Longitudinal beam coupling impedance of unshielded pumping manifolds at the CERN PS

The High-Luminosity LHC (HL-LHC) project aims at increasing beam intensity, hence posing tight constraints on its injector chain. A critical issue in the Proton Synchrotron (PS) is the contribution of numerous pumping manifolds to the longitudinal beam coupling impedance at high frequencies. It causes microwave instabilities that particularly affect ion beams and limit the longitudinal density of proton bunches close to transition energy. This contribution characterizes the impedance of these vacuum components through detailed electromagnetic simulations, examining configurations with and without a pick-up head inserted in the manifold. The effect of damping resistors on the impedance behavior is also investigated. Mitigation strategies, including shielding to prevent beam coupling with the manifold's volume, are evaluated for their effectiveness using electromagnetic simulations, offering solutions for improved beam performance.