Effects of stray magnetic field on the performance of ion microbeam

The ion microbeam employing MeV ions has many applications in the fields of elemental analysis, micro/nano processing, ion implantation, irradiation effects of spacecraft, biological irradiation effects, agricultural breeding and so on. The key aims are to reduce the spot size and to improve the stability of spot position. After more than 40 years of development, a variety of well-known factors degrade the performance of ion microbeam with stray magnetic field being one of the key limiting factors. This paper presents a new study of this important problem with the aim of optimizing the approaches to stray field mitigation. An approach applied here was to employ the WinTRAX beam optical software package to model the microbeam spot size and position on the sample to investigate the effects of stray magnetic field. This paper investigated the uniform stray magnetic field model and the non-uniform stray magnetic field model. A suitable alignment of the lenses is useful but only valid for the specific magnetic rigidity of ions and the determined stray DC magnetic field for which the beamline was aligned. This paper proposed a local correction method to address the influences of AC magnetic field and stray DC magnetic field. The method using the WinTRAX to simulate the stray magnetic field in an ion microbeam can estimate the influence once the stray magnetic field is measured in the ion microbeam laboratory.