We present post-quench analyses of the MIT 800-MHz REBCO insert magnet (H800), unexpectedly quenched during operation in March 2018, and design study of a new 800-MHz HTS insert (H800N). The as-wound H800 was supposed to contribute 18.7 T and, with an LTS background magnet (L500), produce 30.5 T corresponding to a proton resonance frequency of 1.3 GHz. The H800 was operated at 4.2 K in liquid helium and, about 5 min after the power supply reached a target operating current of 251.3 A, it experienced a quench. Because the damage in the H800 was more widespread than it first appeared, we decided to design and build a new insert magnet, H800N. In designing H800N, we tried to eliminate unanticipated flaws in our H800 design. H800N has been designed to be more stable and reliable against quench without permanent damage by: 1) adopting a single solenoid structure composed of 40 stacked double pancake coils with improved cross-over sections; 2) enhancing thermal stability; and 3) reducing excessive current margin for quench protection.

中文翻译：

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MIT 1.3-GHz LTS/HTS NMR 磁体：淬火后分析和新的 800-MHz 插入设计

我们对 MIT 800 MHz REBCO 插入磁体 (H800) 进行了淬火后分析，该磁体在 2018 年 3 月的运行过程中意外淬火，并对新型 800 MHz HTS 插入磁体 (H800N) 进行了设计研究。缠绕时的 H800 应该贡献 18.7 T，并且在使用 LTS 背景磁体 (L500) 的情况下，产生 30.5 T，对应于 1.3 GHz 的质子共振频率。H800 在 4.2 K 的液氦中运行，在电源达到 251.3 A 的目标工作电流约 5 分钟后，它经历了失超。由于 H800 中的损坏比最初出现时更为广泛，因此我们决定设计和制造新的插入式磁铁 H800N。在设计 H800N 时，我们试图消除 H800 设计中意想不到的缺陷。H800N的设计更加稳定可靠，抗失超，不会造成永久性损坏：1）采用由40个堆叠的双扁平线圈组成的单电磁铁结构，并改进了交叉截面；2）增强热稳定性；3) 减少失超保护的过大电流裕度。