The nature of power saturation in traveling wave tubes

The non-linear operating characteristics of a traveling wave tube have been studied using a tube scaled to low frequency and large size. Measurements of electron beam velocity and current as a function of RF phase and amplitude show the mechanism of power saturation. The most important conclusions are: I. There is an optimum set of parameters (QC = 0.2 and γ r0 = 0.5) giving the greatest efficiency. II. There is a best value of the gain parameter “C” which leads to a best efficiency of about 38 per cent. III. A picture of the actual spent beam modulation is now available which shows the factors contributing to traveling wave tube power saturation.