doi:10.1063/1.1774687engBlanco-Viñuela, ECalzas, ACasas-Cubillos, JGomes, PKnoops, SSerio, LVan Weelderen, RExperimental Validation and Operation of the LHC Test String 2 Cryogenic SystemAccelerators and Storage RingsLHC-Project-Report-681CERN-LHC-Project-Report-681The LHC Test String 2 is a 107-m long superconducting magnet string representing a full-cell of the LHC machine. It was designed and commissioned at CERN in order to validate the final design choices and to investigate the collective behavior and operation modes of the LHC machine systems. It has been commissioned and operated since April 2001 and has accumulated more than 8000 hours at its nominal operating temperature of 1.9 K under machine-like conditions. We report on the experimental validation of the supercritical and superfluid helium cooling loops, quench propagation and recovery, heat loads, as well as on investigation of operational performances, advanced control techniques, process control, instrumentation and long term behavior under electrical and thermal cycling.2004-01-29http://cds.cern.ch/record/70911410.1063/1.1774687http://cds.cern.ch/record/709114oai:cds.cern.ch:709114 doi:10.1063/1.1774685engCalzas, AChanat, DKnoops, SSanmartí, MSerio, LLarge Cryogenic Infrastructure for LHC Superconducting Magnet and Cryogenic Component Tests: Layout, Commissioning and Operational ExperienceAccelerators and Storage RingsLHC-Project-Report-682CERN-LHC-Project-Report-682The largest cryogenic test facility at CERN, located at Zone 18, is used to validate and to test all main components working at cryogenic temperature in the LHC (Large Hadron Collider) before final installation in the machine tunnel. In total about 1300 main dipoles, 400 main quadrupoles, 5 RF-modules, eight 1.8 K refrigeration units will be tested in the coming years. The test facility has been improved and upgraded over the last few years and the first 18 kW refrigerator for the LHC machine has been added to boost the cryogenic capacity for the area via a 25,000 liter liquid helium dewar. The existing 6 kW refrigerator, used for the LHC Test String experiments, will also be employed to commission LHC cryogenic components. We report on the design and layout of the test facility as well as the commissioning and the first 10,000 hours operational experience of the test facility and the 18 kW LHC refrigerator.2004-01-29http://cds.cern.ch/record/70911510.1063/1.1774685http://cds.cern.ch/record/709115oai:cds.cern.ch:709115 doi:10.1063/1.1774700engLiu, LRiddone, GTavian, LStudy of the Cooldown and Warmup for the Eight Sectors of the Large Hadron ColliderAccelerators and Storage RingsLHC-Project-Report-683CERN-LHC-Project-Report-683The LHC cryogenic system is based on a five-point feed scheme with eight refrigerators serving the eight sectors of the LHC machine. The paper presents the simplified flow scheme of the eight sectors and the mathematical methods including the program flowchart and the boundary conditions to simulate the cooldown and warmup of these sectors. The methods take into account the effect of the pressure drop across the valves as well as the pressure evolution in the different headers of the cryogenic distribution line. The simulated pressure and temperature profiles of headers of the LHC sector during the cooldown and warmup are given and the temperature evolutions of entire processes of cooldown and warmup are presented. As a conclusion, the functions of the input temperature for the normal and fast cooldown and warmup, the cooldown and warmup time of each sector and the distributions of mass flow rates in each sector are summarized. The results indicate that it is possible to cool down any of the LHC sector within 12.7 days in normal operation and 6.8 days in case of fast operation.2004-01-29http://cds.cern.ch/record/70911610.1063/1.1774700http://cds.cern.ch/record/709116oai:cds.cern.ch:709116 doi:10.1063/1.1774699engChorowski, MFydrych, JKonopka-Cupial, GRiddone, GSummary of the Experimental Studies of Cold Helium Propagation along a scale model of the LHC TunnelAccelerators and Storage RingsLHC-Project-Report-684CERN-LHC-Project-Report-684The Large Hadron Collider will contain more than 95 tons of liquid and supercritical helium. The accelerator will be located in the 26.7 km underground tunnel. Some potential failures of the LHC cryogenic system might be followed by helium discharge into the tunnel and as a consequence the oxygen concentration might decrease below the safe level or the ambient temperature might drop significantly. In order to investigate the helium propagation in the tunnel a dedicated test rig, representing a section of the LHC tunnel at scale 1:13 has been designed and built. The basic construction of the scale model has been also modified by adding special modules to simulate the presence of the LHC