High Power Microwave Amplifiers to generate smart waveforms for magnetic resonance spectroscopy

快波放大器提供了产生极高功率微波脉冲的潜力。影响高功率微波放大器的最新创新是在名义上圆柱形波导的内壁上引入弱螺旋波纹。这种波纹导致麦克斯韦方程组的新解（本征模），这可以被认为是一个非波纹波导模式的空间谐波的耦合。根据为波纹选择的精确几何形状，这些新模式可以在相速度趋于无穷大的区域表现出几乎恒定的群速度。这种安排是理想的可调谐快波放大器，因为线性色散可以与电子束回旋模式的色散在宽频率范围内重叠，从而提供宽带宽，同时提高效率并减轻杂散振荡的风险。这种放大器已经在x波段（约10GHz）展示了兆瓦的能力，具有20%的瞬时带宽和接近30%的效率。它也是可调谐振荡器的理想色散，其中源频率可以通过改变磁场来调节，该磁场支持大轨道束在第二次电子回旋加速器谐波处的电子回旋运动。本文提出在WR-2.2波导波段（320GHz至500GHz）研究可调谐后向波振荡器和放大器，用于磁共振波谱学应用。我们将首先设计和构建一个在360GHz到395GHz频率范围内可调谐的反向波振荡器，应用诸如使用大直径5倍螺旋波纹波导相互作用区域的想法。我们还将开发基于5倍螺旋波纹相互作用区的回旋管行波放大器的新理论和计算模型，工作在365GHz至395GHz频率范围内。

Fast wave amplifiers offer potential to generate extremely high power microwave pulses. A recent innovation impacting high power microwave amplifiers is the introduction of a weak helical corrugation on the inner wall of nominally cylindrical waveguide. Such a corrugation results in new solutions (eigenmodes) to Maxwell's equations, which may be thought of as a coupling of space harmonics of the modes of an uncorrugated waveguide. Depending on the exact geometry chosen for the corrugation, these new modes can exhibit a nearly constant group velocity in a region where the phase velocity tends to infinity. This arrangement is ideal for tuneable fast wave amplifiers, since the linear dispersion can overlap with the dispersion of a cyclotron mode of an electron beam over a wide frequency range giving wide bandwidth, whilst enhancing efficiency and mitigating against the risk of spurious oscillation. Such amplifiers have demonstrated megawatt capability in the X-band (around 10GHz) with 20% instantaneous bandwidth and efficiency approaching 30%. It is also an ideal wave dispersion for tuneable oscillators where the frequency of the source can be adjusted by changing the magnetic field which supports the electron cyclotron motion of a large orbit beam at the 2nd electron cyclotron harmonic.Here we propose to study tuneable backward wave oscillators and amplifiers in WR-2.2 waveguide band (320GHz to 500GHz) for magnetic resonance spectroscopy applications. We will initially design and construct a tuneable backward wave oscillator in the 360GHz to 395GHz frequency range applying ideas such as the use of a large diametre 5-fold helically corrugated waveguide interaction region. We will also develop new theory and computational models of gyrotron travelling wave amplifiers based on a 5-fold helically corrugated interaction region operating in the 365GHz to 395GHz frequency range.