First Results from COLDEX Applicable to the LHC Cryogenic Vacuum System

A cold bore experiment (COLDEX) has been installed in the electron-positron accumulator (EPA) at CERN. The ~2 m long COLDEX cryostat, that may be cooled to below 3 K, is fitted with an actively cooled perforated beam screen to simulate the conditions in the cold arcs of the LHC. Initially, gas desorption yields were obtained using an external synchrotron radiation beam line by exposing the beam screen to grazing incident radiation with a critical energy of 194 eV. In an extended period of EPA operation and during a dedicated period for LHC studies, COLDEX was installed into the EPA ring to study more specifically the influence of the bunched positron and electron beams with the cold bore / beam screen vacuum system. The results from these experiments and some predictions applicable for the LHC will be presented.