Image Curvature Caused by Fringing Fields in Magnetic Sector Mass Spectrometers

Abstract

The fringing field of a magnetic sector analyzer produces a curved image of a line object. This is because rays off the median plane traverse a slightly different fringing field from that traversed by those on the median plane. In this paper, the shape of the image is calculated for a general paraxial ray traveling in a plane inclined to the median plane, under the assumption that the fringing field is two-dimensional. It is found that the image is not only curved, but is broadened by an amount depending on the exact nature of the fringing field. In the special case in which all paraxial rays travel in planes parallel to the median plane, and in which the analyzer is symmetrical, a straight-line object is imaged in a line having a radius of curvature of R/2, where R is the sector radius. In this special case, the shape of the image is independent of the exact nature of the fringing field.