Gyrotron Travelling Wave Amplifier for high field Electron Paramagnetic Resonance and high frequency Dynamic Nuclear Polarisation

该计划的目的是开发一个稳定的，高功率，宽带真空管放大器和亚毫米波固态驱动器，并展示其用于广泛的应用，涵盖从生物化学到物理，电气工程和能源研究的科学范围。在所提出的回旋管放大器中，电子在磁场中沿着螺旋路径行进。该装置的设计使得电子的动能被转移到被限制在同一区域的电磁辐射，从而放大后者。我们将研究一种新的概念，它使用了5倍的螺旋线的内表面上的“圆柱形”波导从根本上修改的电磁波色散，使本征模有限，恒定的群速度在该地区的近无限的相速度。这种新颖的色散首次为360至395 GHz频率范围内的高功率（100 W）、宽带（~ 10%）、高增益（>40 dB）回旋管放大器开辟了潜力。我们已经在W波段（92至98 GHz）频率下进行了初步实验，并将在我们的领先优势的基础上，根据对这一新概念的最佳理解，创建360至395 GHz频率范围内的放大器，并对其进行精确测量增益、带宽、效率和抗振荡稳定性。这一发展将是一项具有重大商业和科学应用的通用技术。这些包括通过动态核极化技术提高NMR灵敏度，高场脉冲电子顺磁共振光谱，材料处理，融合诊断和长距离，高带宽，视线通信。该提案是英国两个领先的毫米波小组之间的合作：斯特拉斯克莱德大学的原子，光束和等离子体小组和STFC卢瑟福阿普尔顿实验室（RAL）的毫米波技术小组。总的来说，这些集团在高功率毫米波源、仪器和组件的开发方面拥有数十年的经验和良好的国际声誉，在商业化、与行业的联系和实现项目目标方面有着良好的记录。这项工作的核心领域将使英国在先进的高频、高功率毫米波放大器和固态源方面处于领先地位，这将在未来几年对高场EPR/DNP光谱学的研究产生影响。在工作过程中，Strathclyde的工作人员将设计回旋管放大器，并将设计交给RAL进行精密制造。其将使用现有技术的计算机控制的铣床切割成具有铅笔芯直径的螺旋。在RAL对其波导特性进行初步测试后，这些组件将被送往Strathclyde进行最终测试，并与定制的电子源和真空外壳集成。RAL还将设计和制造驱动新型放大器所需的倍频器级联：他们将使用GaAs肖特基二极管的新配置来制造这些组件。新的放大器的频率覆盖范围，增益和最大输出功率是这样的，需要世界一流的来源，以提供充分利用放大器特性所需的高输入功率。

The aim of this program is to develop a stable, high power, wideband vacuum tube amplifier and sub-millimetre wave solid state driver, and demonstrate their use for a wide range of applications that cover the scientific spectrum from biochemistry through physics, electrical engineering and energy studies. In the proposed gyrotron amplifer, electrons are made to travel along a helical path in a magnetic field. The design of the device is such that the electrons' kinetic energy is transferred to electromagnetic radiation confined to the same region, thereby amplifying the latter. We will investigate a novel concept which uses a 5-fold helical corrugation on the inside surface of a 'cylindrical' waveguide to radically modify the electromagnetic wave dispersion giving eigenmodes with finite, constant group velocity in the region of near infinite phase velocity. This novel dispersion opens up for the first time the potential for a high power (100 W), broadband (~10 %), high gain (>40 dB) gyrotron amplifier in the 360 to 395 GHz frequency range. We have performed a preliminary experiment at W-band, 92 to 98 GHz, frequencies and will build on our lead to create an amplifier in the 360 to 395 GHz frequency range based on the best understanding of this new concept and perform precision measurements of its gain, bandwidth, efficiency and stability against oscillations. This development would represent a generic technology with major commercial and scientific applications. These include improving NMR sensitivity through Dynamic Nuclear Polarisation techniques, high field pulse Electron Paramagnetic Resonance spectroscopy, materials processing, fusion diagnostics and long range, high bandwidth, line of sight communications. The proposal is a collaboration between two of the UK's leading millimetre wave groups: the Atoms, Beams and Plasmas Group at the University of Strathclyde and the Millimetre Wave Technology Group at the STFC Rutherford Appleton Laboratory (RAL). Collectively these groups have decades of experience and strong international reputations in the development of high power mm-wave sources, instrumentation and components, with a strong track record in commercialisation, links with industry and delivering on project objectives. The proposed work is in a core area that is likely to lead to UK leadership in advanced high frequency, high power millimetre wave amplifiers and solid state sources that will impact on studies on high field EPR/DNP spectroscopy in years to come.In the course of the work, Strathclyde staff will design the gyrotron amplifier and pass the designs to RAL for precision manufacture of the fine features, which will be cut into a helix with the diameter of the pencil lead using state of the art computer controlled milling machines. After preliminary testing of their waveguiding properties at RAL, the components will be passed to Strathclyde for final testing and integration with the custom built electron source and vacuum enclosure. RAL will also design and build the frequency multiplier cascade required to drive the novel amplifier: they will use new configurations of their GaAs Schottky diodes to make these components. The frequency coverage, gain and maximum output power of the new amplifiers are such that world class sources are needed to provide the high input powers necessary to exploit fully the amplifier properties.