Research On Quasi-Optical Electron Cyclotron Maser With Dual Confocal Waveguide

Terahertz(Terahertz,THz)science and technology,as a bridge connecting classical electromagnetic theory and optical theory,has a bandwidth characteristic of 1 to 4 orders of magnitude higher than that of microwaves and a higher energy conversion efficiency than light waves.Terahertz science and technology,as a frontier research subject with great application prospects,can be applied in many fields and aspects such as satellite communications,high-resolution medical imaging,electronic countermeasures,and radar,and has a wide range of application values.Terahertz radiation source is the key to the development of terahertz science.At present,the current terahertz radiation sources are facing a series of problems such as low output power,low beam-wave interaction efficiency,insufficient stability,and mode competition.Therefore,in response to the above-mentioned problems,this paper proposes a new type of quasi-optical electron cyclotron maser with dual confocal waveguide,establishes the electromagnetic theoretical model of the dual confocal waveguide,and combine electromagnetic wave theory and geometric optics theory to analyze electromagnetic characteristics in a confocal waveguide,such as the field distribution characteristics,field distribution expressions,dispersion characteristics,and diffraction loss of each mode in the waveguide.Based on the advantages of the mode density in the dual confocal waveguide being much lower than that of the traditional circular waveguide,this paper study a dual confocal waveguide cyclotron oscillator that is composed of two sets of single confocal waveguides of different sizes to achieve dual-frequency output.This paper gives a detailed design process for the numerical values of some main parameters and optimizes the parameters,including the operating magnetic field,the electron beam guiding center radius,the starting current,etc.Then the simulation of the model is carried out.The simulation results show that the device can simultaneously achieve dual-frequency output of 200GHz and 400GHz.This greatly broadens the application prospects of dual confocal waveguides and provides new ideas for high-power dual-frequency output devices working in the terahertz frequency band.The coupling phenomenon of the superimposed mode in the dual confocal waveguide is studied.It is found that TE_0,n(n takes an odd number)is fed into the dual confocal waveguide,and the superposition modeTE₀^a,_n^nti(n takes an odd number)cannot be coupled in the dual confocal waveguide cavity with slowly varying cross-section,and when TE_0,n(n takes an even number)are fed into the cavity,superposition modeTE₀^a,_n^nti(n takes an even number)can be coupled in the cavity.Therefore,using this unique characteristic in dual confocal waveguides,a compact input coupler with an operating frequency of 220 GHz for dual confocal waveguide cyclotron traveling wave tubes is studied.Compared with the traditional ridge-loaded improved dual confocal waveguide mode input coupler with arm structure.This compact input coupler has the characteristics of simple and compact structure and easy processing,which further reduces the difficulty of assembly and testing of dual confocal waveguide cyclotron traveling wave amplifier experiments.The simulation results such as S-parameters show that the mode conversion effect is great.This structure meets the requirements of the cyclotron amplifier for the working bandwidth of the input coupler.