Fabrication and performance of Nb₃Sn superconducting joints

Nb₃Sn superconducting joints were developed, and the joint characteristics were investigated. The joints were prepared by powder metallurgy to sinter the precursor powders that were mechanically alloyed. The optimized parameters were confirmed through x-ray diffraction studies to confirm the stoichiometry of Nb, Sn, and Cu. First, the precursor powders after mechanical alloying were heat treated without the Nb₃Sn wires. Electron backscatter diffraction was used to quantify the crystal morphology, phase distribution, grain boundaries, physical grain orientation, and so on. Small equiaxed Nb₃Sn grains were formed after heat treatment. The high-angle grain boundaries in Nb₃Sn indicated the complete solid-state diffusion reaction. After the Nb₃Sn was successfully prepared, and the superconducting characteristics were measured, we introduce the Nb₃Sn wires to prepare Nb₃Sn joints and measure their electrical properties. To use the space as economically as possible, the joint was tested under different background fields to estimate the joint resistance under various locations in the magnet. The experimental method and the test results are reported in this work. The joint resistance was tested by using the current decay measure method. The electrical resistance of the Nb₃Sn-Nb₃Sn joints was on the 10⁻¹³ Ω level under the 5.5 T magnetic field.