The Effect of Operation Modes on the Electron Beam Diameter in Condenser Magnetic Lenses System

Abstract

The effect of operation modes of condensing magnetic lenses has been investigated to determining the total demagnification and the diameter of the electron beam coming out of it. The cross-over point inside the electron gun is considered as the object (do) with a diameters ranges of (10 – 100 µm) to find out the optical efficiency of the double lens condensing system and its ability to forming a high précising image of the 1^st real image formed inside electron gun of thermal emission that acts as an actual source of electron beam. The following modes; (weak- weak), (weak- strong), (strong- strong), and (strong- weak); denoted as (#1, #2, #3, #4 respectively); have been studied. The best value for the total demagnification and the diameter of the electron beam has been obtained in the mode of (strong- strong; #3); where the parameters were: (dMt = 1014.199), (d2 = 49.3 nm), while the worst value has been achieved in the mode (weak- weak; #1) (dMt = 31.56267), (d2 = 1584.15 nm). It is found that by increasing the demagnification of the first condenser lens, the demagnification of the final real image produced by the double lens system has been positively affected. It is found that the relationships that obtained between the demagnification and the current density can be used as a calibration curve to obtain the required total demagnification for the electronic beam diameter for any mode according to the purpose of the desired application.