AIP Conf. Proc. AIP Conf. Proc. Experimental Validation of the LHC Helium Relief System Flow Modeling Fydrych J Chorowski M Riddone G 2006 823 745 752 In case of simultaneous resistive transitions in a whole sector of magnets in the Large Hadron Collider, the helium would be vented from the cold masses to a dedicated recovery system. During the discharge the cold helium will eventually enter a pipe at room temperature. During the first period of the flow the helium will be heated intensely due to the pipe heat capacity. To study the changes of the helium thermodynamic and flow parameters we have simulated numerically the most critical flow cases. To verify and validate numerical results, a dedicated laboratory test rig representing the helium relief system has been designed and commissioned. Both numerical and experimental results allow us to determine the distributions of the helium parameters along the pipes as well as mechanical strains and stresses. research-article

AIP Conf. Proc. AIP Conf. Proc. Numerical Analysis of the Final Cooldown of a 3.3 km Sector of the Large Hadron Collider Liu L Riddone G Tavian L 2006 823 547 554 The final cool-down of a 107-m standard cell of LHC, which consists of the helium filling operation at 4.5 K and the further cool-down from 4.5 K to 1.9 K, has been previously simulated and analyzed numerically. To model and analyze the final cool-down process of a whole 3.3-km sector of the LHC, additional boundary conditions must be introduced. In this paper, the slope of the sector, the efficiency of the sub-cooling heat exchanger, the pressure drops and heat loads in different headers of the cryogenic distribution line as well as the fact that both the filling flow of the cold mass and the vaporized flow in the 1.8 K heat exchanger are concurrently supplied have been taken into account. The simulation results, such as the temperature evolution in the LHC magnet cold mass and the pressure profiles in cryogenic line headers during the filling and cool-down from 4.5 K to 1.9 K of a LHC sector are presented. Taking into account the required distribution of the total flow to each cell, all the cells can be filled up to 67% of the volume and further cooled down to 1.9 K simultaneously in 15 to 20 hours. research-article

AIP Conf. Proc. AIP Conf. Proc. Performance Assessment of 35 Cold Hydrodynamic Compressors for the 1.8 K Refrigeration Units of the LHC Millet F Claudet S Ferlin G 2006 823 1837 1844 The cooling capacity below 2 K for the superconducting magnets in the Large Hadron Collider (LHC), at CERN, will be provided by eight refrigeration units of 2400 W at 1.8 K, each of them coupled to one 18 kW at 4.5 K refrigerator. The supply of the series units was linked to successful testing and acceptance of the pre-series units delivered by the two selected vendors. The two pre-series units were temporarily installed in a dedicated test station to validate the overall capacity and to properly assess the performance of specific components such as cold compressors. Then the cold compressor cartridges to be installed in the six series and associated spare cartridges have been intensively and systematically tested in the test station. After a brief description of the test bench and the main achieved features of the pre-series units, we will present the results of the tests of 35 cold compressor cartridges. These tests show isentropic efficiency in the 75% range, excellent reproducibility and interchange ability. Some process and system specificities observed will be reported and finally perspectives will be proposed. research-article

AIP Conf. Proc. AIP Conf. Proc. Cryogenic Test of High Temperature Superconducting Current Leads at Enea Ballarino A Besi-Vetrella U Chambouvet P Della Corte A Di Zenobio A Fiamozzi-Zignani C Mayorga J Napolitano M Turtu S Viola R 2006 823 1269 1275 The LHC (Large Hadron Collider), the accelerator being constructed on the CERN site, involves the operation of more than 8000 superconducting magnets of various current ratings. Essential elements for the powering of these magnets are the HTS current leads. These devices provide the electrical link between the warm cables from/to the power converter and the low temperature superconducting bus bars bringing the current from/to the cryo-magnets. Thus they operate in a temperature range between room temperature and liquid helium temperature. The operation of the LHC will require more than 1000 HTS current leads operating at currents ranging from 600 A to 13000 A. Cryogenic tests of the series of 13000 A and 6000 A HTS current leads are made at ENEA in the framework of a CERN-ENEA collaboration. This report gives an overview of the experimental set-up built in ENEA. The set-up was designed following the typical criterion of a scientific experiment but it was dimensioned to satisfy the schedule of an industrial scale activity, having in mind the large number of components to be tested in a period of less than two years. The related data acquisition system is also described, together with the results of the tests on the current leads. research-article

AIP Conf. Proc. AIP Conf. Proc. Specifications and Performance of Series Superfluid Helium Safety Relief Valves for the LHC Perin A Fontanive V 2006 823 1211 1218 Protecting the LHC magnets requires safety relief valves operating with 1.9 K pressurized superfluid helium at their inlet. Following the evaluation of prototype valves, a specification for the production of the 360 safety relief valves needed for the LHC was issued. The production of the safety valves was then awarded to an industrial contractor. The performance of pre-series valves was assessed for a variety of aspects including thermal performance, leak tightness in superfluid helium, dynamic behavior and resistance to intensive mechanical cycling. After the initial validation phase the series production was completed within the technical requirements of the specification. This paper describes the characteristics of the safety relief valves and the specifications for their industrial production. The performance of the pre-series valves is presented and an overview of the series production phase is given. research-article

