Amorphous Carbon Coatings at Cryogenic Temperatures with LHC Type Beams: First Results with the COLDEX Experiment

Extrapolations of electron cloud data from the Large Hadron Collider (LHC) Run 1 to the High Luminosity upgrade (HL-LHC) beam parameters predict an intolerable increase of heat load on the beam screens of the inner triplets. Amorphous carbon (a-C) coating of the beam screen surface is proposed to reduce electron cloud production, thereby minimising its dissipated power. To validate this solution, the COLDEX experiment has been re-commissioned. Such equipment mimics the performance of the LHC cold bore and beam screen cryogenic vacuum system in presence of LHC beams in the Super Proton Synchrotron (SPS). The main objective of the study is the performance evaluation of a-C coatings while operating the beam screen in the 10 to 60 K temperature range and cold bore below 3 K. This paper reviews the status of COLDEX and the results obtained during its first experimental runs.