Design and Numerical Optimization of a Cusp-Gun-Based Electron Beam for Millimeter-Wave Gyro-Devices

A novel thermionic cusp electron gun operating in the temperature-limited regime that produces a large-orbit electron beam through a nonadiabatic magnetic-field reversal was designed, analyzed, and optimized to give an electron-beam ideal for driving gyro-devices, particularly in the millimeter-to-submillimeter-wavelength range due to its small cross-sectional size. The annular-shaped axis-encircling electron beam had a beam current of 1.5 A at an acceleration potential of 40 kV, a tunable velocity ratio $alpha (= v_{ perp}/v_{z})$ between one and three, an optimized axial velocity spread $Delta v_{z}/v_{z}$ of $sim$ 8%, and a relative alpha spread $Deltaalpha/alpha$ of $sim$10% at an alpha value of 1.65.