Design Of Streak Image Tube And Research And Analysis Of Space Charge Effect

With the rapid development of science and technology,the understanding of the essence of ultrafast phenomenon has become the key to scientific research and deconstruction of micro process.The diagnosis of ultrafast phenomenon is becoming more and more urgent in inertial confinement fusion,basic frontier scientific research,new radar imaging,medicine,physical chemistry and other fields.As a device with high temporal and spatial resolution,streak camera can reproduce ultrafast process.As the most important component of streak camera,the design of streak image converter determines the performance of streak camera,such as temporal resolution,spatial resolution and dynamic range,which is of great significance to meet the application of streak camera in different scenes.Among all indexes,time-resolved scale has more important applications.In order to meet the measurement requirements of streak image tube under picosecond resolution,the electronic optical system and high-frequency structure are studied and designed in this thesis;The space charge effect,which restricts the time resolution of the streak image tube,is analyzed in detail and quantitatively.The research work of this thesis mainly includes the following contents:1.The ultrafast diagnosis technology,the working principle of streak image tube and the theory of space charge effect（SCE）have been investigated in this thesis.Then the research status of streak image tube at home and abroad and the progress of SCE have been analyzed in detail.So here comes a stage that the design goal of streak image tube and the research direction of SCE are established.2.In CST software studio,the deflection system of streak image tube is designed and the whole tube structure of streak image converter is determined.A new type of streak image tube is formed by combining the focusing structure of electrostatic-six electrode cylinder with the slow wave structure of traveling wave deflector.In CST,the S parameter of the traveling wave deflector of the streak image tube is calculated and the dispersion characteristic curve is analyzed to meet the design requirements of the streak image tube.The designed traveling wave deflector with slow wave structure achieves a passband of5.4 GHz while keeping the speed of electromagnetic wave and electron beam basically synchronized.3.Carry out particle simulation in CST to verify and optimize the model.The performances of the streak image tube with the parallel plate deflection system and the streak image tube with the traveling wave deflector are compared,and the deflection sensitivity of the two tube types are calculated respectively.The result of the former is39.43 mm/k V and the latter is 31.41 mm/k V.Through the dynamic scanning analysis of the electron beam in the tube,it can be obtained that the tube with traveling wave deflector can achieve a dynamic time resolution of 1 ps,and the tube with parallel plate deflector can only achieve a dynamic time resolution of 5 ps,which proves the superiority of the traveling wave deflector in the stripe image tube.4.The flight process of electrons in the streak tube of parallel plate deflector with different cathode lengths and current densities was simulated in CST particle studio to obtain the particle beam spot image.The influence of space charge effect（SCE）,on cathode imaging in streak tube was quantitatively analyzed,indicating that SCE will aggravate the distortion of cathode imaging.Under the same current density,it is more likely to affect the cathode imaging with larger area.