He II Co-Current Two Phase Flow at High Vapor Velocities Di Muoio E Jäger B Puech L Rousset B Thibault P Vallcorba R Van Weelderen R Wolf P E 2001 PREPRINT

Optical Investigations of HeII Two Phase Flow Di Muoio E Jäger B Puech L Rousset B Thibault P Van Weelderen R Wolf P E 2002 The LHC development program relies on cryogenic tests of prototype and model magnets. This vigorous program is pursued in a dedicated test facility based on several vertical cryostats working at superfluid helium temperatures. The performance of the facility is detailed. Goals and test equipment for currently performed studies are reviewed: quench analysis and magnet protection studies, measurement of the field quality, test of ancillary electrical equipment like diodes and busbars. The paper covers the equipment available for tests of prototypes and some special series of LHC magnets to come. research-article

AIP Conf. Proc. AIP Conf. Proc. The Test Facility for the Short Prototypes of the LHC Superconducting Magnets Arn A Bottura L Giloux C Mompo R Siemko A Venturini-Delsolaro W Walckiers L 2002 613 106 113 The LHC development program relies on cryogenic tests of prototype and model magnets. This vigorous program is pursued in a dedicated test facility based on several vertical cryostats working at superfluid helium temperatures. The performance of the facility is detailed. Goals and test equipment for currently performed studies are reviewed: quench analysis and magnet protection studies, measurement of the field quality, test of ancillary electrical equipment like diodes and busbars. The paper covers the equipment available for tests of prototypes and some special series of LHC magnets to come. research-article

AIP Conf. Proc. AIP Conf. Proc. Elastic Modulus Measurements of the LHC Dipole Superconducting Coil at 300 K and at 77 K Couturier K Ferracin P Todesco Ezio Tommasini D Scandale Walter 2002 613 377 382 We present measurements of the stress-displacement relation for the superconducting coils used in the Large Hadron Collider main magnets (dipoles and quadrupoles). This mechanical property is relevant to determine the correct amount of azimuthal pre-stress to be imposed on the coil. The hysteresis pattern in the loading and unloading curves is discussed. The stress-displacement curves are used to compute the corresponding elastic moduli and deformations. Measurements are also carried out at liquid nitrogen temperature, using the same framework to interpret experimental data. research-article

AIP Conf. Proc. AIP Conf. Proc. Thermal Contraction Measurements of the Superconducting Coil of the Main Magnets for the Large Hadron Collider Ferracin P Todesco Ezio Tommasini D Scandale Walter 2002 613 372 376 research-article

AIP Conf. Proc. AIP Conf. Proc. Quench Propagation in the Superconducting 6 kA Flexible Busbars of the LHC Calvi M Herzog R Pelegrin-Carcelen J M Sonnemann F 2002 613 583 590 Flexible superconducting cables with currents up to 6 kA will be used to power magnets individually in the insertion regions of the LHC. In case of a quench, the currents in these circuits will decay very fast (with time constants of about 200 ms) such that relatively small copper cross sections are sufficient for these busbars. Quench propagation experiments on a prototype cable and corresponding simulations led to a detailed understanding of the quench behavior of these busbars and to recommendations for the design and application of the cable. Simulations of the quench process in a multi-strand conductor led to a detailed understanding of the way current crosses from superconducting to pure copper strands and how this affects the quench propagation velocity. At nominal current (6 kA), the quench propagation velocities are high (10 m/s) and the hot spot temperature increases rapidly. In this situation, timely quench detection and energy extraction (current reduction) are vital to prevent damage of circuit components. research-article

AIP Conf. Proc. AIP Conf. Proc. Quench Propagation and Heating in the Superconducting 600 A Auxiliary Busbars of the LHC Calvi M Herzog R Sonnemann F 2004 613 575 582 In the Large Hadron Collider (LHC) at CERN 22 km of flexible superconducting cable, the auxiliary busbar cable, will conduct currents of up to 600 A to a large number of corrector magnets distributed throughout the accelerator. A prototype cable with 42 active conductors underwent several experiments to measure the hot spot temperature and the quench propagation velocity as a function of the current. The former was evaluated for various energy extraction scenarios as they are foreseen for the LHC corrector circuits. The experimental results and the heat flow simulations show that the quench behavior in this busbar prototype is strongly influenced by the heat flow through the insulation material (polyimide) into the helium bath, leading to stable configurations above the critical temperature Tc for currents between 250 A and 500 A. Special attention was paid to the study of discontinuities in the wires, like feed-throughs, where the wire is not immersed in liquid helium, and joints, where the wire cross-section is increased. The experiments and simulations led to a thorough understanding of the quench process in the wires of the prototype cable, which resulted in guidelines for the design, the use and the installation of the cable in the LHC. research-article

