17 Wegmann, Christoph Julien Lens, Dieter Zipfel, Bernhard Reinwald, Christoph Klingbeil, Harald RRF IEEE transactions on nuclear science IEEE transactions on nuclear science IEEE New York, NY 0018-9499 10.1109/TNS.2026.3687074 English 1812 - 1822 5 73 Beam phase control loops have become an important sub-system of the low-level radio frequency (LLRF) systems of ion synchrotrons. A wide range of different implementations exists today. The LLRF system at the GSI Helmholtzzentrum für Schwerionenforschung (GSI)/Facility for Antiproton and Ion Research in Europe (FAIR) was designed with the particular goals of modularity, flexibility, scalability, and user-friendly diagnostics possibilities. Based on these requirements, a system focused on the time-domain manipulation of all RF and beam signals was developed. This contribution presents the beam phase control system and demonstrates its effectiveness. The special attention is paid to the operation during the acceleration ramp. Results of two independent beam experiments are presented: one focused on examining the control loop behavior and one applying the system in a practical setting. In both cases, the GSI/FAIR beam phase control system successfully dampens longitudinal dipole mode bunch oscillations. Its performance and behavior matches previous analyses. This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License. For more information, see https://creativecommons.org/licenses/by-nc-nd/4.0/ ; PUB:(DE-HGF)16, ; 0, ; Journal Article 2026 GSI-2026-00725 2026 https://repository.gsi.de/record/368168 https://doi.org/10.1109/TNS.2026.3687074