Vacuum performance of a beam screen with charcoal for the LHC long straight sections

The vacuum chamber inside the cryogenic magnets in the LHC Long Straight Sections will have a beam screen at a temperature between 5 and 20 K to protect the cold bore against the synchrotron radiation, electron and ion exposure. The desorbed molecules of H₂ will leave the inner part of the beam screen through the pumping slots on the beam screen and eventually condense on the cryosorber, which is mounted on the shadowed (outer) part of the beam screen for magnets operating at 4.5 K. The design of the experimental set-up, the results of the adsorption capacity measurements for charcoal, the pumping speed and the capture factor of the beam screen with charcoal for a proposed LHC vacuum chamber configuration are described in this paper.