engJiménez, J MDorier, J LHilleret, NoëlMeaurements of Particulate Contamination and Migration under Vacuum Using a Large Sensitive Area Particle CounterAccelerators and Storage RingsCERN-LHC-98-010-VACA large area (50 cm2) particle counter working under vacuum (10-7 mbar) has been developed at CERN and applied to measurements of particles released by several vacuum components like valves, gauges and ion pumps. This technique has also been applied to study the migration of particles under vacuum with and without an applied electric field. This counter, which is based on the scattering of laser light by particles, will be described and the technical choices commented. The results of the contamination released by vacuum components and the effect of an electric field will be presented.1998-10-22http://cds.cern.ch/record/373139http://cds.cern.ch/record/373139oai:cds.cern.ch:373139 doi:10.1016/S0042-207X(98)00385-6engBojon, J PHilleret, NoëlWeiss, K POrigin of Possible Contamination Introduced by a Turbomolecular Pumping SystemAccelerators and Storage RingsCERN-LHC-98-011-VACTurbomolecular pumping groups are widely used in accelerators for the pre-evacuation and during the bake-out of the vacuum system. A major requirement for these groups, apart from pumping speed considerations, is the cleanliness of the vacuum produced. In an attempt to clarify this question, a bakeable low-pressure vacuum system has been constructed to allow the direct comparison of the contamination introduced by a turbomolecular pump and by an ideally clean cryopump. This contamination has been checked by the quantitative analysis of the residual gas as well as of the gases desorbed from surfaces under electron bombardment. Contamination by the rotary pump oil is only apparent below 40% of the turbomolecular pump nominal rotation speed. When the pump is stopped, the system is contaminated by heavy hydrocarbons which can be eliminated by a 300°C vacuum bake out.1998-10-28http://cds.cern.ch/record/37293410.1016/S0042-207X(98)00385-6http://cds.cern.ch/record/372934oai:cds.cern.ch:372934 doi:10.1016/S0042-207X(98)00365-0engAnashin, V VCalder, RGröbner, OswaldMalyshev, O BA Study of the Photodesorption Process for Cryosorbed Layers of $H_{2}, CH_{4}, CO$ or $CO_{2}$ at Various Temperatures between 3 K and 68 KAccelerators and Storage RingsLHC-Project-Report-261CERN-LHC-Project-Report-261The vacuum performance of the Large Hadron Collider (LHC) at CERN will depend critically on the photodesorption of gas by synchrotron radiation and the re-adsorption of these molecules back onto the cold surface. The results of photon induced molecular desorption by synchrotron radiation with a critical photon energy of 284 eV for H2, CH4, CO or CO 2 cryosorbed on a stainless steel surface are presented. Most measurements have been carried out in a temperature range from about 3 K to 20 K. Measurements for CO2 were also performed at 68 K. The specific method used for this study has been to pre-deposit a known quantity of gas onto a cold surface, to irradiate the surface with a known photon dose and to measure the quantity of gas remaining on the cold surface by recording the pressure during warm-up. The average photodesorption yields of all gas species were found to increase with increasing surface coverage and to reach a saturation value. For H2 this value is approximately 0.5 for a coverage exceeding 10**17 molecules/cm**2 , for CH4 and CO2 saturation occurs at about 0.5 molecules/photon at ~10** 19 molecules/cm**2 , while the corresponding final value for CO is about 0.04 molecules/photon at this coverage.1999-02-03http://cds.cern.ch/record/37863110.1016/S0042-207X(98)00365-0http://cds.cern.ch/record/378631oai:cds.cern.ch:378631