Research On Power Capacity And Reliability Of Gyro-TWT Output Window

As a typical representative of microwave electric vacuum devices,gyrotron travelling tube(gyro-TWT)has the ability to generate average as well as continuous wave power in the millimeter wave range above the kilowatt level.Compared with other vacuum devices,gyro-TWT has higher operating frequency,wider operating band,and higher gain.As one of the key components of the gyro-TWT,the output window has greatly influence on the performance of the entire tube.With the maturity of modern design system and the progress of technology,the operating frequency and output power of the gyro-TWT development gradually increased,which also make the demand for power capacity and reliability higher.In the case of high power output,if the window reflection is too high,the microwave power returned to the high-frequency system will rise significantly,the self-excited oscillations generated will seriously affect the operating of the gyro-TWT.At the same time,due to the existence of dielectric loss of the window,the window will generate a lot of heat when high power microwave pass through,also the temperature difference formed in the window will generate thermal stress,when the thermal stress exceeds the tolerance limit of the window,the window will possibly break.Therefore,in oder to design a low reflection,wide bandwidth,and high power capacity output window,it is necessary to analyze its electrical performance as well as thermal characteristics.The main research of this thesis is as follows.1.The Q-band sapphire single-layer output window is designed according to the half-wavelength theory,heat loss and it’s distribution of the window under 100 k W output power are obtained by HFSS simulation and theoretical calculation.The transfer coefficient of the water cooling is calculated by using Fluent,also the effect of the coolant flow rate on the maximum temperature and heat transfer coefficient on the output window is analyzed.Then the thermal and stress analysis of the designed output window was carried out by ANSYS Workbench,also the temperature distribution and isotropic stress of the window under 100 k W output power are obtained,and the main stresses that damage the output window are analyzed.Finally,the thermal stress of the window is estimated by establishing the output window stress calculation model,and the calculation results match well with the simulation results,which provide theoretical support for the output window stress calculation.2.To address the problem of window deviation due to accumulation of the solder,this thesis designed a three-layer output window structure with non-uniform radius.First,the size of the window is designed by matching the characteristics of the multi-layer window,also the processing and assembly errors are analyzed for redundancy,then the thermal and stress simulation analysis of the improved three-layer window is carried out for the continuous wave and pulsed wave cases respectively.The power capacity of the output window is 18% higher than that of the continuous wave when transmitting a pulse wave with 20% duty cycle.After the design and thermal analysis of the three-layer window,the output window was cold tested for parametric characteristics,thickness measurement,and harsh environment testing,the result shows that the parametric characteristics and assembly quality of the output window are within expected range.3.To address the problem that the existing W-band beryllium oxide super-surface window is damaged many times under 18 k W transmission power,this thesis analyzed the temperature and stress of the original output window,which lead to the result that the temperature difference on the window and the stress on the edge is the main cause of the window damage.For the problem of high edge stress of the window,the middle layer of the output window is thickened to disperse the edge stress;for the problem of high temperature on the output window,the upper and lower sleeves were added on both sides of the output window to increase the heat dissipation capability of the output window.The temperature and stress analysis of the original and improved output window shows that the improved output window has lower working temperature and less thermal stress,which means that the improved output window has higher power capacity.