The Slow Orbit Feedback (SOFB)

Since the beginning of SLS operation global orbit corrections have been successfully applied manually by the operators with the help of the Tcl/Tk CORBA GUI ``oco Client''. Due to the inherent modularity of the CORBA environment, thoroughly tested underlying CORBA components like the ``TRACY Server'' and the ``CDEV Server'' could be combined to implement the SOFB. In this case the operator is ``replaced'' by a C++ CORBA client (``Feedback Client'') which initiates an orbit correction at a given rate (see Fig. 3).

Figure: Schematic View of the SOFB: the ``Feedback Client'' on the `` Model Server'' level replaces the operator driven GUI ``oco Client'' on the `` Console'' level. It gets BPM data from the ``BPM Server'', asks the ``TRACY Server'' for the model predicted corrector pattern and applies the correction through the ``CDEV Server''.

For the SOFB the digital BPM system [7] is operated in an injection triggered mode which provides ``stroboscopic'' position readings averaged over 2 ms at a rate of 3 Hz with a resolution $\approx$ 0.3 $\mu$m. A ``BPM Server'' monitors, collects and sends the BPM data to the ``Feedback Client'' with 2 Hz. A low pass filter is applied to several successive BPM data sets. The data are then sent to the ``TRACY Server'' which predicts a corrector pattern to restore the ``Golden Orbit'' which is defined by the orbit centered in the quadrupoles. Additionally, local bumps at the location of the insertion devices are taken into account in order to steer the photon beam according to the demands of the experiments. Finally, the proposed correction is applied by toggling between the horizontal and the vertical plane resulting in a SOFB correction rate of $\approx$ 0.4 Hz.