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Physics Faculty Publications

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Articles 931 - 960 of 1942

Full-Text Articles in Physical Sciences and Mathematics

Information Transfer By Vector Spin Chirality In Finite Magnetic Chains, Matthias Menzel, Yuriy Mokrousov, Robert Wieser, Jessica E. Bickel, Elena Vedmedenko, Stefan Blügel, Stefan Heinze, Kirsten Von Bergmann, André Kubetzka, Roland Wiesendanger May 2012

Information Transfer By Vector Spin Chirality In Finite Magnetic Chains, Matthias Menzel, Yuriy Mokrousov, Robert Wieser, Jessica E. Bickel, Elena Vedmedenko, Stefan Blügel, Stefan Heinze, Kirsten Von Bergmann, André Kubetzka, Roland Wiesendanger

Physics Faculty Publications

Vector spin chirality is one of the fundamental characteristics of complex magnets. For a one-dimensional spin-spiral state it can be interpreted as the handedness, or rotational sense of the spiral. Here, using spin-polarized scanning tunneling microscopy, we demonstrate the occurrence of an atomic-scale spin spiral in finite individual bi-atomic Fe chains on the (5×1)−Ir(001) surface. We show that the broken inversion symmetry at the surface promotes one direction of the vector spin chirality, leading to a unique rotational sense of the spiral in all chains. Correspondingly, changes in the spin direction of one chain end can be probed tens of …

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Ion Acceleration In A Helicon Source Due To The Self-Bias Effect, Matt Wiebold, Yung-Ta Sung, John E. Scharer May 2012

Ion Acceleration In A Helicon Source Due To The Self-Bias Effect, Matt Wiebold, Yung-Ta Sung, John E. Scharer

Physics Faculty Publications

Time-averaged plasma potential differences up to 165 V over several hundred Debye lengths are observed in low pressure (pn < 1 mTorr) expanding argon plasmas in the Madison Helicon eXperiment (MadHeX). The potential gradient leads to ion acceleration greater than that predicted by ambipolar expansion, exceeding Ei≈7 kTe in some cases. RF power up to 500 W at 13.56 MHz is supplied to a half-turn, double-helix antenna in the presence of a nozzle magnetic field, adjustable up to 1 kG. A retarding potential analyzer (RPA) measures the ion energy distribution function (IEDF) and a swept emissive probe measures the plasma potential. Single and double probes measure the electron density and temperature. Two distinct mode hops, the capacitive-inductive (E-H) and inductive-helicon (H-W) transitions, …

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The M Dwarf Problem In The Galaxy, Vincent M. Woolf, Andrew A. West Apr 2012

The M Dwarf Problem In The Galaxy, Vincent M. Woolf, Andrew A. West

Physics Faculty Publications

We present evidence that there is an M dwarf problem similar to the previously identified G dwarf and K dwarf problems: the number of low-metallicity M dwarfs is not sufficient to match simple closed-box models of local Galactic chemical evolution. We estimated the metallicity of 4141 M dwarf stars with spectra from the Sloan Digital Sky Survey (SDSS) using a molecular band strength versus metallicity calibration developed using high resolution spectra of nearby M dwarfs. Using a sample of M dwarfs with measured magnitudes, parallaxes and metallicities, we derived a relation that describes the absolute magnitude variation as a function …

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Measurement Of The Neutron F2 Structure Function Via Spectator Tagging With Clas, N. Baillie, Gerard P. Gilfoyle, Et. Al. Apr 2012

Measurement Of The Neutron F2 Structure Function Via Spectator Tagging With Clas, N. Baillie, Gerard P. Gilfoyle, Et. Al.

