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Abstract:A thermionic cusp electron gun has been designed, numerically optimized and experimentally measured and is presented. A 40 kV, 1.5 A annular axis-encircling electron beam has been simulated to generate a beam with low velocity and alpha spreads. The electron gun performance has been verified through experiments and the results are given.
Introduction:High-power high-frequency coherent radiation sources in the millimeter to sub-millimeter wavelengths have attracted significant research interest recently. Gyro-devices are promising candidates to fulfil this demand due to their inherent fast-wave interaction. Many gyro-devices operate at harmonics in order to reduce the required magnetic field strength by a factor of s, the harmonic number. In order to drive the harmonic interaction a modeselective electron beam is required. An axis-encircling electron beam is ideal for harmonic interaction as the harmonic of the beam's cyclotron mode only interacts with the azimuthal index of the waveguide mode. The cusp electron gun uses a non-adiabatic magnetic field reversal to impart rotational velocity, through the conservation of canonical momentum [1,2], to the electron beam. Two solenoids, in opposing directions, are required in order to create the cusped magnetic field in-front of the cathode.