accelerator inside the tunnel, tunnel enlargements and the influences of the LHC tunnel elevation. This paper presents and discusses the results of the performed experiments. Helium-air mixture flows corresponding to different initial conditions of the ventilation air and discharged helium have been visualized. Five types of mixture flow have been observed. Measured oxygen concentration and temperature profiles have been presented for the different flow patterns. The results have been scaled to the LHC conditions.2004-01-29http://cds.cern.ch/record/70911710.1063/1.1774699http://cds.cern.ch/record/709117oai:cds.cern.ch:709117revised version number 1 submitted on 2004-02-03 15:22:11 doi:10.1063/1.1774720engDunkel, OLegrand, PSievers, PA Warm Bore Anticryostat for Series Magnetic Measurements of LHC Superconducting Dipole and Short Straight Section MagnetsAccelerators and Storage RingsLHC-Project-Report-685CERN-LHC-Project-Report-685All LHC twin-aperture magnets will be tested under operating conditions to verify their performance. The field measurement equipment works at ambient temperature and pressure. Each magnet is therefore equipped with two warm bore anticryostats. As a consequence a total of nearly 80 anticryostats of different lengths have to be assembled, handled and serviced during the test period. Two main constraints determine the frame for the design of these anticryostats: inside a given beam pipe aperture of 50 mm kept at 1.9 K, a warm bore aperture of 40 mm must provide the highest possible mechanical stability and robustness for numerous mounting cycles as well as the lowest possible heat losses towards the cryogenic system. In addition, compatibility with high magnetic fields and an insulation vacuum of about 10-7 mbar have to be maintained. This paper describes how a satisfactory mechanical stability as well as heat losses in the order of 0.8 W/m are achieved with a design based on very careful space and material optimization. Other aspects like assembly, installation, thermal behavior and temperature control during the operation are described.2004-01-29http://cds.cern.ch/record/70911810.1063/1.1774720http://cds.cern.ch/record/709118oai:cds.cern.ch:709118 doi:10.1063/1.1774639engBrown, DDella Corte, AFiamozzi-Zignani, CGharib, AHagedorn, DietrichRout, CTurtu, SCryogenic Testing of High Current By-pass Diode Stacks for the Protection of the Superconducting Magnets in the LHCAccelerators and Storage RingsLHC-Project-Report-686CERN-LHC-Project-Report-686For the protection of the LHC superconducting magnets, about 2100 specially developed by-pass diodes were manufactured by DYNEX SEMICONDUCTOR LTD (Lincoln, GB) and about 1300 of these diodes were mounted into diode stacks and submitted to tests at cryogenic temperatures. To date about 800 dipole diode stacks and about 250 quadrupole diode stacks for the protection of the superconducting lattice dipole and lattice quadrupole magnets have been assembled at OCEM (Bologna,Italy) and successfully tested in liquid helium at ENEA (Frascati, Italy). This report gives an overview of the test results obtained so far. After a short description of the test installations and test procedures, a statistical analysis is presented for test data during diode production as well as for the performance of the diode stacks during testing in liquid helium, including failure rates and degradation of the diodes.2004-01-29http://cds.cern.ch/record/70911910.1063/1.1774639http://cds.cern.ch/record/709119oai:cds.cern.ch:709119 doi:10.1063/1.1774658engIjspeert, Albertten Kate, H H JWhat is Common in the Training of the Large Variety of Impregnated Corrector Magnets for the LHCAccelerators and Storage RingsLHC-Project-Report-687CERN-LHC-Project-Report-687The Large Hadron Collider (LHC) will be equipped with about 5000 superconducting corrector magnets of 10 different types, ranging from dipoles through quadrupoles, sextupoles and octupoles to decapoles and dodecapoles. Four wires are used with 2 copper/superconductor ratios. Magnet lengths range from 0.15 m to 1.4 m. However, the magnets are all epoxy-impregnated and wound with enameled monolithic wires. The paper highlights the features that are common in the training of all these different magnets and uses that to give some clues for the possible origin of the training.2004-01-29http://cds.cern.ch/record/70912010.1063/1.1774658http://cds.cern.ch/record/709120oai:cds.cern.ch:709120 doi:10.1063/1.1774640engDenz, RGharib, AHagedorn, DietrichRadiation Resistance and Life Time Estimates at Cryogenic Temperatures of Series produced By-pass Diodes for the LHC Magnet ProtectionAccelerators and Storage RingsLHC-Project-Report-688CERN-LHC-Project-Report-688For the protection of the LHC superconducting magnets about 2100 specially developed by-pass diodes have been manufactured in industry and more