Integration of orbit control with real-time feedback

The Advanced Photon Source uses two distinct control programs for orbit control and stability-a full-featured workstation-based program for orbit control (sddscontrollaw) and an EPICS-based system, the Real-Time Fast Feedback System (RTFS), to reduce orbit motion. The sddscontrollaw program has been ported to EPICS and moved from the UNIX environment to an EPICS IOC attached to the RTFS. This EPICS-based program uses the RTFS's reflective memory to gather beam position information and write corrector power supplies, thus avoiding variable network latencies. This allows the orbit control to run at a correction rate 50 times that of the workstation implementation, which virtually eliminates orbit motion caused by insertion device gap changes. Issues raised by the integration of orbit control into the real-time feedback system and performance improvements are discussed.