Operation and performance analyses of 350 and 700 MHz low-/high-temperature superconductor nuclear magnetic resonance magnets: A march toward operating frequencies above 1 GHz
Operation and performance analyses of 350 and 700 MHz low-/high-temperature superconductor nuclear magnetic resonance magnets: A march toward operating frequencies above 1 GHz
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DOI：
10.1063/1.3065538
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发表时间：
2009-01-15
影响因子：
3.2
通讯作者：
Iwasa, Yukikazu
中科院分区：
文献类型：
--
作者：
Hahn, Seungyong;Bascunan, Juan;Iwasa, Yukikazu
自2000年以来，麻省理工学院（MIT）弗朗西斯·比特磁体实验室开展了一个三期项目，其最终目标是完成一个1吉赫兹高分辨率低温/高温超导（LTS/HTS）核磁共振（NMR）磁体。在LTS/HTS磁体组件中，一个高温超导插入件被放置在低温背景磁体的冷孔内。到目前为止，已经设计、建造和测试了两个LTS/HTS磁体：第一阶段的350兆赫兹（LH350）磁体和第二阶段的700兆赫兹（LH700）磁体。该项目的目标最近从最初的1吉赫兹升级到了新的1.3吉赫兹。在本文中，我们对这两个LTS/HTS NMR磁体进行了广泛的性能分析。通过谐波分析对LH350和LH700的空间均匀性和时间稳定性进行了研究，并讨论了在这两个磁体运行中凸显的四个关键问题：（1）场常数降低；（2）“大”的剩余Z1梯度及其时间衰减；（3）大的单周期田形场梯度；（4）高温超导插入件中屏蔽电流感应场。
Since 2000, a three-phase program with a final goal to complete a 1 GHz high-resolution low-/high-temperature superconductor (LTS/HTS) nuclear magnetic resonance (NMR) magnet has been conducted at the Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology (MIT). In a LTS/HTS magnet assembly, a HTS insert is placed in the cold bore of a LTS background magnet. To date, two LTS/HTS magnets have been designed, constructed, and tested: a 350 MHz (LH350) in phase 1 and a 700 MHz (LH700) in phase 2. The program's target has recently been upgraded from the original goal of 1 GHz to a new goal of 1.3 GHz. In this paper, we present extensive performance analyses of the two LTS/HTS NMR magnets. Spatial homogeneity and temporal stability of LH350 and LH700, examined with harmonic analysis, and four key issues that became evident in the operation of these two magnets are discussed: (1) field constant reduction, (2) "large" residual Z1 gradient and its temporal decay, (3) large one-periodic tesseral field gradients, and (4) screening-current-induced field in the HTS inserts.