Effect Of X-ray Framing Camera Magnetic Lens Structure To The Electron Beam Imaging Quality

Since the electromagnetic lens was used in electron imaging, it has been widely applied in various fields, such as medical science, biology, detectors and so on. Due to the effect of electric field force and lorentz force, the electromagnetic lens can be used to focusing and imaging the electron beam, whose process is similar to the optical lens. Electromagnetic lens consists of electrostatic lens and magnetic lens: The lens using electric field for the electron beam imaging is called "electrostatic lens"; The lens using magnetic field for the electron beam imaging is called "magnetic lens". Because of its simple structure, convenient adjustment, strong anti-interference capability, Magnetic lens is mainly applied for focusing electron beam on the tube, electron microscope, vacuum devices and other equipment. Also, it has significant application in ultra-fast diagnostic equipment, such as short magnetic focusing type X-ray framing camera(XFC).X-ray framing camera with microchannel plate(MCP) as the core component, gets high accuracy of spatial and time resolution image, and the measurement data of X-ray framing camera is the important basis of analyzing the ultrafast process. In recent years, X-ray framing camera has played an important part in the fields of inertial confinement fusion(ICF), Z pinch(Z- pinch)researches, and high energy density physics(HEDP). As an important part of image convert tube, the magnetic lens has a critical impact on image quality and spatial resolution. Therefore, the analysis and design of the structure of magnetic lens to improve the image quality become important. In this paper we study the influence of magnetic lens structure on imaging quality of electron beam. Mainly including the following contents:The Lorentz software is used to establish the model of image converter tube. This software embedded boundary and finite element calculation method can be used in magnetic lens structure. The electrons initial energy and angular distribution can be configured with this software, and the magnetic field distribution on the axis is obtained. The electron trajectory and the position distribution on the phosphor screen is also obtained to optimize the design of the magnetic lens.Under the magnetic lens magnification of 1:1, the simulation results show that the spatial resolution on the axis is 16.0 lp/mm. The off axis spatial resolutions of 5 mm and 10 mm from the center of the cathode are 7.7 lp/mm and 4.1 lp/mm respectively. Compared with the experimental result of 10 lp/mm, the experimental results agree with the simulation results. The spatial resolution as a function of slit width of magnetic lens is simulated, the results show that the spatial resolution is improved by increasing the slit width. The spatial resolution as a function of inner diameter of magnetic lens is also studied. By increasing inner diameter of the magnetic lens to 1.25 times of the original data, the spatial resolution on axis is 23.4 lp/mm, the off axis spatial resolutions of 5 mm and 10 mm from the center of the cathode are 17.9 lp/mm and 11.7 lp/mm, respectively.