Preparation of a small-size superconducting joint for C-doped 30-filament MgB2 wires

A preparation method of a small-size MgB2 superconducting joint with 2.0 mm diameter for C-doped 30-filament MgB2 wires is presented in this paper. Herein, an unreacted in situ C-doped monofilament wire was utilized as the connecting structure, since it contains a low quantity of dense precursor which needs less pressure during fabrication, avoiding distortion of the multifilament in the parent wires, as shown in SEM images. After heat treatment, the formed C-doped MgB2 bulk with small volume in the joint has the ability to release heat quickly, resulting in good stability. The morphology of the joint proved the MgB2-MgB2 interface between the monofilament and 30-filament wire had been successfully connected. The joint sintered at 600 degrees C for 2 h shows an apparent superconducting transition with Tc-on = 33.49 K and has negligible resistance below 30.56 K as depicted in the R-T curve. It also has approximately 40% J(c) value of the parent 30-filament wire, at 4.2 K in 3 T.