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.

The applied pretension on the conductor and support condition during coil fabrication has a great effect on the stress state of the coil. Otherwise, the thermal contraction properties of mandrels and coils would cause residual thermal stress during cool down. A combined homogeneous cylinder method was used to analyze the mechanical performance of winding process for the condition of no mandrel support. A finite-element model of solenoid was created to calculate the stress of winding process and cool down. The mandrel support conditions of fixed support at ends of former and radial support along the whole inner surface of former were researched. Mechanical behaviors of one coil used for a 9.4-T magnetic resonance imaging magnet during winding process and cool down were studied based on the aforementioned approach.

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