doi:10.1063/1.4706908engDelruelle, NBarth, KDudarev, APassardi, GTen Kate, H H JFirst Operational Experience and Performance Optimization of the ATLAS Magnet Cryogenic SystemAccelerators and Storage RingsCERN-ATS-2012-008The ATLAS magnet system, comprising a superconducting central solenoid and three superconducting toroids, has been successfully ramped up for the first time to the nominal operational current of 20.4 kA on 4th August 2008. Since then, new cryogenic operational challenges have been raised, like the smoothing of steady-state parameters, the enhancing of transient procedures to minimize thermal shocks on the magnet cold masses, the optimization of the complex cryogenic system in order to reduce the compressors electric consumption and finally how to avoid regular clogging of the shield refrigerator by water contamination. This paper presents the heat load identification of the various cryogenic sub-systems done at 4.5 K and how one of these loads was reduced, what was gained - in term of electrical consumption - by tuning the turbines settings of the main refrigerator and finally the first consolidation of the cryogenic system implemented in order to minimize the detector downtime during LHC beam runs.2012-01-15http://cds.cern.ch/record/141638810.1063/1.4706908http://cds.cern.ch/record/1416388oai:cds.cern.ch:1416388 doi:10.1063/1.4707041engPereira, HHaug, FSantos Silva, PKuster, MLang, PCooling System for a Frame-Store PN-CCD Detector for Low Background ApplicationAccelerators and Storage RingsCERN-ATS-2012-007The astroparticle physics experiment CERN Axion Solar Telescope (CAST) aims to detect hypothetical axions or axion-like particles produced in the Sun by the Primakoff process. A Large Hadron Collider (LHC) prototype superconducting dipole magnet provides a 9 T transverse magnetic field for the conversion of axions into detectable X-ray photons. These photons are detected with an X-ray telescope and a novel type of frame-store CCD detector built from radio-pure materials, installed in the optics focal plane. A novel type of cooling system has been designed and built based on krypton-filled cryogenic heat pipes, made out of oxygen-free radiopure copper, and a Stirling cryocooler as cold source. The heat pipes provide an efficient thermal coupling between the cryocooler and the CCD which is kept at stable temperatures between 150 and 230 K within an accuracy of 0.1 K. A graded-Z radiation shield, also serving as a gas cold-trap operated at 120 K, is implemented to reduce the surface contamination of the CCD window and suppress background radiation.2012-01-15http://cds.cern.ch/record/141638710.1063/1.4707041http://cds.cern.ch/record/1416387oai:cds.cern.ch:1416387 doi:10.1063/1.4707066engPerinic, GClaudet, SAlonso-Canella, IBalle, CBarth, KBel, J FBenda, VBremer, JBrodzinski, KCasas-Cubillos, JCuccuru, GCugnet, MDelikaris, DDelruelle, NDufay-Chanat, LFabre, CFerlin, GFluder, CGavard, EGirardot, RHaug, FHerblin, LJunker, SKlabi , TKnoops, SLamboy, J PLegrand, DMetselaar, JPark, APerin, APezzetti, MPenacoba-Fernandez, GPirotte, ORogez, ESuraci, AStewart, LTavian, L JTovar-Gonzalez, AVan Weelderen, RVauthier, NVullierme, BWagner, UFirst Assessment of Reliability Data for the LHC Accelerator and Detector Cryogenic System ComponentsAccelerators and Storage RingsCERN-ATS-2012-006The Large Hadron Collider (LHC) cryogenic system comprises eight independent refrigeration and distribution systems that supply the eight 3.3 km long accelerator sectors with cryogenic refrigeration power as well as four refrigeration systems for the needs of the detectors ATLAS and CMS. In order to ensure the highest possible reliability of the installations, it is important to apply a reliability centred approach for the maintenance. Even though large scale cryogenic refrigeration exists since the mid 20th century, very little third party reliability data is available today. CERN has started to collect data with its computer aided maintenance management system (CAMMS) in 2009, when the accelerator has gone into normal operation. This paper presents the reliability observations from the operation and the maintenance side, as well as statistical data collected by the means of the CAMMS system.2012-01-15http://cds.cern.ch/record/141638410.1063/1.4707066http://cds.cern.ch/record/1416384oai:cds.cern.ch:1416384 doi:10.1063/1.4707060engPerin, ABrodzinski, KPirotte, OKrieger, BWidmer, AOperational Experience and Consolidations for the Current Lead Control Valves of the Large Hadron ColliderAccelerators and Storage RingsCERN-ATS-2012-005The