Charged particle focusing systems have many valuable uses, including those wherein the charged particles are accelerated. The focusing systems for many charged particle systems employ multiple quadrupole lenses in parallel with the optical axis. For high energy applications, increased beam current is desired and this can be achieved by enlarging the effective beam converging angle. However, the size of the beam converging angle is limited by the spherical aberration, which is present to some extent in all designs of probe-forming systems, thus optimum spatial resolution can typically only be achieved at the expense of a reduction in beam current.
The current invention describes a lens system with sextuplet quadrupole arrangement that permits focusing of ion beams at various focal lengths, thus mitigating intrinsic aberration of the lens to achieve optimal small beam size without a need for reduced beam current. This technology improves the resolution of ion beam focusing within a fixed lens system to achieve an optimum small beam spot.