Test Results of a 1.2 kg/s Centrifugal Liquid Helium Pump for the ATLAS Superconducting Toroid Magnet System

The toroid superconducting magnet of ATLAS-LHC experiment at CERN will be indirectly cooled by means of forced flow of liquid helium at about 4.5 K. A centrifugal pump will be used, providing a mass flow of 1.2 kg/s and a differential pressure of 40 kPa (ca. 400 mbar) at about 4300 rpm. Two pumps are foreseen, one for redundancy, in order to feed in parallel the cooling circuits of the Barrel and the two End-Caps toroid magnets. The paper describes the tests carried out at CERN to measure the characteristic curves, i.e. the head versus the mass flow at different rotational speeds, as well as the pump total efficiency. The pump is of the "fullemission" type, i.e. with curved blades and it is equipped with an exchangeable inducer. A dedicated pump test facility has been constructed at CERN, which includes a Coriolis-type liquid helium mass flow meter. This facility is connected to the helium refrigerator used for the tests at CERN of the racetrack magnets of the Barrel and of the End-Cap toroids

Heterogeneity and cross-sectional dependence in panels: Heterogeneous vs. homogeneous estimators

This paper focuses on the comparison of homogeneous and heterogeneous panel data estimators, including partially heterogeneous ones, in presence of cross-sectional dependence generated by common factors and spatial error dependence. Our specifications allow us to con-sider and contrast weak cross-sectional dependence and strong cross-sectional dependence in a general linear heterogeneous panel data model. An overview of the estimation procedures, including heterogeneous, homogeneous and partially heterogeneous estimators, is presented. Then, an extensive Monte Carlo study is conducted using a general framework encompassing recent contributions in the literature especially in terms of considering common factors and spatial dependence simultaneously. Our simulation results show that, even for small individual and time dimensions, heterogeneous estimators perform better in terms of bias, root mean squared error, size and size adjusted power compared to homogeneous estimators. Last, the superiority of the heterogeneous estimators is confirmed by an empirical application relating fiscal decentralization and government size in 22 OECD countries over the period 1973-2017

Cryogenic Facilities at 1.9 K for the Reception of the Superconducting Wires and Cables of the LHC Dipoles Magnets

CERN's LHC project has moved to an implementation phase. The fabrication of 1600 high-field superconducting magnets operating at 1.9 K will require about 6400 km of Nb-Ti cables. A cryogenic test facility has therefore been set up in order, on the one hand, to verify the quality of individual wires and, on the other hand, to control the critical current of the assembled cables. The facility is composed of a helium liquefier, a transfer line, a dewar and pumps. The paper describes the fully automatic operation of this installation and the different test cycles applied to these wires and cables

Cryogenics for the CERN Solar Axion Telescope (CAST) using a LHC Dipole Prototype Magnet

The axion, an as yet hypothetical particle predicted from the solution of the strong CP problem, constitutes a prime candidate for the galactic dark matter and also arises in supersymmetry and superstring theories. If existing, axions should be copiously produced in stellar interiors and there are theoretical expectations for a low-energy axion emission spectrum peaked around a mean energy of ~ 4.4 keV. To provide the experimental proof, a solar axion telescope is at present installed at CERN, which is expected to be in total 10-12 times more efficient than the present largest set-up in operation at the University of Tokyo. The telescope will use a decommissioned 10-m long LHC superconducting dipole prototype magnet, providing a magnetic field of 9 T in operation, to catalyse the solar axion to photon conversion, which then can be detected by low-background x-ray detectors. The paper describes the external and proximity cryogenic systems and their integration into the overall telescope assembly

Cryogenic Characteristics of the ATLAS Barrel Toroid Superconducting Magnet

ATLAS, one of the experiments of the LHC accelerator under commissioning at CERN, is equipped with a large superconducting magnet the Barrel Toroid (BT) that has been tested at nominal current (20500 A). The BT is composed of eight race-track superconducting coils (each one weights about 45 tons) forming the biggest air core toroidal magnet ever built. By means of a large throughput centrifugal pump, a forced flow (about 10 liter/second at 4.5 K) provides the indirect cooling of the coils in parallel. The paper describes the results of the measurements carried out on the complete cryogenic system assembled in the ATLAS cavern situated 100 m below the ground level. The measurements include, among other ones, the static heat loads, i.e., with no or constant current in the magnet, and the dynamic ones, since additional heat losses are produced, during the current ramp-up or slow dump, by eddy currents induced on the coil casing

Low Temperature Gaseous Helium and very High Turbulence Experiments

Cryogenic gaseous helium gives access to extreme turbulent experimental conditions. The very high cooling helium flow rates available at CERN have been used to reach Reynolds numbers up to Re ~ 10**7 in a round jet experiment. First results are discussed

Ultimate Performance of the ATLAS Superconducting Solenoid

A 2 tesla, 7730 ampere, 39 MJ, 45 mm thin superconducting solenoid with a 2.3 meters warm bore and 5.3 meters length, is installed in the center of the ATLAS detector and successfully commissioned. The solenoid shares its cryostat with one of the detector's calorimeters and provides the magnetic field required for the inner detectors to accurately track collision products from the LHC at CERN. After several years of a stepwise construction and test program, the solenoid integration 100 meters underground in the ATLAS cavern is completed. Following the on-surface acceptance test, the solenoid is now operated with its final cryogenic, powering and control system. A re-validation of all essential operating parameters is completed. The performance and test results of underground operation are reported and compared to those previously measured

A Cryogenic High-Reynolds Turbulence Experiment at CERN

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

Standalone vertex finding in the ATLAS muon spectrometer

A dedicated reconstruction algorithm to find decay vertices in the ATLAS muon spectrometer is presented. The algorithm searches the region just upstream of or inside the muon spectrometer volume for multi-particle vertices that originate from the decay of particles with long decay paths. The performance of the algorithm is evaluated using both a sample of simulated Higgs boson events, in which the Higgs boson decays to long-lived neutral particles that in turn decay to bbar b final states, and pp collision data at √s = 7 TeV collected with the ATLAS detector at the LHC during 2011