Effects of linear quadrupole fringe field overlap on transverse matching to an radio frequency quadrupole

Along many low energy beam transport (LEBT) systems transverse hadron beam matching to a subsequent radio frequency quadrupole (RFQ) is performed by magnetic quadrupole multiplets. Large apertures combined with short distances between the quadrupoles lead to overlap of individual singlet fields and significantly impact on the effective beam optics. Systematic measurements of beam transmission through an RFQ have been done and compared to beam dynamics simulations. For the latter, simplified hard-edge quadrupole fields were replaced by measured field data. It turned out that the hard-edge model is not sufficiently accurate to achieve acceptable agreement between calculated and measured beam properties.