Progress of 140 GHz gyro-amplifier using confocal waveguide

We report on the progress of a 140 GHz pulsed gyro-amplifier system being developed at MIT for enhanced Dynamic Nuclear Polarization for NMR (DNP-NMR). A confocal geometry configuration is being studied as an approach to an overmoded interaction waveguide. The new amplifier differs from a previous version by incorporating improvements to structural construction, optimized input coupling, and sever design¹. The confocal geometry consists of two curved mirrors spaced equal to their radii of curvature (R = L = 6.8 mm, width = 5 mm). The operating frequency of 140 GHz is supported by the higher-order HE₀₆ mode. In order to suppress lower-order modes, the confocal geometry has open sides to allow radiation to leak out of the confined structure. By an appropriate design of the confocal parameters, these lower-order modes should have a greater loss per unit length than the mode of operation. The two severs (length 2.51cm, minimum width 0.74 mm) help to prevent oscillations by providing high attenuation within the waveguide.