Molecular desorption by synchrotron radiation and sticking coefficient at cryogenic temperatures for H2,CH4, CO and CO2

A cryogenic vacuum system has been used to study both the surface pumping of gases and the molecular photodesorption yield from OFE copper in the temperature range from 5 to 300 K. The sticking coefficient on a 'bare surface' was found to increase with decreasing temperature of the substrate and below 20 K, to be in the range of a few per cent for all gas species studied. The molecular photodesorption yield for the 'bare surface' was found to decrease with decreasing temperature and below 20 K, after an accumulated photon dose of 3.1 X 10(22) photons m(-1), to be in the range of 10(-4) molecules photon(-1) for H-2 and 10(-5) molecules photon(-1) for the other gas species. These measured values are used to predict the evolution of the gas densities in the large hadron collider (LHC). Implications to the LHC are discussed. (C) 2002 Elsevier Science Ltd. All rights reserved.