than one thousand of these diodes have been mounted into stacks and tested in liquid helium. By-pass diode samples, taken from the series production, have been submitted to irradiation tests at cryogenic temperatures together with some prototype diodes up to an accumulated dose of about 2 kGy and neutron fluences up to about 3.0 1013 n cm-2 with and without intermediate warm up to 300 K. The device characteristics of the diodes under forward bias and reverse bias have been measured at 77 K and ambient versus dose and the results are presented. Using a thermo-electrical model and new estimates for the expected dose in the LHC, the expected lifetime of the by-pass diodes has been estimated for various positions in the LHC arcs. It turns out that for all of the by-pass diodes across the arc elements the radiation resistance is largely sufficient. In the dispersion suppresser regions of the LHC, on a few diodes annual annealing during the shut down of the LHC must be applied or those diodes may need to be replaced after some time.2003-01-29http://cds.cern.ch/record/70912410.1063/1.1774640http://cds.cern.ch/record/709124oai:cds.cern.ch:709124 doi:10.1063/1.1774719engBourcey, NCapatina, OParma, VPoncet, ARohmig, PSerio, LSkoczen, BlazejTock, J PWilliams, L RFinal Design and Experimental Validation of the Thermal Performance of the LHC Lattice CryostatsAccelerators and Storage RingsLHC-Project-Report-689CERN-LHC-Project-Report-689The recent commissioning and operation of the LHC String 2 have given a first experimental validation of the global thermal performance of the LHC lattice cryostat at nominal cryogenic conditions. The cryostat designed to minimize the heat inleak from ambient temperature, houses under vacuum and thermally protects the cold mass, which contains the LHC twin-aperture superconducting magnets operating at 1.9 K in superfluid helium. Mechanical components linking the cold mass to the vacuum vessel, such as support posts and insulation vacuum barriers are designed with efficient thermalisations for heat interception to minimise heat conduction. Heat inleak by radiation is reduced by employing multilayer insulation (MLI) wrapped around the cold mass and around an aluminium thermal shield cooled to about 60 K. Measurements of the total helium vaporization rate in String 2 gives, after substraction of supplementary heat loads and end effects, an estimate of the total thermal load to a standard LHC cell (107 m) including two Short Straight Sections and six dipole cryomagnets. Temperature sensors installed at critical locations provide a temperature mapping which allows validation of the calculated and estimated thermal performance of the cryostat components, including efficiency of the heat interceptions.2004-01-29http://cds.cern.ch/record/70912510.1063/1.1774719http://cds.cern.ch/record/709125oai:cds.cern.ch:709125 doi:10.1063/1.1774565engGarion, CSkoczen, BlazejAnisotropic Constitutive Model of Strain-induced Phenomena in Stainless Steels at Cryogenic TemperaturesAccelerators and Storage RingsCERN-AT-2004-005-CRIA majority of the thin-walled components subjected to intensive plastic straining at cryogenic temperatures are made of stainless steels. The examples of such components can be found in the interconnections of particle accelerators, containing the superconducting magnets, where the thermal contraction is absorbed by thin-walled, axisymetric shells called bellows expansion joints. The stainless steels show three main phenomena induced by plastic strains at cryogenic temperatures: serrated (discontinuous) yielding, gamma->alpha' phase transformation and anisotropic ductile damage. In the present paper, a coupled constitutive model of gamma->alpha' phase transformation and orthotropic ductile damage is presented. A kinetic law of phase transformation, and a kinetic law of evolution of orthotropic damage are presented. The model is extended to anisotropic plasticity comprising a constant anisotropy (texture effect), which can be classically taken into account by the Hill yield surface, and plastic strain induced anisotropy. For such a model the shape of the yield surface in the stress space varies as a function of the plastic strains. The constitutive model creates a bridge between material science (experiments) and structural analysis. It has been used to predict the response of beam vacuum and cryogenic bellows to monotonic and cyclic loads developed in the interconnections of the Large Hadron Collider at CERN.2004-01-29http://cds.cern.ch/record/70895710.1063/1.1774565http://cds.cern.ch/record/708957oai:cds.cern.ch:708957 doi:10.1063/1.1774599engBottura, LBruzzone, P LMarinucci, CAnalysis of Current Redistribution in a CICC under Transient Heat PulsesAccelerators and Storage RingsCERN-AT-2004-004-MTMWe have performed experiments and simulations of the