AIP Conf. Proc. AIP Conf. Proc. Automatic Management Systems for the Operation of the Cryogenic Test Facilities for LHC Series Superconducting Magnets Tovar-Gonzalez A Axensalva J Herblin L Lamboy J P Vullierme B 2006 823 1227 1234 Prior to their final preparation before installation in the tunnel, the ~1800 series superconducting magnets of the LHC machine shall be entirely tested at reception on modular test facilities. The operation 24 hours per day of the cryogenic test facilities is conducted in turn by 3-operator teams, assisted in real time by the use of the Test Bench Priorities Handling System, a process control application enforcing the optimum use of cryogenic utilities and of the "Tasks Tracking System", a web-based e-traveller application handling 12 parallel 38-task test sequences. This paper describes how such computer-based management systems can be used to optimize operation of concurrent test benches within technical boundary conditions given by the cryogenic capacity, and how they can be used to study the efficiency of the automatic steering of all individual cryogenic sub-systems. Finally, this paper presents the overall performance of the cryomagnet test station for the first complete year of operation at high production rate. research-article

AIP Conf. Proc. AIP Conf. Proc. Commissioning of the LHC Cryogenic System Serio L Calzas A Ferlin G Gilbert N Gruehagen Henning Knoops S Parente C Sanmartí M 2006 823 1599 1606 The cryogenic system for the Large Hadron Collider accelerator is presently in its final phase of installation and commissioning at nominal operating temperatures. The refrigeration capacity for the LHC will be produced using eight large cryogenic plants installed on five technical sites and distributed around the 26.7-km circumference ring located in a deep underground tunnel. The status of the cryogenic system commissioning is presented together with the experience gained in operating and commissioning it. research-article

AIP Conf. Proc. AIP Conf. Proc. The Local Helium Compound Transfer Lines for the Large Hadron Collider Cryogenic System Parente C Allen W Munday A Wiggins P 2006 823 1607 1613 The cryogenic system for the Large Hadron Collider (LHC) under construction at CERN will include twelve new local helium transfer lines distributed among five LHC points in underground caverns. These lines, being manufactured and installed by industry, will connect the cold boxes of the 4.5-K refrigerators and the 1.8-K refrigeration units to the cryogenic interconnection boxes. The lines have a maximum of 30-m length and may possess either small or large re-distribution units to allow connection to the interface ports. Due to space restrictions the lines may have complex routings and require several elbowed sections. The lines consist of a vacuum jacket, a thermal shield and either three or four helium process pipes. Specific internal and external supporting and compensation systems were designed for each line to allow for thermal contraction of the process pipes (or vacuum jacket, in case of a break in the insulation vacuum) and to minimise the forces applied to the interface equipment. Whenever possible, flexible hoses were used instead of bellows to allow for thermal compensation of the process pipes. If necessary, compensation units were integrated in the vacuum jacket. The thermal design was performed to fulfil the specified heat-load budget. This paper presents the main technical design choices for the lines together with their expected performance. research-article

AIP Conf. Proc. AIP Conf. Proc. Performance Assessment of 239 Series Sub-cooling Heat Exchangers for the Large Hadron Collider Riddone G Gilbert N Roussel P Moracchioli R Tavian L 2006 823 523 530 Helium sub-cooling heat exchangers of the counter-flow type are used to minimize the vapor fraction produced in the final expansion of the 1.9 K distributed cooling loops used for cooling the superconducting magnets of the Large Hadron Collider (LHC). These components are of compact design, featuring low-pressure drop and handling very low pressure vapor at low temperature. Following a qualification phase of prototypes, a contract has been placed in European industry for the supply of 239 heat exchanger units. Different levels of extracted heat load require three different variants of heat exchangers. This paper will describe the manufacturing phase with emphasis on the main difficulties encountered to keep the production quality after a brief recall of the prototype phase. Finally, the acceptance tests performed at room temperature and at the nominal cryogenic condition at the factory and at CEA-Grenoble will be presented. research-article

AIP Conf. Proc. AIP Conf. Proc. Comparison between Normal and HeII Two-phase Flows at High Vapor Velocities Van Weelderen R Perraud S Rousset B Thibault P Wolf P E 2006 823 1669 1676 We present results on helium co-current two-phase flow experiments at high vapor velocity obtained with the use of the new CEA/SBT 400 W/1.8 K refrigerator [1]. For vapor velocities larger than typically 4 m/s, a mist of droplets develops from the bulk liquid interface accompanied by an increase in heat transfer at the wall. Experiments were conducted in a 10 m long, 40 mm I.D. straight pipe, both in helium II and in helium I to compare these two situations. The respective roles of vapor density, vapor velocity and liquid level on atomization were systematically investigated. Light scattering experiments were performed to measure sizes, velocities and interfacial areas of droplets in a complete cross section. In-house-made heat transfer sensors located in the mist allowed us to deduce an upper value of the extra cooling power of the dispersed phase. The practical interest of atomized flow for cooling large cryogenic facilities is discussed by considering the balance between increase in heat transfer and pressure drops it induces. research-article

