Research On Electron Optical System And High Frequency Structure Of Gyrotron Travelling Wave Tubes

Gyrotron travelling wave tube?gyro-TWT?is a kind of vacuum electronic device which is based on the principle of electron cyclotron maser instability.As an amplifier working in the fast-wave regime,gyro-TWT features in high frequency,high output power,and wide bandwidth.Gyro-TWT has attracted worldwide attention and interest due to its various potential applications in high resolution radar,millimeter-wave communication,electronic countermeasure,material processing,etc.As key parts of a gyro-TWT,electron optical system?including electron gun and collector?is used to produce electron beams and collect the residual electrons.The generation of high-quality electron beams,as well as the efficient collection of the residual electron beams,is closely related to the efficiency and lifetime of a gyro-TWT.The beam-wave interaction occurs in the high frequency structure,whose quality determines whether the tube can be stably operated or not.Therefore,it is essential to design the electron optical system and high frequency structure of a gyro-TWT with high quality.Supported by the special project fund“Technology of XXX gyrotron travelling wave tube”,this thesis is intended to perform a deep study of the electron optical system and high frequency structure of a gyro-TWT,main research aspects and innovations are as follows:1.The theory of magnetron injection gun?MIG?is derived and rearranged,and the design equations and confining equations are proposed.The graphical user interface?GUI?program of MIG design is completed and the initial designs of MIG with single and double anodes are given in detail.The GUI-based MIG verification program,which can offer an automatic verification between different simulation tools,is accomplished.By employing this code,the verification process can be efficiently improved with minimum errors.To promote the optimizing efficiency of electron guns,the simulating annealing algorithm?SAA?and genetic algorithm?GA?are introduced to optimize the gun.By employing numerical methods,the electron gun can be automatically optimized with superior quality.The optimizing processes of SAA and GA in a cusp gun are presented detailedly.Based on the design and optimizing tools,the optimizations of electron guns for gyro-TWTs,gyrotron backward wave oscillators?gyro-BWOs?,and gyrotron oscillators are finished.The innovative designs of electron gun with sectorial emitters,dual-band electron gun,and electron gun able to work at multiple frequency bands are proposed.2.The key technologies concerning the design of electron guns are studied.A further study of velocity spread is performed,and the contributions of initial thermal velocity and cathode surface roughness to velocity spread are discussed.The velocity spreads with regard to different distribution functions of electron emitting angles are figured.The thermal and deformation analysis of the electron gun is performed.Through optimizing the geometry of electron gun,a filament-winding configuration with“L”form is achieved to obtain a rather smooth temperature distribution along the emitter.The transverse and axial deformation values of the electron gun are simulated and the comparisons of beam qualities before and after deformation are given.The sideband emission phenomenom of the electron gun is investigated.The forming of sideband emission and its effect on the beam quality is described.The methods of suppressing the sideband emission are introduced and their effectiveness is verified by the target-shooting experiments.The influence of inhomogeneous emission of the emitter on the beam quality is studied and the results considering current densities with Gaussian distribution are given.The concept of curved cathode is presented and this novel design is applied to the electron guns with different structures working at various frequency bands to achieve a good beam quality.3.The optimized design of undepressed collectors of gyro-TWTs is presented.The MATLAB code for calculating the dissipated power densities on the inner collector wall is written and there is a good agreement between the theoretical and simulation results.The curved collectors are proposed and the considerations of microwave transmission properties and secondary electron emission are included.The temperature distribution of the collector is obtained by using the built-in particle-thermal module in simulation tool.Compared to the straight-line collectors,the curved ones have a wider collecting area,lower dissipated power densities,and more uniform temperature distribution.The local hot spot can be effectively avoided in curved collectors.The field sweeping systems which are usually utilized in the collector designs in MW-level gyrotron oscillators,are adopted in the optimization of a gyro-TWT collector for the first time.Based on the straight-line collector configuration,an optimized transverse and vertical field sweeping system is obtained to get a reduced dissipated power density.4.The study of high frequency structure is performed.The small-signal theory?linear theory?of beam-wave interaction is derived and rearranged and the corresponding MATLAB codes are written.The gain and bandwidth of high frequency structure are predicted by the linear theory and the methods of calculating the thresholds of absolute instabilities and backward wave oscillations by using linear theory are given in detail.The large-signal theory?nonlinear theory?considering the structure loss and velocity spread is derived and the corresponding GUI-based code is finished.The theoretical results agree well with the simulation ones.Based on the stable parameters predicted by the linear theory,the performance of the high frequency structure is estimated by the nonlinear code and the calculated results are analyzed.The nonlinear optimizing GUI code based on the GA concept has been finished.The optimizing process will be automatically performed according to the design goals.The design efficiency will be greatly improved by using this optimizing code.5.According to the project requirements of the laboratory,based on the novel design concepts and optimal design methods,the design of a Q band pulse gyro-TWT which works at fundamental TE₀₁ mode,is completed and the hot test is performed.The gyro-TWT can work stably and good test results are obtained.