The influence of stray DC magnetic fields in MeV ion nanobeam systems

This paper evaluates the lens aberrations in microbeam and nanobeam systems caused by stray DC magnetic fields. Stray DC fields are far less influential on focussed beam spots than stray AC fields, but in order to achieve good beam-spot resolution the beamline must be aligned to the stray DC fields in the laboratory. The relative thickness of the optical elements compared to the curvature of the beam in such fields causes aberration where the beam axis differs from the optical axis of the lens system. In this paper numerical ray tracing has been used to study the influence of stray DC magnetic fields on beam resolution at the sub-micron level using typical field strengths for the Earth's magnetic field as a case study.