Physics Faculty Publications

We report on the first measurement of the F2 structure function of the neutron from semi-inclusive scattering of electrons from deuterium, with low-momentum protons detected in the backward hemisphere. Restricting the momentum of the spectator protons to ≲ 100° MeV/c and their angles to ≳ 100° relative to the momentum transfer allows an interpretation of the process in terms of scattering from nearly on-shell neutrons. The Fn2 data collected cover the nucleon-resonance and deep-inelastic regions over a wide range of Bjorken x for 0.65 < Q2 < 4.52 GeV2, with uncertainties from nuclear corrections estimated to be less than …

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Measurement Of The Neutron F2 Structure Function Via Spectator Tagging With Clas, N. Baillie, S. Tkachenko, J. Zhang, P. Bosted, S. Bültmann, M. E. Christy, H. Fenker, K. A. Griffioen, C. E. Keppel, S. E. Kuhn, K. P. Adhikari, D. Adikaram, M. J. Amaryan, H. Baghdasaryan, G. Dodge, N. Guler, C. E. Hyde, A. Klein, A. Klimenko, L. B. Weinstein Apr 2012

Measurement Of The Neutron F2 Structure Function Via Spectator Tagging With Clas, N. Baillie, S. Tkachenko, J. Zhang, P. Bosted, S. Bültmann, M. E. Christy, H. Fenker, K. A. Griffioen, C. E. Keppel, S. E. Kuhn, K. P. Adhikari, D. Adikaram, M. J. Amaryan, H. Baghdasaryan, G. Dodge, N. Guler, C. E. Hyde, A. Klein, A. Klimenko, L. B. Weinstein

Physics Faculty Publications

We report on the first measurement of the F2 structure function of the neutron from the semi-inclusive scattering of electrons from deuterium, with low-momentum protons detected in the backward hemisphere. Restricting the momentum of the spectator protons to ≲ 100MeV/c and their angles to ≳ 100° relative to the momentum transfer allows an interpretation of the process in terms of scattering from nearly on-shell neutrons. The Fn2 data collected cover the nucleon-resonance and deep-inelastic regions over a wide range of Bjorken x for 0.65 < Q2 < 4.52 GeV2, with uncertainties from nuclear corrections estimated to be less …

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Mid-Infrared Upconversion Spectroscopy Based On A Yb:Fiber Femtosecond Laser, Todd Johnson, Scott A. Diddams Apr 2012

Mid-Infrared Upconversion Spectroscopy Based On A Yb:Fiber Femtosecond Laser, Todd Johnson, Scott A. Diddams

Physics Faculty Publications

We present a system for molecular spectroscopy using a broadband mid-infrared laser with near-infrared detection. Difference frequency generation of a Yb:fiber femtosecond laser produced a mid-infrared (MIR) source tunable from 2100–3700 cm-1 (2.7–4.7 μm) with average power up to 40 mW. The MIR spectrum was upconverted to near-infrared wavelengths for broadband detection using a two-dimensional dispersion imaging technique. Absorption measurements were performed over bandwidths of 240 cm-1 (7.2 THz) with 0.048 cm-1 (1.4 GHz) resolution, and absolute frequency scale uncertainty was better than 0.005 cm-1 (150 MHz). The minimum detectable absorption coefficient per spectral element was …

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Measurement Of The Generalized Form Factors Near Threshold Via Γ*P→Nπ+ At High Q2, K. Park, Gerard P. Gilfoyle, Et. Al. Mar 2012

Measurement Of The Generalized Form Factors Near Threshold Via Γ*P→Nπ+ At High Q2, K. Park, Gerard P. Gilfoyle, Et. Al.

Physics Faculty Publications

We report the first extraction of the pion-nucleon multipoles near the production threshold for the nπ+ channel at relatively high momentum transfer (Q2 up to 4.2 GeV2). The dominance of the s-wave transverse multipole (E0+), expected in this region, allowed us to access the generalized form factor G1 within the light-cone sum-rule (LCSR) framework as well as the axial form factor GA. The data analyzed in this work were collected by the nearly 4π CEBAF Large Acceptance Spectrometer (CLAS) using a 5.754-GeV electron beam on a proton …

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Utilizing (P,D) And (P,T) Reactions To Obtain (N,F) Cross Sections In Uranium Nuclei Via The Surrogate-Ratio Method, R. O. Hughes, C. W. Beausang, T. J. Ross, J. T. Burke, N. D. Scielzo, M. S. Basunia, C. M. Campbell, R. J. Casperson, H. L. Crawford, J. Escher, J. Munson, L. Phair, J. J. Ressler Feb 2012

