Coupled bunch mode zero correction using orbit measurements and rf system phase feedback

The target bandwidth of the Advanced Photon Source Upgrade (APS-U) fast orbit feedback (FOFB) is dc-1000 Hz where the synchrotron tune will be between 100 and 560 Hz. This overlap places coupled bunch mode 0 (CBM0) induced horizontal position offsets within the FOFB bandwidth range, affecting our ability to achieve APS-U goals for beam stability. In this article, we present a new feedback technique to damp CBM0 oscillations using the existent FOFB controller framework with no additional hardware and software requirements. Based on the theory of synchrotron oscillations, we developed a feedback algorithm that uses the beam horizontal position measurements at dispersive beam position monitors (BPM) as input and the low level rf (LLRF) phase as an actuator. We demonstrated via experiments in the present APS storage ring that this configuration can correct CBM0 oscillations, and also it can work simultaneously with orbit feedback used to damp ordinary betatron orbit. The simulation model for the proposed orbit to rf phase feedback system is implemented in matlab/simulink to guide us in the controller design. Simulation responses are in good agreement with measurements.