Research And Design Of Quasi Optical Mode Generator For High Power Gyrotron

Gyrotron,as a high power microwave source,has a very important application in industry and national defense.In gyrotron,the rotating high-order mode is transformed into transverse Gaussian beam which is easy to transmit and use by quasi-optical mode converter.In order to verify the performance of the quasi-optical mode converter,a low power test is required.An important part of cold measurement is to excite the source field for measurement.Two methods to generate the source field are widely used at home and abroad,namely waveguide mode excitation method and quasi-optical mode excitation method.The former has better mode conversion efficiency and is suitable for excitation of low-order modes with low frequency.Although the conversion efficiency of the latter is not high,it has good mode separation ability and is suitable for exciting high-purity high-frequency high-order modes.In this paper,quasi-optical mode generator is studied.The design of coaxial cavity with side hole is the focus and difficulty of this paper.The mode spectral density of high-order mode is large,so it is difficult to separate the high-order mode from the hollow waveguide resonator.Therefore,the method of introducing inner conductor into the circular waveguide to form a coaxial cavity can change the mode spectral density within a certain range and enhance the mode selection ability of the cavity.Based on the first-order passive transmission line equation and its boundary conditions,a numerical simulation program is written to calculate the characteristic equation of the high frequency field of the gradual change resonator,and the field distribution,resonance frequency and quality factor of the target mode are obtained.The design of coaxial cavity with side hole is the focus and difficulty of this paper.The mode spectral density of high-order mode is large,so it is difficult to separate the high-order mode from the hollow waveguide resonator.Therefore,the method of introducing inner conductor into the circular waveguide to form a coaxial cavity can change the mode spectral density in a certain range and enhance the mode selection ability of the cavity.Based on the first-order passive transmission line equation and its boundary constraints,a numerical simulation program is written to calculate the characteristic equation of the high frequency field of the gradual change resonator,and the field distribution,resonance frequency and quality factor of the target mode are obtained.At present,the design of quasi-optical mode generator only involves low-order mode in China,especially for TE₆₂ mode of 94GHz.In this paper,the related theory is studied deeply,the program is written,the simulation is established and optimized,and the TE_28,8-mode exciter of 140GHz and TE_25,10-mode exciter of 170GHz are designed innovatively.The main mode purity of TE_28,8 is 93.4%,Q value is 2106,resonance frequency is140GHz;the main mode purity of TE_25,10 is 91.2%,Q value is 1840,resonance frequency is 170GHz.The former is connected to the quasi-optical mode converter for simulation testing,and the result reaches the expected effect.