Characterization of Nb3Sn superconductors for hybrid magnets

Nb3Sn superconductors are examined to select proper conductors for hybrid magnets outserts (that is a superconductor solenoid wound on the outside of a Bitter magnet) at the National High Magnetic Field Laboratory. The materials are subject to both thermal and mechanical stresses when in service. The stresses are complex due to the thermal contraction of the conduit applying extra stresses to the conductors. The final thermal stress levels can be well beyond the yield stress of some components in the superconductor composite and therefore plastic flow occurs in these components, such as Cu stabilizer and Cu-Sn matrix. If the plastic deformation strain is large, deformation strain in Nb3Sn superconductor filaments can be difficult to estimate. The differences in conductor design also render the estimation of the strain status difficult. It is well documented that the critical current is strongly affected by strain in the Nb3Sn superconductors. Therefore, we have characterized the microstructure and critical current of the superconductors with respect to the strain of various Nb3Sn superconductors. Other relevant properties are also measured and related to the fabrication, design and microstructure of the conductors. This paper reports our efforts in characterization of the Nb3Sn superconductors for hybrid magnets.