Research Of Electron Optical System Of Traveling-wave Tube In Short Millimeter Band

With the development of short millimeter wave technology,vacuum electronic devices play an indispensable role in the development and application of short millimeter waves.Due to their characteristics of high working frequency,wide frequency band,huge output power and large gain,they are widely used in electronic countermeasures,biological medical,satellite communications and radar detection,etc.As the "heart" of most vacuum electronic devices,electron optical system(EOS),which is an energy conversion device,provides a suitable electron beam for the vacuum electronic device to operate normally.Traveling-wave tube(TWT)is one of the significant vacuum electronic devices,which relies on the interaction between electron beam and high frequency signal in the slow wave circuit to amplify the power of the high frequency signal.The TWT is one of the "O" type vacuum electronic devices,whose size is proportional to the electromagnetic wavelength.In the short millimeter wave band,the shorter the operating wavelength,the smaller the size of the EOS is.Thus,the design goal of the EOS of short millimeter wave TWT is to achieve high beam density,strong space charge effect,good beam laminarity,low beam pulsation and high beam transmission rate.This is a great challenge for the design of EOS.During the period of my master‘s study,according to the requirement of TWTs in different frequency bands,the finished design includes two classic Pierce electron guns,a terahertz electron gun and their magnetic focusing system.Taking the EOS of short millimeter wave TWT as the research object,the main work content of this paper is introduced as follows:1.According to the operating parameters of the TWT,such as voltage,current,beam channel radius and current density of the cathode surface,the basic outline of Pierce electron gun was calculated by Vaughan iterative algorithm.In order to determine the structural parameters of the electron gun,the electron gun was simulated in the ORION.The OPERA-3D software was used to optimize the structure of the electron gun and the optimization methods were introduced for improving the performance of electron beam.2.Based on the operating parameters of the electron gun,such as voltage,current and beam waist radius,the design of the periodic permanent magnet(PPM)focusing system was initially carried out.By calculating the Brillouin magnetic field and the plasma wavelength,the appropriate range of the period and axial magnetic field of the PPM focusing system can be calculated.The calculation method of PPM structural parameters was introduced,and the simulation was completed by the OPERA-3D software.In order to introduce the setting method of the magnetic field transition area and the magnetic field insertion mode,the electron gun and PPM focusing system were jointly modeled and simulated3.According to the future development of TWT,a G-band EOS was designed.The design process of the electron gun and magnetic focusing system were introduced in detail.The structure of electron gun and magnetic focusing system was optimized by the OPERA-3D software.Under the conditions of high beam compression ratio and unsatisfactory laminarity,the electron beam was improved by adding a protective shell with its thickness of 0.1 mm outside the cathode.The magnetic focusing system adopted two schemes,the PPM focusing system and the uniform magnetic focusing system.The simulation results show that the transmission rate of the electron beam is 100%.But the electron beam focused by the uniform field is more stable than the electron beam focused by the PPM4.After the components were processed,assembled and welded,the transmission rate and magnetic system of the TWT were tested,and the experimental result was analyzed.At the end of the paper,the work content during my time in the research group was summarized and the suggestion of the future work was pointed out.