Transient analysis of beam interaction with antisymmetric mode in truncated periodic structure using 3-dimensional computer code "SOS"

Transient plasma-physics/electromagnetic codes were used to analyze microwave tube circuits excited by an unmodulated electron beam. The objective was to assess the value of Mission Research Corporation\´s codes "SOS" and "MAGIC" (for 3- and 2-dimensional analysis, respectively) for analysis of oscillation in microwave tubes. For the 2-D case the Q of a cavity due to beam loading was obtained and corroborated by other methods. For the 3-D cases the computed resonance frequencies in a resonated section of coupled-cavity TWT were corroborated by cold-test measurement. Despite the coarse frequency resolution inherent in the relatively short-duration transient analysis performed for a higher-order antisymmetric mode, it was possible to isolate several of the resonances sufficiently to determine the negative Q due to beam loading. Thus the capability of these programs to perform quantitative stability analysis on microwave tube circuits plus beam was demonstrated.