Reduction of the Horizontal Antidamping in the Desy Electron Synchrotron

In the DESY electron synchrotron the horizontal betatron oscillations are antidamped because of the isomagnetic combined-function lattice. Since the main task of the synchrotron is to supply electrons and positrons at the highest possible injection energy for the storage ring PETRA, a reduction of the horizontal antidamping would be very advantageous for the following reasons: - smaller horizontal beam emittance improves injection efficiency in PETRA - injection energy for PETRA could be 8 GeV instead of 7 GeV - the repetition rate of presently 50 Hz could be reduced to 12.5 Hz without affecting the accumulation rate in PETRA. This would have further advantages for the operation of the synchrotron. Using the existing backleg windings of the magnets, the antidamping can be reduced as measurements show. Adding quadrupoles to the synchrotron magnet lattice would allow to introduce horizontal damping. The variation of the horizontal beam size during acceleration is shown.