SYNCHROTRON-RADIATION-INDUCED GAS DESORPTION FROM A PROTOTYPE LARGE HADRON COLLIDER BEAM SCREEN AT CRYOGENIC TEMPERATURES

The performance of the vacuum system of the Large Hadron Collider will depend critically on the syhchrotron radiation induced gas desorption and on the readsorption of molecules on the cold surfaces. The presen t design of the system is based on a so-called beam screen inserted in the 1.9 K cold bore of the magnets. Gas molecules desorbed will there fore readsorb on the beam screen which is held at a temperature betwee n 5 and 20 K. Pumping slots in the beam screen enable some of the deso rbed gas to be pumped onto the 1.9 K surface of the cold bore. (C) 199 6 American Vacuum Society.