Large Hadron Collider superconducting magnets are powered by more than 1400 gas cooled current leads ranging from 120 A to 13000 A. The gas flow required by the leads is controlled by solenoid proportional valves with dimensions from DN 1.8 mm to DN 10 mm. During the first months of operation, signs of premature wear were found in the active parts of the valves. This created major problems for the functioning of the current leads threatening the availability of the LHC. Following the detection of the problems, a series of measures were implemented to keep the LHC running, to launch a development program to solve the premature wear problem and to prepare for a global consolidation of the gas flow control system. This article describes first the difficulties encountered and the measures taken to ensure a continuous operation of the LHC during the first year of operation. The development of new friction free valves is then presented along with the consolidation program and the test equipment developed to validate the upgraded valves prior to their installation into the LHC.2012-01-15http://cds.cern.ch/record/141638010.1063/1.4707060http://cds.cern.ch/record/1416380oai:cds.cern.ch:1416380 doi:10.1063/1.4707069engPerin, APapaphilippou, YRussenschuck, SSchoerling, DPossible Cryogenic Configurations for the Superconducting Magnets of the Damping Rings of the Compact Linear Collider (CLIC)Accelerators and Storage RingsCERN-ATS-2012-004The Compact Linear Collider is a future electron-positron linear collider currently under study. Before being injected into the main linear accelerating structures, both the electron and the positron beams must pass through damping rings that will drastically reduce their emittance in all three dimensions. The required emittance reduction is achieved by passing the particle beams through alternating magnetic fields in superconducting wiggler magnets that result in the emission of intense synchrotron radiation. This article describes possible cooling schemes and possible cryogenic configurations to keep the magnets at operating temperature while removing the heat generated by the synchrotron radiation.2012-01-15http://cds.cern.ch/record/141637810.1063/1.4707069http://cds.cern.ch/record/1416378oai:cds.cern.ch:1416378 doi:10.1393/ncc/i2012-11260-3engSearcy, JMeasurement of the top quark pair production cross section in pp collisions at $sqrt{s}$=7 TeV in $\mu$ + $\tau$ final states with ATLASDetectors and Experimental TechniquesATL-PHYS-PROC-2012-009A measurement of the cross section of top quark pair production in proton$-$proton collisions at a center-of-mass of 7 TeV at the LHC using events with an isolated $mu$ and a $ au$ lepton decaying hadronically is reported. In addition to a $mu$ and a $ au$ lepton, large missing transverse energy and two or more jets are required. At least one of the jets must be identified as originating from a $b$ quark. To identify $ au$ leptons, the analysis uses a multivariate technique based on boosted decision trees. A data sample collected by ATLAS corresponding to an integrated luminosity of 1.08 ${ m fb}^{-1}$ yields [ sigma_{tar{t}} = 142pm 21 stat pm^{20}_{16}syst pm 5 ( ext{lumi.}) ext{pb.} ]2012-01-16http://cds.cern.ch/record/141635010.1393/ncc/i2012-11260-3Physicshttp://cds.cern.ch/record/1416350oai:cds.cern.ch:1416350 doi:10.1063/1.4706925engGranieri, P PBaudouy, BFour, ALentijo, FMapelli, APetagna, PTommasini, DSteady-State Heat Transfer Through Micro-Channels in Pressurized He IIAccelerators and Storage RingsCERN-ATS-2012-010The operation of the Large Hadron Collider superconducting magnets for current and high luminosity future applications relies on the cooling provided by helium-permeable cable insulations. These insulations take advantage of a He II micro-channels network constituting an extremely efficient path for heat extraction. In order to provide a fundamental understanding of the underlying thermal mechanisms, an experimental setup was built to investigate heat transport through single He II channels typical of the superconducting cable insulation network, where deviation from the macro-scale theory can appear. Micro-fabrication techniques were exploited to etch the channels down to a depth of ~ 16 mm. The heat transport properties were measured in static pressurized He II and analyzed in terms of the laminar and turbulent He II laws, as well as in terms of the critical heat flux between the two regions.2011-01-15http://cds.cern.ch/record/141639310.1063/1.4706925http://cds.cern.ch/record/1416393oai:cds.cern.ch:1416393