LEP Tunnel Movements at Point 1 caused by LHC Civil Engineering

The excavation of underground openings causes the surrounding ground to move towards the newly created opening. The magnitude of the movement is dependant of various factors, such as the shape and the size of the excavation, the geotechnical ground conditions, the in-situ ground stress, the distance from the excavation, etc. The excavation technique and the rock support measures are to be adapted to the prevailing ground conditions to limit the displacements to an acceptable level. From the output of the numerical analyses for the design of the underground structures, data can be obtained to determine the predicted movements. For the particular case of the LHC excavations at Point 1 in close proximity to the existing LEP tunnel, a facility had to be designed and installed in the LEP tunnel to allow adjustments of the machine alignment to compensate for the tunnel movements. The design was based on the predicted displacements, and the adequacy of the facility has been validated during excavation

Novel Technique for the UX15 Cavern Vault Support System

The overall LHC project schedule requires the civil engineering work to begin before the final LEP shutdown. The new caverns for the ATLAS experiment will be built in and around the existing underground structures at point 1. In order to make the best possible use of the time available for the LHC civil engineering before the shutdown of LEP, a particular arrangement for the construction of the UX15 cavern vault has been developed. The basic concept of this arrangement consists of the excavation of the cavern top heading and the installation of the concrete vault immediately afterwards, prior to the subsequent bench excavation after LEP shutdown. A temporary support of the dead weight of the concrete roof will be achieved by the suspension of the roof by 38 no. pre-stressed ground anchors of 225 tons capacity each. This support system will work up to the construction of the cavern base slab and walls and the completion of the permanent concrete lining

Civil Engineering Construction of Underground Works

For the first time at CERN, new shafts and caverns will be excavated inside a surface building. The LHC civil engineering construction for the ATLAS experiment has been designed such that the experimental hall will be completed to the extent that it can provide a secure, weatherproof and sound insulated covering to the shaft excavation area. The construction of the two access shafts and the experimental cavern will follow and will be carried out inside the building. This unconventional method of working allows the excavation of the Molasse rock in the dry, which is essential for this type of rock, and ensures reduced environmental pollution by noise and dust. The paper will present the technical infrastructure required for this particular construction method, explain its advantages and disadvantages, and compare it with a conventional method of underground excavations to be used on the same work site for the construction of the service cavern

Two new caverns for LHC experiments: ATLAS and CMS

The LHC will utilize much of the existing infrastructure already constructed for the LEP. However, to house the new ATLAS and CMS detectors, two huge cavern complexes are required at Point 1 and Point 5 on the LEP. The civil engineering design criteria for the two caverns are presented. Attention is directed to the decisive constraints for the design, such as adverse geological ground conditions, the three-dimensional complexity of the shafts, caverns and tunnels, and the existing LEP structures in the vicinity of the new works which remain operational for the first two years of the project. the paper will demonstrate the different basic requirements of the new underground structures at Point 1 and Point 5. The comparison of the two projects from a civil engineering point of view will aim at explaining why different technical solutions have been adopted for the design and construction of these works

Civil engineering status report for the ATLAS & CMS worksites

Construction work on the civil engineering contracts at Point 1 and Point 5 started in 1998. The new surface buildings and underground structures are necessary to accommodate the ATLAS and CMS detectors for the LHC Project. The principal underground works at both points consist of two new shafts, two caverns along with a number of small connection tunnels and galleries. At Point 1, the works are 90% complete. Most of the surface buildings as well as the shafts and one of the two new caverns have been completed, and the construction of the second cavern is well underway. At Point 5, the works are 70% complete. Most of the surface buildings as well as the shafts and the pillar have been completed. With excavation of the two large caverns complete, the concreting of the final linings has started. The aim of this paper is to present the status of the civil engineering on these worksites and in particular the challenges encountered constructing the experimental caverns

Magneto-transport in impurity-doped few-layer graphene spin valve

Using Keldysh nonequilibrium Green's function method we study the spin-dependent transport through impurity-doped few layer graphene sandwiched between two magnetic leads with an arbitrary mutual orientations of the magnetizations. We find for parallel electrodes magnetizations that the differential conductance possesses two resonant peaks as the applied bias increases. These peaks are traced back to a buildup of a magnetic moment on the impurity due to the electrodes spin polarization. For a large mutual angle of the electrodes magnetization directions, the two resonant peaks approach each others and merge into a single peak for antiparallel orientation of the electrodes magnetizations. We point out that the tunneling magnetoresistance (TMR) may change sign for relatively small changes in the values of the polarization parameters. Furthermore, we inspect the behaviour of the differential conductance and TMR upon varying the temperature.Comment: 8 pages, 7 figures, accepted by Phys. Rev.

