“…Many codes for the simulation of positive ion beam extraction from ion sources, such as IGUN [1,2] , PB-GUNS [3] , KOBRA [4] , OOPIC [5] , MICHELLE [6] etc, are widely used in many fields, and the results calculated by using these codes are consistent with the experimental data. Recently, electron optics simulator (EOS), a novel fully three-dimensional finite-element design tool of electron gun and collector, has been developed by University of Electronic Science and Technology of China [7] . The EOS is developed in C++ language under the WINDOWS XP with SP2 operating system.…”