Study of noise in crossed-field electron guns

Mechanisms responsible for the noise in crossed-field guns are being investigated. Our theory assumes that the excess noise results from feedback effects, in the space-charge-limited régime, arising from continuous interaction between the electric field and the beam of electrons reflected back to the cathode. We have extended an analytical method developed many years ago for the study of space-charge smoothing of shot noise in unmagnetized diodes. First-order equations describe the perturbations in the potential and transmitted current arising from a harmonically varying current injected from the cathode at a specific velocity. The perturbation problem is solved for all possible velocities of the injected current. The perturbation currents arriving at the anode are then combined to determine the current spectral density.