Beam-Based-Alignment (BBA)

The BPM stations in the SLS storage ring are rigidly attached to the girders and serve as supports for the vacuum system. According to the specifications of the BPM support and the straightness rulers on the girders, the quadrupole-BPM offsets are known to within $\pm$50 $\mu$m [2]. The presented beam-based alignment technique allows to measure these offsets for the adjacent quadrupole-BPM combinations with $\mu$m precision. These offsets can be used to calibrate the mechanical positioning system (POMS) which monitors relative position changes of BPMs with respect to adjacent quadrupoles using linear encoders [3].