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Description
Longitudinal coupled-bunch instabilities in the CERN Proton Synchrotron (PS) were an important limitation to double the intensity of the beam for the High-Luminosity LHC. The main RF system has been identified as a root cause of the instability. An upgrade of the final amplifier was implemented in 2021 to reduce its beam coupling impedance. Despite this upgrade, coupled-bunch instabilities are still observed. However, the change in dominant mode number hints towards a modified spectral distribution of the impedance. Although the instability is mitigated by dedicated coupled-bunch feedback, investigations were conducted to improve the simulation model. In this contribution, a campaign to perform beam-based impedance measurements of the 10 MHz RF system is presented to refine the longitudinal impedance model of the PS. In addition, the measurement results of parameter scans varying intensity and longitudinal emittance are compared to the instability thresholds obtained with tracking simulations.
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