Superconducting Joints Made With Internal-Magnesium-Diffusion-Processed MgB2 Wires

MgB₂ , which has a critical temperature T_c of 39 K, is a candidate for the practical application of liquid-helium-free magnetic resonance imaging systems. Since the discovery of MgB₂, the performance of MgB₂ wires and the technology required to manufacture long-length conductors have been significantly improved. Wires processed by internal magnesium diffusion (IMD) show high performance in comparison with powder-in-tube-processed MgB₂ wires. Our group has been developing high-performance IMD wires. In this study, a joint connecting two IMD-processed MgB₂ wires was fabricated. The maximum critical current in the connected wires was 1/3 lower than that in a normal IMD-processed wire at each considered magnetic field strength. However, the critical current of the joint at 3 T was equal to that of a normal IMD-processed wire at 10 T, suggesting that this joint would be effective at magnetic fields of around 3 T. Furthermore, a joint resistance of 10^-13 Ω was obtained by measuring the current decay at the joint.

I. Introduction

MgB₂, which has a critical temperature of 39 K, is a candidate for the practical application of superconducting magnet coil for liquid-helium-free magnetic resonance imaging (MRI) systems [1]. Since the discovery of MgB₂, the superconducting performance, especially critical current density of MgB₂ wires and the technology required to manufacture long-length conductors have been significantly improved. Furthermore, long-length MgB₂ wires have been made commercially available for various practical applications [2]. Many studies on MgB₂ coils for MRI magnet systems have been investigated using these long-length wires. The superconducting properties of MgB₂ wires have also undergone improvements. In particular, wires processed by internal magnesium diffusion (IMD) show high performance in comparison with powder-in-tube (PIT)-processed MgB₂ wires. Our group has been developing high-performance IMD-processed wires with and values of over 100 and 10 kA/cm² at 4.2 K and 10 T, respectively [3], [4].