Influence of the interelectrode gap width on the quality of focusing of electrostatic mirrors with rotational symmetry

Abstract

The influence of the width of the interelectrode gap on the focusing quality of electrostatic mirrors with rotational symmetry, the electrodes of which are coaxial cylinders of equal diameter separated by gaps of finite width, has been studied. Formulas, convenient for the numerical calculation of the exact values of the axial potential distribution in such mirrors, are proposed. Using the obtained formulas in numerical calculations and taking into account the width of the interelectrode gap, the geometric and electrical parameters of two- and three-electrode mirrors were determined, which provide spatial focusing of beams of charged particles simultaneously with the elimination of time-of-flight chromatic aberrations and spherical and axial chromatic spatial aberrations, the most important factors in terms of influence on the resolution of time-of-flight mass spectrometers and electron microscopes. It is shown that the width of the interelectrode gap has a significant effect on the quality of focusing of electrostatic mirrors with cylindrical electrodes.