Effect of electron lenses on beam noise

Some types or electron guns used to form the beam of a low-noise beam type microwave amplifier (e.g. traveling-wave tube) impress sharp potential discontinuities or velocity jumps on this beam. These discontinuities produce strong electrostatic lenses. This paper presents a theory supported by experimental results, showing that the effect of such lenses is to increase the beam noise. Further, axial magnetic fields are shown to reduce this undesirable effect.