A Discrete Cavity Analysis for Coupled-Cavity Travelling Wave Tubes

Coupled-cavity travelling wave tubes (CC-TWTs) are important to applications which require broad-band amplification and high gain. Classical Pierce theory [1] has treated the beam-circuit interaction as being continuous and uniform in the axial direction, which is taken to extend to infinity. However, it is important to test the limit of this treatment of beam-circuit interaction in real systems where the tubes are finite in length and discrete cavity effects may become important. Discrete cavity analysis allows us to treat individually tunable cavities, which was not possible with classical Pierce’s analysis. In this paper, we extend the previous preliminary work on the discrete cavity model by Wong et al [2] . An eigen-analysis method is used to obtain the cold-tube dispersion relationship for multi cavity systems, where the effects of cavity number, quality factor, and cavity coupling will be examined. The model will then be extrapolated to include the electron beam, and the hot-tube results will be examined. The relationship between this type of analysis and the classical Pierce analysis will also be discussed.