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China Fusion Engineering Test Reactor (CFETR)" is a new generation of tokamak which aims to bridge the gaps between the fusion experimental reactor ITER and the demonstration reactor (DEMO). The superconducting magnet system is the core component in tokamak and future fusion reactor, and the superconducting magnet system for CFETR will be a big challenge due to the higher magnetic field is required. Based on the current design, the maximum field of Toroidal Field (TF) coil is around 14.5 T, and for Center Solenoid (CS) coil, the maximum field would be even higher. Now the significant work is developing highperformance Cable-in-Conduit Conductor (CICC) for these high field coils. Obviously, a test facility is necessary for developing new CICCs. It is well known that SULTAN facility plays an important and successful role in ITER conductor development, almost all ITER sample conductors were tested at SULTAN. But it's hard to satisfy future test work due to its magnetic field limitation (<12 T). Now in China, a new program has been launched to build a new conductor test facility which has similar functions to SULTAN, but can provide background field up to 15 T. This paper will introduce the concept design of the magnet system of the superconducting conductor test facility.

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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