operated in a 160 mm diameter dear bore with a background field of 18 T in saturated superfluid helium, generating a central field of 21.5 T without any training behavior. A double walled dewar, the outer diameter of which was 60 mm, was also developed. With this dewar, the nem system provides a temperature-variable bore of 50 mm.