Angular Aberrations in Sector Shaped Electromagnetic Lenses for Focusing Beams of Charged Particles

Abstract

The general expression for the second-order angular aberration of sector shaped electromagnetic lenses consisting of superimposed uniform magnetic and radial electric fields used for the plane focusing of diverging beams of charged particles is derived. The result is applied to the special cases of pure magnetic and pure electric field lenses. The ion optics of a mass spectrometer employing sector electric and magnetic lenses in tandem and which has first-order velocity focusing and second-order angular focusing is obtained.