MEASUREMENT AND CORRECTION OF PARASITIC SEXTUPOLE COMPONENTS IN MAGNETIC QUADRUPOLE LENSES

Abstract

Most experimental measurements of the parasitic aberration of magnetic quadrupole lenses used in probe forming lens systems for MeV light ions have revealed parasitic sextupole components, possibly from manufacturing defects. These parasitic sextupole components can seriously degrade the resolution of the focused probe. Radial and angular displacements of the individual poles of a quadrupole are modelled and the conditions where correction of the resulting parasitic sextupole component is possible by shunting the currents in the windings of individual poles are investigated. It is found that, apart from some special cases, correction is not possible by shunting a single pole. Details are als..