Terahertz Gyrotron Mode Converter And The Coaxial Output Structure Study

In recent years , the gyrotron was subjected to extensive studies as one of the highest Terahertz sources in power today. And as the main component of the mode converter and the output structure is the key of the gyrotron , it basically determines the performance of the gyrotron. In the dissertation, the mode converter and output structures were discussed, and several valuable achievements are listed as the followings:1. Adopting abnormally slick waveguide as the output structure in the 220GHz gytotron output apparatus that we studyed. Firstly we do it from coupling wave theory, and on the base of outspread theory of perpendicular function unwrapping the waveguide inner field with the series form of electric and magnetism wave, then the coupling wave equations and currently expression of coupling coefficient was educed. When we counting the concretely waveguide which bent was axised and gradual radius changed, infulling the matched data, then we will get the concreted coupling coefficient and coupling functions, and then get the achieved functions of TE_0,n-TE_0,n-1,TE₀₁-TE₁₁.Through the optimized analyze with the software of HFSS/CST, and adopting the rematch phase technique, we achieved the high efficiency output of THz gyrotron whose diameter was 5mm, and frequency was 220GHz. This results provided important consult for THz gyrotron mode converter.3. The output structure of 225GHz coaxial gyrotron was designed, and the output coaxial TE₀₃ mode was converted into circular waveguide TE₀₃ mode. Combining the characteristic of output cavity, and the field equation of TE₀₃ in this dissertation, numerically simulated the relation of different inner axis, and length with the output efficiency, and the bandwidth of 225GHz coaxial gyrotron.Through the theory analyze and numerical simulation, we get the relation that when the outer axis and length was fixed, the smaller the inner axis the larger the outputefficiency and bandwidth. Samely as the condition that when the leng of outer axis lengthe subtrated the inner axis length equal to nλ_?/2 (n=1,2,3,......), the smallert thereflecter , the higher of efficiency and bandwidth. This results contributed the design of TE₀₃ coaxial output structure to circular waveguide mode converter which radius of inner and outer axis was 0.5mm,10mm, and the cutting length was 9λ_?/2. And it'soutput efficiency as high as 99.98% in the center frequency, almost completely transmission, and it's bandwidth was 3.974 GHz when the transmission efficiency was 96.2%, approached to 4GHz. This result completely satisfied the need of machining and experiment, and offer an important gist for the manufacture and the study need.