BEAM-BASED ALIGNMENT AT BESSY

The theoretical background for the beam-based alignment is presented. It is shown that the shift of the orbit, as the focussing strength of one quadrupole magnet is changed, can be described by the perturbed or unperturbed linear lattice parameters. This has been applied to check the longterm stability of the closed orbit with respect to the axes of the magnets, to redefine the zero readings of the standard beam position monitors, and to align the beam to the center of the quadrupole magnets at BESSY.