International Committee for Future Accelerators

Dedicated electron cloud diagnostics developed at the Advanced Photon Source (APS) enabled for the first time detailed characterization of the electron cloud (EC) properties in a highintensity positron and electron storage ring. From in situ measurements of the electron flux and energy distribution at the vacuum chamber wall, electron cloud production mechanisms and details of the beam-cloud interaction could be inferred. Strong amplification of the cloud was observed under certain machine conditions, sometimes referred to as beam-induced multipacting (BIM). Significant longitudinal variation of the cloud was also observed, due primarily to geometrical details of the vacuum chamber. These experimental data have contributed to a better understanding of the physics of the EC and its interaction with the beam, in particular, details of EC amplification and the sensitivity of key parameters relating to EC generation. The former (amplification) involves modeling studies of the beam-cloud dynamics. The latter (parameter sensitivity) involves benchmarks of the simulation code POSINST using APS data. More recently, there are plans to install a superconducting undulator (SCU) in the APS storage ring. Preliminary calculations show that EC-induced heating under specific machine conditions may impact the SCU design. Highlights of experimental data for both positron and electron beams are given, as well as modeling results.