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:
|Frequency Band||Horizontal RMS||Vertical RMS|
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: