Research On Thermal Analysis Of Output Window And Collector For High Mode Gyrotron In W Band

The millimeter-wave band is between 30 GHz and 300 GHz,whose frequency band is high,so that the available frequency band is wide and the carrying information capacity is large.On the other hand,the wavelength of the millimeter-wave ranging is from 1 mm to 10 mm,it has a strong penetration.Due to its broadband and short wavelength,it has broad application space in satellite communication,space exploration,electromagnetic countermeasures,directional weapons and other fields.In addition,gyrotron is an important device of the wavelength source,so the research of it is very significant.The history of the development of the gyrotron dates back to 1960s.After the first gyrotron was developed by the former Soviet Union,research on gyrotron became a hot topic.At present,the trend of research of gyrotron is towards high power and frequency.However,some development difficulties will arise.When gyrotron uses the fundamental mode and the frequency is high,it is difficult to achieve power output since the high frequency structure is so small that the power capacity is limited.On the contrary,if the operating mode is higher mode,the above problem can be solved well.At the same time,in order to achieve high power output,the energy of the electron beam and the electromagnetic wave is high,so that energy of the output window and collector is very high.Therefore,it is of great significance to study the thermal characteristics of the output window and collector.In this paper,the temperature distribution of the output window and collector of high cryotron is studied with the higher-order TE mode and at the frequency of 94 GHz.Firstly,for higher-order TE modes,there are angularly asymmetric TE_mn and angularly symmetric TE_0nn modes.It is difficult for the simulation software to calculate a complete three-dimensional since the size of window of the higher-order mode gyrotron is large,so the structure needs to be angularly symmetrically processed.We find that this method is not suitable by solving the S-parameters in HFSS if the operating mode is TE_mn.Therefore,the selected mode is TE₀₃.Secondly,the thickness of the output window,whose material is sapphire,is calculated according to the microwave transmission theory and optimized in HFSS.When the thickness is 0.526 mm,the S₁₁and S₂₁ parameter are-52 dB and-0.03 dB,respectively.Thirdly,the optimized model is imported into ANSYS Workbench to perform steady-state thermal analysis on the output window.When the transmission power is 100 kW,the maximum and minimum temperature of the window are 286.71? and 32.08?,that is,the temperature difference is more than the critical,the output window will be broken.In order to ensure the safe operation,the critical transmission power capacity,which is 57 kW,needs to be analyzed.However,high-power gyrotrons usually work in pulse mode.It is necessary to ensure that the output window can withstand a duration of impact,so we use Comsol software to perform transient thermal analysis on the output window.When the transmission power is 100 kW and the impact time reaches 120 s,the temperature distribution of the output window tends to be stable.In addition,when the electromagnetic wave lasts less than 20 s,the output window can work normally and safely.The thermal characteristics of the collector of the high-power gyrotron is studied by CST particle and multiphysics studio.Firstly,the relevant parameters of the magnetron injection electron gun is calculated according to the theory of electron cyclotron maser and optimized in MAGIC.Then,the temperature distribution on the collector is calculated.When the electron beam power is 275 kW,the maximum temperature of the collector is 332.00?.In order to reduce the temperature of the collector by optimizing the collector model and adding a defocus coil.The maximum temperature results are obtained by these two methods are 258.00? and 330.00?,respectively.Finally,when combining the two optimization methods,the maximum temperature on the collector can be reduced to 248.00?.