Beneficial influence of Hf and Zr additions to Nb4at.%Ta on the vortex pinning of Nb${}_3$Sn with and without an O source

Abstract

Here we show that addition of Hf to Nb4Ta can significantly improve the high field performance of Nb${}_3$Sn, making it suitable for dipole magnets for Future Circular Collider (FCC). A big challenge for the FCC is that a realistic production target for FCC Nb3Sn requires ~30% improvement over current conductor performance. Recent success with internal oxidation(IO) of Nb-Zr precursor has shown significant improvement in the layer J${}_c$ of Nb${}_3$Sn wires, albeit the complication of providing an internal O${}_2$ diffusion path and avoiding degradation of irreversibility field(${}_{irr}$). We compare Zr and Hf additions to the standard Nb4Ta alloy of maximum H${}_{c2}$ and H${}_{irr}$. Nb4Ta rods with 1Zr or 1Hf were made into monofilament wires with and without SnO${}_2$ and their properties measured over the entire superconducting range up to 31 T. We found that group IV alloying of Nb4Ta raises H${}_{irr}$, though adding O${}_2$ still degrades this slightly. As noted in Nb1Zr studies, the pinning force density F${}_p$ is strongly enhanced and its peak value shifted to higher field by IO. A surprising result of this work is that we found better properties in Nb4Ta1Hf without SnO${}_2$, F${}_{pmax}$ achieving 2.35 times that of the standard Nb4Ta alloy, while the oxidized Nb4Ta1Zr alloy achieved 1.54 times that of the Nb4Ta alloy. The highest layer J${}_c$ (16 T, 4.2 K) of 3700 A/mm${}^2$ was found in the SnO${}_2$-free wire made with Nb4Ta1Hf alloy. Using a standard A15 cross-section fraction of 60% for modern PIT and RRP wires, we estimated that a non-Cu J${}_c$ of 2200 A/mm${}^2$ is obtainable in modern conductors, well above the 1500A/mm${}^2$ FCC specification. Moreover, the best properties were obtained without SnO${}_2$, the Nb4Ta1Hf alloy appears to open a straightforward route to enhanced properties in Nb${}_3$Sn wires.

arXiv comment7 pages, 6 figures

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Cited by in corpus (7)

• Superconducting materials: Challenges and opportunities for large-scale applications
• Modern and Future Colliders
• Thermodynamic approach for enhancing superconducting critical current performance
• Ta, Ti and Hf effects on Nb${}_3$Sn high-field performance: temperature-dependent dopant occupancy and failure of Kramer extrapolation
• APC Nb${}_3$Sn superconductors based on internal oxidation of Nb-Ta-Hf alloys
• Influence of Nb Alloying on Nb Recrystallization and the Upper Critical Field of Nb3Sn
• Pressure-induced symmetry lowering in Nb3Sn1-x superconductor