SOFB Implementation

For the SOFB the digital BPM system is operated in an injection triggered batch processing mode with 32 kHz bandwidth. By averaging over 64 orbit samples, corresponding to an interval of 2 ms, it is possible to get ``stroboscopic'' position readings at a rate of 3 Hz with an error $<$ 0.5 $\mu$m. The ``BPM Server'' in Fig. 1 monitors, collects and sends the BPM data to the ``Feedback Client'' with 2 Hz. BPMs disabled on the EPICS level are automatically excluded from the SOFB loop. The same holds for correctors which have reached their maximum strength. The ``TRACY Server'' predicts a corrector pattern which restores the ``Golden Orbit'' defined by the ``oco Client''. Finally, the ``CDEV Server'' applies the proposed correction, which is toggling between the horizontal and vertical planes. Fine tuning of the feedback loop is done through a low pass filter, correcting on the average over several successive BPM data sets, and gain adjustment. By default the SOFB averages over 3 data sets and applies 75 % of the proposed correction. Thus a full SOFB cycle takes 3 s. It remains to be added that the SOFB runs only for one previously set BPM gain. This ensures that transients visible at current induced BPM gain changes are not seen by the SOFB.