Investigation of low‐frequency beam motion at the Advanced Photon Source

The storage ring of the Advanced Photon Source has relatively tight tolerance requirements for beam stability. The tolerances of the rms beam motion in the insertion device straight sections are set to be less than 4.4 μm and 17 μm in the vertical and horizontal planes, respectively, in a bandwidth of 4–50 Hz. Sources of beam motions have been investigated for mechanical vibrations of the magnets and vacuum chambers induced by ground motion and water systems and for power supply ripple. Horizontal beam motions in a bandwidth of 9–12 Hz have been significantly reduced 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 of S1A sextupoles has been identified as a source of beam motion in a bandwidth of 5–8 Hz. The eddy current induced by the ripple field in the sextupole produced a vertical dipole field to drive the beam horizontally. After modification of the sextupole power supp...