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Title: Ta, Ti and Hf effects on Nb 3Sn high-field performance: temperature-dependent dopant occupancy and failure of Kramer extrapolation

Abstract

The increasing demand for improving the high-field (16-22 T) performance of Nb 3Sn conductors requires a better understanding of the properties of modern wires much closer to irreversibility field, H Irr. In this study we investigated the impact of Ta, Ti and Hf doping on the high-field pinning properties, the upper critical field, H c2, and H Irr. We found that the pinning force curves of commercial Ti and Ta doped wires at different temperatures do not scale and that the Kramer extrapolation, typically used by magnet designers to estimate high-field critical current density and magnet operational margins from lower field data, is not reliable and significantly overestimates the actual H Irr. In contrast, new laboratory scale conductors made with Nb-Ta-Hf alloy have improved high-field J c performance and, despite contributions by both grain boundary and point defect pinning mechanisms, have more predictable high-field behavior. Using Extended X-ray Absorption Fine Structure spectroscopy, EXAFS, we found that for the commercial Ta and Ti doped conductors, the Ta site occupancy in the A15 structure gradually changes with the heat treatment temperature whereas Ti is always located on the Nb site with clear consequences for H c2. Finally, this work reveals the stillmore » limited understanding of what determines H c2, H Irr and the high-field J c performance of Nb 3Sn and the complexity of optimizing these conductors so that they can reach their full potential for high-field applications.« less

Authors:
ORCiD logo [1]; ORCiD logo [1];  [2]; ORCiD logo [1];  [1];  [1];  [1]; ORCiD logo [1]
  1. Florida State Univ., Tallahassee, FL (United States)
  2. Argonne National Lab. (ANL), Argonne, IL (United States)
Publication Date:
Research Org.:
Florida State Univ., Tallahassee, FL (United States)
Sponsoring Org.:
USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25); CERN; National Science Foundation (NSF); State of Florida; Canadian Light Source
OSTI Identifier:
1593300
Grant/Contract Number:  
SC0012083; AC02-06CH11357; DMR-1644779
Resource Type:
Accepted Manuscript
Journal Name:
Superconductor Science and Technology
Additional Journal Information:
Journal Volume: 32; Journal Issue: 12; Journal ID: ISSN 0953-2048
Publisher:
IOP Publishing
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; 36 MATERIALS SCIENCE; Nb3Sn; EXAFS; site occupancy; irreversibility field; Kramer’s extrapolation; pinning mechanisms

Citation Formats

Tarantini, Chiara, Balachandran, Shreyas, Heald, Steve M., Lee, Peter J., Paudel, Nawaraj, Choi, Eun Sang, Starch, William L., and Larbalestier, David C. Ta, Ti and Hf effects on Nb3Sn high-field performance: temperature-dependent dopant occupancy and failure of Kramer extrapolation. United States: N. p., 2019. Web. doi:10.1088/1361-6668/ab4d9e.
Tarantini, Chiara, Balachandran, Shreyas, Heald, Steve M., Lee, Peter J., Paudel, Nawaraj, Choi, Eun Sang, Starch, William L., & Larbalestier, David C. Ta, Ti and Hf effects on Nb3Sn high-field performance: temperature-dependent dopant occupancy and failure of Kramer extrapolation. United States. doi:10.1088/1361-6668/ab4d9e.
Tarantini, Chiara, Balachandran, Shreyas, Heald, Steve M., Lee, Peter J., Paudel, Nawaraj, Choi, Eun Sang, Starch, William L., and Larbalestier, David C. Mon . "Ta, Ti and Hf effects on Nb3Sn high-field performance: temperature-dependent dopant occupancy and failure of Kramer extrapolation". United States. doi:10.1088/1361-6668/ab4d9e.
@article{osti_1593300,
title = {Ta, Ti and Hf effects on Nb3Sn high-field performance: temperature-dependent dopant occupancy and failure of Kramer extrapolation},
author = {Tarantini, Chiara and Balachandran, Shreyas and Heald, Steve M. and Lee, Peter J. and Paudel, Nawaraj and Choi, Eun Sang and Starch, William L. and Larbalestier, David C.},
abstractNote = {The increasing demand for improving the high-field (16-22 T) performance of Nb3Sn conductors requires a better understanding of the properties of modern wires much closer to irreversibility field, H Irr. In this study we investigated the impact of Ta, Ti and Hf doping on the high-field pinning properties, the upper critical field, H c2, and H Irr. We found that the pinning force curves of commercial Ti and Ta doped wires at different temperatures do not scale and that the Kramer extrapolation, typically used by magnet designers to estimate high-field critical current density and magnet operational margins from lower field data, is not reliable and significantly overestimates the actual H Irr. In contrast, new laboratory scale conductors made with Nb-Ta-Hf alloy have improved high-field J c performance and, despite contributions by both grain boundary and point defect pinning mechanisms, have more predictable high-field behavior. Using Extended X-ray Absorption Fine Structure spectroscopy, EXAFS, we found that for the commercial Ta and Ti doped conductors, the Ta site occupancy in the A15 structure gradually changes with the heat treatment temperature whereas Ti is always located on the Nb site with clear consequences for H c2. Finally, this work reveals the still limited understanding of what determines H c2, H Irr and the high-field J c performance of Nb3Sn and the complexity of optimizing these conductors so that they can reach their full potential for high-field applications.},
doi = {10.1088/1361-6668/ab4d9e},
journal = {Superconductor Science and Technology},
number = 12,
volume = 32,
place = {United States},
year = {2019},
month = {11}
}

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