Design Overview of the MIT 1.3-GHz LTS/HTS NMR Magnet with a New REBCO Insert

We present a design overview of the MIT 1.3-GHz LTS/HTS NMR magnet (1.3G) with a newly designed 835-MHz REBCO insert (H835) as a replacement of the 800-MHz REBCO insert that was damaged when it quenched during operation in 2018. The new H835 contributes 19.6 T as designed, with an LTS back-ground magnet of 10.9 T, toward a total field of 30.5 T that corre-sponds to a proton resonance frequency of 1.3 GHz. The H835 is de-signed to be stable within 1.3G design constraints. The design also prevents the entire insert from permanent damage in the improba-ble event like a quench. Key design features are: 1) a single-solenoid structure, composed of 38 stacked metal-co-wound no-insula-tion and 4 stacked no-insulation double-pancake coils with mechan-ically improved cross-over sections; 2) enhanced thermal stability; and 3) reduced excessive current margin with a detect-and-activate-the-heater method. This paper includes: 1) electromagnetic and me-chanical design of the H835; 2) cryogenics overview; 3) quench pro-tection schemes; and 3) discussion on the next steps toward the 1.3G.

本研究介绍了麻省理工学院（MIT）1.3 GHz低温超导体（Low Temperature Superconductor, LTS）/高温超导体（High Temperature Superconductor, HTS）核磁共振（Nuclear Magnetic Resonance, NMR）磁体系统（下称1.3G系统）的设计概况：该系统采用全新设计的835 MHz稀土钡铜氧化物（Rare Earth Barium Copper Oxide, REBCO）插入式磁体（下称H835），替代2018年运行过程中因失超损坏的800 MHz REBCO插入式磁体。
按设计指标，全新的H835可提供19.6 T的磁场强度，搭配10.9 T的LTS主背景磁体，最终总磁场可达30.5 T，对应质子共振频率为1.3 GHz。
H835的设计在1.3G系统的约束范围内具备良好稳定性。
此外，即便遭遇失超这类极罕见工况，该设计也可避免整个插入式磁体发生永久性损坏。
其核心设计特点包括：1）采用单螺线管结构，由38层堆叠的金属共绕无绝缘绕组，以及4层堆叠的无绝缘双饼线圈组成，且过渡段的机械结构经过优化；2）热稳定性得到增强；3）通过“检测并启动加热器”的方法降低了冗余电流裕度。
本文涵盖以下内容：1）H835的电磁与机械设计；2）低温系统概述；3）失超保护方案；以及4）针对1.3G系统后续研发方向的讨论。