Design Of Double Beam Electron Gun Of Gyrotron Traveling Wave Tube

Gyrotron traveling wave tube(gyro-TWT)is a high-power amplifier based on relativistic electron cyclotron maser mechanism.It has a wide application prospect in radar,communication and other fields because of its broadband and high-power characteristics in millimeter wave band.Electron gun is the core component of gyro-TWT.Its function is to provide electron beam for high-frequency electron beam wave interaction.High quality cyclotron electron beam is the premise and foundation of efficiency and broadband beam wave interaction in gyro-TWT.In recent years,with the development of gyro-TWT,its working frequency band has gradually expanded from microwave band to millimeter wave band,and even to terahertz band.However,with the continuous expansion of the working band of gyro-TWT,the size of its high-frequency interaction space also decreases,resulting in the continuous reduction of the guiding center radius of the electron beam.For example,for the gyro-TWT working in TE₀₁ mode,the radius of the interaction system in Ka-band(32GHz-35GHz)is about 5.6mm,while the radius of the interaction system in G-band(210GHz-220GHz)is only about 0.89mm,the electron beam radius is correspondingly smaller.When the magnetic compression ratio remains unchanged,a smaller guiding center radius requires a smaller electron gun emission radius.In the traditional single beam electron gun,smaller emission radius means smaller emission area.When the ratio of space charge density to Langmuir space charge limit and the electron emission capacity per unit area of cathode emission material are limited,the electron beam current emitted by the electron gun of gyro-TWT in high frequency band(such as W-band)is also small.This is contrary to the large current required for high-power output of gyro-TWT in high frequency band.Therefore,it is necessary to design the corresponding electron gun,which can also emit electron beams with larger beam current under these limited conditions.In order to improve the emission current of the electron gun,combined with the research requirements of the National Natural Science Foundation Project(Grant No:62171108),this paper uses the characteristics that the coupling coefficient of the working mode of TE₀₂ mode gyro-TWT has two maximum points in the radial direction,sets the guiding center radius of the electron beam at these two extreme points at the same time,and introduces the double beam electron gun scheme to increase the emission current of the gyro-TWT,improve the quality of electron beam and increase the output power of gyro-TWT.The new double beam electron gun has two cathode emission bands,which can not only effectively increase the cathode emission area and then increase the emission current,but also make full use of the limited high-frequency interaction space and improve the quality of cyclotron electron beam.In this thesis,the new double beam gyro-TWT electron gun is studied in detail.The main research work is as follows:1:Firstly,the electron gun of gyro-TWT is analyzed theoretically.Based on this theoretical analysis,the initial structural parameters of a W-band single anode electron gun are designed.The CST automatic modeling and simulation program is compiled,and the initial parameters obtained from theoretical analysis and calculation combined with the target parameters of the electron gun are input into the CST software for automatic modeling and optimization.When the working voltage is 60k V and the working current is 8A,the optimal design results of velocity ratio of 1.23,transverse velocity spread less than 2.5%are obtained.2:The structural scheme of a new double beam electron gun is proposed.Using the theoretical analysis and calculation results and CST automatic modeling and simulation program,combined with the target parameters,the optimal design of W-band TE₀₂ mode gyro-TWT double beam electron gun is completed.Under a given working magnetic field,the velocity ratios of the inner and outer beams of the double beam electron gun are 1.1and 1.2 respectively,the transverse velocity spread of the inner is within 1%and outer rings is within 2.4%,the working voltage is 60k V,and the working current is 3A and 10A respectively.In the optimization process,it is also found that the double electron beams interact with each other,and the electron gun space effect electric field is the superposition of the double electron beam space charge effect.3:The internal structure of the optimized double electron beam electron gun cathode is designed,modeled,thermal analysis and thermal efficiency optimization,and redundancy analysis is carried out.When the total emission beam current is 13A,only36W power is required,and within the deformation and assembly error range of axial0.3mm and radial 0.2mm,the change of double beam transverse velocity spread is less than 1.6%,and the change of velocity ratio is less than 0.06.In order to flexibly control the emission current of the inner and outer emission bands,a double heating filament structure is also introduced into the cathode of the double electron beam electron gunThe main innovations are:1:On the basis of theoretical analysis and calculation,the CST automatic modeling and simulation program is compiled to realize the automatic modeling and optimization of gyro-TWT electron gun,which shortens the design cycle of electron gun and saves computing resources.2:A new structure scheme of double electron beam gyro-TWT electron gun is proposed to realize the high current and high quality emission of gyro-TWT electron gun.3:A double heating filament structure is proposed to realize the flexible regulation of the emission current of the inner and outer emission bands.