Combination of magnetic and electric quadrupole lenses as zoom Sextuplet ion microprobe focusing system with minimum spherical aberration

Abstract

The new generation nuclear microprobe system at the Louisiana Accelerator Center in the University of Louisiana at Lafayette consists of a 6.25m beam line that employs the magnetic quadrupole Sextuplet lens system. This Sextuplet is a zoom system having the same demagnifications, the same focal lengths and the same positions of the focal points in (xoz) and (yoz) planes as in the case for the Russian quadruplet. It also can have the same spherical aberrations in both planes. The parameters which allow obtaining the lowest coefficients of spherical aberration are found for different geometrical configurations of electric and magnetic quadrupole lenses. Specifically, the configuration of a combined Sextuplet consisting of two magnetic and four electrostatic lenses or consisting of two electrostatic and four magnetic lenses is studied and compared with magnetic and electrostatic Sextuplets. The values of the chromatic and spherical aberrations for these combined systems are compared and the minimum spot radius and the half-widths of the corresponding slits for some optimal magnetic and electrostatic Sextuplets are given.