Nonlinear Theory And Simulation Of Beam Wave Interaction Of Gyrotrons

Gyrotron is one of the most promising novel millimeter wave devices. In the millimeter wave and submillimeter wave bands, it is able to produce high power, high efficiency and high gain. The Gyrotron has a certain bandwidth, and the performance is stable. It has great value in the millimeter wave high power radar, electronic warfare, microwave weapons, communications and other aspects of a very wide range of applications. The Gyrotron is currently one of the hot research object of the electric vacuum devices.Beam wave interaction in the gyrotron directly determines the efficiency and the working performance of electronic devices. Therefore, the study of gyrotron device of beam-wave interaction is the most widely studied topic, also is the most important and key device research content. Scholars at home and abroad spent a lot of time and energy to develop the program used for the gyrotron device simulation and optimization. In this dissertation, based on the depth analysis of gyrotron device development, application prospect and research status, the nonlinear self-consistent beam wave interaction theory and computer aided design are studied. The main work and innovation are as follows:1. From the basic theory of electromagnetic field, this dissertation derived the gyrotron of electron beam and the high frequency field interaction nonlinear self-consistent equations, established nonlinear self-consistent beam wave interaction theory model, which is applicable for Gyrotron oscillators, Gyroklystron amplifier and Gyro-travelling wave tude. This model uses a simplified description of the fields as a superposition of transverse electric and transverse magnetic eigenmodes of the waveguide. Accordingly, the Maxwell equation is simplified as the mode of voltage and current of complex amplitude on time and axial coordinates of the partial differential equations (i.e. generalized telegrapher’s equations). Therefore, the solving electromagnetic field problem is transformed into solving the generalized telegrapher’s equations.The complex amplitudes of the modes vary slowly with time. The basic time scale for updating the radiation field is a fraction of the cavity fill time, rather than a fraction of the high frequency period. On this basis, the loss of boundary integral in the generalized telegrapher’s equations is processed, making these equations to calculate the fields in the loss of structure.2. Electronic equations of motion use the guiding center approximation. In the guiding center coordinate system, this dissertation introduces two kinds of hypothesis. One hypothesis is that the particles traverse the cavity in a time shorter than evolution time of the electromagnetic fields. Based on the hypothesis, particles transit the device before the envelope of the the radiation changes significantly. This allows us to describe the electron motion equations, the axial coordinates as independent variables. There is then no need to perform the usual interpolations on the axial grid of a particle location and the numercial operations of "gather" and "scatter", which is time consuming. The other hypothesis is that the axial magnetic field is strong. In this assumption, the Larmor radius is smaller than the cavity characteristic length and the particles essentially follow the magnetic-field lines.The introduction of the two hypotheses can be simplified equations of electron motion, thereby, reducing the amount of computation.With all electronic trajectories, it can calculate the current source. Then, the particles initial conditions are given. Transverse velocity of the electrons from the gyrotron satisfies the Gaussian distribution, distribution model of the velocity spread in the gyroklystron amplifier beam-wave interaction is established. In addition, we solved numerically the theory model of generalized telegrapher’s equations and the electron motion equations. Using the unconditionally stable classical implicit format to difference combined with the boundary conditions, a numerical model of generalized telegrapher’s equations is established.3. Using the beam wave interaction self-consistent nonlinear theory model, a Ka band two cavities gyroklystron amplifier is numerically studied. The beam-wave interaction energy changes is discussed, and the input power, electron beam voltage, magnetic field, horizontal and vertical velocity ratio effects on efficiency and output power are analyzed. This dissertation use particle simulation software MAGIC to optimize and simulate the designed Ka band two cavities gyroklystron amplifier. The calculated results of the two methods were compared and analyzed. MAGIC simulation results and the self-consistent nonlinear theory program results are basically consistent, which verifies the self-consistent nonlinear theory. The program can be used as a gyrotron device preliminary design tool, which can greatly shorten the gyrotron device simulation time, accelerate device design process, and also deepen understanding of the amplifier of electron beam and wave interaction mechanisms and the physical process. Therefore, the work on gyrotron device development has important guiding significance. On this basis, the design and simulation of a Ka-band two harmonics three cavities of the gyroklystron amplifier is presented. The dissertation studied the gyrotron device nonlinear process and characteristic, and discussed electronic injection voltage, current and magnetic field, frequency and other working parameters on the device. Through the analysis of nonlinear characteristics, we determined the gyrotron optimum working parameters, and achieved the design goals.This dissertation also use particle simulation software MAGIC to optimize and simulate the designed Ka-band two harmonics of the three cavities gyroklystron amplifier.4. Using the beam wave interaction self-consistent nonlinear theory simplified model, this dissertation study a94GHz second harmonics complex cavity gyrotron. By continuously adjusting the the complex cavity of dimension, it get a set of optimized parameters and give the impact of the changes in different parameters of the complex cavity gyrotron characteristics. Then, this dissertation use MAGIC to optimize and simulate the94GHz two harmonics complex cavity gyrotron.5. Using the high frequency software HFSS, particle in cell simulation software MAGIC and the generalized telegrapher’s equations, this dissertation discusses two kinds of loss structures on the gyrotrons. At the same time, the analysis of the loss of the structure and its application is given. Based on the theory model, this dissertation studied the Gyro-travelling wave tude with loss structure. The loss of the thickness of the dielectric layer, the dielectric constant of the gyrotron traveling wave tube on output power is analyzed, and further the nonlinear characteristics of the Gyro-travelling wave tude is studied in detail. Then, we use simulation software MAGIC to compare and validate the Gyro-travelling wave tude.