Utilizing (P,D) And (P,T) Reactions To Obtain (N,F) Cross Sections In Uranium Nuclei Via The Surrogate-Ratio Method, R. O. Hughes, C. W. Beausang, T. J. Ross, J. T. Burke, N. D. Scielzo, M. S. Basunia, C. M. Campbell, R. J. Casperson, H. L. Crawford, J. Escher, J. Munson, L. Phair, J. J. Ressler

Physics Faculty Publications

The surrogate ratio method has been tested for (p,d) and (p,t) reactions on uranium nuclei. 236U and 238U targets were bombarded with 28-MeV protons and the light ion recoils and fission fragments were detected using the Silicon Telescope Array for Reaction Studies detector array at the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory. The (p,df) reaction channels on 236U and 238U targets were used as a surrogate to determine the σ[236U(n,f)]/σ[234U(n, …

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Upper Limits For The Photoproduction Cross Section For The Φ−−(1860) Pentaquark State Off The Deuteron, H. Egiyan, Gerard P. Gilfoyle, Et. Al. Jan 2012

Upper Limits For The Photoproduction Cross Section For The Φ−−(1860) Pentaquark State Off The Deuteron, H. Egiyan, Gerard P. Gilfoyle, Et. Al.

Physics Faculty Publications

We searched for the Φ--(1860) pentaquark in the photoproduction process off the deuteron in the Ξ-π--decay channel using CLAS. The invariant-mass spectrum of the Ξ-π- system does not indicate any statistically significant enhancement near the reported mass M = 1.860 GeV. The statistical analysis of the sideband-subtracted mass spectrum yields a 90%-confidence-level upper limit of 0.7 nb for the photoproduction cross section of Φ--(1860) with a consecutive decay into Ξ-π- in the photon-energy range 4.5 GeV < Eγ < 5.5 GeV.

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Α−Α Cross-Links Increase Fibrin Fiber Elasticity And Stiffness, Christine C. Helms, Robert A.S. Ariens, S. Uitte De Willige, Kristina F. Standeven, Martin Guthold Jan 2012

Α−Α Cross-Links Increase Fibrin Fiber Elasticity And Stiffness, Christine C. Helms, Robert A.S. Ariens, S. Uitte De Willige, Kristina F. Standeven, Martin Guthold

Physics Faculty Publications

Fibrin fibers, which are ∼100 nm in diameter, are the major structural component of a blood clot. The mechanical properties of single fibrin fibers determine the behavior of a blood clot and, thus, have a critical influence on heart attacks, strokes, and embolisms. Cross-linking is thought to fortify blood clots; though, the role of α–α cross-links in fibrin fiber assembly and their effect on the mechanical properties of single fibrin fibers are poorly understood. To address this knowledge gap, we used a combined fluorescence and atomic force microscope technique to determine the stiffness (modulus), extensibility, and elasticity of …

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Practicality Of Compensating The Loss In The Plasmonic Waveguides Using Semiconductor Gain Medium, Jacob B. Khurgin, Greg Sun Jan 2012

Practicality Of Compensating The Loss In The Plasmonic Waveguides Using Semiconductor Gain Medium, Jacob B. Khurgin, Greg Sun

Physics Faculty Publications

We consider the issue of compensating the loss in plasmonic waveguides with semiconductor gain material and show that, independent of specific geometry, full loss compensation in plasmonic waveguides with significantly sub-wavelength light confinement (less than λ/4n) requires current density well in excess of 100 kA/cm2. This high current density is attributed to the unavoidable shortening of recombination time caused by the Purcell effect inherent to sub-wavelength confinement. Consequently, an injection-pumped plasmonic laser that is truly sub-wavelength in all three dimensions (“spaser”) would have threshold current densities that are hard to obtain in any conceivable semiconductor device.

