Noise of low-energy electron beam

Noise diagnostics were performed on a tungsten hair-pin cathode operating in a vacuum (3 · 10^-3 Pa). The cathode operates in thermal emission mode at several temperatures based on the level of heating. Several acceleration voltages have been used starting at 5 kV, 10 kV and 20 kV up to 30 kV. There were two modes - with and without electron beam scanning. Both setups were compared from the point of view of the noise spectral density value. Shot noise is about one order below the current noise spectral density of the electron beam. Therefore, in this case the shot noise spectral density can be neglected. Noise spectral density is 1/f type at the frequency band 0.1 to 10 Hz for cathode with thin film of tungsten oxides. For accelerating voltage from 5 to 20 kV noise in the frequency band from 2 to 20 Hz can be described by the g-r noise with noise spectral density proportional to square of a beam current. At accelerating voltage 30 kV a new g-r noise component appears which is related to electric field distribution among anode; condensers, stigmators and objective.