Amorphous carbon coatings at cryogenic temperatures with LHC type beams: first results with the COLDEX experiment

Extrapolations of the Large Hadron Collider (LHC) Run 1 observations to the High Luminosity upgrade (HLLHC) beam parameters predict intolerable increase of heat load on the beam screens of the Inner Triplets due to electron cloud. Amorphous carbon (a-C) coating of the beam screen surface is proposed to reduce electron cloud build-up, thereby minimising its dissipated power. In order to validate this baseline, COLDEX (COLD bore EXperiment) has been re-commissioned. Such experiment mimics the performance of the LHC cold bore and beam screen cryogenic vacuum system in the Super Proton Synchrotron (SPS). The main objectives of the study is the performance qualification of a-C coatings with LHC type beams while operating the beam screen in the 10 K to 60 K temperature range and the cold bore below 4.5 K. This paper reviews the status of COLDEX and the results obtained during its first experimental runs.