This section lists the specifications of orbit stability. The stored beam motion is easily characterized in terms of RMS and is a proxy of photon beam motion. If the beam motion (as read by a family of BPMs) is out of specification that we set below, then it is possible that the photon beam motion is excessive.

The real-time feedback system has a running measurement of a subset of BPM readbacks filtered through different single-pole low-pass filters. The RMS is calculated after the filtering stage. This RMS calculation approximates the integral of power spectral density over various frequency bands. See Figure 1 for processing details. The specifications are determined by multiplying the values obtained during normal runnning conditions times a factor between 1.5 and 2. The extra factor allows for slightly imperfect conditions or different bunch patterns.

Here are the specifications:

- BPMs used: Up to eighty narrow band BPMs of the P1 family.
- Motion of all BPMs are averaged.
- RMS specification:
Frequency Band Horizontal RMS Vertical RMS (Hz) (m) (m) 0.017-30 3.0 1.5 0.017-100 6.0 3.0 0.017-767 8.0 5.0

Note that the specification values are not based on the dimensions of the electron beam (for the time being).

Other items related to orbit stability:

- Orbit Stabilization at the Advanced Photon Source, presented at the
DOE-BES review of the APS, May 24, 2005, by Glenn Decker
pdf
- Overview of orbit correction (presentation given at the 2002
International Beam Stability Workshop) pdf
- High-level software (presentation given at the 2002
International Beam Stability Workshop)
pdf