High-performance superconducting joints are essential for realizing persistent-mode magnets.
Herein, we propose a concept and fabrication of such superconducting joints, which yielded
reliable performance in the operating temperature range of 4.2–25 K. MgB2–MgB2 joints in
magnets are known to result in deterioration of localized electrical, thermal, and mechanical
properties. To overcome these problems, the ends of the two wires are inserted into a pellet press,
which is then filled with a mixture of unreacted magnesium and boron powders, followed by heat
treatment. The critical current capacity and joint resistance were precisely evaluated by the
standard four-probe method in open-circuit and by field-decay measurements in a closed-loop,
respectively. These joints demonstrated up to 66% of the current-carrying capacity of unjoined
wire at 20 K, 2 T and joint resistance of 1.4 × 10−12 Ω at 4.2 K in self-field.