High power mm and sub-mm wave amplifiers for high frequency ESR/DNP, high resolution radar and remote sensing

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In a gyrotron, electrons gyrating in a magnetic field are coupled to electromagnetic radiation in such a manner that the radiation is amplified by extracting the electron kinetic energy. We will investigate a novel concept which uses a helical corrugation on the inside surface of a 'cylindrical' waveguide to radically modify the 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 (5kW), broadband (10%), high gain >40dB, efficient (30%) gyrotron amplifier in the 90GHz to 100GHz frequency range and above. We have performed a preliminary experiment at X-band (8GHz to 10GHz) frequencies and will build on our lead to create an amplifier in the W-band (90GHz to 100GHz) frequency band based on the best understanding of this new concept and perform precision measurements of its gain, bandwidth, efficiency and stability against oscillations. New theory and computational models benchmarked against W-band experimental data will be used to demonstrate the potential for this novel amplifier to generate high frequency (360GHz to 400GHz and 460GHz to 500GHz), high power (~0.5kW), broadband (10%), pulsed and continuous coherent radiation crucially needed by the many known applications.