Research On Output Transition And High Mode Purity Of Gyro-TWT

With excellent performance in oscillation and amplification in millimeter and sub-millimeter bands,the gyrotron has been widely used in communications,radar,high-power micro-millimeter-wave,electronic warfare,controlled thermonuclear fusion,new materials,and high-energy physics.In addition,it has opened up broad prospects.Although only with decades of development,the gyrotron has formed a large family.In this dissertation,the design of the output transition section and the mode suppressor based on the coupling principle are studied to improve the efficiency of gyrotron beam wave interaction and the purity of the output mode.The typical gyrotron device generally consists of an electron gun system,an input system,a high-frequency interaction structure,an output system,and a collector system.The high-frequency structure radius is determined by the working mode and working frequency in the waveguide.Radius of the collector is generally larger than the high-frequency structure in order to increase the collection power,so an output transition section needs to be designed to solve the difference in radius between the two.The output transition section is used as a transition between the high-frequency structure and the collector.There are several factors to consider when designing:1)Quick detuning of the beam wave to improve the interaction efficiency and output power;2)Reduce the generation of mode reflection and parasitic mode due to the waveguide longitudinal mismatch in the transitional segment;3)Avoiding the injection electron bombard the output gradient segment resulting in uniform collection and local temperature rise.The beam-wave interaction analysis in the transitional section is difficult because the single-mode traveling wave transmission in the uniform waveguide becomes a multi-mode traveling-standing wave transmission in the transition section.The rigorous correction of multi-mode interaction is complicated.This paper uses a method of successive approximation to simplify the analysis.The gradient waveguide and gradient magnetic field are equivalent to an infinite number of uniform waveguides and an infinite number of constant magnetic fields,respectively.Through the analysis of the gradient waveguide radius and the gradient magnetic field,the following conclusions are get:When the waveguide radius detuning rate is 10%or the magnetic field mismatch rate is 4%,the beam wave interaction in the gradual transition cannot be effectively performed.According to this conclusion,in the design of the gradual transitional section,we proposed a new idea of slowy decreasing the radius of the gradual transitional to achieve the goal of reducing the working mode reflection and parasitic modes,while rapidy changing the magic field to achieve fast ending beam wave interaction.High-power microwave sources often have problems that the output mode is not pure.For example,in the output transition section,it is inevitable that there will be parasitic mode generated by the mode conversion.The use of an over-mode output waveguide will lead to the possibility of this impure increase.Therefore,based on the coupling principle,an equal-interval and equal-intensity TE02 mode suppressor is designed to solve this problem.Verified by software simulation,the TE02 mode suppressor suppresses the spurious mode in the main waveguide.At the same time,the TE02 mode suppressor effectively ensures the high efficiency and high purity output of the working mode in the main waveguide.