Novel Traveling Wave Tubes for CW and Pulsed DNP NMR

 描述(申请人提供)：本申请建议开发250 GHz行波管振荡器(第一年和第二年)和250 GHz行波管放大器(第三年和第四年)，用于动态核极化(DNP)核磁共振实验。在DNP中，高频微波源被用来照射电子-核跃迁，电子自旋库中的高自旋极化通过超精细和偶极相互作用转移到核SPI系统。由此产生的核磁共振信号增强已被证明超过400倍，因此DNP核磁共振现在被认为是核磁共振波谱的重大进步。电子自旋系统激发所需的微波频率在毫米到太赫兹范围内-对于g=2电子，在400 MHz、600 MHz和800 MHz的1H频率下分别为263 GHz、395 GHz和527 GHz。到目前为止，DNP实验一直依赖于为DNP魔角旋转(MAS)实验开发的连续功率输出为20至50瓦的回旋管振荡器。回旋管现在已经可以商业使用，在过去的五到十年里，全世界已经安装了大约30个这样的系统。然而，回旋管既昂贵又相对较大，后者造成了定位问题。行波管源将大大降低DNP光谱仪的微波源的成本和尺寸。如果行波管源被成功开发，它将允许DNP核磁共振技术传播到世界各地的数百个实验室，从而使突破性的DNP方法广泛应用于生物医学研究社区。行波管向高频、高功率方向发展是现代真空电子器件研究的热点。我们团队有一个正在进行的研究计划，研究W波段95 GHz行波管放大器，最近成功地展示了一种采用过模结构的创新95 GHz行波管。拟议的研究将建立在20瓦、250 GHz行波管振荡器的设计、制造和演示的成功基础上。该装置将采用一种新颖的相互作用结构，允许较大的电子束隧道，从而最大限度地减少连续工作时的束流截留和结构发热。行波管将与现有的380 MHz核磁共振波谱仪一起用于DNP研究，从而在实验上演示了行波管在DNP中的应用。我们的结构概念可扩展到更高的频率，如395或527 GHz。放大器在DNP核磁共振实验中也非常有吸引力，在DNP核磁共振实验中，时域光谱技术可以产生巨大的增强，并且与CW交叉效应机制不表现出磁场相关性。我们将建造一个行波管放大器，以实现更高的输出功率，在250 GHz，使用脉冲电子束，在几微秒的时间尺度上，200W。该功放可以用现有的硬件进行测试，节省了大量的成本。我们还将演示从行波管到位于核磁共振探头中的样品的输出功率的高效传输。总而言之，这些研究将代表行波管应用于DNP核磁共振的完整解决方案。

 DESCRIPTION (provided by applicant): This application proposes the development of a 250 GHz traveling wave tube (TWT) oscillator (years one and two) and a 250 GHz TWT amplifier (years three and four) for utilization in dynamic nuclear polarization (DNP) NMR experiments. In DNP, a high frequency microwave source is used to irradiate electron-nuclear transitions and the high spin polarization present in the electron spin reservoir is transferred to the nuclear spi system through the hyperfine and dipolar interactions. The resulting enhancements in NMR signals have been demonstrated to exceed a factor of 400, and thus DNP NMR is now considered a major advance in NMR spectroscopy. The required microwave frequency for the electron spin system excitation is in the millimeter to terahertz regime - 263 GHz, 395 GHz and 527 GHz for g=2 electrons at 400 MHz, 600 MHz and 800 MHz 1H frequencies respectively. To date, DNP experiments have relied on gyrotron oscillators with continuous power output of 20 to 50 Watts developed for DNP magic angle spinning (MAS) experiments. Gyrotrons are now commercially available and about 30 such systems have been installed worldwide in the past five to ten years. However, gyrotrons are both costly and relatively large, the latter creating issues with siting. A TWT source will dramatically lower the cost and size of the microwave source for DNP spectrometers. If the TWT source is successfully developed, it will allow dissemination of DNP NMR techniques to hundreds of laboratories worldwide, thus making the breakthrough DNP method widely available to the biomedical research community. Extending the operation of TWTs to higher frequency and power is an area of intensive exploration in modern vacuum electron device research. Our group has an ongoing research program to investigate TWT amplifiers at 95 GHz in W-Band and have recently successfully demonstrated an innovative 95 GHz TWT in an overmoded structure. The proposed research will build upon that success in the design, fabrication and demonstration of a 20 Watt, 250 GHz TWT oscillator. The proposed device will use a novel interaction structure that allows a relatively large electron beam tunnel, thus minimizing beam interception and structure heating in continuous operation. The TWT will be used with an existing 380 MHz NMR spectrometer for DNP research, thus demonstrating experimentally the application of a TWT to DNP. Our structure concept is scalable to higher frequencies, such as 395 or 527 GHz. An amplifier is also very attractive for DNP NMR experiments, where time-domain spectroscopic techniques can produce large enhancements and in contrast to CW Cross Effect mechanisms do not exhibit a magnetic field dependence. We will build a TWT amplifier to achieve higher output power, 200 W at 250 GHz, using pulsed electron beams on the time scale of several microseconds. The amplifier can be tested with existing hardware, a large cost savings. We will also demonstrate highly efficient transmission of the output power from the TWT to the sample located in the NMR probe. Collectively, these studies will represent a complete solution of the application of the TWT to DNP NMR.