Precise centering method for triplet of magnetic quadrupole lenses using single rigid frame

Abstract

Separated probe-forming systems can be applied to enhance the resolution of a scanning nuclear microprobe with a comparatively large working distance to accommodate the detectors at backward angles. In such systems, magnetic quadrupole lenses are placed at the considerable distance and hence require their precise alignment with the beam axes. Violation of this requirement results in a considerable increasing of a spot size on the target for a constant beam current. Positioning of magnetic quadrupole lenses in a doublet can be implemented in a single-unit design, where a yoke and poles of two lenses are made from one piece of soft iron by precise electrical discharge machining. In a case of triplet, lens manufacturing as a single-unit has technological difficulties. A lens triplet configuration presented in this work comprises placement of three single magnetic quadrupole lenses in a single rigid frame. An approach to lens alignment by the magnetic field reconstruction method was developed and successfully realized.