Nonlinear corrections in the CR storage ring at FAIR

The large acceptance Collector Ring at FAIR is designed to provide a stochastic pre-cooling of either antiprotons (Pbar) or Rare Isotopic Beams (RIB) injected in the ring. In addition, for mass measurement of exotic short-lived nuclides, the CR will be tuned in the special isochronous ion-optical setting, in which it will be used as a Time-Of-Flight (TOF) spectrometer. In order to reach necessary time resolution, the octupole corrector magnets will be installed in the CR. The nonlinear field imperfections of the magnets and fringing fields of the wide aperture quadrupole magnets excite high-order chromatic aberrations, which lead to the beam losses. This is especially important for the large momentum acceptance antiproton and RIB ion-optical modes. To improve the dynamic aperture and to reach necessary time resolution for TOF sextupole and octupole corrections are planned to be applied in the ring.