Turnaround feed-forward correction at the ILC

The RTML turnaround feed-forward correction scheme, as proposed in the ILC BCD, is considered. Instabilities in the challenging Damping Ring extraction system may give rise to beam transverse bunch-by-bunch jitter, as well as drift across the bunch train. A system is outlined in which the bunch trajectory is measured with an upstream pair of BPMs and corrected with a pair of downstream fast kickers. The beam turnaround time 0.5 mus allows signal processing and calculation of the correction. A feed-forward algorithm is formulated and expressions are derived for the main system parameters (BPM resolution, system zero offset stability, kicker voltage, kicker gain compression error) and procedures (matrix measurement, feed-forward gain adjustment). This analysis enables further consideration of the tolerances, and provides a basis for the engineering design.