| Traveling wave tubes have a series of advantages such as wide working frequency band,large output power,high efficiency,strong environmental adaptability,etc.It is a widely used high power microwave millimeter wave amplifier device.In the slow wave structure of the traveling wave tubes,the electron beam and the electromagnetic wave continuously exchange energy,and the electromagnetic wave is effectively amplified.The electron gun,as an important part of the traveling wave tubes to generate electron beams,has a crucial influence on the performance of the traveling wave tubes.As the frequency band increases,the electron tunnel radius of the electron gun becomes smaller and smaller.When the wave band reaches the millimeter wave and above,the thermal deformation of the electron gun and dimensional errors caused by the processing and assembly will greatly affect the laminarity and beam transmission of the electron beam,which will seriously affect the overall performance of the traveling wave tubes.Therefore,designing a high-stability electron gun with low sensitivity to structural parameter changes is an effective guarantee for high-performance and high-reliability millimeter-wave traveling wave tubes.This paper adopts the idea of cathode immersed flow,that is,the magnetic field lines penetrate into the cathode,and this part of the magnetic field lines are consistent with the trajectories of the electrons emitted from the cathode surface.The CST simulation software was used to design an electron gun that can be used for millimeter wave traveling wave tubes and its corresponding immersed flow PPM focusing system.The simulation results show that the gun has higher stability than the traditionally designed electron gun:It has better static beam transmission when considering processing error and thermal deformation.And when considering the beam-wave interaction,the performance of the traveling wave tube using the immersed flow electron optical system is not sensitive to dimensional errors,and has better interaction performance.The main work of this paper follows:1.The design of cylindrical beam electron gun and immersed flow focusing system for millimeter wave traveling wave tubes:The method of cathode immersed flow is introduced,and its significance in the design of high-frequency traveling wave tube electron optical system is illustrated.Then we use CST simulation software to design a D-band cylindrical beam electron gun.After that,two sets of magnetic focusing systems were also designed using CST software,including a non-immersed flow focusing system that does not consider the magnetic field of the cathode and a specially designed immersed flow focusing system for the magnetic field near the cathode surface.2.Thermal analysis of the electron gun:According to the dimention of the electron gun obtained by simulation optimization,the structural design was carried out.The steady-state thermal analysis and thermal deformation analysis of the electron gun were performed using ANSYS Workbench software to obtain the thermal deformation data of the electron gun during actual work and provide the deformation data for the stability analysis.3.Research on stability improvement of immersed flow electron gunAccording to the actual engineering experience,analyze the influence of errors caused by the processing and assembly and dimentional changes caused by thermal deformation on the electron beam transmission and laminarity.The analysis results show that the axial displacement of the cathode in the immersed flow electron gun is 50um forward and backward,the radial displacement is 50um,and the cathode inclination angle is within 2~o,and the electron beam can maintain the beam transmission of more than 95%.When considering thermal deformation,the beam transmission of the immersed flow electron gun is 10.2%higher than that of the non-immersed flow electron gun.4.Influence of immersed flow electron gun on performance of beam-wave interaction:In order to analyze the influence of the immersed flow electron optical system on the traveling wave tube beam-wave interaction,we analyzed the high-frequency characteristics and beam-wave interaction process of the traveling wave tube with the D-band folded waveguide slow wave structure.The peak power at the center frequency of140GHz is 54W,the gain is 37.3dB,and the bandwidth is 8GHz.A PIC simulation considering the dimentional error of the cathode was carried out.The simulation results show that the immersed flow electron gun can reduce the effect of the dimentional error on the beam-wave interaction performance.5.Experimental test of immersed flow magnetic system:The immersed flow PPM focusing system is processed and debugged,and finally the focusing system consistent with the simulation result is obtained. |
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