Superconducting joints between MgB2/Ni and MgB2/Nb composite wires, their transport currents and micro-structure

Superconducting joints between single-core MgB2/Ni and MgB2/Nb wires made by an internal Mg diffusion (IMD) process have been manufactured by using scarf joints architecture. Joint's transport current were measured at 4.2 K and external magnetic fields of 2-8 T and compared with the currents of used MgB2 wires. Structure of selected joints were analysed by an optical microscope. It was found that addition of boron powder between the joined wires allows the creation of superconducting current paths. Observed Mg-Ni interaction inside the joint area reduces the creation of well-connecting MgB2 phase, and consequently, degrades the critical current of joint by 6.7% of wire's Ic. Joints between MgB2/Nb wires have no inter-metallic interactions, and consequently, large critical currents up to 60% of wire's Ic can obtained. Presented results show that wires with inert metallic sheath and added boron powder could be used for the fabrication of applicable superconducting joints and MgB2 coils working in persistent mode.

Automated summary

Superconducting joints between single-core MgB2/Ni and MgB2/Nb wires were manufactured using an internal Mg diffusion (IMD) process and scarf joints architecture. The transport currents of the joints were measured and compared with the currents of the used MgB2 wires under different conditions. The structure of the joints was analyzed by an optical microscope. It was found that adding boron powder between the joined wires allows for the creation of superconducting current paths. The interaction between Mg and Ni inside the joint area affects the formation of the MgB2 phase and degrades the critical current, while joints between MgB2/Nb wires have no inter-metallic interactions and show large critical currents.