A superconducting joint for GdBa2Cu3O7−δ-coated conductors

Yeonjoo Park,Heesung Ann,Myungwhon Lee,Yoon Hyuck Choi,Haigun Lee

doi:10.1038/am.2014.18

Yeonjoo Park, Heesung Ann + Show 3 more

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https://doi.org/10.1038/am.2014.18

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Abstract

Second-generation (2G) GdBCO-coated conductors (CCs) are promising for superconducting magnet applications because of their high critical current (Ic) density, low dependency of the Ic on the external magnetic field, good mechanical properties and reasonable cost, which offer opportunities to develop ultra-high-field magnets. However, they have not been used in high-temperature superconducting (HTS) applications with persistent current mode (PCM) operation such as nuclear magnetic resonance/magnetic resonance imaging magnets owing to unavailability of fabrication techniques for proper joining and contacts. Here we report a resistance-free joint, termed a ‘superconducting joint’, for 2G GdBCO CCs that forms a direct connection to establish a superconducting closed loop for PCM operation. The Ic value of the joined CCs is identical to that of the parent conductors in a liquid nitrogen bath (77 K). Moreover, the initially induced magnetic field of a model GdBCO coil containing a superconducting joint is maintained without decreasing, indicating the complete absence of electrical resistance. Thus, this fabrication method is a unique practical solution for lengthening the 2G HTS CCs and, more importantly, achieving PCM operation in 2G HTS magnet applications, including ultra-high-field nuclear magnetic resonance/magnetic resonance imaging magnets generating more than 1 GHz.

Highlights

Since the development of YBCO in 1987, the improvement of secondgeneration (2G) rare earth barium copper oxide-coated conductors (CCs) has been a triumph of scientific insight, sophisticated processing and determined scale-up efforts.[1,2,3,4,5]. These CCs are promising for superconducting magnet applications because of their high Ic density, low dependency of the Ic on the external magnetic field, good mechanical properties and reasonable cost, which offer opportunities to develop ultra-high-field magnets.[6,7,8]. These CCs have not been used in superconducting devices with persistent current mode (PCM) operation such as magnets for magnetic resonance applications owing to the unavailability of fabrication techniques for proper joining and contacts.[9,10,11,12]
We report a ‘superconducting joint’ for 2G GdBCO CCs, that is, a direct connection between two superconducting layers formed without soldering that can establish a superconducting closed loop for PCM operation
The time-dependent changes in a magnetic field generated by a current flowing in a circular loop containing an high-temperature superconducting (HTS) joint are measured over many days

Summary

Introduction

An ideal joint for 2G high-temperature superconducting (HTS) CCs requires perfect physical, chemical and mechanical continuity and uniformity throughout the CC-joint-CC connection, as well as sufficient metallurgical capacity without the formation of deleterious constituents, mechanical soundness and good performance under varying conditions, including closed-loop conditions for PCM operation. Various joining methods such as soldering are unsuitable for such joints because of their high joint resistance (20– 2800 nO).[13,14] the physical continuity and uniformity necessary for obtaining a good Ic and electrical resistance have not been achieved, precluding PCM operation. Achieving superconducting joints for 2G HTS CCs that maintain the electrical characteristics of the parent CCs remains a challenge.[15,16]

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Conclusion