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Chiral Magnetization Configurations In Magnetic Nanostructures In The Presence Of Dzyaloshinski-Moriya Interactions, Naoise Grisewood, John Eves, Timothy Usher, Hans-Benjamin Braun Jan 2012

Chiral Magnetization Configurations In Magnetic Nanostructures In The Presence Of Dzyaloshinski-Moriya Interactions, Naoise Grisewood, John Eves, Timothy Usher, Hans-Benjamin Braun

Physics Faculty Publications

Many low-dimensional systems, such as nanoscale islands, thin films, and multilayers, as well as bulk systems, such as multiferroics, are characterized by the lack of inversion symmetry, a fact that may give rise to a Dzyaloshinskii-Moriya (DM) interaction. For sufficient strength, the DM interaction will favor spiral spin configurations of definite chirality. In order to harness such systems for applications, it is important to understand the conditions under which these spiral spin configurations form and how they can be controlled via an external field. Here, we present exact solutions of the 1D magnetization profiles in such systems for arbitrary material …

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To The Continuum And Beyond: Structure Of U Nuclei, R. O. Hughes, C. W. Beausang, T. J. Ross, J. T. Burke, N. D. Scielzo, M. S. Basunia, C. M. Campbell, R. J. Casperson, H. L. Crawford, J. Munson, L. Phair, J. J. Ressler Jan 2012

To The Continuum And Beyond: Structure Of U Nuclei, R. O. Hughes, C. W. Beausang, T. J. Ross, J. T. Burke, N. D. Scielzo, M. S. Basunia, C. M. Campbell, R. J. Casperson, H. L. Crawford, J. Munson, L. Phair, J. J. Ressler

Physics Faculty Publications

An experiment was performed at the 88-inch cyclotron at LBNL to investigate the structure of uranium isotopes and concurrently test the so-called surrogate ratio method. A 28 MeV proton beam was used to bombard 236U and 238U targets and the outgoing light ions were detected using the STARS silicon telescope allowing isotopic assignments and the excitation energy of the compound nucleus to be measured. A fission detector was placed at backward angles to give particle-fission coincidences, while the six clover germanium detectors of the LIBERACE array were used for particle-γ coincidences. The (p,d) reaction channels on 236U …

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Comment On “Observation Of A Narrow Structure In 1H(Γ,KS0)X Via Interference With Φ-Meson Production”, M. Anghinolfi, Gerard P. Gilfoyle, Et. Al. Jan 2012

Comment On “Observation Of A Narrow Structure In 1H(Γ,KS0)X Via Interference With Φ-Meson Production”, M. Anghinolfi, Gerard P. Gilfoyle, Et. Al.

Physics Faculty Publications

In Ref. [1], the authors claim to observe a narrow structure in the mass spectrum constructed from the (pKL) system using data from the CLAS detector. The interpretation of this narrow structure given in Ref. [1] is as follows: “It may be due to the photoproduction of the Θ+pentaquark or some unknown Σ* resonance.” The authors go on to say that “it is unlikely for the observed structure to be due to a Σ* resonance.”

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Repeatability Of The Seasonal Variations Of Ozone Near The Mesopause From Observations Of The 11.072-Ghz Line, Alan E. E. Rogers, P. P. Erickson, V. L. Fish, J. J. Kittredge, S. S. Danford, J. M. Marr, Martina Arndt, J. Sarabia, D. Costa, S. K. May Jan 2012

Repeatability Of The Seasonal Variations Of Ozone Near The Mesopause From Observations Of The 11.072-Ghz Line, Alan E. E. Rogers, P. P. Erickson, V. L. Fish, J. J. Kittredge, S. S. Danford, J. M. Marr, Martina Arndt, J. Sarabia, D. Costa, S. K. May

Physics Faculty Publications

Ground-based observations of the 11.072-GHz line of ozone were made from January 2008 through the middle of September 2011 to estimate the maximum in the nighttime ozone in the upper mesosphere at an altitude of about 95 km for a region centered at 38°N, 290°E. The measurements show seasonal variation with a high degree of repeatability with peaks in ozone concentration about a month following each equinox. A significant increase in ozone concentration above the yearly trend occurred in 2010 from mid-November until the end of December, which the authors attribute to delay in the start of the meridional circulation …

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A New Model For Mixing By Double-Diffusive Convection (Semi-Convection): I. The Conditions For Layer Formation, G. M. Mirouh, P. Garaud, S. Stellmach, Adrienne L. Traxler, T. S. Wood Jan 2012

