New Mechanism of Noise Reduction in Electron Beams

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Abstract
Experiments have demonstrated that the basic noise quantities of an electron beam can be transformed and optimized by varying the field configuration and flow characteristics in the multivelocity region near the cathode. Tube noise figures as low as 2.9 db and numerical values of beam noisiness 2π/kTc(S−Π) <0.27 have been attained at microwave frequencies (S band). A detailed investigation of the conditions for minimum beam noisiness is presented. The beam is injected from the edge of the cathode into a highly divergent electric field and results in a distorted potential profile which greatly extends the low-velocity region below ½ v. It is shown that these features satisfy the physical conditions necessary for realizing a quasi-one-dimensional model in which the transforming properties of a ``multivelocity noise transducer'' can be adjusted by varying the rate of acceleration through this region. The experiments also suggest other models and possible approaches for further theoretical and experimental investigation.