Nonlinear Characteristic Optimization Of Traveling Wave Tubes

The traveling wave tube(TWT),which has a long history of development,has been widely used in various fields such as national defense,satellite,and electronic warfare after decades of development of vacuum electronic devices.TWT has high power capacity,stability,and wide bandwidth,which are important advantages in competition with solid-state amplifiers.However,as the input power increases,the output power and gain characteristics of the TWT will increasingly deviate from the linear relationship,resulting in nonlinear distortion phenomena.If these phenomena are not effectively suppressed,they will greatly affect the development prospects of vacuum electronic devices such as TWTs in fields such as satellites and communication systems.There are many relevant characteristic parameters of the TWT’s nonlinearity,and usually,suppressing one characteristic will also improve other non-characteristic situations.This article mainly focuses on the theoretical mechanism and suppression methods of the TWT’s phase nonlinearity,conducts research on the design of the TWT structure using the structure optimization method of phase velocity jump and genetic algorithm optimization program,and proposes an optimization scheme aimed at suppressing its nonlinear characteristics through the optimization design of the slow wave structure.The main work of this thesis is as follows:Firstly,an in-depth study was conducted on the theory of interaction between electron beam and wave in traveling wave tubes.Starting from the excitation equation of electromagnetic fields by electron beams in high-frequency structures,using Van der Pol’s large signal theory,a self-consistent set of ordinary differential equations describing the interaction between electromagnetic waves and electron beams in traveling wave tubes was derived.A one-dimensional simulation program for beam-wave interaction in traveling wave tubes was developed using numerical methods(fourth-order Runge-Kutta method).The program was used to obtain the phase information of electromagnetic fields and electron beams,which helped to understand the phase nonlinear characteristics of folded waveguide traveling wave tubes.Secondly,the one-dimensional nonlinear simulation program was modified and combined with genetic algorithms.The simulation program was optimized for fast computation,mainly by reducing the computational cost of the space charge field calculation,to reduce the time cost of iterative optimization using genetic algorithms and improve the optimization efficiency.Thirdly,by analyzing the nonlinear characteristics of folded waveguide traveling wave tubes,a phase velocity jump technique was used to optimize the nonlinear characteristics of the tubes.A three-segment folded waveguide slow wave structure was employed,and the structural parameters of each segment were adjusted to achieve linearization design in the middle segment,thus improving the phase nonlinear characteristics of the traveling wave tube.Finally,genetic algorithms were used in combination with the one-dimensional simulation program to optimize the nonlinear characteristics of the traveling wave tube.Genetic algorithms have the advantage of being able to search for and implement optimization solutions without considering the specific internal workings of the problem.The goal of the optimization was to improve the phase nonlinear characteristics of the folded waveguide traveling wave tube by improving the structural parameters of the three-segment design.Simulation results showed that the optimized parameters effectively improved the phase nonlinear characteristics of the folded waveguide traveling wave tube.