条纹变像管时间畸变的分析

摘要

Streak cameras applied to inertial confinement fusion research and flashless imaging lidar require large working areas. However, the larger the working area, the bigger the temporal distortion is. And the temporal distortion has a great influence on the detecting precision of the streak camera, resulting in an image distortion on the screen. Yet previous streak camera design work emphasized shorter time resolution and higher special resolution with paying less attention to the temporal distortion extent. Key factors that may affect the temporal distortion are thoroughly analyzed in this paper. We calculate the electric field of a small-size streak tube with the aid of the Computer Simulation Technology Particle Studio software which is a three-dimensional electromagnetic simulation software based on finite integration technology. Axial electric field distributions at different distances to the axis of the small-size streak tube are displayed. The electron trajectories launched from different points on photocathode of the streak tube are tracked through interpolating pre-calculated electromagnetic field to the particle position. It is known that curved photocathode can reduce the temporal distortion, so we calculate the temporal distortions of streak tubes whose radii of curvature of the photocathode are 30 mm, 35 mm, 40 mm, 45 mm, 50 mm, and 55 mm respectively to ascertain how the curvature influences the temporal distortion. The results show that the temporal distortion is mainly produced in the photocathode-to-deflector region, and it is negligible in the equipotential region. Also, bigger radius of curvature of the photocathode leads to a positive temporal distortion, and smaller one leads to a negative temporal distortion. And the absolute value of the temporal distortion increases with the increase of the slit length. The small-size streak tube whose radius of curvature of the photocathode is 40 mm owns the smallest temporal distortion. We also calculate the temporal distortions of electrons launched from the different positions of the photocathode with different initial energies, and the initial energy has little influence on the temporal distortion. To sum up, the dominating factor that produces the temporal distortion is the curvature of the photocathode. The slit image under a ramp sweeping voltage on screen is curved due to the temporal distortion. And the bigger the temporal distortion, the greater the curvature of the slit image is. Besides, a linear relation between the temporal distortion and deflection of the slit image is displayed. The spatial resolutions of the streak tubes with the radii of curvature of the photocathode 30 mm, 40 mm, 50 mm are calculated respectively. And the small-size streak tube whose radius of curvature of the photocathode is 30 mm has the highest spatial resolution. The radius of curvature of the streak tube photocathode should be carefully selected according to actual requirements for the streak camera. Through the analysis we provide a significant guidance for streak tube design.%应用于惯性约束核聚变和非扫描式激光雷达等的条纹变像管要求具有较大的探测面积，条纹变像管的探测面积越大，其时间畸变就越大，从而影响条纹相机的探测精度，且会导致荧光屏上成像畸变。本文计算了条纹变像管内部的电场分布，并追踪电子运行轨迹，对条纹变像管的时间畸变进行了分析。结果表明：造成条纹变像管时间畸变较大的区域是阴极到偏转板前的部分；其主要影响因素是阴极曲率半径，且阴极曲率半径存在一个最佳值使得条纹变像管的时间畸变最小，大于该最佳值，条纹变像管会产生正的时间畸变，反之，条纹变像管会产生负的时间畸变；时间畸变的绝对值随着光电子从阴极发射的初始高度的增大而增大；光电子初始能量对条纹变像管的时间畸变的影响很小。同时，模拟了不同阴极曲率半径下由于时间畸变不同导致的动态扫描狭缝像的弯曲情况，时间畸变越小，狭缝像弯曲程度越小。