A New Model For Mixing By Double-Diffusive Convection (Semi-Convection): I. The Conditions For Layer Formation, G. M. Mirouh, P. Garaud, S. Stellmach, Adrienne L. Traxler, T. S. Wood

Physics Faculty Publications

The process referred to as "semi-convection" in astrophysics and "double-diffusive convection in the diffusive regime" in Earth and planetary sciences occurs in stellar and planetary interiors in regions which are stable according to the Ledoux criterion but unstable according to the Schwarzschild criterion. In this series of papers, we analyze the results of an extensive suite of three-dimensional (3D) numerical simulations of the process, and ultimately propose a new 1D prescription for heat and compositional transport in this regime which can be used in stellar or planetary structure and evolution models. In a preliminary study of the phenomenon, Rosenblum et …

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Model For Triggering Of Non-Volcanic Tremor By Earthquakes, Naum I. Gershenzon, Gust Bambakidis Jan 2012

Model For Triggering Of Non-Volcanic Tremor By Earthquakes, Naum I. Gershenzon, Gust Bambakidis

Physics Faculty Publications

There is evidence of tremor triggering by seismic waves emanating from distant large earthquakes. The frequency content of both triggered and ambient tremor are largely identical, suggesting that this property does not depend directly on the nature of the source. We show here that the model of plate dynamics developed earlier by us is an appropriate tool for describing tremor triggering. In the framework of this model, tremor is an internal response of a fault to a failure triggered by external disturbances. The model predicts generation of radiation in a frequency range defined by the fault parameters. Thus, although the …

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Broadband 180 Degree Universal Rotation Pulses For Nmr Spectroscopy Designed By Optimal Control, Thomas E. Skinner, Naum I. Gershenzon, Manoj Nimbalkar, Wolfgang Bermel, Burkhard Luy, Steffen J. Glaser Jan 2012

Broadband 180 Degree Universal Rotation Pulses For Nmr Spectroscopy Designed By Optimal Control, Thomas E. Skinner, Naum I. Gershenzon, Manoj Nimbalkar, Wolfgang Bermel, Burkhard Luy, Steffen J. Glaser

Physics Faculty Publications

Broadband inversion pulses that rotate all magnetization components 180 degrees about a given fixed axis are necessary for refocusing and mixing in high-resolution NMR spectroscopy. The relative merits of various methodologies for generating pulses suitable for broadband refocusing are considered. The de novo design of 180 degree universal rotation pulses using optimal control can provide improved performance compared to schemes which construct refocusing pulses as composites of existing pulses. The advantages of broadband universal rotation by optimized pulses (BURBOP) are most evident for pulse design that includes tolerance to RF inhomogeneity or miscalibration. We present new modifications of the optimal …

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A Mems Photoacoustic Detector Of Terahertz Radiation For Chemical Sensing, Nathan E. Glauvitz, S. Blazevic, Ronald A. Coutu Jr., Michael N. Kistler, Ivan Medvedev, Douglas T. Petkie Jan 2012

A Mems Photoacoustic Detector Of Terahertz Radiation For Chemical Sensing, Nathan E. Glauvitz, S. Blazevic, Ronald A. Coutu Jr., Michael N. Kistler, Ivan Medvedev, Douglas T. Petkie

Physics Faculty Publications

A piezoelectric Microelectromechanical system (MEMS) cantilever pressure sensor was designed, modeled, fabricated, and tested for sensing the photoacoustic response of gases to terahertz (THz) radiation. The sensing layers were comprised of three thin films; a lead zirconate titanate (PZT) piezoelectric layer sandwiched between two metal contact layers. The sensor materials were deposited on the silicon device layer of a silicon-on-insulator (SOI) wafer, which formed the physical structure of the cantilever. To release the cantilever, a hole was etched through the backside of the wafer and the buried oxide was removed with hydrofluoric acid. Devices were then tested in a custom …

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Di-Electron Spectrum At Mid-Rapidity In P+P Collisions At √S=200 Gev, L. Adamczyk, S. Bueltmann, I. Koralt, D. Plyku, Y. Zoulkarneeva, Star Collaboration Jan 2012

