Superconducting properties of diffusion processed niobium-Tin tape

The properties that make Nb
3
Sn an outstanding material for use in high-field superconducting solenoids are its high critical temperature (18.1°K), its high critical current density (in excess of 200 000 A/cm
²
at 100 kG and 4.2°K), and its high critical field (221 kG at 4.2°K). Since Nb
3
Sn is a brittle material, special techniques are required for its use. These techniques fall into two groups : 1) the conductor is initially fabricated from Nb and Sn in an unalloyed configuration, and this conductor is then wound into a solenoid and converted to Nb
3
Sn by heat treatment of the entire solenoid; 2) the alloyed Nb
3
Sn conductor is prepared in a very thin configuration. Thus, although it is brittle, it is still flexible enough to be wound directly into a finished solenoid. Extensive experimentation with the second technique has been undertaken and will be discussed with particular emphasis on the properties of laminated conductors as confirmed by performance of superconducting solenoids.