Structure of a picosecond electron beam inside a vacuum diode

The structure of a picosecond (∼150 ps) electron beam in the cathode-anode gap of a vacuum diode is determined. The electron beam is modeled in the form of flat quasiparticles with a definite charge density which follow one after another in equal time intervals. It is shown that the expansion of concentric layers of the beam under the action of the electric and magnetic self-fields strongly depends on the current strength. The experimental confirmation of the computed estimates is illustrated by recording the structure of the electron beam at the anode using a film which is sensitive to electron radiation.