Experimentelle Bestimmung der öffnungsfehlerkonstante von Elektronenkanonen / Experimental Determination of the Spherical Aberration Constant of Electron Guns

Due to the spherical aberration of electron guns, rays with large inclinations will not pass through the cross-over (the image of the entrance pupil). In order to calculate the constant of spherical aberration, it is necessary to know the transverse aberration as a function of the ray inclination at the cathode. Because measurements near the cathode are not possible, the size of the entrance pupil has been determined by theoretical considerations. The additional knowledge of cross-over size and inclinations of the emerging rays is then sufficient for obtaining the ray data at the cathode. The cross-over has been determined indirectly, ray inclination and transverse aberration in the cross-over plane have been measured by means of a shadow method.