Study Of Multistage Depressed Collector For 220 GHz Sheet Beam Traveling-wave Tubes

Traveling-wave tube(TWT)has been widely used because of its characteristics of wide band and high gain.Terahertz TWT has the advantages of high frequency,compact size,wide band,high efficiency and high power,etc,which can play a huge role in military,aviation,communication,medicine,and so on.It is one of the key technologies in the world.When working in the terahertz band,the limitations of the pencil beam itself will hinder the further improvement of the efficiency and power of the TWT,so the sheet beam TWT has come into the attention of researchers.When a terahertz TWT is working,electron beam will only transform a small part of energy in the beam-wave interaction,and the electronic efficiency is very low.Most of the electrons will carry a large amount of energy into the collector,so that the remaining energy of electrons will dissipate in the way of heat loss,resulting in a waste of energy and a reduction of device life.The depressed collector can solve the above problems well,by recycling the remaining energy of electrons,and improve the efficiency of the TWT.The main task of this paper is to study the multistage depressed collector for the 220 GHz sheet beam TWT,and conduct thermal analysis on it.The main work and innovations are as follows:1.The conditions of electron beam in the entrance of the collector are analyzed,and the co-simulation between the PIC solver module and the Tracking solver module of the CST is carried out.On this basis,the single-stage depressed collector is designed and optimized,and the collection efficiency is 91.21% without considering the secondary electron emission.The single-stage depressed collector was machined and assembled.2.On the basis of the single-stage depressed collector and combined with the characteristics of sheet beam,a high efficiency three-stage depressed collector with rectangular entrance and elliptical cavity is designed.After optimization,the collection efficiency is up to 94.3%.The secondary electron emission model in CST is studied,and the simulations of the single-stage and three-stage depressed collector are carried out by using the Forman secondary electron emission model,the collection efficiencies are 90.56% and 93.3%,respectively.3.The relationship between depressed collector series and collection efficiency is explored and a four-stage depressed collector is designed for verification.In order to break through the limit of depressed collector series,a multistage depressed collector with magnetic field deflection is proposed.The collection efficiency of the new collector reaches 98.86% in the simulation and there is no back-streaming observed.4.The thermal analysis of the designed three-stage depressed collector is carried out,in order to reduce the working temperature of the collector,a heat sink fin is added.The simulation results show that under the same conditions,the working temperature of the collector with fin decreases about 100? at both the highest and lowest points,and the heat dissipation effect is significantly improved.Then,influence of the parameters of the fin on the temperature of the collector is analyzed.Based on this,the structure of the fin is optimized,and a fin cutting structure is presented.Finally,the thermal stress of the collector is analyzed,and the maximum thermal deformation of the collector is within the acceptable range.