Recent discrete model for small-signal analysis of traveling-wave tubes

Abstract

The numerical simulations of the wave-particle interaction, as it occurs in particular in traveling-wave tubes, require new tools especially to investigate near the band edges of those devices. We propose a new approach (not limited to traveling-wave tubes) using field decomposition allowing an important reduction of degrees of freedom: the discrete model. To assess its validity, we compare it in a small-signal regime with Pierce’s four-wave theory. For both models, we take the same simplified fluid model and we express the associated circuit-beam impedances. We show analytically and with a numerical example that the newly developed reduced model is very close to the Pierce model, especially where the latter is well established. Small deviations do occur at the edges of the amplification band, where Pierce’s model is known to lose its accuracy while the reduced model offers a valid physical interpretation.