r:x~eriments hav,e demonstrated that the basic noise quantities of an electron beam can be transformed and optImIZed by var~g the field configuration and flow c~aracteristics in the multivelocity region near the cathode. Tube .nolSe figu.res as low as 2.9 ?b and numerIcal values of beam noisiness 211-/kT.(S-ll) <0.27 have been attaIned at mIcrowave frequencies (S band). A detailed investigation of the conditions for minimum .beam noisiness is p:esent;d. The beam i~ injected from the edge of the cathode into a highly divergent electrIC ~eld and results III a distorted potential profile which greatly extends the low-velocity region below !. v. It. IS shown th~t the~e features satisf~ the physical conditions necessary for realizing a quasi-one-dll~enslOnal mod.el III which the transf?rnung properties of a "multivelocity noise transducer" can be adjusted .by varymg ilie rate of acceleration through this region. The experiments also suggest other models and possible approaches for further theoretical and experimental investigation.
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