In August 2016, Prof. Ma’s group fabricated the first 100 m class 122 iron-based superconducting (‘122’ IBS) wire by using the traditional powder-in-tube (PIT) process. This 115 m long Sr122 wire exhibited a uniform distribution of critical current density Jc throughout the wire with a minimum Jc of 1.2×104 A/cm2 (4.2 K, 10 T), demonstrating the great potential of iron-based superconductors in large-scale applications. This study was supported by the Beijing Municipal Science and Technology Commission, the National ‘973’ Program, the National Natural Science Foundation of China and the Beijing Training Project for the Leading Talents in S & T.
Early in 2008 and 2009, the first ‘1111’ and ‘122’ IBS wire was fabricated using PIT method by this group, respectively. By adopting silver as sheath material to prevent the non-superconducting reaction layer formed during heat treatment, ex-situ precursor to improve the quality of superconducting phase and mechanical deformation such as flat rolling, hot isostatic pressing and uniaxial pressing to improve the mass density of superconducting cores, the transport Jc of ‘122’ IBS wires and tapes has been rapidly increased in the recent years. High transport Jc exceeding 105 A/cm2 at 4.2 K and 10 T has been achieved in densified and textured Sr122 tapes, demonstrating that the Jc performance has reached the level desired for practical applications.
FIG. 1 The world’s first 100 meter-class iron-based superconducting wire developed in the Institute of Electrical Engineering, Chinese Academy of Sciences (IEECAS).
Based on the experience in high-performance short samples and subsequently developed multifilamentary wire process, Prof. Ma’s group started the research for long-length iron-based superconducting wires. In 2014, by a scalable rolling process, they fabricated the first 11 m long Sr122 tape. The Jc of this tape exhibits a uniform distribution, fluctuating between 2.12 and 1.68×104 A/cm2 (4.2 K, 10 T), with an average Jc value of 1.84×104 A/cm2. After that, they moved on to fabricate 100 meter-class tapes, for which higher-level homogeneity of precursor powder and uniformity of deformation process are indispensable. In August 2016, Prof. Ma’s group successfully fabricated a 115 m long Sr122 superconducting tape using the traditional powder-in-tube process, which shows a uniform Jc distribution throughout the tape with a minimum Jc of 1.2×104A/cm2 (4.2 K, 10 T). This milestone work has been announced in the 2016 Applied Superconductivity Conference recently held in Denver, USA.
The 115 m long Sr122 tape is the world’s first 100 meter-class iron-based superconducting wire, which demonstrates the great potential in large-scale manufacture, and is of great significance for promoting the practical application of iron-based superconductors. They believe that for iron-based superconducting wires, there is still much room for enhancing Jc performance and reducing material costs, and now the path towards real application is being opened up.
