Optimization in spot sizes of focused MeV ion beam by precise adjustment of lens-current excitations

Effects of lens-current excitations and object slit width on the beam spot sizes have been investigated to minimize the spot size in a microbeam line with 1.5 MeV helium ions, focused by piezo-driven object slits and a magnetic quadrupole doublet. Deviation of a lens-current excitation by 0.5% gave rise to an 80% increase in the beam spot size. A minimum spot size of 0.9 µm ×1.2 µm was obtained by an improvement in the adjustment of the lens-current excitations.