Title: Beneficial influence of Hf and Zr additions to Nb4at%Ta on the vortex pinning of Nb₃Sn with and without an O source

Abstract

In this paper we show that addition of Hf to Nb4Ta can significantly improve the high field performance of Nb₃Sn, making it suitable for dipole magnets for a machine like the 100 TeV Future Circular Collider (FCC). A big challenge of the FCC is that the desired non-Cu critical current density (J _c ) target of 1500 A mm^–2 (16 T, 4.2 K) is substantially above the best present Nb₃Sn conductors doped with Ti or Ta (~1300 A mm^–2 in the very best sample of the very best commercial wire). Recent success with internal oxidation of Nb–Zr precursor has shown significant improvement in the layer J _c of Nb₃Sn wires, albeit with the complication of providing an internal oxygen diffusion pathway and avoiding degradation of the irreversibility field H _Irr. We here extend the Nb1Zr oxidation approach by comparing 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 SnO₂ and their properties measured over the entire superconducting range at fields up to 31 T. We found that Group IV alloying of Nb4Ta does raise H _Irr, though O₂ additionmore » still slightly degrades it. As noted in earlier Nb1Zr work with an O source, the pinning force density F _p is strongly enhanced and its peak value shifted to higher field by internal oxidation. A surprising result of this work is that we found better properties in Nb4Ta1Hf without SnO₂, 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 SnO₂-free wire made with Nb4Ta1Hf alloy. Using a standard A15 cross-section fraction of 60% for modern powder-in-tube and rod restack process wires, we estimated that a non-Cu J _c of 2200 A mm^–2 is obtainable in modern conductors, well above the 1500 A mm^–2 FCC specification. Moreover, since the best properties were obtained without SnO₂, the Nb4Ta1Hf alloy appears to open a straightforward route to enhanced properties in Nb₃Sn wires manufactured by virtually all the presently used commercial routes employed today.« less

Authors:

Balachandran, Shreyas  ^[1];

• Search DOE PAGES for author "Balachandran, Shreyas"
• Search DOE PAGES for ORCID "0000-0002-0077-8504"

Tarantini, Chiara  ^[1];

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• Search DOE PAGES for ORCID "0000-0002-3314-5906"

Lee, Peter J.  ^[1];

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• Search DOE PAGES for ORCID "0000-0002-8849-8995"

Kametani, Fumitake ^[2]; Su, Yi -Feng ^[1]; Walker, Benjamin ^[2]; Starch, William L. ^[1]; Larbalestier, David C.  ^[2]

• Search DOE PAGES for author "Larbalestier, David C."
• Search DOE PAGES for ORCID "0000-0001-7098-7208"

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+ Show Author Affiliations

1. National High Magnetic Field Lab, Tallahassee, FL (United States)
2. National High Magnetic Field Lab, Tallahassee, FL (United States); FAMU/FSU College of Engineering, Tallahassee, FL (United States)

Publication Date:

Wed Feb 27 00:00:00 EST 2019

Research Org.:

Florida State Univ., Tallahassee, FL (United States)

Sponsoring Org.:

USDOE Office of Science (SC), High Energy Physics (HEP)

OSTI Identifier:

1503648

Grant/Contract Number:  

SC0012083

Resource Type:

Accepted Manuscript

Journal Name:

Superconductor Science and Technology

Additional Journal Information:

Journal Volume: 32; Journal Issue: 4; Journal ID: ISSN 0953-2048

Publisher:

IOP Publishing

Country of Publication:

United States

Language:

English

Subject:

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; 43 PARTICLE ACCELERATORS; 36 MATERIALS SCIENCE; Nb3Sn; Future Circular Collider; alloying; high magnetic field; critical current density; superconductor