Design And Optimization Of Low Velocity Spread Magnetron Injection Gun

Gyrotron travelling wave tube(gyro-TWT)is a kind of high power microwave source,which is based on the theory of electron cyclotron master instability.Due to its remarkable features such as high power and wide frequency band,gyro-TWT has become the most promising potential and application prospects millimeter-wave coherent radiation sources.Gyro-TWT has attracted worldwide attention due to its broad application in fields such as high-power millimeter-wave radar,plasma diagnostics and high-energy particle accelerators.The quality of the electron beam generated by the magnetron injection gun as a core component of the gyro-TWT,directly affects the efficiency of the gyro-TWT.Therefore,the key to the design of magnetron injection gun(MIG)is to reduce velocity spread,that is to obtain high-quality electron beam.This thesis focuses on the research of magnetron injection gun that generates small cyclotron electron beams.The main work and innovation of this thesis are as follows: 1.The basic principles and the Initial design principle of MIG are researched and analyzed.The initial designs of MIG are given in detail.In addition,the design equations and confining equations are proposed.A concise introduction to the working principle and application of the numerical simulation software EGUN for electronic trajectories is accomplished.In order to improve the efficiency of MIG design and optimization,two numerical analysis algorithms—simulated annealing algorithm and genetic algorithm—are proposed.In order to have a clear direction of optimization for MIG,the influence of some important parameters on the performance of electron beam is analyzed.The initial design and the numerical optimization process of MIG with single(W band)and double(Q band)anodes are given in detail.By introducing a curved anode structure and using an optimized MIG program based on a simulated annealing algorithm,the velocity ratio of the electron beam of the Q-band MIG is at 1.6,and the longitudinal velocity spread decreases from 2.04% to 0.72%.After introducing curved cathode structure and using the electron gun optimization program based on the genetic algorithm,the velocity ratio of the electron beam of the W-band MIG is kept at 1.26,and the longitudinal velocity spread is reduced from 5.1% to 1.5%.The electron gun with curve structure is applied to improve the performance of electron beam.2.Inverse MIG is emissing electron beam from inner surface of emission band.The advantage is that the space of cathode heating filament is large.The structure of Inverse MIG is simple.The high pressure oil is used for cooling,so that the temperature of front and rear electrodes can be effectively controlled.Sideband electron emission and velocity spread can effectively reduce.Inverse MIG is dual-band,single-emission that increases utilization and the variety of electron guns.By using an electron gun optimization program based on a genetic algorithm,the velocity ratio reaches a target value and is validated using CST.Thermal analysis has been finished for MIG.By optimizing the cathode assembly of the electron gun,the heating efficiency of the filament is improved and the temperature distribution of the sideband is reduced.3.Broadband magnetron injection gun can generate high-quality cyclotron electron beam in the full frequency band(26.5~40GHz).Its advantages: due to the wide frequency band,saving cost,it brings great convenience to gyro-TWT.From engineering application consideration,the broadband single anode MIG is simpler than the double anode MIG in structure nd the requirement for the power is lower.And the front and rear electrode is formed into a straight structure that effectively reduces the impact of secondary electrons.The improvement of MIG's structure also improves the heating efficiency of the cathode and reduces the electron emission rate of the sideband.