Electrostatic Russian quadruplet with high demagnification and minimum influence of geometric aberrations

Based on a combined analytical and numerical modelling, a high-quality probe-forming system is proposed and developed. The Matrizant method is applied to minimize the beam spot size for a fixed beam current. For quadrupoles consisting of four metallic rods, the electric field inside of the quadruplet is computed using an accurate version of the boundary element method. The influence of the rod diameter on the beam spot size is studied for different emittances. The sensitivity of the system to energy spread and mechanical defects is also investigated.