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本文对同心球和实际系统的场分布进行了比较,分析了产生几何象差的原因,提出了选择电极几何尺寸时应遵循的一般原则。理想同心球系统仅存在色球差和场曲;在平面屏上会出现枕形畸变;要得到平面象,要求从轴上到轴外n=R_e/R_a逐渐减小(即非球面系统);提高轴外阴极面场强E_c有利于改善场曲;若使管拉长(长焦距),则有利改善轴外象质;阳极孔增大有利于减小场曲;等比例放大R_e和R_a可减小畸变。实际系统常是轴对称的,故阴极面场强从轴上到轴外不同;沿轴外主轨迹的场分布比轴上更密集,使单元电子束受到更强的会聚作用;轴外场围绕主轨迹非旋转对称;对轴外
In this paper, the field distribution of the concentric sphere and the actual system are compared, the reason of the geometric aberration is analyzed, and the general principles to be followed when selecting the geometry of the electrode are proposed. The ideal concentric sphere system has only chromospheric errors and field curvature; pincushion distortion occurs on the plane screen; to obtain a plane image, it is required that n = R_e / R_a be gradually reduced from on-axis to off-axis (ie, aspherical system) If the length of the tube is elongated (long focal length), it will be beneficial to improve the out-of-axis image quality; the increase of the anode hole will help to reduce the curvature of field; and the proportional amplification R_e and R_a may be Reduce distortion. The actual system is often axisymmetric, so the field strength of the cathode surface varies from on-axis to off-axis; the field distribution along the main trajectory outside the axis is more dense than the axis, which makes the unit electron beam more strongly convergent; Track non-rotational symmetry; off-axis