A Benchtop Cryogen-Free 23.5-T/25-mm-RT-Bore Magnet for 1-GHz microcoil NMR Spectroscopy

项目摘要 在本计画中，我们提出发展一台无冷冻剂的23.5-T高温超导（HTS） 用于1 GHz微线圈核磁共振（NMR）光谱的磁体。更高的磁场提供更好的 分辨率和灵敏度，能够分析更大的分子，如复杂的蛋白质，但目前 可用的≥1-GHz NMR磁体非常昂贵并且需要巨大的安装场地，限制了≥1-GHz NMR 世界上的一些实验室。根据定义，台式微线圈NMR磁体是紧凑的，因此其 成本将比标准NMR磁体的成本低近一个数量级，并且可放置在 工作台。此外，无LHe操作使用户能够独立于供应短缺的冷却源。 作为前期工作（R21 GM 129688），我们已经完成了一个12.5 mm冷孔高温超导REBCO磁体 原型，并成功地运行它高达25 T在10 K冷却的制冷机只有，没有液氦， 验证我们的高场REBCO磁体设计与建议的屏蔽电流减少方法。基于 根据这些初步成果和开创性的设计理念，我们将首先设计和建造一个无冷冻剂、屏蔽 具有1.5 m的5高斯边缘场半径的全REBCO 23.5-T/25-mm-RT-孔磁体，然后将其转换为 非NMR场23.5-T磁体到台式1-GHz微线圈NMR磁体，具有<0.1的高均匀性 ppm，在5 mm直径、10 mm长度的圆柱体体积上。我们还打算使用一个内部建立的核磁共振 探针，以证明拟议的磁铁。这种台式磁铁将采用所有的创新设计， 在我们初步的R21计划中，原型磁体验证了操作概念：1）全高温超导成分 和运行在4.2 K以上，仅由制冷机冷却，第一次>4.2-K操作中的所有超高- 场超导磁体; 2）超薄铜层无绝缘绕组技术， REBCO磁体非常紧凑，机械坚固，自我保护; 3）单个线圈形成， 与传统的多嵌套高场NMR磁体相比， 4）操作温度控制的屏蔽电流降低方法， REBCO线圈内的应力和磁场误差; 5）传导冷却操作的低温设计。我们 拟采用铁的被动屏蔽，将5高斯半径缩小到1.5 m以内。以实现目标 场均匀性，我们将采用三超导，铁磁，室温匀场 该技术将由我们的1.3 GHz/54 mm高分辨率NMR磁体补充，目前正在 在FBML的发展，我们正在开发创新的场匀场技术。我们设想 台式无冷冻剂的1-GHz微线圈NMR磁体将成为一种非常强大和负担得起的研究工具 对于基于核磁共振的结构生物学社区谁热切期待更高的工作频率。我们 我相信，我们提出的台式磁体的使能技术将有望引领高温超导磁体 技术到液氦自由>1-GHz核磁共振磁体。

Project Summary In this project we propose to develop a benchtop cryogen-free 23.5-T high-temperature superconducting (HTS) magnet for 1-GHz microcoil nuclear magnetic resonance (NMR) spectroscopy. Higher-field magnet offers better resolution and sensitivity, enabling analysis of larger molecules like complex proteins, however currently available ≥1-GHz NMR magnets are very expensive and require a vast installation site, limiting ≥1-GHz NMR spectroscopy to a few labs in the world. A benchtop microcoil NMR magnet by definition is compact and thus its cost will be less by nearly an order of magnitude than that of the standard NMR magnet, and placeable on a workbench. Also, LHe-free operation enables the user to be independent from a cooling source in short supply. As a preliminary work (R21GM129688), we have completed a 12.5-mm-cold-bore HTS REBCO magnet prototype and successfully operated it up to 25 T at 10 K cooled by a cryocooler only, without liquid helium, verifying our high-field REBCO magnet design with the proposed screening-current reduction method. Based on these preliminary results and pioneering design concept, we will first design and build a cryogen-free, shielded all-REBCO 23.5-T/25-mm-RT-bore magnet having a 5-gauss fringe field radius of 1.5 m, and then convert this non-NMR-field 23.5-T magnet to a benchtop 1-GHz microcoil NMR magnet having a high homogeneity of <0.1 ppm over a 5-mm-diameter, 10-mm-length cylindrical volume. We also intend to use an in-house built NMR probe to demonstrate the proposed magnet. This benchtop magnet will incorporate all the innovative design and operation concepts validated by the prototype magnet in our preliminary R21 program: 1) all-HTS composition and operation at above 4.2 K cooled only by a cryocooler, the first ever >4.2-K operation among all ultra-high- field superconducting magnets; 2) extremely-thin-copper-layered no-Insulation winding technique that makes a REBCO magnet very compact, mechanically robust, and self-protecting; 3) a single coil formation that leads, compared with the traditional multi-nested high-field NMR magnet, to simpler and more affordable manufacturing processes; 4) operational temperature-controlled screening-current reduction method which reduces peak stresses within the REBCO coil and field errors; and 5) cryogenic design for conduction-cooling operation. We intend to adopt a passive shielding by using iron to reduce the 5-gauss radius within 1.5 m. To achieve a target field homogeneity, we will adopt three—superconducting, ferromagnetic, and room-temperature—shimming technique which will be complemented by our 1.3-GHz/54-mm high-resolution NMR magnet, currently under development at the FBML, for which we are developing innovative field-shimming techniques. We envision this benchtop cryogen-free 1-GHz microcoil NMR magnet will become a very powerful and affordable research tool for the NMR based structural biology community who eagerly anticipates higher operating frequencies. We believe that the enabling technologies of our proposed benchtop magnet is poised to lead HTS magnet technology to liquid-helium-free >1-GHz NMR magnets.