Analysis and simulation of point-focusing property of a quadrupole lens pair

A pair of quadrupole lens has excellent imaging performance, electrostatic quadrupole lens can focus the electron beam into a line, quadrupole lens pairs have the ability to focus the electron beam into a point. The point-focusing property of a quadrupole lens pair was investigated in this paper, using the electron ray tracing simulation program SIMION. The simulation of electron distribution quantitatively showed that the fringing field at both ends and the aberration in the crossover image caused an electron beam blur. The aberration of a quadrupole lens pair as a function of the electron initial kinetic energy was discussed, and the result indicated that the aberration would be effectively reduced if the kinetic energy of electrons increased. 10000 electrons were flown in a SIMION simulation and the entry angle 0 is randomly varied so that -1°<α⁰<1°, the size of diffuse spot at the focal plane reduced to 3.2 μm×28 μm as the kinetic energy of electrons increased to 1×10⁵ eV.