A detailed account of the correction of parasitic sextupole fields in a magnetic quadrupole lens

Abstract

Most nuclear microprobes for focusing MeV light ion beams use quadrupole lenses as the final demagnifying element. However the spatial resolution attainable in most microprobes is limited by parasitic sextupole fields in the quadrupole lenses. These sextupole fields can be corrected by imbalancing the currents flowing through the pole piece coils of magnetic quadrupoles, or making the pole piece voltages of electrostatic quadrupoles asymmetric. This paper describes in detail the procedure for correcting the parasitic sextupole field present in a magnetic quadrupole lens using the shadow image method.