Nonlinear Beam-wave Interaction Analysis For The Folded Waveguide Traveling Wave Tube

Vacuum electronic devices have an indispensable position in the field of communication. Traveling wave tube (TWT) is the most prominent, the most widely used one among them. TWTs are usually classified based on the slow wave structure (SWS),which can reflect the performance of TWTs. On the basis of the Helix TWT with the characteristic of wide band and the Coupled Cavity TWT with the characteristic of large power capacity, researchers proposed a Folded Waveguide (FWG) TWT that combines the characteristics of these two types of TWTs. After years of researches, people's understanding of the design, manufacture, testing and other aspects involved in the development process of FWG TWT is getting deeper. However, due to the researches on the FWG TWT and the loaded type of it are still in the primary stage, researchers usually require the use of particle-in-cell (PIC) simulation software as a reference in the design of FWG TWT. However, due to the long operation time, the use of such software is not conducive to shorten the design cycle. Therefore, this paper presents a nonlinear analysis method for the interaction of FWG TWT based on the coupled cavity cascade model,which can lay a foundation for the further study of FWG TWT in the future and provide some reference for other new type while shorten the design period of FWG TWT at the meantime.In this paper, the high frequency characteristic analysis method and the interaction analysis method of the FWG SWS are studied. The calculation results from a program that based on the above analysis methods are compared with the experimental results. The main works are as follows:1. Each electrical period of the FWG SWS was divided into a number of microwave components with different transmission characteristics. Then the high frequency characteristics of the FWG SWS are obtained.2. When analyzing the beam-wave interaction of FWG TWT based on coupled cavity cascade model, a nonlinear analysis method is obtained by transmission matrix,electron motion equations and field equations which contain a certain coupling coefficient between them.3. A beam-wave interaction nonlinear analysis program, which contains interface and a series of practical functions such as saving calculation results and loading history results, was written using above method.4. This program was used to calculate two FWG TWTs which have been tested by experiment. The comparison between experimental test results and calculation results shows the accuracy and fast computation speed of this program, which verified the feasibility of this nonlinear analysis method.