Analytical studies of top-up safety for the Advanced Photon Source

The Advanced Photon Source (APS) is a 7 GeV, third-generation synchrotron radiation source. To provide more stable beam for users, we are pursuing a new operating mode called “top-up.” In this mode, the beam current is not allowed to decay as it normally would, but instead is maintained at a high level through frequent injection. A safety question with top-up mode is, during injection with photon shutters open, can the injected beam ever exit a photon beamline? This might happen, for example, due to a full or partial short of a dipole coil. We discuss a number of analytical calculations that can be used to quickly assess top-up safety for a general ring. We also apply these results to the specific case of the APS. A companion paper in this conference discusses detailed tracking procedures for assessing safety