Fabrication of NbTi Superconducting Joints for 400-MHz NMR Application

NbTi superconducting joints (SJs) for a 400-MHz nuclear magnetic resonance (NMR) magnet system were fabricated using the superconducting solder matrix replacement in an open-air condition. A detection device for testing the resistance of SJ has been established. The results show that the overall resistance of SJs is 9.58 × 10
^-12
Ω under the background field of 1 T by summation of individual joint resistance. The resistance of SJs and the capability for current load should meet the demands of the NMR system. The SJs are placed inside the cylindrical vessel above the magnet. The magnetic flux inside the top of the vessel is no more than 0.3 T to assure performance of joints. As results, there is only 0.0001 ppm for homogeneity deviation caused by SJs on this NMR system, and therefore, the negative effect is negligible.