Research On The Collector Of High Power Quasi-optical Output Gyrotron

The gyrotron has been widely used in various fields as a high-power microwave device,and the electron cyclotron resonant interaction is a key factor for heating,current drive,and startup on the ITER tokamak.The gyrotron is also the heating source of the stellarator W7-X developed by the Institute for Plasma Physics,Germany.The gyrotron also has many applications in active denial system(ADS),medical research,and plasma heating.In the past few decades,great progress has been made in high power,high efficiency,mode control and numerical simulation.The efficiency of 140 GHz continuous wave megawatt gyrotron is generally 20%~40%,therefore,when the electron beam enters into the collector after the interaction,it still has very high energy,the spent electron energy is collected on the wall of the collector and dissipated as heat power.And power dissipation can cause an increase in the temperature of the tube wall which could cause the inner wall of the oxygen-free copper material to change and be damaged.During the operation of the gyrotron,the power dissipation of the electron beam on the collector will cause an increase in the temperature of the collector wall,excessive temperature will cause the inner wall of the oxygen-free copper material to change and be damaged,which will seriously affect the stability of the gyrotron.Moreover,if the temperature is too high,the insulation between the collector and the high-frequency structural system will be deteriorated,and the vacuum inside the tube will be reduced,which will affect the working stability of the gyrotron.Therefore,it is important to reduce the temperature of the collector of the gyrotron and to study the thermal characteristics of the collector.Based on the existing working frequency of 140 GHz and the output power of 1 MW gyrotron,this paper discusses the defocusing scheme for the collector and analyzes the corresponding thermal characteristics,from the view of reducing the power dissipation density and temperature on the collector,the defocusing scheme for the gyrotron is designed,which lays a theoretical foundation for the actual test in the next step.Mainly includes the following aspects.This article mainly includes the following aspects:1.Firstly,the basic theory of electro-optical system is introduced,and three ways of heat transfer are analyzed.The convective heat transfer between fluid and solid surface applied in the collector region is introduced.The trajectory equation of electrons in the gyrotron and the adiabatic compression of the convergent magnetic field are introduced.The adiabatic compression theory is the theoretical premise of the subsequent analysis and optimization of defocusing.2.In order to meet the requirements of high power output,the defocusing optimization of the collector of the 140 GHz gyrotron is introduced.The three defocusing schemes including the compensation coils,the vertical field scanning system(VFSS)and the transverse field scanning system(TFSS).The power density distribution of the TFSS and the original case in the collector is analyzed.It is found that the falling point range of the electron beam on the collector is 380 mm,which is nearly 10 times larger than the original falling point range,which greatly improves the power capacity of the collector.3.The co-simulation of CST studio was used to study the thermal characteristics of the collector,and the advantages of CST co-simulation compared with other traditional thermal analysis software were analyzed and the convective heat transfer coefficient in thermal analysis theory is analyzed.The temperature changes of the collectors without the defocusing coils at different water flow rates and the corresponding thermal deformation are obtained.The corresponding temperature distribution and thermal deformation are analyzed when the water flow rate is 15 m/s under the action of TFSS.