A delay technique for phase focusing and efficiency enhancement in traveling-wave tubes

Traveling-wave tube efficiency is generally limited by the beam-bunching process. Premature saturation occurs when a substantial number of relatively energetic electrons slip out of the decelerating phase of the r-f wave. A phase-focusing technique has been developed whereby electron bunches are preconditioned at low signal levels. A delay in the r-f wave is introduced in order to promote formation of the beam bunch in a relatively low decelerating field. At a higher signal level the tight beam bunch is introduced into the maximum decelerating field with the result that many electrons simultaneously yield a substantial percentage of their kinetic energy to the r-f wave. Simulations using one-dimensional large-signal analysis show interaction efficiencies up to 50% with a relatively compact velocity distribution in the spent beam. Computer simulated results will be displayed and experimental results discussed.