Orbit Stability

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.

Figure 1: Schematic of the RMS processing details. Signals are first filtered, then root-mean-squared. Then all BPMs are averaged.

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)	($\mu$m)	($\mu$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