This paper presents construction details and test results of a persistent-mode 0.5-T MgB2 magnet developed at the Francis Bitter Magnet Lab, MIT. The magnet, of 276-mm inner diameter and 290-mm outer diameter, consisted of a stack of 8 solenoidal coils with a total height of 460 mm. Each coil was wound with monofilament MgB2 wire, equipped with a persistent-current switch and terminated with a superconducting joint, forming an individual superconducting loop. Resistive solder joints connected the 8 coils in series. The magnet, after being integrated into a testing system, immersed in solid nitrogen, was operated in a temperature range of 10-13 K. A two-stage cryocooler was deployed to cool a radiation shield and the cold mass that included mainly ~60 kg of solid nitrogen and the magnet. The solid nitrogen was capable of providing a uniform and stable cryogenic environment to the magnet. The magnet sustained a 0.47-T magnetic field at its center persistently in a range of 10-13 K. The current in each coil was inversely calculated from the measured field profile to determine the performance of each coil in persistent-mode operation. Persistent-current switches were successfully operated in solid nitrogen for ramping the magnet. They were also designed to absorb magnetic energy in a protection mechanism; its effectiveness was evaluated in an induced quench.

中文翻译：

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用于 MRI 的持久模式 0.5 T 固体氮冷却 MgB2 磁铁

本文介绍了麻省理工学院 Francis Bitter Magnet 实验室开发的持久模式 0.5-T MgB2 磁铁的构造细节和测试结果。内径为 276 毫米、外径为 290 毫米的磁铁由 8 个总高度为 460 毫米的螺线管线圈组成。每个线圈都用单丝 MgB2 线缠绕，配备有持续电流开关并以超导接头终止，形成单独的超导回路。电阻焊点将 8 个线圈串联。将磁体集成到测试系统中后，浸入固体氮中，在 10-13 K 的温度范围内运行。部署了两级低温冷却器来冷却辐射屏蔽和主要包括约 60 kg 的冷物质固体氮和磁铁。固体氮能够为磁体提供均匀且稳定的低温环境。磁铁在其中心持续承受 0.47-T 的磁场，范围为 10-13 K。每个线圈中的电流从测量的场分布中反向计算，以确定每个线圈在持久模式操作中的性能。持续电流开关在固体氮中成功运行，以提高磁铁的斜率。它们还设计用于在保护机制中吸收磁能；在诱导淬火中评估了其有效性。每个线圈中的电流是根据测量的场分布反向计算的，以确定每个线圈在持续模式操作中的性能。持续电流开关在固体氮中成功运行，以提高磁铁的斜率。它们还设计用于在保护机制中吸收磁能；在诱导淬火中评估了其有效性。每个线圈中的电流从测量的场分布中反向计算，以确定每个线圈在持续模式操作中的性能。持续电流开关在固体氮中成功运行，以提高磁铁的斜率。它们还设计用于在保护机制中吸收磁能；在诱导淬火中评估了其有效性。