High Frequency Gyrotron for DNP/NMR Research.

描述（由申请人提供）：本研究计划的重点是研究和开发一种广泛可调谐的高频（527 GHz）回旋管振荡器，用于动态核极化固体核磁共振波谱（DNP/SSNMR）。在核磁共振中，由于观察到的原子核的小回旋磁比，信号强度本质上是低的。DNP/NMR实验可以提供20到400的信号增强，使DNP/NMR成为阐明生物系统结构、功能和动态特性的重要技术。这些技术在高磁场下的全面实施受到两个问题的限制：1.)产生140 - 600 GHz区域微波的高功率微波源的缺乏；2.)基本上所有核磁共振磁体都以持续模式在固定场下工作，这使得很难将微波频率与EPR频谱中的正确频率匹配以优化DNP。该提案要求资助开发一种高稳定性回旋加速器振荡器，以解决这两个问题。10至50瓦，527 GHz回旋管，可调谐带宽为2 GHz，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。这种光谱仪应该在非常高的磁场中提供戏剧性的信号增强，当代核磁共振研究目前正在进行。527 GHz回旋管的发展面临着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大大降低回旋管增益；高频时欧姆损耗大；以及超导磁体的有限孔径。在具有高Q腔的传统回旋管振荡器中，光束参数的变化使频率调谐范围小于0.1%，不适合这种应用。我们提出了一种新颖的调谐方法：即通过改变磁场和利用耦合一系列高阶轴向模式的回旋管腔来构建527 GHz回旋管。所提出的527 GHz回旋管振荡器将大大受益于我们在330 GHz可调谐回旋管振荡器上的成功研究成果。我们最近展示了在1.2 GHz的调谐范围内，330 GHz回旋管的输出功率超过21瓦。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，简单和方便的操作条件。该方案给出了一个527 GHz回旋管的完整设计方案，证明了所预测的功率水平和调谐范围是可行的。在计划研究的第一年，我们将完成330 GHz可调谐回旋管的大范围测试、优化和调试，同时设计和订购527 GHz回旋管的长交付期项目。资助这一延续提案对于维持生物分子核磁共振波谱这一重要领域的进展至关重要。

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.