Di-Electron Spectrum At Mid-Rapidity In P+P Collisions At √S=200 Gev, L. Adamczyk, S. Bueltmann, I. Koralt, D. Plyku, Y. Zoulkarneeva, Star Collaboration

Physics Faculty Publications

We report on the mid-rapidity mass spectrum of di-electrons and cross sections of pseudoscalar and vector mesons via e+e- decays, from √s = 200 GeV p + p collisions, measured by the large-acceptance experiment STAR at the Relativistic Heavy Ion Collider. The ratio of the di-electron continuum to the combinatorial background is larger than 10% over the entire mass range. Simulations of di-electrons from light-meson decays and heavy-flavor decays (charmonium and open charm correlation) are found to describe the data. The extracted ω → e+e- invariant yields are consistent with previous measurements. The mid-rapidity …

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System Size And Energy Dependence Of Near-Side Dihadron Correlations, G. Agakishiev, M. M. Aggarwal, Z. Ahammed, A. V. Alakhverdyants, I. Alekseev, J. Alford, B. D. Anderson, C. D. Anson, S. Bueltmann, I. Koralt, D. Plyku Jan 2012

System Size And Energy Dependence Of Near-Side Dihadron Correlations, G. Agakishiev, M. M. Aggarwal, Z. Ahammed, A. V. Alakhverdyants, I. Alekseev, J. Alford, B. D. Anderson, C. D. Anson, S. Bueltmann, I. Koralt, D. Plyku

Physics Faculty Publications

Two-particle azimuthal (Δφ) and pseudorapidity (Δη) correlations using a trigger particle with large transverse momentum (PT)in d+Au, Cu+Cu, and Au+Au collisions at √ sNN = 62.4 GeV and 200 GeV from the STAR experiment at the Relativistic Heavy Ion Collider are presented. The near-side correlation is separated into a jet-like component, narrow in both Δφ and Δη, and the ridge, narrow in Δφ but broad in Δη. Both components are studied as a function of collision centrality, and the jet-like correlation is studied as a function of the trigger and associated PT. The behavior of the …

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Superconducting Spoke Cavities For Electron And High-Velocity Proton Linacs, J. R. Delayen Jan 2012

Superconducting Spoke Cavities For Electron And High-Velocity Proton Linacs, J. R. Delayen

Physics Faculty Publications

Spoke resonantors are currently under development for many proton machines but these structures are also considered for high beta electron linacs as well. These structures compare well to traditional elliptical cavities.

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Measurement Of Exclusive Πº Electroproduction Structure Functions And Their Relationship To Transverse Generalized Parton Distributions, Clas Collaboration, K. P. Adhikari, M. J. Amaryan, R. P. Bennett, S. Koirala, S. E. Kuhn, M. Mayer, L. B. Weinstein, I. Bedlinsky, V. Kubarovsky Jan 2012

Measurement Of Exclusive Πº Electroproduction Structure Functions And Their Relationship To Transverse Generalized Parton Distributions, Clas Collaboration, K. P. Adhikari, M. J. Amaryan, R. P. Bennett, S. Koirala, S. E. Kuhn, M. Mayer, L. B. Weinstein, I. Bedlinsky, V. Kubarovsky

Physics Faculty Publications

Exclusive π0 electroproduction at a beam energy of 5.75 GeV has been measured with the Jefferson Lab CLAS spectrometer. Differential cross sections were measured at more than 1800 kinematic values in Q2, xB , t , and ϕπ , in the Q2 range from 1.0 to 4.6  GeV2 , −t up to 2  GeV2 , and xB from 0.1 to 0.58. Structure functions σT+ϵσL , σTT , and σLT were extracted as functions of t for each of 17 combinations of Q2 and xB . …

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Development Of Superconducting 500 Mhz Multi-Spoke Cavity For Electron Linacs, Dmitry Gorelov, Charles H. Boulware, Terry Grimm, Jean R. Delayen, C. S. Hopper, R. G. Olgave, Subashini U. De Silva Jan 2012

