Performance Improvements of the Bessy Ii Storage Ring by Optimizing the Phase Acceptance*

Linear optics modifications in order to improve injection efficiency and for the installation of two IDs in one straight section demand an optimization of the sextupole correction scheme. Four harmonic sextupole families were sufficient with the earlier 8-fold symmetric lattice. Today there are ten families of harmonic sextupole magnets in addition to the three families of chromatic sextupoles. This paper describes our experimental approach to find better settings for these harmonic sextupoles based on the direct optimization of the injection efficiency with a longitudinal phase offset between storage ring and the injector in our case a booster synchrotron. As demonstrated in the paper, the resulting improvement of the phase acceptance of the ring leads to increased momentum acceptance by suppressing 3 order non-systematic resonances. This increases not only the injection efficiency for long bunches but also the Touschek lifetime, the largest contribution to the overall lifetime of low emittance storage rings.