Thermal-hydraulic Analysis And Design Of Collector And High Frequency Structure Of High Power Gyro-TWT

Gyrotron traveling wave tube?Gyro-TWT?is an important millimeter-wave device,which is widely applied in the field of military and other fields.Gyro-TWT contains of electron gun,high frequency structure and collector.Its working principal as follows:the cathode of the electron gun emits electrons that do a spiral movement and enter the high frequency structure.Electron beam interacts with the electromagnetic field and transfers its expands the energy to the microwave.Finally,the rest of electrons are recycled by collector.With the increasing of working frequency,the requirement of Gyro-TWT's performance becomes higher and higher.In the stage of beam-wave interaction,in order to restrain the self-oscillation and other competitive patterns,there are many circular beryllia ceramics inside the high frequency structure.The heat dissipation power is deposited on the surface of the ceramics,which result in the rise in the temperature of the high-frequency structure.After electrons entering the collector part,they hit the inner wall of the collector and the electrons'kinetic energy is converted into heat energy,which causes the rise in temperature of collector.As the power capacity of the Gyro-TWT increases continuously,the temperature of the oxygen-free copper becomes higher and higher and the volume fraction of phase transition increases.The heat dissipation of the fluid is slow or even stopped,and the uneven heating of inner wall results in oxidation,corrosion and burning to oxygen-free copper.In order to improve the performance of the Gyro-TWT,external water cooling system is necessary to reduce the temperature.To solve the above issues,this paper designs and compares a variety of water cooling systems of collector and high frequency structure which are based on the working principle of Gyro-TWT,fundamentals of thermal analysis and the theory of fluid mechanics.It conducts thermal analysis through ANSYS Fluent.This paper contains the following contents and innovations:1.The thermal analysis of collector.The traditional collector can not satisfy the large turbulence of the fluid.On the basis of the straight groove,the circular groove added at the bottom of the straight groove,the square groove added at the blade,the island structure and the helical structure are designed respectively.In order to increase the heat dissipation area of the water cooling structure,the thickness of the collector,the number of water tanks,and the depth of the water tank are simulated.The heat dissipation of helical structure is obviously effective.The volume fraction of fluid phase transition is small and the temperature of the inner wall of the collector is reduced to 99°C.Compared with the conventional collector,the power capacity of the helical structure has increased by 74%.2.Thermal analysis of high frequency structure.When the output power of the conventional Gyro-TWT increase from 10 kW to 30 kW,the oxygen-free copper is damaged,the vacuum environment of high frequency structure is polluted and the Gyro-TWT cannot maintain a stable operation for a long time.In order to improve the power capacity of Gyro-TWT,the traditional straight groove type,island type and helical type of high frequency structure are simulated respectively.When the power ratio of the conventional high frequency structure is greater than 30%,the volume fraction of fluid phase transition increases,the heat dissipation efficiency drops sharply and the output power is low.When the power duty ratio of island cooling structure is less than 55%,the fluid flow rate is slow and the heat cannot be taken away in time.The lowest temperature of the ceramics is 300°C,which is slightly higher than the conventional type.The fluid rate of helical structure is up to 12 m/s and the volume of phase transition is close to 10^-5,that achieves better heat dissipation.When the power duty of high frequency structure is 50%,the maximum temperature of the ceramics is 200°C.Compared with the conventional type,the ceramics temperature has dropped from 300°C to 200°C and the power capacity has increased by 67%.When water cooling structure of the collector and high frequency structure are both helical type,the heat dissipation efficiency is the best,and the goal of improving the performance of the Gyro-TWT is achieved.Based on good cold test results,they have been processed into physical objects and are applied to thermal tests.No local burning and ignition were found under operation conditions.