AIP Conf. Proc. AIP Conf. Proc. A Large-scale Test Facility for Heat Load Measurements down to 1.9 K Dufay L Policella C Rieubland Jean Michel Vandoni Giovanna 2002 613 98 105 Laboratory-scale tests aimed at minimizing the thermal loads of the LHC magnet cryostat have gone along with the development of the various mechanical components. For final validation of the industrial design with respect to heat inleaks between large surfaces at different temperatures, a full-scale test cryostat has been constructed. The facility reproduces the same pattern of temperature levels as the LHC dipole cryostat, avoiding the heat inleaks from local components like supports and feedthroughs and carefully minimizing fringe effects due to the truncated geometry of the facility with respect to the LHC cryostats serial layout. Thermal loads to the actively cooled radiation screen, operated between 50 K and 65 K, are measured by enthalpy difference along its length. At 1.9 K, the loads are obtained from the temperature difference across a superfluid helium exchanger. On the beam screen, the electrical power needed to stabilize the temperature at 20 K yields a direct reading of the heat losses. Precise in-situ calibration is achieved by subcooling the thermal screen, thereby zeroing radiative heat loads. Minimizing fringe effects has been rewarded by a high precision measurement, yielding one of the more accurate quantifications to date of an industrial application of MLI. The influence of possible openings in the thermal screen is monitored both at the 1.9 K bath and with a radiation sensitive bolometer. research-article

AIP Conf. Proc. AIP Conf. Proc. Plastic Strain Induced Damage Evolution and Martensitic Transformation in Ductile Materials at Cryogenic Temperatures Garion C Skoczen Blazej 2002 613 170 177 The Fe-Cr-Ni stainless steels are well known for their ductile behaviour at cryogenic temperatures. This implies development and evolution of plastic strain fields in the stainless steel components subjected to thermo-mechanical loads at low temperatures. The evolution of plastic strain fields is usually associated with two phenomena: ductile damage and strain induced martensitic transformation. Ductile damage is described by the kinetic law of damage evolution. Here, the assumption of isotropic distribution of damage (microcracks and microvoids) in the Representative Volume Element (RVE) is made. Formation of the plastic strain induced martensite (irreversible process) leads to the presence of quasi-rigid inclusions of martensite in the austenitic matrix. The amount of martensite platelets in the RVE depends on the intensity of the plastic strain fields and on the temperature. The evolution of the volume fraction of martensite is governed by a kinetic law based on the accumulated plastic strain. Both of these irreversible phenomena, associated with the dissipation of plastic power, are included into the constitutive model of stainless steels at cryogenic temperatures. The model is tested on the thin-walled corrugated shells (known as bellows expansion joints) used in the interconnections of the Large Hadron Collider, the new proton storage ring being constructed at present at CERN. research-article

AIP Conf. Proc. AIP Conf. Proc. An Experimental Study of Cold Helium Dispersion in Air Chorowski M Konopka G Riddone G 2002 613 1452 1459 The Large Hadron Collider (LHC) presently under construction at CERN, will contain about 100 tons of helium mostly located in the underground tunnel and in caverns. Potential failure modes of the accelerator, which may be followed by helium discharge to the tunnel, have been identified and the corresponding helium flows calculated. To verify the analytical calculations of helium dispersion in the tunnel, a dedicated test set-up has been built. It represents a section of the LHC tunnel at a scale 1:13 and is equipped with a controllable helium relief system enabling the simulation of different scenarios of the LHC cryogenic system failures. Corresponding patterns of cold helium dispersion in air have been observed and analysed with respect to oxygen deficiency hazard. We report on the test set-up and the measurement results, which have been scaled to real LHC conditions. research-article

