High Frequency Gyrotron for DNP/NMR Research.

描述(申请人提供)：建议的研究计划集中于研究和开发一种广泛可调的高频(527 GHz)回旋振荡器，用于动态核极化固态核磁共振谱(DNP/SS核磁共振)。在核磁共振中，由于观察到的原子核的旋磁比很小，信号强度本质上很低。DNP/核磁共振实验可以提供20-400倍的信号增强，使DNP/核磁共振成为阐明生物系统结构、功能和动力学性质的重要技术。这些技术在强磁场下的全面实施受到两个问题的限制：1)在140-600 GHz和2 GHz范围内产生微波的高功率微波源不足。)事实上，基本上所有的核磁共振磁体都以持续模式在固定场中工作，这使得将微波频率与EPR谱中的正确频率匹配以优化DNP变得困难。这项提案要求提供资金，以开发一种高稳定性的回旋振荡器，为这两个问题提供解决方案。10到50瓦、527 GHz、带宽可调2 GHz的回旋管将与800 MHz核磁共振光谱仪一起使用，使其成为世界上磁场最高的DNP/核磁共振光谱仪。这台光谱仪应该能在目前正在进行的核磁共振研究的极高磁场中提供显著的信号增强。527 GHz回旋管的开发带来了独特的科学和工程挑战，包括：在低电压和二次谐波回旋频率下工作时，回旋管的增益大大降低；在高频下，欧姆损耗很高；以及超导磁体的内径尺寸有限。传统的高Q腔回旋振荡器的束流参数变化给出了不到0.1%的频率调谐范围，不适合这种应用。我们提出了一种新的调谐方法来构建527 GHz回旋管：即通过改变磁场和利用耦合一系列高阶轴向模的回旋管腔来实现。所提出的527 GHz回旋管振荡器将从我们对330 GHz可调谐回旋管振荡器的研究中获得极大的成功。我们最近展示了330 GHz回旋管在1.2 GHz的调谐范围内超过21瓦的输出功率。通过改变磁场、电压和腔体温度来实现调谐。因此，无需提供谐振器的机械调谐即可完成调谐，从而确保更稳定、更简单和更方便的操作条件。该方案给出了一个527 GHz回旋管的完整设计，表明预测的功率水平和调谐范围是可行的。在拟议研究的第一年，我们将完成330 GHz可调谐回旋管的广泛测试、优化和调试，同时设计和订购527 GHz回旋管的长交货期项目。这项延续建议的资金对于保持生物分子核磁共振光谱这一重要领域的进展至关重要。 与公众健康相关：拟议的研究旨在建立一种高频微波源，它将极大地提高核磁共振(核磁共振)光谱仪的灵敏度，从而大大加快生物固体核磁共振实验中的光谱获取。这种新型的回旋管微波源将是世界上用于增强核磁共振研究的最高频率的源，当应用于800 MHz核磁共振光谱仪时，应该可以揭示独特的分子结构信息。改进的技术将增加对淀粉样蛋白和膜蛋白结构的了解，这是了解它们在生物系统中作用的关键。

DESCRIPTION (provided by applicant): The proposed research program is focused on the research and development of a widely tunable, high frequency (527 GHz) gyrotron oscillator for application to dynamic nuclear polarization solid-state nuclear magnetic resonance spectroscopy (DNP/SSNMR). In NMR, signal intensities are intrinsically low due to the small gyromagnetic ratios of the observed nuclei. DNP/NMR experiments can provide signal enhancements of 20 to 400, making DNP/NMR an important technique for elucidating the structure, function, and dynamic properties of biological systems. The full implementation of these techniques at high magnetic fields has been limited by two problems: 1.) the paucity of high power microwave sources that generate microwaves in the region 140 - 600 GHz and 2.) the fact that essentially all NMR magnets operate at fixed field in persistent mode, making it difficult to match the microwave frequency to the correct frequency in the EPR spectrum to optimize DNP. This proposal requests funding to develop a high-stability gyrotron oscillator that provides a solution to these two problems. The 10 to 50 Watt, 527 GHz gyrotron with a tunable bandwidth of 2 GHz will be used in conjunction with an 800 MHz NMR spectrometer, making it the highest magnetic field DNP/NMR spectrometer in the world. This spectrometer should provide dramatic signal enhancement at the very high magnetic fields where contemporary NMR research is currently being performed. The development of the 527 GHz gyrotron presents unique scientific and engineering challenges, including: greatly reduced gyrotron gain when operating at a low voltage and at the second harmonic gyro-frequency; high ohmic loss at high frequency; and the limited bore size of the superconducting magnet. Variation of beam parameters in a conventional gyrotron oscillator with a high Q cavity gives a frequency tuning range of less than 0.1 %, inadequate for this application. We propose to build the 527 GHz gyrotron with a novel tuning approach: namely, by varying the magnetic field and by utilizing a gyrotron cavity that couples a series of high order axial modes. The proposed 527 GHz gyrotron oscillator will benefit greatly from the highly successful results of our research on a tunable 330 GHz gyrotron oscillator. We have recently demonstrated more than 21 Watts of output power from a 330 GHz gyrotron over a tuning range of 1.2 GHz. Tuning was accomplished by varying the magnetic field, the voltage and the cavity temperature. The tuning was thus accomplished without having to provide mechanical tuning of the resonator, assuring more stable, simple, and convenient operating conditions. The proposal presents a complete design of a 527 GHz gyrotron showing that the predicted power level and tuning range are feasible. During year one of the proposed research, we will complete wide-range testing, optimization and commissioning of the tunable 330 GHz gyrotron while designing and ordering long lead time items for the 527 GHz gyrotron. Funding of this continuation proposal is crucial to maintaining progress in this important field of NMR spectroscopy of biomolecules. PUBLIC HEALTH RELEVANCE: The proposed research is directed at building a high frequency microwave source that will greatly enhance the sensitivity of Nuclear Magnetic Resonance (NMR) spectrometers and will therefore dramatically speed up spectral acquisition in NMR experiments on biological solids. The novel gyrotron microwave source will be the highest frequency source in the world for use in enhanced NMR research and, when applied to an 800 MHz NMR spectrometer, should reveal unique molecular structure information. The improved techniques will lead to increased understanding of the structure of amyloid and membrane proteins which are key to understanding their role in biological systems.