A ReBCO coated conductor maintains high current-carrying capability under a high magnetic field and superior mechanical performance. As a promising candidate material for high-field high-temperature superconductor magnets, it has been designed for application in the China Fusion Engineering Test Reactor CS coil, with a maximum magnetic field requirement higher than 17 T. In practical application of the ReBCO tapes, the characteristic I c response with respect to electromagnetic (EM) and thermal stress is important for safe operation of the magnet. In this paper, a nine-turn solenoid magnet was wound from 4 m of CORC cable and tested at 4.2 K in a background magnetic field of up to 19 T. The aim is to check the stability of the current-carrying properties of the ReBCO cable under combined thermal and EM loads. The solenoid coil results in a combined peak magnetic field on the conductor of 19.4 T at a critical current of 888 A. Furthermore, no performance degradation was observed after 20 cycles of operation at 800 A (90% I c ) under a background field of 19 T and 10 cycles of warm-up-cool-down between 77 K and room temperature. This demonstrates the stable performance of ReBCO conductors for high-field magnet application with EM and thermal cycles.

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This paper proposes a new passive shimming method to design correction iron pieces for compensating field impurities generated by the main magnets of high field magnetic resonance imaging (MRI) for human body imaging. First, the relationship formula of a magnetic dipole to any field point in space is established. Then, a sensitivity matrix in the form of spherical harmonic expansions can be set up based on the contribution of each shim piece to each field point. Next, an optimization procedure of linear programming is applied to determine the location and thickness of the ferromagnetic shim pieces. This is different from the previous methods that consider that all magnetic moments for each magnetized iron piece are located only at its central position, which may cause some intrinsic errors. This method takes the shim piece’s volume into account and gives more accurate results in a sensitivity matrix by means of integration in the azimuthal and axial directions while the radial (thickness) direction remains constant. Finally, a case study combining the analytical method and a 3D finite element analysis simulation demonstrates that the new approach provides better results in terms of homogeneity. The method presented can also be used to design passive shims for various practical MRI applications.

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