A fast and accurate one-dimensional large-signal model for coupled-cavity TWTs has been developed that can be used interactively for the optimization of a TWT design. Different modeling techniques for enhancing the speed of the large-signal model with no loss in accuracy are discussed. It has been shown that the speed of the model can be increased by (1) suitable selection of the basic integration parameters such as the number of electron discs per RF cycle and number of integration steps per cavity, (2) choosing a suitable method of integration of the relativistic equation of motion, (3) optimizing the iteration processes through each cavity and each section, and (4) efficient calculation of the space-charge forces. The model has been tested for the low-space-charge high-efficiency NASA CTS 200-W tube and for a high-space-charge high-gain tube. The characteristics of a 58-cavity tube for a single value of input power and frequency can be computed in less than 1.5 min of CPU time on a VAX 11/785 computer. This is at least 5 to 6 times faster than the previous models with the same accuracy.
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