Side-jumps in the spin-Hall effect: construction of the Boltzmann collision integral

We present a systematic derivation of the side-jump contribution to the spin-Hall current in systems without band structure spin-orbit interactions, focusing on the construction of the collision integral for the Boltzmann equation. Starting from the quantum Liouville equation for the density operator we derive an equation describing the dynamics of the density matrix in the first Born approximation and to first order in the driving electric field. Elastic scattering requires conservation of the total energy, including the spin-orbit interaction energy with the electric field: this results in a first correction to the customary collision integral found in the Born approximation. A second correction is due to the change in the carrier position during collisions. It stems from the part of the density matrix off-diagonal in wave vector. The two corrections to the collision integral add up and are responsible for the total side-jump contribution to the spin-Hall current. The spin-orbit-induced correction to the velocity operator also contains terms diagonal and off-diagonal in momentum space, which together involve the total force acting on the system. This force is explicitly shown to vanish (on the average) in the steady state: thus the total contribution to the spin-Hall current due to the additional terms in the velocity operator is zero.Comment: Added references, expanded discussion, revised introductio

Quantum Diagrammatic Theory of the Extrinsic Spin Hall Effect in Graphene

We present a rigorous microscopic theory of the extrinsic spin Hall effect in disordered graphene based on a nonperturbative quantum diagrammatic treatment incorporating skew scattering and anomalous---impurity concentration-independent---quantum corrections on equal footing. The leading skew scattering contribution to the spin Hall conductivity is shown to quantitatively agree with Boltzmann transport theory over a wide range of parameters. Our self-consistent approach---where all topologically equivalent noncrossing diagrams are resummed---unveils that the skewness generated by spin--orbit-active impurities deeply influences the anomalous component of the spin Hall conductivity, even in the weak scattering regime. This seemingly counterintuitive result is explained by the rich sublattice structure of scattering potentials in graphene, for which traditional Gaussian disorder approximations fail to capture the intricate correlations between skew scattering and side jumps generated through diffusion. Finally, we assess the role of quantum interference corrections by evaluating an important subclass of crossing diagrams recently considered in the context of the anomalous Hall effect, the $X$ and $\Psi$ diagrams [Ado et al., EPL 111, 37004 (2015)]. We show that $\Psi$ diagrams---encoding quantum coherent skew scattering---display a strong Fermi energy dependence, dominating the anomalous spin Hall component away from the Dirac point. Our findings have direct implications for nonlocal transport experiments in spin--orbit-coupled graphene systems

Spin-orbit scattering in quantum diffusion of massive Dirac fermions

Effect of spin-orbit scattering on quantum diffusive transport of two-dimensional massive Dirac fermions is studied by the diagrammatic technique. The quantum diffusion of massive Dirac fermions can be viewed as a singlet Cooperon in the massless limit and a triplet Cooperon in the large-mass limit. The spin-orbit scattering behaves like random magnetic fields only to the triplet Cooperon, and suppresses the weak localization of Dirac fermions in the large-mass regime. This behavior suggests an experiment to detect the weak localization of bulk subbands in topological insulator thin films, in which a narrowing of the cusp of the negative magnetoconductivity is expected after doping heavy-element impurities. Finally, a detailed comparison between the conventional two-dimensional electrons and Dirac fermions is presented for impurities of orthogonal, symplectic, and unitary symmetries.Comment: 5 pages, 3 figures, 2 tables. To be submitted, comments are welcom

State-dependent impedance of a strongly coupled oscillator-qubit system

We investigate the measurements of two-state quantum systems (qubits) at finite temperatures using a resonant harmonic oscillator as a quantum probe. The reduced density matrix and oscillator correlators are calculated by a scheme combining numerical methods with an analytical perturbation theory. Correlators provide us information about the system impedance, which depends on the qubit state. We show in detail how this property can be exploited in the qubit measurement.Comment: 8 pages, 16 image