Status of the High Field Cable Test Facility at Fermilab

Fermi National Accelerator Laboratory (FNAL) and Lawrence Berkeley National Laboratory (LBNL) are building a new High Field Vertical Magnet Test Facility (HFVMTF) for testing superconducting cables in high magnetic field. The background magnetic field of 15 T in the HFVMTF will be produced by a magnet provided by LBNL. The HFVMTF is jointly funded by the US DOE Offices of Science, High Energy Physics (HEP), and Fusion Energy Sciences (FES), and will serve as a superconducting cable test facility in high magnetic fields and a wide range of temperatures for HEP and FES communities. This facility will also be used to test high-field superconducting magnet models and demonstrators, including hybrid magnets, produced by the US Magnet Development Program (MDP). The paper describes the status of the facility, including construction, cryostat designs, top and lambda plates, and systems for powering, and quench protection and monitoring

Field Quality Measurements in a Single-Aperture 11 T Nb3Sn Demonstrator Dipole for LHC Upgrades

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Ballistic anisotropic magnetoresistance

Electronic transport in ferromagnetic ballistic conductors is predicted to exhibit ballistic anisotropic magnetoresistance (BAMR) - a change in the ballistic conductance with the direction of magnetization. This phenomenon originates from the effect of the spin-orbit interaction on the electronic band structure which leads to a change in the number of bands crossing the Fermi energy when the magnetization direction changes. We illustrate the significance of this phenomenon by performing ab-initio calculations of the ballistic conductance in ferromagnetic Ni and Fe nanowires which display a sizable BAMR when the magnetization changes direction from parallel to perpendicular to the wire axis

Search for narrow resonances below the Upsilon mesons

We have investigated the invariant mass spectrum of dimuons collected by the CDF experiment during the 1992-1995 run of the Fermilab Tevatron collider to improve the limit on the existence of narrow resonances set by the experiments at the SPEAR e+e- collider. In the mass range 6.3-9.0 GeV/c^2, we derive 90% upper credible limits to the ratio of the production cross section times muonic branching fraction of possible narrow resonances to that of the Y(1S) meson. In this mass range, the average limit varies from 1.7 to 0.5%. This limit is much worse at the mass of 7.2 GeV/c^2 due to an excess of 250+-61 events with a width consistent with the detector resolution.Comment: 20 pages, 9 figures. This version has some typos fixed in the text and bibliography. A reference was added in bibliography. Submitted to Phys. Rev. D With this last submission we provide the version accepted for publication in Phys.Rev.

Direct Observation of the Dynamics of Latex Particles Confined inside Thinning Water-Air Films

The dynamics of micrometer-size polystyrene latex particles confined in thinning foam films was investigated by microscopic interferometric observation. The behavior of the entrapped particles depends on the mobility of the film surfaces, the particle concentration, hydrophobicity, and rate of film formation. When the films were stabilized by sodium dodecyl sulfate, no entrapment of particles between the surfaces was possible. When protein was used as a stabilizer, a limited number of particles were caught inside the film area due to the decreased mobility of the interfaces. In this case, extraordinary long-ranged (>100 Ìm) capillary attraction leads to two-dimensional (2D) particle aggregation. A major change occurs when the microspheres are partially hydrophobized by the presence of cationic surfactant. After the foam films are opened and closed a few times, a layer of particles simultaneously adsorbed to the two interfaces is formed, which sterically inhibits any further film opening and thinning. The particles within this layer show an excellent 2D hexagonal ordering. The experimental data are relevant to the dynamics of defects in coating films, Pickering emulsions, and particle assembly into 2D arrays

Magnetic field measurements of LHC inner triplet quadrupoles fabricated at Fermilab

Fermilab, as part of the US-LHC Accelerator Project, is producing superconducting low-beta quadrupole magnets for the Large Hadron Collider (LHC). These 5.5 m long magnets are designed to operate in superfluid helium at 1.9 K with a nominal gradient of 205 T/m in the 70 mm bore. Two quadrupoles separated by a dipole orbit corrector in a single cryogenic assembly comprise the Q2 optical elements of the final focus triplets in the LHC interaction regions. The field quality of the quadrupoles is measured at room temperature during construction of the cold masses as well as during cold testing of the cryogenic assembly. We summarize data from the series measurements of the magnets and discuss various topics of interest

Robust isothermal electric switching of interface magnetization: A route to voltage-controlled spintronics

Roughness-insensitive and electrically controllable magnetization at the (0001) surface of antiferromagnetic chromia is observed using magnetometry and spin-resolved photoemission measurements and explained by the interplay of surface termination and magnetic ordering. Further, this surface in placed in proximity with a ferromagnetic Co/Pd multilayer film. Exchange coupling across the interface between chromia and Co/Pd induces an electrically controllable exchange bias in the Co/Pd film, which enables a reversible isothermal (at room temperature) shift of the global magnetic hysteresis loop of the Co/Pd film along the magnetic field axis between negative and positive values. These results reveal the potential of magnetoelectric chromia for spintronic applications requiring non-volatile electric control of magnetization.Comment: Single PDF file: 27 pages, 6 figures; version of 12/30/09; submitted to Nature Material