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。在名义上为圆柱形的波导管内壁上引入一个弱螺旋线是最近影响高功率微波放大器的一个创新。这样一个波纹导致麦克斯韦方程的新的解（本征模），其可以被认为是无波纹波导的模式的空间谐波的耦合。取决于所选择的精确几何形状的双折射，这些新的模式可以表现出一个几乎恒定的群速度在一个区域中的相速度趋于无穷大。这种布置对于可调谐快波放大器是理想的，因为线性色散可以在宽的频率范围上与电子束的回旋模式的色散重叠，从而给出宽的带宽，同时提高效率并减轻寄生振荡的风险。这种放大器在X波段（约10GHz）具有兆瓦级的能力，瞬时带宽为20%，效率接近30%。这也是一个理想的波色散的可调谐振荡器，其中源的频率可以通过改变磁场，支持电子回旋运动的一个大的轨道束在第二电子回旋谐波。我们将初步设计和构建一个可调谐的返波振荡器在360 GHz至395 GHz的频率范围内应用的想法，如使用一个大直径的5倍螺旋波纹波导相互作用区。我们还将开发新的理论和计算模型的回旋行波放大器的基础上的5倍螺旋波纹的相互作用区域在365 GHz至395 GHz的频率范围内工作。

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.