Spherical Aberration Corrections for the Electrostatic Gridded Lens

摘要

Two methods of spherical aberration corrections of an electrostatic gridded lens have been studied with ray tracing simulations. Both methods are based on modifying electrostatic field on the periphery of the lens. In a simplest case such modification is done by extending the part of the grid support on its radial periphery in axial direction. In alternative method the electric field on the radial periphery of the lens is modified by applying an optimum voltage on an electrically isolated correcting electrode. It was demonstrated, that for a given focal length the voltage on this lens can be optimized for minimum aberration The performance of lenses is presented as a lens contribution to the beam RMS normalized emittance.