Development Of Superconducting 500 Mhz Multi-Spoke Cavity For Electron Linacs, Dmitry Gorelov, Charles H. Boulware, Terry Grimm, Jean R. Delayen, C. S. Hopper, R. G. Olgave, Subashini U. De Silva

Physics Faculty Publications

Multi-spoke cavities are well-known options for acceleration of heavy and light ions. A recently developed multi-spoke cavity for β=1 presents an attractive opportunity to use this cavity type for electron accelerators. One of the main attractive features of this cavity type is its compactness for relatively low frequency. A simplified design at 500 MHz allowed building of a multi-spoke cavity and cryomodule in a 2-year time frame with confidence and development of effective manufacturing techniques. It also constitutes an important step in proving the usefulness of this kind of cavity design for new applications in the electron machines. Niowave is …

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High Power Test Of Rf Separator For 12 Gev Upgrade Of Cebaf At Jefferson Lab, S. Ahmed, M. Wissmann, J. Mammosser, M. Spata, C. Hovater, Geoffrey A. Krafft, Jean R. Delayen Jan 2012

High Power Test Of Rf Separator For 12 Gev Upgrade Of Cebaf At Jefferson Lab, S. Ahmed, M. Wissmann, J. Mammosser, M. Spata, C. Hovater, Geoffrey A. Krafft, Jean R. Delayen

Physics Faculty Publications

CEBAF at JLab is in the process of an energy upgrade from 6 GeV to 12 GeV. The existing setup of the RF separator cavities in the 5th pass will not be adequate enough to extract the highest energy (11 GeV) beam to any two existing halls (A, B or C) while simultaneously delivering to the new hall D in the case of the proposed 12 GeV upgrade of the machine. To restore this capability, several options including the extension of existing normal conducting (NC) and a potential 499 MHz TEM-type superconducting (SC) cavity design have been investigated using computer …

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Meic Design Progress, S. Ahmed, Y. Zhang, Y.S. Derbenev, D. Douglas, R. Ent, A. Hutton, A. Kimber, G.A. Krafft, R. Li, F. Lin, V. S. Morozov, P. Nadel-Turonski, E. W. Nissen, R. Rimmer, F.C. Pilat, T. Satogata, C. Tennant, Balsa Terzić, H. Wang, S. Wang, B. C. Yunn, D. P. Barber, Y. Filatov, C. Hyde, A. M. Kondratenko, S. L. Manikonda, P. N. Ostroumov, M. K. Sullivan Jan 2012

Meic Design Progress, S. Ahmed, Y. Zhang, Y.S. Derbenev, D. Douglas, R. Ent, A. Hutton, A. Kimber, G.A. Krafft, R. Li, F. Lin, V. S. Morozov, P. Nadel-Turonski, E. W. Nissen, R. Rimmer, F.C. Pilat, T. Satogata, C. Tennant, Balsa Terzić, H. Wang, S. Wang, B. C. Yunn, D. P. Barber, Y. Filatov, C. Hyde, A. M. Kondratenko, S. L. Manikonda, P. N. Ostroumov, M. K. Sullivan

Physics Faculty Publications

This paper will report the recent progress in the conceptual design of MEIC, a high luminosity medium energy polarized ring-ring electron-ion collider at Jefferson lab. The topics and achievements that will be covered are design of the ion large booster and the ERL-circulator-ring-based electron cooling facility, optimization of chromatic corrections and dynamic aperture studies, schemes and tracking simulations of lepton and ion polarization in the figure-8 collider ring, and the beam-beam and electron cooling simulations. A proposal of a test facility for the MEIC electron cooler will also be discussed.

