| The traditional vacuum electronic devices generally use the thermionic cathode as the electron emission material,but it has suffered my limitations.Compared with thermionic cathode,the carbon nanotube cold cathode has advantages of working at room temperature,large emission current density,and generation modulated current.Therefore,the application of carbon nanotubes in TWT to realize miniaturization and instantaneous start of devices has great application prospect.At present,the main work of the carbon nanotube cold cathode traveling wave tube is still focused on the electron optical design of the electron gun or the simulation calculation of the whole tube under DC.The application of the actual cold cathode electron gun to the traveling wave tube has not been sufficiently researched,and there are no reports of practical carbon nanotube cold cathode traveling wave tube devices.In this thesis,combined with the previous work of the group,the simulation research on the carbon nanotube cold cathode traveling wave tube was carried out.The main contents are as follows:1.According to the characteristics of the emission current of the carbon nanotube cold cathode electron gun used in practice,the slow wave structure,energy transfer structure,cut-off and attenuator of the beam-wave interaction structure are designed.The structural parameters of each component are optimized by using CST software,and the transmission characteristics of the beam-wave interaction system are simulated and optimized.Finally,at the center frequency of 18.2GHz,the standing wave ratio of the interaction structure is 1.55,which basically meets the design needs.2.The main parameters of beam-wave interaction,working voltage and focusing magnetic field are determined.Afterwards,a complete tube model including electron emission surface,input and output structure,helix slow wave structure and other structures are established through the particle studio of CST,and PIC simulation calculations were performed.The result shows that the output signal amplitude is enlarged by 17dB and the output signal spectrum is relatively pure when the input frequency is 18.2Ghz.3.According principle of pre-modulation electron gun,based on the field emission theory,the pre-modulated electron gun electron optics is designed,by using the reentrant resonant cavity structure working in TM010 mode,and the resonant cavity is excited by means of electric field coupling.After optimization,the maximum amplitude of the electric field intensity on the cathode surface is 6×105V/m.On this basis,the PIC simulation of the emission of the carbon nanotube cold cathode pre-modulated electron gun is carried out by using the CST software.When the electrostatic field strength is 5 V??m,6 V??m and 7 V??m,the modulation currents with average currents of 2.2×10-3A,2.4×10-3A and 2.5×10-3A are obtained respectively.At the same time,the influence of the input signal frequency change on the current modulation depth is studied.When the frequency deviates from the resonance frequency,the modulation depth drops rapidly.Finally,the results of the interaction between the modulation current and the direct current are compared.It is found that the output power of the modulation current is 1.4 times that of the unused modulation current. |
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