Speaker
Description
After over 50 years of application, Nb₃Sn remains by far the most economical superconductor for magnetic fields beyond the reach of Nb-Ti but new challenges such as the Future Circular Collider, FCC, require critical current density (Jc) values well-beyond what is possible with available commercial Nb₃Sn wire. Furthermore, future high field magnets will also require higher Jc margins to allow for the introduction of additional stabilizer and for structural elements to overcome the very high Lorentz forces. To meet the Jc challenge we have achieved a significant performance improvement by introducing Hf and other additions to the starting Nb alloy, in designs that can be adapted to existing Nb₃Sn commercial strands. This approach can be realized more readily in internal Sn strands than previous attempts that have used internal oxidation compatible only with a PIT design. In our prototype Hf addition wires, based on standard high-field Nb-Ta alloy, we can obtain Nb₃Sn layer Jc (16 T, 4.2 K) values of over 3700 A/mm² which, if extrapolated to an RRP conductor design, corresponds to a non-Cu Jc (16 T, 4.2 K) of over 2200 A/mm² (almost 50% higher than the preliminary FCC target specification of 1500 A/mm²). The Hf-addition wire has three times the layer Jc of our Nb-Ta alloyed control samples (no addition). If this level of increase can also be applied to low-hysteresis loss conductors, such as those developed for ITER, then a wide range of applications will be impacted, such as future fusion devices and NMR magnets. By systematically exploring the impact of different alloying elements, we demonstrate the potential for further improvements in properties.
Acknowledgments: This work was supported by the U.S. Department of Energy under Award DE-SC0012083 and CERN under Framework Collaboration Agreement KN2713. A portion of this work was performed at the National High Magnetic Field Laboratory, which is supported by NSF Cooperative Agreement DMR-1644779 and the State of Florida.
