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

该计划的目标是开发稳定、高功率、宽带真空管放大器和亚毫米波固态驱动器，并展示它们的广泛应用，涵盖从生物化学到物理、电气工程和能源研究的科学光谱。在所提出的回旋管放大器中，电子在磁场中沿螺旋路径传播。该装置的设计是这样的，即电子的动能被转移到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，即在圆柱形波导的内表面上使用5倍螺旋波纹来从根本上改变电磁波的色散，从而在接近无限相速的区域提供有限的、恒定的群速度本征模。这种新型色散首次为在360-395 GHz频率范围内实现高功率(100W)、宽带(~10%)、高增益(&gt；40db)的回旋管放大器提供了可能性。我们已经在W波段、92到98 GHz的频率上进行了初步实验，并将在我们的领先优势的基础上，基于对这一新概念的最佳理解，在360到395 GHz的频率范围内创造一个放大器，并对其增益、带宽、效率和抗振荡稳定性进行精确测量。这一发展将代表一种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、高场脉冲电子顺磁共振光谱、材料处理、聚变诊断和远程、高带宽、视线通信来提高核磁共振灵敏度。这项提议是英国两个领先的毫米波小组的合作成果：斯特拉斯克莱德大学的原子、光束和等离子体小组，以及STFC卢瑟福·阿普尔顿实验室(RAL)的毫米波技术小组。总体而言，这些集团在高功率毫米波光源、仪器仪表和组件的开发方面拥有数十年的经验和强大的国际声誉，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。拟议中的工作位于一个核心领域，该领域可能导致英国在先进的高频、高功率毫米波放大器和固态源领域处于领先地位，这将对未来几年的高场EPR/DNP光谱研究产生影响。在工作过程中，Strathclyde的工作人员将设计回旋放大器，并将设计传递给ral进行精细特征的精密制造，这些细微特征将使用最先进的计算机控制的铣床切割成铅笔芯直径的螺旋。在RAL对它们的波导性进行初步测试后，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：他们将使用新配置的砷化镓肖特基二极管来制造这些组件。新放大器的频率覆盖范围、增益和最大输出功率都是如此，因此需要世界级的信号源来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.