ARCHITECTURE

In contrast to the centralized PC-based SOFB, the FOFB runs the feedback algorithm in parallel on 12 DSP boards. The diagonal structure of the SVD-inverted corrector/BPM response matrix allows a decentralization of the feedback algorithm which nevertheless realizes a global orbit correction scheme. The FOFB is an integral part of the Digital BPM system (DBPM) [4] which is distributed over 12 sectors. Each BPM sector handles 6 DBPMs and controls 6 correctors in both transverse planes (Fig. 1).

Figure 1: The Fast Orbit Feedback (FOFB) is integrated in the 12 BPM/corrector sectors. A dedicated fiber optic network provides communication between adjacent sectors.

Adjacent BPM sectors are directly connected via fast fiber optic links. This allows the calculation of the required corrector kicks per sector based on 18 beam positions at a rate of 4 kHz. The resulting kicks are fed into one PID controller per corrector. The SOFB running on a central PC-based beam dynamics server initializes and monitors the FOFB, taking into account the number of available BPMs and correctors. The central RF frequency is used as an additional control parameter to correct off-energy orbits. Frequency corrections are carried out by the SOFB. Dispersion orbits must not be corrected by the FOFB and are therefore subtracted before each correction step. Due to the localized FOFB structure 12 independent dispersion fits on 18 beam positions are performed. This deficiency in turn leads to a gradual build-up of a dispersion related horizontal corrector pattern with a nonzero mean which is periodically corrected by the otherwise passive SOFB.