A superconducting joint for GdBa2Cu3O7−δ-coated conductors

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. We report the world’s first superconducting joint for second-generation GdBa2Cu3O7-δ-coated conductors (2G GdBCO CCs) based on atomic diffusion in GdBCO with partial melting and oxygen diffusion into the oxygen-deficient GdBCO lattices. Producing the superconducting joint requires multiple processes, including fabrication of microholes, peeling off stabilizers, heat treatment and oxygenation annealing. The Ic value of the joined and parent CCs at 77 K are identical, and the initially induced magnetic field of a model coil containing the joint is maintained without decreasing. This method is a unique solution for achieving persistent current mode operation in 2G high-temperature superconducting magnet applications. Researchers in South Korea have solved the problem of how to join two high-temperature superconducting materials together while preserving their electrical and magnetic properties. Superconducting materials are pivotal for a range of scientific instruments including MRI machines and particle accelerators. Established connection methods, however, have resulted in high resistance at the join. Haigun Lee and colleagues at Korea University have developed a technique that does not have this problem. When their ‘superconducting joint’ is added to a coil arrangement, the induced magnetic field remains unchanged, further indicating the lack of resistance and maintenance of superconductivity. The multi-step process includes the partial melting of the conductor and annealing under high-pressure oxygen. The join could be incorporated in high-temperature superconducting materials that form closed circuits and operate without the need for an external power supply for applications ranging from analytical instruments to medical scanners.