Polarized beams in LEP

The renewed interest in polarized beams at the Z energy has stimulated a new round of studies. The asymptotic polarization degree, as calculated with the first-order theory, now reaches 85%, with the help of new asymmetric wigglers and polarization maximisation. Further spin tracking shows a strong excitation of higher-order satellite resonances due to the large beam energy spread in LEP. However they can be weakened by a refined compensation of the linear spin resonances. The resulting polarization degree is larger than 50% with a rise time of 36 minutes. A spin rotator of the Richter-Schwitters type has been designed for installation in the LEP straight sections. Magic phase advances for the rotator magnets have allowed an almost complete spin-matching. After optical matching, the optics is unaffected except for a tilt of the closed orbit of 15 mrad and a non-vanishing derivative of the vertical dispersion at hte interaction point (IP). The residual depolarization calculated with SLIM is found to be insignificant. Although various aspects need to be studied in more depth, the set of results obtained so far tend to show that polarized beams should be possible in LEP