A high performance quadrupole quintuplet lens system for the CSIRO-GEMOC nuclear microprobe

Abstract

A new probe forming system for the CSIRO-GEMOC nuclear microprobe, based on a quadrupole quintuplet lens configuration is described. The lens system uses a novel quadrupole lens design with a 30 mm pole-tip extension, which allows a working distance of 85 mm. Each quadrupole has cut-outs at 45°, in the yoke positioned between poles, to allow unrestricted access for detectors into a target chamber at 135° to the beam. Four cut-outs are used to maintain four-fold symmetry. Each lens has a bore of 14 mm. The extra degrees of freedom in the quintuplet configuration allow optimisation to reduce spherical aberration, to minimise spherical and parasitic aberration cross-terms (involving θφ), and to..