Investigation of open-loop beam motion at low frequencies at the APS

Sources of transverse beam motion in the APS storage ring have been investigated for ground-motion- and water-system-induced vibrations of the magnet and vacuum systems, and for power supply ripple. The displacement of magnets in a bandwidth of 4-30 Hz have been reduced significantly by inserting viscoelastic damping pads between the girder supports and pedestals, and by welding the magnet cooling headers to the ceiling of the storage ring tunnel. Current ripple on magnet power supplies was identified as a source of horizontal beam motion. Beam motion was measured without the closed-orbit feedback system activated. At β_x=15.4 m and β_y=10.4 m the rms beam motion in the 0.02-30 Hz band was 22.7 μm and 6.3 μm in the horizontal and vertical planes, respectively. A few narrow-band structures of the horizontal beam motion spectrum in the 1-4 Hz band have to be investigated further to identify the sources