The Nature of Power Saturation in Traveling Wave Tubes

The highest possible efficiency of the traveling wave tube has been estimated from many different points of view. In his first paper on the subject 1 J. R. Pierce showed that according to small signal theoiy, when the dc beam current reaches 100 per cent modulation an efficiency of "=i r o) is indicated,* and thus the actual efficienc3 might be limited to something like this value. Upon later consideration 2 he concluded that the ac convection current could be twice the dc current and t h a t one might expect an efficiency of V = 2C (2)