Vacuum calculations for the LHC experimental beam chambers

The vacuum stability is studied for the LHC experimental beam vacuum chambers of ALICE, ATLAS, and CMS. The present baseline design includes sputtered non-evaporable getter (NEG) coating over the whole chamber inner surface providing distributed pumping and an antimultipactor coating. The data are presented for the dominant gas species (H/sub 2/, CH/sub 4/, CO and CO/sub 2/) in a baked system. It results that the distributed pumping is necessary for vacuum stability of CO. Lumped pumping with sputter ion pumps (SIP) is also indispensable for the stability of CH/sub 4/. The operational constraints with NEG technology are described.