Field reconstruction technique for testing magnetic quadrupole lenses

A number of analytical instruments make use of strong magnetic quadruple lenses. Performance properties of such instruments are determined by the presence of lens aberrations that arise from the structure of the lens magnetic field. This paper describes a technique for reconstruction and analysis of the 3-D field of the magnetic quadrupole lens. Measurements of the radial B-r or longitudinal B-z component of the field are used as boundary conditions for the Laplace equation for magnetic scalar potential. Application of the charged density method for the solution of the boundary-value problem allows the field and its multipole components to be determined to a high accuracy. The field reconstruction technique can be used for determination of both intrinsic and parasitic multipole components of the field in a magnetic quadrupole lens. This technique is suitable either for a single magnetic multipole lens or for a magnetic multipole lens system. (C) 1997 Elsevier Science B.V.