current distribution process in a CICC with the aim to understand better the coupled thermal, hydraulic and electric process that leads to a stable or unstable transient cable behaviour. The cable, wound from 128 Nb$_{3}$Sn and pure copper strands, has been tested in the SULTAN facility. A resistive heater, glued on the jacket of the conductor, has been used to start the transient, and the response has been monitored with arrays of Hall plates. In this paper we report the results of simulations, especially the computed Hall signals, and compare them to the experimental data. Based on the experimental results and their interpretation we postulate that large temperature gradients must develop in the helium stream in the cable cross sections during the transient heat pulse.2004-01-29http://cds.cern.ch/record/70895510.1063/1.1774599http://cds.cern.ch/record/708955oai:cds.cern.ch:708955 doi:10.1063/1.1774746engHaug, FBottura, LBroggi, FJunker, SQuench Induced Pressure Rise in the Cooling Pipes of the Atlas Barrel Toroid ModelAccelerators and Storage RingsCERN-AT-2004-003-ECRThe ATLAS superconducting magnet system consists of a Barrel Toroid, two End-Cap Toroids and a Solenoid. Eight individual racetrack coils will be assembled to form the Barrel Toroid with overall dimensions of 26 m length and 20 m diameter. In order to verify the design concept a 9 m long short version of a single Barrel Toroid coil was built. A test program was conducted at the CERN cryogenic test facility which included the evaluation of the pressure rise in the helium cooling channels during quenches of the coil. A specific experimental set-up with cold pressure transducers and capillaries was installed for online measurement of the pressure signals. In addition a computer model was used to simulate these events. The data obtained are presented.2004-01-29http://cds.cern.ch/record/70895210.1063/1.1774746http://cds.cern.ch/record/708952oai:cds.cern.ch:708952 doi:10.1063/1.1774689engDelruelle, NHaug, FJunker, SPassardi, GiorgioPengo, RPirotte, OThe Common Cryogenic Test Facility for the Atlas Barrel and End-Cap Toroid MagnetAccelerators and Storage RingsCERN-AT-2004-002-ECRThe large ATLAS toroidal superconducting magnet made of the Barrel and two End-Caps needs extensive testing at the surface of the individual components prior to their final assembly into the underground cavern of LHC. A cryogenic test facility specifically designed for cooling sequentially the eight coils making the Barrel Toroid (BT) has been fully commissioned and is now ready for final acceptance of these magnets. This facility, originally designed for testing individually the 46 tons BT coils, will be upgraded to allow the acceptance tests of the two End-Caps, each of them having a 160 tons cold mass. The integrated system mainly comprises a 1.2 kW@4.5 K refrigerator, a 10 kW liquid-nitrogen precooler, two cryostats housing liquid helium centrifugal pumps of respectively 80 g/s and 600 g/s nominal flow and specific instrumentation to measure the thermal performances of the magnets. This paper describes the overall facility with particular emphasis to the cryogenic features adopted to match the specific requirements of the magnets in the various operating scenarios.2004-01-29http://cds.cern.ch/record/70895010.1063/1.1774689http://cds.cern.ch/record/708950oai:cds.cern.ch:708950 doi:10.1063/1.1774678engBarth, KDelikaris, DPassardi, GiorgioPezzetti, MPirotte, OStewart, LVullierme, BWalckiers, LZioutas, KonstantinCommissioning and First Operation of the Cryogenics for the CERN Axion Solar Telescope (CAST)Accelerators and Storage RingsCERN-AT-2004-001-ECRA new experiment, the CERN Axion Solar Telescope (CAST) was installed and commissioned in 2002. Its aim is to experimentally prove the existence of an as yet hypothetical particle predicted by theory as a solution of the strong CP problem and possible candidate for galactic dark matter. The heart of the detector consists of a decommissioned 10-m long LHC superconducting dipole prototype magnet, providing a magnetic field of up to 9.5 T. The whole telescope assembly is aligned with high precision to the core of the sun. If they exist, axions could be copiously produced in the core of the sun and converted into photons within the transverse magnetic field of the telescope. The converted low-energy solar axion spectrum, peaked around a mean energy of 4.4 keV, can then be focused by a special x-ray mirror system and detected by low-background photon detectors, installed on each end of the telescopes twin beam pipes. This paper describes the external and proximity cryogenic system and magnet commissioning as well as the first operational experience with the overall telescope assembly.2004-01-29http://cds.cern.ch/record/70894910.1063/1.1774678http://cds.cern.ch/record/708949oai:cds.cern.ch:708949