Mass spectrometers with energy focusing: Combinations of magnetic and electric sector fields whose mean planes of deflection are tilted with respect to each other

Abstract

First a combination of two sector fields is considered, for instance a homogeneous magnetic field followed by an electric cylinder condenser. The mean planes of deflection of the fields are tilted with respect to each other by an oblique angle. Such a combination has astigmatic focusing properties for paraxial rays of ions of certain mass and energy coming from an object point assumed at a certain distance before the first field on the incoming central ray. At different distances from the field combination are formed. calculated in first order, two real or virtual straight astigmatic focusing lines which are perpendicular to each other and to the outgoing central ray. By proper assumptions of the dimensions of the combination it can be arranged that its first order energy dispersion and one real of its astigmatic focusing lines have exactly the same direction. Then by addition of a third sector field (again a homogeneous magnetic field) it can be achieved that the astigmatic focusing will be changed into a stigmatic one while at the same time the energy dispersion can be reduced to small values. The mass dispersion of this three field combination in the given numerical example is about perpendicular to the direction of the energy dispersion.