Progress towards top-up mode operations at the Advanced Photon Source

The Advanced Photon Source (APS) is a 7-GeV, third-generation synchrotron radiation source. To provide a more stable beam for users, in September 1998 we began commissioning a new operating mode called “top-up.” In this mode, the beam current does not decay but is maintained at a high level using frequent injection, while photon shutters are open and photon beams are delivered to users. The exhaustive analysis for top-up safety will be reviewed as well as the hardware and software required for top-up operation. Operational experience so far includes testing aspects of top-up injection, delivering beam to X-ray users for a few hours with fractional current stability of 0.001, and routinely providing beam to users by refilling the ring to 100 mA every 12 hours with shutters open. Top-up performance issues encountered are short-lived orbit and emittance transients during the injection event, which appear in user experiments as X-ray beam brightness dips. Planned system modifications to reduce these beam tran...