Speaker
Description
Recent studies showed that the broadband impedance can significantly alter the longitudinal multi-bunch instability threshold. The results of the beam-based impedance measurement campaign in the Large Hadron Collider (LHC) reveal a significant discrepancy with predictions based on the present impedance model. A larger imaginary impedance with a lower roll-off frequency would reproduce the observations. Since the impedance will be impacted by the High-Luminosity (HL) LHC upgrades, longitudinal beam stability needs to be carefully re-evaluated. This contribution discusses the outcome of the semi-analytical analysis for the HL-LHC parameters together with the updated broadband impedance model. Future measurements are proposed to probe the multi-bunch instability threshold driven by the partially compensated main RF cavity impedance, and results of corresponding macroparticle simulations using the BLonD code are presented. Finally, possible mitigation measures for further raising the instability threshold are discussed.
Funding Agency
Research supported by the HL-LHC project
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