Superconductors in SQUID-Based Ultralow Field NMR—Flux-Trapping in Type-II Wires
Superconductors in SQUID-Based Ultralow Field NMR—Flux-Trapping in Type-II Wires
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基于 SQUID 的超低场 NMR 中的超导体——II 型导线中的磁通捕获
DOI：
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发表时间：
2015
影响因子：
1.8
通讯作者：
M. Burghoff
中科院分区：
文献类型：
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作者：
Seong;Rainer Korber;Kiwoong Kim;Kwon;S. Lee;J. Shim;M. Burghoff
最近在发展超低场核磁共振(核磁共振)方面的努力集中在增加预极化场(BP)强度上。高达数百毫秒的强大BP是高质量核磁共振信号的必备条件。然而，BP需要在毫秒内完全移除，以便在样品磁化消失之前进行自旋弛豫信号测量。在之前的研究中，我们比较了三个由Nb、NbTi和Pb制成的拾取线圈，我们发现只有由PbI超导体制成的拾取线圈不受BP线圈的强磁场影响，并产生尖锐的核磁共振信号。其他由第二类超导体制成的线圈都开始受到降级的核磁共振信号的影响，BP超过了某个阈值。在这里，我们给出了NbTi和Pb线的磁化环的详细测量，并论证了我们先前研究中提出的反脉冲策略可以最小化俘获磁通并恢复自旋弛豫信号。我们认为，这种反脉冲策略可以应用于超导BP线圈，从而使反脉冲可以中和由于其强大的内场而被困在BP线圈内的磁通，从而大大提高BP强度的极限。
Recent efforts in the development of ultralow field nuclear magnetic resonance (NMR) have focused on increasing prepolarizing field (BP) strength. The strong BP, which is up to hundreds of milliteslas, is mandatory for high-quality NMR signals. However, BP needs to be completely removed within milliseconds so that spin relaxation signal measurement can take place before the sample magnetization wears off. In a previous study, where we compared three pick-up coils made of Nb, NbTi, and Pb, we found that only the pick-up coil made of Pb, which is a type-I superconductor, was unaffected by the strong magnetic field from the BP coil and produced a sharp NMR signal. The other coils made of type-II superconductors all began to suffer from a degraded NMR signal with BP above a certain threshold. Here, we show detailed measurement of magnetization loops of NbTi and Pb wires and argue that the counter pulse strategy suggested in our previous study can minimize the trapped flux and recover the spin relaxation signal. We argue that this counter pulse strategy can be applied to superconducting BP coils, so that the counter pulses can neutralize flux trapped inside the BP coil due to its strong internal field, thereby dramatically increasing the limit on the BP strength.