Impedance reduction for LHC collimators

The LHC at CERN is equipped with a sophisticated collimation system, aimed at protecting superconducting magnets against quenches in case of losses from the circulating beams. The collimation system is one of the major contributors to the machine impedance at top energy. A relevant hardware upgrade of the system will take place in the context of the High Luminosity LHC (HL-LHC) project; one of the main objectives is to make stabilisation of the brighter HL-LHC beams reachable within the capabilities of the Landau octupoles. In fact, a relevant fraction of the carbon–based collimators will be exchanged with new ones, the jaws of which are made of materials more optimised in terms of impedance; hence, the footprint of the collimation system will be significantly reduced. The present contribution gives an overview of the baseline low-impedance upgrade of the LHC collimation system as foreseen by the HL-LHC project and the expected impact on impedance. Additional options that could further improve the footprint of the collimation system on the machine impedance are briefly summarised.