engEvans, Lyndon RLebrun, PProgress in construction of the LHCAccelerators and Storage RingsLHC-Project-Report-239CERN-LHC-Project-Report-239The Large Hadron Collider (LHC) project, approved by the CERN Council in December 1994, has now fully entered its construction phase, with the detailed technical definition of the major systems, and the adjudication of a number of large procurement contracts. We first recall the main features and characteristics of the LHC, report on the advances in definition of the layout and optics as well as on preparation of the injector complex, and review recent progress in the key technical systems of the main ring: magnets, cryogenics and vacuum, as well as civil construction, which has started following acceptance by authorities in the Host States.1998-09-25http://cds.cern.ch/record/367978http://cds.cern.ch/record/367978oai:cds.cern.ch:367978 engDahlerup-Petersen, KHalvarsson, BjornValbuena, RA 20 kA Test Bench for High-Precision Current MeasurementsAccelerators and Storage RingsLHC-Project-Report-270CERN-LHC-Project-Report-270The d.c. currents in the LHC dipole and quadrupole chains will require settings and adjustments with a precision of a few ppm. For an ultimate current level of 13 kA this represents an unprecedented accuracy. Compared to the requirements of previous accelerators at CERN, such as the LEP, this is a factor of ten better in accuracy at more than twice the current. State-of-the-art, zero-flux current transducers from Industry will be used for the precision measurements. As no existing laboratory would be capable of performing the calibrations of these transducers to the required precision, a major upgrading of the current Standards laboratory at CERN was decided. The paper describes the various phases of the project, from field calculations and design to construction and final commissioning of this unique test bench. The highly automated facility allows determination of off-sets, linearity and drift of transducers up to 20 kA but provides equally the means to study the sensitivity of the transducers to external stray fields as generated by currents in adjacent busbars.1999-02-09http://cds.cern.ch/record/379596http://cds.cern.ch/record/379596oai:cds.cern.ch:379596 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 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 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 engPoncet, AlainOverview of Current UHV Activities on CERN AcceleratorsAccelerators and Storage RingsCERN-LHC-98-009-CRIEver since its birth, 45 years ago, CERN has been active in Ultra High Vacuum Science and Technology, faced with the ever-increasing demands of its storage rings and particle accelerators. In many instances, newly discovered beam-gas particle limiting phenomena have led to new developments and solutions in pumping hardware, surface preparations, thin films, etc. Today, the CERN new challenge is to construct the Large Hadron Collider. This machine, like its predecessors, demands new solutions in UHV techniques.1998-10-05http://cds.cern.ch/record/367411http://cds.cern.ch/record/367411oai:cds.cern.ch:367411 engHenrichsen, K NMagnetic Field Measurements in Beam Guiding MagnetsAccelerators and Storage RingsCERN-LHC-98-008-MMSElectromagnets used as beam guiding elements in particle accelerators and colliders require very tight tole-rances on their magnetic fields and on their alignment along the particle path. This article describes the methods and equipment used for magnetic measurements in beam transport magnets. Descriptions are given of magnetic resonance techniques, various induction coil methods, Hall generator measurements, the fluxgate magnetometer as well as the recently developed method of beam based alignment. References of historical nature as well as citations of recent work are given. The present commercial availability of the different sensors and asso-ciated equipment is indicated. Finally we shall try to analyze possible future needs for developments in those fields.1998-10-26http://cds.cern.ch/record/372933http://cds.cern.ch/record/372933oai:cds.cern.ch:372933 doi:10.1016/S0168-9002(98)01265-0engBarouch, GBay, ABouchigny, SCharpak, GeorgesDerré, JDidierjean, FrançoisFaivre, Jean-ClaudeGiomataris, IoanisKochowski, ClaudeKunne, FabienneLe Goff, J MLehár, FLemoigne, YLoucatos, Sotirios SLugol, J CMagnon, APerroud, Jean-PierrePlatchkov, S KPuill, GaelRebourgeard, P CThers, DZaccone, HenriDevelopment of a fast gaseous detector: "micromegas"Accelerators and Storage RingsCERN-LHC-98-005-EET1998-08-19http://cds.cern.ch/record/36961510.1016/S0168-9002(98)01265-0http://cds.cern.ch/record/369615oai:cds.cern.ch:369615