Formation of space-charge bunches in a multivelocity-electron-beam-based microwave oscillator with a cathode unshielded from the magnetic field

The influence of the magnitude and configuration of the magnetic field on the parameters of electron bunches formed in a multivelocity electron beam is analyzed. It is shown that the use of a cathode unshielded from the magnetic field and a nonuniform magnetic field increasing along the drift space enables the formation of compact electron bunches. The ratio between the current density in such bunches and the beam current density at the entrance to the drift space reaches 10⁶, which results in a substantial broadening of the output microwave spectrum due to an increase in the amplitudes of the higher harmonics of the fundamental frequency.