Conceptual designs of 1.5 and 3.0 T full-body magnetic resonance imaging (MRI) magnets using conduction cooled MgB2 superconductor are presented. The sizes, locations, and number of turns in the eight coil bundles are determined using optimization methods that minimize the amount of superconducting wire and produce magnetic fields with an inhomogeneity of less than 10 ppm over a 45 cm diameter spherical volume. MgB2 superconducting wire is assessed in terms of the transport, thermal, and mechanical properties for these magnet designs. Careful calculations of the normal zone propagation velocity and minimum quench energies provide support for the necessity of active quench protection instead of passive protection for medium temperature superconductors such as MgB2. A new 'active' protection scheme for medium Tc based MRI magnets is presented and simulations demonstrate that the magnet can be protected. Recent progress on persistent joints for multifilamentary MgB2 wire is presented. Finite difference calculations of the quench propagation and temperature rise during a quench conclude that active intervention is needed to reduce the temperature rise in the coil bundles and prevent damage to the superconductor. Comprehensive multiphysics and multiscale analytical and finite element analysis of the mechanical stress and strain in the MgB2 wire and epoxy for these designs are presented for the first time. From mechanical and thermal analysis of our designs we conclude there would be no damage to such a magnet during the manufacturing or operating stages, and that the magnet would survive various quench scenarios. This comprehensive set of magnet design considerations and analyses demonstrate the overall viability of 1.5 and 3.0 T MgB2 magnet designs.

中文翻译：

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用于 1.5 和 3.0 T 全身 MRI 系统的传导冷却 MgB2 磁体的概念设计


提出了使用传导冷却 MgB2 超导体的 1.5 和 3.0 T 全身磁共振成像 (MRI) 磁体的概念设计。八个线圈束的尺寸、位置和匝数是使用优化方法确定的，这些方法最大限度地减少超导线的数量，并在直径 45 厘米的球形体积上产生不均匀性小于 10 ppm 的磁场。 MgB2 超导线材根据这些磁体设计的传输、热和机械性能进行评估。对法向区传播速度和最小失超能量的仔细计算为中温超导体（如 MgB2）采用主动失超保护而不是被动保护的必要性提供了支持。提出了一种针对基于中等 Tc 的 MRI 磁体的新“主动”保护方案，并且模拟表明该磁体可以受到保护。介绍了多丝 MgB2 线持久接头的最新进展。对失超传播和失超期间温升的有限差分计算得出的结论是，需要主动干预来降低线圈束中的温升并防止损坏超导体。首次对这些设计中的 MgB2 线和环氧树脂中的机械应力和应变进行全面的多物理场和多尺度分析和有限元分析。根据我们设计的机械和热分析，我们得出结论，在制造或操作阶段不会对这种磁体造成损坏，并且磁体能够承受各种失超情况。这套全面的磁体设计考虑因素和分析证明了 1.5 和 3.0 T MgB2 磁体设计的整体可行性。