AIP Conf. Proc. AIP Conf. Proc. Results of the Cryogenic Tests of the Superconducting Magnets forming the Barrel Toroid of the ATLAS Experiment Pengo R Barth K Berriaud C Delruelle N Dudarev A Junker S Pirotte O 2006 823 1628 1634 The Barrel Toroid magnet of the ATLAS experiment will be built from eight 25 m x 5 m racetrack shaped superconducting coils that are symmetrically placed around the central axis of the detector. Prior to their final assembly in the underground cavern of the LHC, these magnets are individually tested at ground level in order to verify the expected overall performances. A dedicated facility has been commissioned and the testing of the coils, at their nominal electrical and thermal operating conditions, has been carried out. The paper presents the results obtained during the cool-down phase from ambient temperature, the steady-state operation at 4.5 K, the 20 kA current ramping up/down and the thermal recovery after a fast energy dump of up to 138 MJ stored energy. Included are the measurements of the various thermal loads in both static and dynamic conditions. research-article

AIP Conf. Proc. AIP Conf. Proc. Cryogenic Tests of the Atlas Liquid Argon Calorimeter Fabre C Bremer J Chalifour M Gonidec A Passardi Giorgio 2006 823 1635 1642 The ATLAS liquid argon calorimeter consists of the barrel and two end-cap detectors housed in three independent cryostats filled with a total volume of 78 m3 of liquid argon. During cool-down the temperature differences in the composite structure of the detectors must be kept within strict limits to avoid excessive mechanical stresses and relative displacements. During normal operation the formation of gas bubbles, which are detrimental to the functioning of the detector, must be prevented and temperature gradients of less than 0.7 K across the argon bath are mandatory due to the temperature dependence of the energy measurements. Between April 2004 and May 2005 the barrel (120 t) and one end-cap (219 t) underwent qualification tests at the operating temperature of 87.3 K using a dedicated test facility at ground level. These tests provided a validation of the cooling methods to be adopted in the final underground configuration. In total 6.9 GJ and 15.7 GJ were extracted from the calorimeters and a temperature uniformity of the argon bath of less than 0.4 K was achieved. research-article

AIP Conf. Proc. AIP Conf. Proc. Commissioning of the Helium Refrigerator System for the Compact Muon Solenoid (CMS) Detector of LHC Perinic G CERN Dupont T 2006 823 2026 2033 At CERN a new helium refrigeration plant specified for a cooling capacity of 800 W at 4.45 K, 4500 W between 60 K and 80 K and 4 g/s liquefaction simultaneously has been installed and commissioned. In a first operation phase, the plant will provide the refrigeration capacity for the cool down and the operation of the superconducting solenoid of the CMS experiment during the magnet tests at the surface of the LHC interaction point 5. On completion of the tests a part of the refrigeration plant will be dismantled and moved to its final underground position next to the CMS experimental cavern. This paper compiles the commissioning activities starting from the compressor station up to the intermediate cryostat interfacing the refrigerator cold box with the magnet thermosiphon cooling system. It reports the problems encountered and the lessons learned during the commissioning phase and summarizes the results of the refrigeration power measurements in the transient cool-down and the steady-state operation modes. research-article

AIP Conf. Proc. AIP Conf. Proc. Commissioning of the Cryogenic System for the ATLAS Superconducting Magnets Delruelle N Baynham D Elwyn Bradshaw T Haug F ten Kate H H J Passardi Giorgio Pengo R Pezzetti M Pirotte O Rochford J 2006 823 2018 2025 The paper describes the test results of the helium cryoplant for the superconducting magnets of the ATLAS particle detector at CERN. It consists of two refrigerators used in common by all the magnets and of two proximity cryogenic systems (PCS) interfacing respectively the toroids and the central solenoid. Emphasis is given to the commissioning of the refrigerators: the main unit of 6 kW equivalent capacity at 4.5 K and the thermal shield refrigerator providing 20 kW between 40 K and 80 K. The first unit is used for refrigeration at 4.5 K and for the cooling of three sets of 20 kA current leads, while the second one provides, in addition to the 20 kW refrigeration of the thermal shields, 60 kW for the cool-down to 100 K of the 660 ton cold mass of the magnets. The tests, carried out with the equipment in the final underground configuration, are extended to the PCS that includes the large liquid helium centrifugal pumps (each providing 1.2 kg/s) for forced-flow cooling of the magnets and the complex distribution system needed to fulfil their different operating requirements. research-article