Low velocity spread axis encircling electron beam forming system

A novel electron gun and beamforming system for axis encircling electron beams has been designed. Simulations of the electron trajectories, including thermal velocities, have shown transverse and longitudinal velocity spreads of 0.5% and 1.6%, respectively, for a beam with an alpha of 2.1 and a 1.1 microperveance. The use of an asymmetric field reversal and an initially converging beam greatly reduces the length required for adiabatic compression of the beam. External control of the beam position and angular velocity makes it easy to optimize cyclotron-resonance-maser or peniotron interactions for differing radial cavity modes and cyclotron harmonics. Using this design, the beam radius, guiding center radius, annular width, alpha, and angular velocity can all be varied over a wide range by adjusting the gun electrode voltages and solenoid currents. The result is a short, flexible beamforming system which produces a low-velocity-spread, high-transverse-energy, axis-encircling electron beam. The computer codes used have yielded excellent correlation between simulation and experiment on a wide variety of gun designs.<>