A fourth-order aberration theory for magnetic momentum-analysing systems

Abstract

Finite radial and axial source extensions, finite radial and axial acceptance angles, as well as incident beam momentum spread, introduce aberrations in the ionic motion through magnetically focusing systems intended for charged-particle momentum analysis. A fourth-order theoretical formalism accounting for an arbitrary combination of these aberrations is presented. It is shown that a relevant aberration classification scheme may be based upon the intra-aberration coupling degree, irrespective of the aberration order. For magnetically focusing systems possessing a radial symmetry plane, the principle of complementary radial and axial aberrations is formulated. The merits of the present aberration theory are finally demonstrated through a calculation of important ion- optical characteristics of the high-resolution magnetic spectrograph designed by the Massachusetts Institute of Technology group for Los Alamos Meson Physics Facility.