System for obtaining longitudinal beam polarization at PEP with vertical dipoles located outside of the interaction region

A spin rotation system (SRS) is proposed in which the central orbit is bent by vertical dipoles located outside of the interaction region. The spin is rotated as before by the (g-2) precession in these magnets. Some important features of the system are the following: (1) there is no reduction in luminosity resulting from adding the SRS; (2) somewhat less (about 30 percent less) synchrotron power is radiated than in the Schwitters-Richter scheme; (3) low-field vertical bending magnets and masks are included in the SRS in order to shield the detector from the synchrotron radiation, at least in part; (4) selection of either the SRS mode or the conventional operating mode is achieved simply by choice of alternative settings of magnet currents; and (5) the interaction region is left completely unencumbered for disposition of the experimental apparatus