Effects of Circuit Manufacturing Errors on Small Signal Gain and Phase in a Traveling Wave Tube

Summary form only given. Motivated by the current interest in vacuum slow wave THz sources, where difficult-to-manufacture miniature slow wave circuits are required, we evaluate the effects of geometrical random errors introduced during the circuit manufacturing processes on the small signal gain and phase characteristics of a traveling wave tube amplifier. A continuum model is used. Random perturbations are introduced through the gain parameter C, the velocity mismatch b, and the cold tube circuit loss d, in Pierce notation. The perturbations are incorporated in the differential equations describing the beam-circuit interaction in such a way that the Pierce dispersion relation is recovered for an ideal tube free of manufacturing errors. We employ these differential equations in a Monte-Carlo study to determine the rms effects on small signal gain and phase of the different types of errors. Our study shows that effects of a perturbation in the circuit phase velocity dominate those due to perturbations in the gain parameter C and loss d. More importantly, we find that the effects on gain and phase depend not only on the magnitude of the manufacturing errors, but also on the axial distribution of these errors. The analytic theory and our numerical results, including the statistics of the variations in the output gain and output phase, will be presented.