A versatile and modular quasi optics-based 200GHz dual dynamic nuclear polarization and electron paramagnetic resonance instrument.
A versatile and modular quasi optics-based 200GHz dual dynamic nuclear polarization and electron paramagnetic resonance instrument.
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DOI：
10.1016/j.jmr.2015.12.012
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发表时间：
2016-03
期刊：
影响因子：
--
通讯作者：
Han S
中科院分区：
文献类型：
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作者：
Siaw TA;Leavesley A;Lund A;Kaminker I;Han S
高磁场（bbb3t）和低温（~2 - 90k）下的固态动态核极化（DNP）作为一种核磁共振信号增强技术已经引起了人们的极大兴趣，并取得了重大的技术进步。尽管如此，目前最先进的DNP操作状态还不能合理选择样品和冷冻条件，也不能先验地预测DNP的性能，而是依赖于纯粹的经验方法。合理优化DNP条件的重要一步是获得DNP仪器能力，以诊断DNP性能并阐明DNP机制。所需的诊断包括测量“DNP功率曲线”，即DNP增强的微波（MW）功率依赖性，“DNP谱”，即DNP增强的MW频率依赖性，电子顺磁共振（EPR）谱和连续波DNP典型的长时间MW辐照后EPR谱的饱和和光谱扩散特性，以及各种电子和核自旋弛豫参数。即使是这些DNP参数的基本测量也需要在高磁场下的通用仪器，目前还没有商用仪器。在本文中，我们描述了这种DNP仪器的详细设计，该仪器由一个在193 - 201 GHz之间可调谐的固态MW源供电，输出高达140 MW的MW功率。准光学（QO）桥和波纹波导控制传输和反射MW的质量和路径，其中波纹波导将开放空间QO桥的MW耦合到超导磁体内部的样品上，反之亦然。至关重要的是，固态MW源的多功能性能够自动获取扫频DNP谱、DNP功率曲线、MW功率和传输诊断以及扫频连续波（CW）和脉冲EPR实验。以QO MW桥为中心的DNP仪器的灵活性将提供一种有效的方法来收集DNP数据，这对于理解实验和样品条件之间的关系以及DNP性能至关重要。该仪器平台的模块化适用于未来的升级和扩展，以包括满足当代DNP需求的新实验功能，包括同时操作两个或多个MW源，时域DNP，电子双共振测量，脉冲EPR操作，或简单地实现更高功率的MW放大器。
Solid-state dynamic nuclear polarization (DNP) at higher magnetic fields (>3 T) and cryogenic temperatures (~2–90 K) has gained enormous interest and seen major technological advances as an NMR signal enhancing technique. Still, the current state of the art DNP operation is not at a state at which sample and freezing conditions can be rationally chosen and the DNP performance predicted a priori, but relies on purely empirical approaches. An important step towards rational optimization of DNP conditions is to have access to DNP instrumental capabilities to diagnose DNP performance and elucidate DNP mechanisms. The desired diagnoses include the measurement of the “DNP power curve”, i.e. the microwave (MW) power dependence of DNP enhancement, the “DNP spectrum”, i.e. the MW frequency dependence of DNP enhancement, the electron paramagnetic resonance (EPR) spectrum and the saturation and spectral diffusion properties of the EPR spectrum upon prolonged MW irradiation typical of continuous wave (CW) DNP, as well as various electron and nuclear spin relaxation parameters. Even basic measurements of these DNP parameters require versatile instrumentation at high magnetic fields not commercially available to date. In this article, we describe the detailed design of such a DNP instrument, powered by a solid-state MW source that is tunable between 193 – 201 GHz and outputs up to 140 mW of MW power. The quality and pathway of the transmitted and reflected MWs is controlled by a quasi-optics (QO) bridge and a corrugated waveguide, where the latter couples the MW from an open-space QO bridge to the sample located inside the superconducting magnet and vice versa. Crucially, the versatility of the solid-state MW source enables the automated acquisition of frequency swept DNP spectra, DNP power curves, the diagnosis of MW power and transmission, and frequency swept continuous wave (CW) and pulsed EPR experiments. The flexibility of the DNP instrument centered around the QO MW bridge will provide an efficient means to collect DNP data that is crucial for understanding the relationship between experimental and sample conditions, and the DNP performance. The modularity of this instrumental platform is suitable for future upgrades and extensions to include new experimental capabilities to meet contemporary DNP needs, including the simultaneous operation of two or more MW sources, time domain DNP, electron double resonance measurements, pulsed EPR operation, or simply the implementation of higher power MW amplifiers.