AIP Conf. Proc. AIP Conf. Proc. Update of a Cooldown and Warmup Study for the Large Hadron Collider Liu L Riddone G Tavian L 2002 613 76 83 The paper presents the inventory of components and materials for LHC magnets, especially for main dipoles and quadrupoles. A mathematical model for LHC transient modes, such as cooldown and warmup of a magnet, a standard cell and the eight LHC sectors, has been developed on the basis of the up-to-date layout of the LHC machine, and validated by experimental data. The model considers the momentum and continuity equations, as well as the energy equations for helium and materials. Based on the simulation results, the heat transfer in the magnets has been studied and the transient modes optimized. research-article

AIP Conf. Proc. AIP Conf. Proc. Non-Linear Advanced Control of the LHC Inner Triplet Heat Exchanger Test Unit Blanco-Viñuela E CERN Casas-Cubillos J CERN De Prada-Moraga C Valladolid U. Cristea S Valladolid U. 2002 613 1597 1604 The future Large Hadron Collider (LHC) at CERN will include eight interaction region final focus magnet systems, the so-called "Inner Triplet", one on each side of the four beam collision points. The Inner Triplets will be cooled in a static bath of pressurized He II nominally at 1.9 K. This temperature is a control parameter and has very severe constraints in order to avoid the transition from the superconducting to normal resistive state. The main difference in these special zones with respect to a regular LHC cell is higher dynamic heat load unevenly distributed which modifies largely the process characteristics and hence the controller performance. Several control strategies have already been tested at CERN in a pilot plant (LHC String Test) which reproduced a LHC half-cell. In order to validate a common control structure along the whole LHC ring, a Nonlinear Model Predictive Control (NMPC) has been developed and implemented in the Inner Triplet Heat Exchanger Unit (IT-HXTU) at CERN. Automation of the Inner Triplet setup and the advanced control techniques deployed based on the Model Based Predictive Control (MBPC) principle are presented. research-article

AIP Conf. Proc. AIP Conf. Proc. He II Heat Exchanger Test Unit for the LHC Inner Triplet Blanco-Viñuela E Darve C Huang Y Nicol T H Peterson T Van Weelderen R 2002 613 147 154 The Inner Triplet Heat Exchanger Test Unit (IT-HXTU) is a 30-m long thermal model designed at Fermilab, built in US industry, fully automated and tested at CERN as part of the US LHC program to develop the LHC Interaction Region quadrupole system. The cooling scheme of the IT-HXTU is based on heat exchange between stagnant pressurized He II in the magnet cold mass and saturated He II (two-phase) flowing in a heat exchanger located outside of and parallel to the cold mass. The purposes of this test are, among others, to validate the proposed cooling scheme and to define an optimal control strategy to be implemented in the future LHC accelerator. This paper discusses the results for the heat exchanger test runs and emphasizes the thermal and hydraulic behavior of He II for the inner triplet cooling scheme. research-article

AIP Conf. Proc. AIP Conf. Proc. Study of Materials and Adhesives for Superconducting Cable Feedthroughs Perin A Macias-Jareño R Métral L 2002 613 551 558 Powering superconducting magnets requires the use of cryogenic feedthroughs for the superconducting cables capable of withstanding severe thermal, mechanical and electrical operating conditions. Such feedthrough shall provide the continuity of the superconducting circuit while ensuring a hydraulic separation at cryogenic temperature. A study about the adhesive and polymers required for the production of thermal shock resistant feedthroughs is presented. The strength of the busbar to adhesive joints was first investigated by compression/shear tests as well as pin and collar tests performed with four epoxy adhesives. After the selection of the most appropriate adhesive, pin and collar tests were performed with four different polymers. Based on the results, a superconducting cable feedthrough for 6 busbars of 6 kA and 12 busbars of 120 A was constructed and successfully tested. research-article

