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Abstract：High field nuclear magnetic resonance spectrometer (NMR) is an important scientific instrument in the fields of biology and chemistry, mainly used for qualitative and quantitative analysis of organic and inorganic substance structures. High field NMR superconducting magnets require higher magnetic field strength, smaller magnetic field uniformity, lower magnetic field drift, and smaller stray field range. This article introduces the design and optimization process of an ultra compact 800MHz (18.79T) NMR superconducting magnet. With the design requirements of the 800MHz (18.79T) NMR superconducting magnet as the goal, a nonlinear multi-objective programming optimization algorithm is proposed. Through this method, the optimization results of multiple objective parameters are output, and the magnetic aperture, magnetic field uniformity, and stray field (5 Gauss line) are optimized. The spatial position, electromagnetic density, and electromagnetic stress of different coils are obtained, and the stability of the magnet coil design is evaluated using coil load rate and safety margin indicators. The 800MHz NMR superconducting magnet adopts a technical path combining low-temperature NbTi superconducting wire and high-temperature ReBCO superconducting tape. The coupled electromagnetic stress of the low-temperature coil and high-temperature coil is calculated, and the stress and deformation distribution of the coil skeleton is analyzed. Mechanical simulation analysis is also carried out on key components such as the low-temperature system and suspension rod of the magnet. The optimization results show that the room temperature aperture of the magnet is greater than 54mm, and the homogeneity of the magnet design (without adding a uniform field coil) is 1.15ppm@18mm DSV, magnet stray field (5Guass line) is 2.3m in the axial direction and 1.63m in the radial direction from the center of the magnetic field. The minimum safety margin of the magnet coil is 15.87%, and the maximum circumferential stress of the magnet coil is 180Mpa. The stress-strain of the magnet skeleton is less than the yield stress of the material. The magnet meets the design requirements and provides necessary reference for the engineering prototype of the 800MHz superconducting magnet.
Index Terms：High Field NMR，Superconducting Magnet，Homogeneity，Warm Bore，Stray Field，Safety Margin, Electromagnetic stress, High Temperature Superconductor
