| Streak camera is a diagnostic tool with high time resolution and plays an important role in the study of ultrafast process such as inertial confinement fusion(ICF), et al. In laser fast ignition ICF, to study temporal and spatial information of X-ray radiation, X-ray streak camera with femtosecond time resolution is demand. Although the femtosecond streak camera has a lot of work and progress in preliminary research, but dynamic range is too small. Streak tube is the core device of streak camera, an X-ray femtosecond streak tube with certain and practical value dynamic range is provided and developed. Beside, the main indicators of X-ray streak camera, spatial and temporal resolution, dynamic range, etc. is researched on and improved, the design improved streak tube and the approaches and methods improved the performance of X-ray streak camera is continued to research.On the basis of summarization of the streak camera development, research on the X-ray femtosecond streak tube design and performance improvement, the main work of this paper includes the following aspects:1. The approaches of realize femtosecond time resolution is researched. Temporal resolution is analysis by the logical sequence of parameter introduced, approach improved and technical analysis. Spatial and temporal modulation transfer function is introduced to evaluate space-time performance, the physical significance of the function, calculation method and advantages are introduced. Two methods of calculation of dynamic range of streak camera are introduced. Finally, the approaches and key technologies are put forward to realize X-ray femtosecond streak camera, using plane focus X-ray streak tube, depress the space charge effect, increase the potential distribution on axis and reduce the length of focusing area.2. Design and simulation plane focusing streak tube using Matlab programming. Firstly,based on the system of electrode distribution and voltage value, the finite difference method and Gauss- Seidel over relaxation iteration method to speed up the convergence is used to getdistribution of electric field in tube. In calculation of electronic flight trajectory in tube, using Monte Carlo method is used for sampling electronic initial state: energy, direction angle,azimuth angle, launching area, time distribution. The fourth-order Runge-Kutta method to calculate electron trajectory, in which Lagrange interpolation is used to calculate electric field values of electronic placement. The space charge effect is considered in electron emission and flight processes.3. X-ray femtosecond streak camera simulation results. First of all, For different evaluation formulas of time spread, the six relatively accurate time spread values of optoelectronic initial energy distribution are calculated when UV and X-ray band incident photocathode, including the Henke model using a relatively rapid sampling method. The relationship of electronic time spread between emission current density and accelerating flied is analyzed. Electrons redistribute themselves inside the pulse a linear velocity chirp develops on the electron pulse in acceleration region is found, which are different curves from in free propagation region. Simulation shows that the limits of space and time resolution are 28.5lp/mm and 392 fs, dynamic range is 66 of the plane focus X-ray femosecond tube.4. To improve the performance of plate structure X-ray femtosecond streak camera, an accelerating structure is designed. This structure has the acceleration mesh and slit channel.Considering the actual X-ray incident CsI photocathode in ICF experiment, photoelectron energy dispersion is larger and the affect of space charge effect, Monte Carlo method is used to study the electron trajectory structure in the streak tub with this accelerating structure.Results show that spatial resolution of X-ray femtosecond streak camera with the acceleration structure is 21lp/mm, time resolution is 497 fs, which are improved by 90% and 29%respectively compared to traditional plate structure streak camera. The structure is simple and practicality.5. Post-accelaration technology is an important technology for improving the X-ray streak camera performance and is carefully researched in this paper. Four aspects of Post-accelaration technology are researched, which are electron optics, minimum detectable photon density, mesh moiré fringes, the collision between electron and mesh. The large deflection sensitivity is undertaken, the phosphor screen quantum efficiency is made full use and dynamic range camera is improved in Post-accelaration X-ray streak camera. Voltagedisturbance in equipotential region caused by mesh is studied and it provides reference in the choice of mesh. Moiré fringes in the streak camera are analyzed, which is interference for space imaging, and the method of reduce the influence of moiré fringes is studied.6. The establishment of experimental platform and experiment. X-ray Femtosecond streak tube is developed. In static and dynamic work mode, femtosecond streak camera system is set up, tested and standardized. Incident by 266 nm UV light of Ti: sapphire femtosecond pulse laser, time resolution of streak camera is 780 fs, the maximum dynamic range is 96.3, and engineering dynamic range is 18.2, which has a certain practicality.High-performance screen and partition plate cathode for Post-accelaration system are produced. An X-ray picosecond streak camera with Post-accelaration system is tested, the experimental result show that in the middle area of phosphor screen reached 15 lp/mm,margin reached 10 lp/mm, engineering dynamic range of 2412, which is more than twice of the highest dynamic range of domestic report. Peak sampling method used by LLNL laboratory is introduced and used for streak image analysis, spatial MTF curve of streak camera is get.The main innovation points are:1. Six relatively accurate time spread values of optoelectronic initial energy distribution are calculated when UV and X-ray band incident photocathode, including a relatively rapid sampling method for the Henke model.2. Electronic flight is researched in accelerating region between photocathode and mesh.Electrons redistribute themselves inside the pulse a linear velocity chirp develops on the electron pulse in acceleration region is found, which are different curves from in free propagation region. Theoretical explanation is given.3. The accelerating structure is design for improving traditional plate structure X-ray femtosecond streak camera. In calculation and simulation, the study demonstrates that time and space performance of X-ray streak camera with this structure is improved.4. Post-accelaration technology is used to improve dynamic range of X-ray streak camera. Four aspects of Post-accelaration technology are researched, which are voltage disturbance in equipotential region caused by mesh, minimum detectable photon density,mesh moiré fringes, the collision between electron and mesh. The value of Post-accelarationtechnology is proven in the experiment of X-ray picosecond axisymmetric streak camera. The engineering dynamic range of camera is 2412, which is more than twice of the highest dynamic range of domestic report. |
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