AIP Conf. Proc. AIP Conf. Proc. Advanced Superconducting Technology for Global Science Lebrun P 2002 613 3 14 The Large Hadron Collider (LHC), presently in construction at CERN, the European Organisation for Nuclear Research near Geneva (Switzerland), will be, upon its completion in 2005 and for the next twenty years, the most advanced research instrument of the world's high-energy physics community, providing access to the energy frontier above 1 TeV per elementary constituent. Re-using the 26.7-km circumference tunnel and infrastructure of the past LEP electron-positon collider, operated until 2000, the LHC will make use of advanced superconducting technology - high-field Nb-Ti superconducting magnets operated in superfluid helium and a cryogenic ultra-high vacuum system - to bring into collision intense beams of protons and ions at unprecedented values of center-of-mass energy and luminosity (14 TeV and 1034 cm-2.s-1, respectively with protons). After some ten years of focussed R&D, the LHC components are presently series-built in industry and procured through world-wide collaboration. After briefly recalling the physics goals, performance challenges and design choices of the machine, we describe its major technical systems, with particular emphasis on relevant advances in the key technologies of superconductivity and cryogenics, and report on its construction progress. research-article

Conclusions on 8 Years Operation of the LEP 4.5 K Refrigeration System at CERN Bangert N Claudet S Gayet P Sanmartí M 2002 After 11 years of operation the Large Electron/Positron collider (LEP) was stopped in November 2000. Since 1993 a cryogenic system has been used to supply up to 72 superconducting (SC) cavity modules, using four large liquid-helium refrigerators at 4.5 K. We review eight years of operation of one of the world's largest helium cryogenic systems, its evolution and cooling capacity availability correlated to the LEP increasing energy program. Failure statistics, availability, recovery time after breakdowns and reliability are analyzed, and the most relevant problems encountered during the operation and their cure exposed. The operational organization is also briefly described. research-article

AIP Conf. Proc. AIP Conf. Proc. The Proximity Cryogenic System for the ATLAS Toroidal Magnets Baynham D Elwyn Bradshaw T Brown G Cragg D Crook M Haug F Mayri C Orlowska A H Passardi Giorgio Pengo R ten Kate H H J Rochford J Sole D 2002 613 155 160 ATLAS is a very high-energy detector for the Large Hadron Collider (LHC) at CERN. The superconducting magnet used to provide the required magnetic field consists of four sub-systems: a central solenoid and a very large toroidal magnet comprising two end-cap magnets and the barrel toroid magnet. The associated cryogenic system, currently in the final specification and procurement phase has been sub-divided into three parts: internal, proximity and external. The internal cryogenics minimizes and extracts the heat loads to/from the 4.5 K cold mass and its thermal shields, while the proximity cryogenics takes the cooling capacity generated by the external common system and distributes it to the four magnets according to the various operating scenarios. Two independent proximity cryogenic systems have been designed taking into account the difference in cooling principle of the solenoid and the three toroids, respectively. research-article

AIP Conf. Proc. AIP Conf. Proc. A Cryogenic High-Reynolds Turbulence Experiment at CERN Bézaguet Alain-Arthur Dauvergne J P Knoops S Lebrun P Pezzetti M Pirotte O Bret J L Chabaud B Garde G Guttin C Hébral B Pietropinto S Roche P Barbier-Neyret J P Baudet C Gagne Y Poulain C Castaing B Ladam Y Vittoz F 2002 613 1399 1406 The potential of cryogenic helium flows for studying high-Reynolds number turbulence in the laboratory has been recognised for a long time and implemented in several small-scale hydrodynamic experiments. With its large superconducting particle accelerators and detector magnets, CERN, the European Laboratory for Particle Physics, has become a major world center in helium cryogenics, with several large helium refrigerators having capacities up to 18 kW @ 4.5 K. Combining a small fraction of these resources with the expertise of three laboratories at the forefront of turbulence research, has led to the design, swift implementation, and successful operation of GReC (Grands Reynolds Cryogéniques) a large axisymmetric turbulent-jet experiment. With flow-rates up to 260 g/s of gaseous helium at ~ 5 K and atmospheric pressure, Reynolds numbers up to 107 have been achieved in a 4.6 m high, 1.4 m diameter cryostat. This paper presents the results of the first runs and describes the experimental set-up comprehensively equipped with "hot" wire micro-anemometers, acoustic scattering vorticity measurements and a large-bandwidth data acquisition system. research-article