Simulation Of Carbon Nanotube Cold Cathode Terahertz Backward Wave Oscillator

Terahertz wave(0.1-10THz)is located between the microwave and infrared light of the electromagnetic spectrum.It has excellent penetration and non-destructive detection capabilities and is widely used in aerospace,wireless communication,safety inspection and biomedicine.As a vacuum electron terahertz radiation source,the backward wave oscillator can generate terahertz signals with high power,broadband tuning and high frequency,and has commercial potential.Compared with the traditional hot cathode,the field emission carbon nanotube cold cathode has the characteristics of faster start-up speed,low power consumption,simple structure and high micro-emission current density.It can produce high-brightness electron beams and has certain advantages for vacuum electron terahertz radiation sources.This paper focuses on the simulation of1THz backward wave oscillator based on carbon nanotube cold cathode.The main work of this thesis is as follows:The high-brightness electron beam generated by carbon nanotube cold cathode electron optical system was studied by particle simulation software.Based on the experimental results of wire-like carbon nanotubes,two Ni80Cr20 alloy wires with carbon nanotubes were embedded in the cell,and a model of a near-axis small cyclotron magnetron injection electron gun was established to explore the feasibility of using high-brightness electron beams.The particle simulation software was used to optimize the relevant parameters,and the optimized design scheme of the electron gun with voltage of23.6 k V,current of 141 m A,transverse and longitudinal velocity ratio of 0.165,electron beam outer radius of 0.051 mm and current density of 2040 A/cm~2 was obtained.The high frequency structure of backward wave oscillator is studied.The disk-loaded waveguide structure is selected,and its one-cycle structure is analyzed by CST software,and the beam-wave interaction characteristics of the high-frequency structure of the backward wave oscillator are studied.According to the linear theory,the high frequency working voltage and frequency are determined,and the optimization parameters are obtained.The structure is excited by a high-brightness cyclotron electron beam generated by a linear electron beam and a carbon nanotube cold cathode,respectively.The output power and frequency spectrum under two conditions are obtained,and the output frequency is basically the same.The electron beam excited backward wave oscillator generated by the carbon nanotube cold cathode can produce a power output of hundreds of milliwatts in the frequency range near 1THz.