Five magnetic quadrupole lenses with four power supplies as a single-stage lens system of a nuclear microprobe

Abstract

The present work was undertaken to improve the parameters of existing nuclear microprobes based on a triplet lens system by transforming them into quintuplet. In such a probe-forming system, a single-unit doublet, which is easy to adjust precisely, acts as the first two lenses and has two independent power supplies. The final three lenses from a conventional high excitation triplet have their two power supplies. Optimization for the quintuplet was performed in order to get a probe with the maximum acceptance normalized to a given probe size at the target. Variants and values of the doublet excitation and its position along the beam line were determined during the optimization. The results of our numerical simulation have shown an increase of the maximum normalized acceptance and greater demagnifications for the quintuplet in comparison with the conventional triplet. At the same time, the position of the single-unit doublet along the beam line does not affect significantly the microprobe characteristics. The advantage of using the single-unit doublet as the first two lenses in the quintuplet is confirmed by calculations of the required lens positioning accuracy.