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Stable Highly Conductive Zno Via Reduction Of Zn Vacancies, David C. Look, Timothy C. Droubay, Scott A. Chambers Jan 2012

Stable Highly Conductive Zno Via Reduction Of Zn Vacancies, David C. Look, Timothy C. Droubay, Scott A. Chambers

Physics Faculty Publications

Growth of Ga-doped ZnO by pulsed laser deposition at 200 °C in an ambient of Ar and H2produces a resistivity of 1.5 × 10−4 Ω-cm, stable to 500 °C. The resistivity can be further reduced to 1.2 × 10−4 Ω-cm by annealing on Zn foil, which reduces the compensating Zn-vacancy acceptor concentration NA to 5 × 1019 cm−3, only 3% of the Ga-donor concentration ND of 1.6 × 1021 cm−3, with ND and NA determined from a degenerate mobility theory. The plasmon-resonance wavelength is only 1060 …

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Structural, Magnetic, And Electron Transport Properties Of Mnbi:Fe Thin Films, Parashu Kharel, X. Z. Li, V. R. Shah, N. Al-Aqtash, K. Tarawneh, Renat F. Sabirianov, R. Skomski, D. J. Sellmyer Jan 2012

Structural, Magnetic, And Electron Transport Properties Of Mnbi:Fe Thin Films, Parashu Kharel, X. Z. Li, V. R. Shah, N. Al-Aqtash, K. Tarawneh, Renat F. Sabirianov, R. Skomski, D. J. Sellmyer

Physics Faculty Publications

The structural, magnetic, and electron transport properties ofMn55=xFexBi45 (x¼0, 2, 4, 5, 8, 11, 13, 16) films prepared by multilayer deposition and annealing using e-beam evaporation have been investigated. Fe doping has produced a significant change in the magnetic properties of the samples including the decrease in saturation magnetization and magnetocrystalline anisotropy and increase in coercivity. Although the magnetization shows a smooth decrease with increasing Fe concentration, the coercivity jumps abruptly from 8.5 kOe to 22 kOe as Fe content changes from 4% to 5%, but the change in coercivity is small as the concentration goes beyond 5%. The temperature …

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A Shell Model Study Of The High Spin States Of 88Y, M. Bunce, P. H. Regan, V. Werner, A. Anagnostatou, C. W. Beausang, M. Bowry, R. J. Casperson, D. Chen, N. Cooper, P. Goddard, R. O. Hughes, G. Ilie, P.J.R. Mason, B. Pauerstein, M. W. Reed Jan 2012

A Shell Model Study Of The High Spin States Of 88Y, M. Bunce, P. H. Regan, V. Werner, A. Anagnostatou, C. W. Beausang, M. Bowry, R. J. Casperson, D. Chen, N. Cooper, P. Goddard, R. O. Hughes, G. Ilie, P.J.R. Mason, B. Pauerstein, M. W. Reed

Physics Faculty Publications

Experiments were carried out at the Wright Nuclear Structure Laboratory at Yale University using the 21MV ESTU Tandem Van de Graaff accelerator with the purpose of studying 88Y. A beam of 18O impinged at laboratory energies of 60, 65 and 70 MeV on a 600 μg/cm 2 74Ge target with a thick (10mg/cm 2) 197Au backing. This experiment was performed with the specific aim of accessing medium spin states of the nucleus of interest. A second experiment was undertaken to populate the nucleus of interest in higher spin states by impinging the same 18 …

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Beam Dynamics Studies For Transverse Electromagnetic Mode Type Rf Deflectors, Shahid Ahmed, Geoffrey A. Krafft, Kirsten Deitrick, Subashini U. De Silva, Jean R. Delayen, Mike Spata, Michael Tiefenback, Alicia Hofler, Kevin Beard Jan 2012

Beam Dynamics Studies For Transverse Electromagnetic Mode Type Rf Deflectors, Shahid Ahmed, Geoffrey A. Krafft, Kirsten Deitrick, Subashini U. De Silva, Jean R. Delayen, Mike Spata, Michael Tiefenback, Alicia Hofler, Kevin Beard

Physics Faculty Publications

We have performed three-dimensional simulations of beam dynamics for transverse electromagnetic mode (TEM) type rf deflectors: normal and superconducting. The compact size of these cavities as compared to the conventional TM110 type structures is more attractive particularly at low frequency. Highly concentrated electromagnetic fields between the parallel bars provide strong electrical stability to the beam for any mechanical disturbance. An array of six 2-cell normal conducting cavities or a single cell superconducting structure is enough to produce the required vertical displacement at the target point. Both the normal and superconducting structures show very small emittance dilution due to the …

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