The Design and Simulation of a Cusp Electron Beam Source for a W-Band Gyro-BWO Experiment

Presented is the design of a cusp electron gun that is be used in a Gyrotron-Backward Wave Oscillator which is operating in the W-Band (75 - 110 GHz) frequency range. A cusp gun uses a non-adiabatic magnetic field reversal to impart azimuthal motion on an electron beam forming an axis-encircling beam. The cusp gun was designed to generate a beam of 2 A at 40 kV with a pitch factor of 1.65, in order to operate at a centre frequency of 94 GHz. The beam had an axial velocity spread of 7.4% with a beam radius spread of 12.2% and alpha spread of 10.1%.