Research On Electronic Optical System Of 340GHz Traveling Wave Tube

Compared with millimeter waves,terahertz waves have unique advantages in physics,such as low quantum energy and good penetration,and are widely used in basic science and military and defense fields.As the prerequisite and basis for the development of terahertz technology,terahertz radiation sources have always been the focus of research.As a high-power terahertz source,the terahertz traveling wave tube(TWT)has become a research hotspot at home and abroad because of its high power,high efficiency,and wide bandwidth.The electron optical system of the TWT includes electron gun,magnetic focusing system and collector.However,in the terahertz frequency band,due to the high frequency,the key size in the structure of the electron optical system is small,and the electron transmission channel is narrow.Electron guns in high-frequency devices usually require high current density and high area compression ratio.Therefore,in order to obtain electron beam with low fluctuation and good laminarity,the design requirements for the electron gun are very strict.At the same time,due to the enhancement of the electron space charge effect,the requirements for the focusing system are also more stringent.In this paper,the electronic optical system of the 340 GHz,10W cylindrical electron beam modified sine waveguide TWT is the research object,and the electron gun and the corresponding magnetic focusing system are designed.The main research work consists of the following aspects:1.The basic principle of TWT electron gun and the theory of thermionic cathode emission are described.Analyze the influence of temperature on thermionic emission,compare the calculation results of thermionic emission and space charge limited emission at the initial thermal velocity of electrons,and determine that the electron gun adopts the space charge limited emission method.According to the design requirements of the 340 GHz TWT electron gun,the Vaughan iterative algorithm was used to complete the basic outline design of the Pierce electron gun.The simulation of the structure parameters of the electron gun was initially completed in the Ukrainian software TAU,and the CST software was optimized to design the electron gun that meets the design specifications.The electron gun works voltage is 17 kV,the electron beam current is 38.5mA,and the beam waist radius is 0.035 mm.2.Introduce the design principle of periodic permanent magnet(PPM)focusing system,and then use Maxwell 2D software and CST software for simulation.On the basis of the previously designed focusing system,after analyzing the joint adjustment results of the magnetic focusing system and the electron gun corresponding to the magnetic ring with different opening conditions,the double-opening PPM focusing system is finally used to match the electron gun.The simulation results show that the magnetic field can ensure the electron beam transmission process,the pulsation is very small and electron beam transmission efficiency is 100%.The focusing system is currently being processed,and the finished PPM focusing system will be tested in the future.3.Explain the basic theory of heat transfer,use Workbench software to perform thermal analysis on the electron gun to determine the working temperature of the electron gun,and then perform thermal deformation analysis to obtain the thermal deformation data of the electron gun.According to the thermal deformation analysis,it is necessary to analyze the influence of the deformation of the cathode and the focusing electrode on the electron beam transmission,and then take this deformation into consideration in the actual assembly to offset the effect of the thermal displacement on the performance of the electron gun and the TWT.4.Integrated design of traveling wave tube.First,according to the particle distribution characteristics of the electron waist position,Matlab software is used to process the macroparticle information,and the new particle information is used as the particle source of the beam-wave interaction,so that the calculated result of interaction is closer to the experimental data,and then the beam-wave interaction results of the ideal emission source and the actual emission source are analyzed.At the same time,the particle data after interaction is processed to solve the problem of incompatibility between interaction calculation and collector calculation,and a single-stage depressurization collector is designed.In the case of secondary electrons,the collector efficiency is 88%.