Design Of The Electron-optical System For A G-band EIK

Electromagnetic waves with a frequency in the range of 0.1 to 10THz are called terahertz waves,and they can be widely used in military communications,satellite communications,wireless local area networks,biomedicine and other aspects,due to the high working frequency,low quantum energy,good penetrability,and excellent directivity.The extended interaction klystron(EIK)is a device that can work in the terahertz band and has a high power output.It combines the advantages of the traveling wave tube and the klystron.With the development of terahertz technology in recent years,EIK has been well applied in the fields of communication,national defense,biomedicine,etc.EIK is mainly composed of electron-optical system,high-frequency system,input-output system and so on.It mainly amplifies the signal by modulating the electron beam.The characteristics of the electron beam,such as operating voltage,current of the electron beam,and recovery efficiency of the collector,have a crucial impact on the performance of the EIK.Therefore,the research of the electron-optical system is one of the core works of the design of an EIK.The studies on the electron-optical system of an EIK at 220GHz has been made in this thesis.The main work and innovation include the following three parts:1.Using the CST,which is a 3D electromagnetic simulation software,a circular electron gun which has one anode with beam current of 228mA,voltage of 18kV and waist radius of 0.128mm has been designed.In order to improve the performance of the electron gun,and considering the limitation of the current density of the present cathode material,an electron gun with current of 214mA,waist radius of 0.12mm,compression ratio of 156,and cathode's current density of only 3A/cm~2 were optimized.2.The uniform focusing system has been designed with the ANSYS MAXWELL2D,which is a 2D electromagnetic simulation software,and CST respectively,and the two results are in good agreement.After the joint adjustment of the electron-optical system,under the focusing magnetic field of 0.8T,the electron beam has a radius of less than 0.12mm above the length of at least 15mm,which meets the requirements of the interaction.In the actual manufacturing of the EIK,block magnetized is often used instead of radial magnetized.Therefore,the radial magnetized of the uniform magnetic system in CST is also discussed in this thesis.It is found that the more blocks magnetized,the more similar the magnetic field is to the radial magnetized,the number of magnetized blocks should be increased as much as possible.3.The design of a multi-stage depressed collector has been carried out.According to the particle distribution characteristics after the beam-wave interaction,the particle data was divided into blocks,and after optimization,a three-stage depressed collector with a recovery efficiency of 89.5%was obtained.In addition,the performance of the collector when using several materials with different coefficients of secondary electron emission as the materials of the electrode was compared.It is found that the use of electrode materials with lower coefficients of secondary electron can improve the recovery efficiency of the collector generally.Finally,in order to ensure the stability and reliability of the collector,thermal analysis has also been performed based on the simulation results of the collector,and the temperature distribution meets the requirements of the EIK.