Gridded Electron Guns and Modulation of Intense Beams

Gridded guns are useful for producing modulated electron beams. This modulation is generally limited to simple gating of the beam but may be used to apply structure to the beam pulse shape. In intense beams, this structure spawns space-charge waves whose dynamics depend in part on the relative strengths of the velocity and density variations which comprise the initial current modulation. In this paper, the strengths of beam current and velocity modulation produced in a gridded electron gun are calculated, and it is shown that under normal conditions, the initial modulation is dominated by density variation rather than velocity variation.