Measuring the effects of fast beam loss on the Advanced Photon Source Upgrade storage ring collimators

The Advanced Photon Source Upgrade (APS-U) storage-ring (SR) is equipped with five horizontal collimators used to intercept 6-GeV electrons during fast whole-beam aborts and protect the rest of the SR. The collimators are located in sectors 37, 38, 39, 40, and 1. A fan-out kicker (FOK) system has been installed to reduce damage to the collimators during whole-beam loss events. Since APS-U began commissioning in April 2024, dozen of these events have taken place; in most, but not all cases, the FOK system has worked properly. Turn-by-turn beam position monitors provide beam centroid dynamics data during the loss events; however, limited diagnostics prevent in situ evaluation of the collimator beam-facing jaw surfaces. During maintenance periods in August 2024 as well as January and May 2025, some of the collimators were extracted from the vacuum chamber and examined. Faint beam strike damage was observed on the S01 collimator jaw, but more significant effects were seen on the S38 jaw. Measurements of beam motion during fast aborts is presented as well as microscopy images of the S38 damage. Coupled simulations results are compared with observations.