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

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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.