Noise in space charge limited field emission devices

The noise suppression in space charge limited field emitter cathodes is calculated, and it is shown that the noise can be more strongly space charge suppressed than in thermionic cathodes. The velocity fluctuation noise of the field emitter cathode is also calculated under arbitrary space charge conditions. The results are used to evaluate the noise figure of traveling wave tubes. Low noise figures are possible if the noise suppression of the space charge limited field emitter remains intact at microwave frequencies.