Investigations on the possible beneficial effects of a centered orbit on the performance of the low beta-y lattice

The APS storage ring is routinely operated with beam steering for the users. The resulting orbit distortions (local bumps at the source point locations might reach 1 to 2 mm) could have a detrimental impact on the lattice performance via the off-centered path of the beam in the sextupoles. Resulting effects could include the following: modulation of the lattice functions, emittance growth, dynamic aperture and energy acceptance reduction, and lifetime reduction. The goal of the present study was to make a comparative analysis of the performance of the low beta-y optics when the machine is operated with the user`s orbit and with a centered orbit. Theoretical investigations as well as results of machine studies performed during the October--November run are presented in this Note. Since, to some extend, gradient errors could also induce similar perturbations, the unambiguous identification of the source of errors might be difficult. Some possibilities for discriminating between the different errors are also discussed