Physics Commons^™

Domain Size And Structure In Exchange Coupled [Co/Pt]/Nio/[Co/Pt] Multilayers, Andrew G. Baruth, Shireen Adenwalla

Shireen Adenwalla Papers

We investigate the competing effects of interlayer exchange coupling and magnetostatic coupling in the magnetic heterostructure ([Co/Pt]/NiO/[Co/Pt]) with perpendicular magnetic anisotropy (PMA). This particular heterostructure is unique among coupled materials with PMA in directly exhibiting both ferromagnetic and antiferromagnetic coupling, oscillating between the two as a function of spacer layer thickness. By systematically tuning the coupling interactions via a wedge-shaped NiO spacer layer, we explore the energetics that dictate magnetic domain formation using high resolution magnetic force microscopy coupled with the magneto-optical Kerr effect. This technique probes the microscopic and macroscopic magnetic behavior as a continuous function of thickness and …

Assessing Laser Lifetime Test Performance, Joe Weichman, Hamid Hemmati, Malcolm Wright

STAR Program Research Presentations

Assessing expected component lifetime is necessary in developing instruments for future space-flight projects to ensure long term operation in the challenging environment. Although semiconductor diode lasers have widespread use in terrestrial applications, their use in space is still an emerging technology that requires on-going testing to demonstrate their capability. The project called for re-establishing the test setup for assessing lifetime performance of 20 continuously running 200mW 830 nm diode lasers. These lasers underwent previous testing based on parameters for NuSTAR’s laser metrology system, and met the six month lifetime project requirements under nominal operating conditions. Laser testing is currently underway …

Variable Renewable Energy In Modeling Climate Change Mitigation Scenarios, Falko Ueckerdt, Robert J. Brecha, Gunnar Luderer, Patrick Sullivan, Eva Schmid, Nico Bauer, Diana Böttger

Physics Faculty Publications

This paper addresses the issue of how to account for short‐term temporal variability of renewable energy sources and power demand in long‐term climate change mitigation scenarios in energy‐economic models. An approach that captures in a stylized way the major challenges to the integration of variable renewable energy sources into power systems has been developed. As a first application this approach has been introduced to REMIND‐D, a hybrid energy‐economy model of Germany. An approximation of the residual load duration curve is implemented. The approximating function endogenously changes depending on the penetration and mix of variable renewable power. The approach can thus …

Quantifying Multiple Types Of Damping Acting On Bronze-Wound Guitar Strings, Jonathan Christian

Purdue Polytechnic Masters Theses

The goal of this study was to quantify the contributions of multiple damping types acting on guitar strings for each mode over a wide frequency range so that design variables could be identified to one day create frequency based damping in guitar strings. Structural dynamic testing was used to obtain the time-response of a vibrating string in open air and in a vacuum. From this signal, each harmonic was filtered and the decay envelope was curve-fitted with a function that was a linear summation of decay functions. From the curve-fits, the damping coefficients for aerodynamic, friction, and material damping were …

Logistic Curves, Extraction Costs And The Effective Size Of Oil Resources, Robert J. Brecha

Physics Faculty Publications

The size of potential fossil fuel resources is an issue of perennial interest and controversy. Fundamentally, there appears to be a conflict in interpretation of available data for both past and future extraction histories. As fossil-fuel prices rose dramatically over the past several years, the question of resources once again became acute. In this paper we concentrate on conventional and non-conventional oil resources and make four main points, with the overarching theme that one can determine an effective oil resource that represents significantly less availability for consumption than usually posited by tallying resources in place.

First, looking at oil production …

Prioritizing Investment In Residential Energy Efficiency And Renewable Energy: A Case Study For The U.S. Midwest, Robert J. Brecha, Austin Mitchell, Kevin P. Hallinan, J. Kelly Kissock

Physics Faculty Publications

Residential building energy use is an important contributor to greenhouse gas emissions and in the United States represents about 20% of total energy consumption. A number of previous macro-scale studies of residential energy consumption and energy-efficiency improvements are mainly concerned with national or international aggregate potential savings. In this paper we look into the details of how a collection of specific homes in one region might reduce energy consumption and carbon emissions, with particular attention given to some practical limits to what can be achieved by upgrading the existing residential building stock. Using a simple model of residential, single-family home …

Analysis Of Interband, Intraband, And Plasmon Polariton Transitions In Silver Nanoparticle Films Via In Situ Real-Time Spectroscopic Ellipsometry, S. A. Little, R. W. Collins, S. Marsillac

Electrical & Computer Engineering Faculty Publications

The dielectric function of Ag nanoparticle films, deduced from an analysis of in situ real-time spectroscopic ellipsometry (RTSE) measurements, is found to evolve with time during deposition in close consistency with the film structure, deduced in the same RTSE analysis. In the nucleation regime, the intraband dielectric function component is absent and plasmon polariton behavior dominates. Only at nuclei contact, does the intraband amplitude appear, increasing above zero. Both intraband and plasmon amplitudes coexist during surface smoothening associated with coalescence. The intraband relaxation time increases rapidly after surface smoothening is complete, also in consistency with the thin film structural evolution.

Magnetism Of Cluster-Deposited Y–Co Nanoparticles, Balamuruga Balamurugan, Ralph Skomski, Xingzhong Li, V. R. Shah, George C. Hadjipanayis, Jeffrey E. Shield, David J. Sellmyer

Nebraska Center for Materials and Nanoscience: Faculty Publications

Nanoparticles of YCo₂, YCo_3, and YCo₅ are produced by cluster-deposition and investigated both structurally and magnetically. The nanoparticles have sizes of less than 10 nm and are superparamagnetic at 300 K, irrespective of stoichiometry. As-produced nanoparticles exhibit disordered structures with magnetic properties differing from those of the bulk particles. The temperature-dependent magnetization curves of the nanoparticles reveal blocking temperatures from 110 to 250 K, depending on stoichiometry. The magnetic anisotropy constant K₁ of disordered YCo₅ nanoparticles of 7.8 nm in size is 3.5×10⁶ergs/cm³, higher than those of the disordered YCo …

Structure And Magnetism Of Mnau Nanoclusters, X. Wei, Damien Le Roy, Ralph Skomski, Xingzhong Li, Zhiguang Sun, Jeffrey E. Shield, M. J. Kramer, David J. Sellmyer

Nebraska Center for Materials and Nanoscience: Faculty Publications

Equiatomic MnAu clusters with average sizes of 4 and 10 nm are produced by inert-gas condensation. As-produced clusters are used to form both dense cluster films and films with clusters embedded in a W matrix with a cluster volume fraction of 25%. Both structure and magnetism are size-dependent. Structural analysis of the 10 nm clusters indicate a distorted tetragonal body-centered cubic structure with lattice parameters a=0.315 and c=0.329 nm. The 4 nm clusters have a partially ordered tetragonal L10 structure with lattice parameters a=0.410 nm and c=0.395 nm. Magnetic properties of the clusters show evidence at …

Establishing Building Recommissioning Priorities And Potential Energy Savings From Utility Energy Data, Kevin P. Hallinan, Philip Brodrick, Jessica Northridge, J. Kelly Kissock, Robert J. Brecha

Physics Faculty Publications

An energy reduction program for commercial buildings is implemented for a SW Ohio natural gas utility. The aim of this study is to demonstrate that historical utility data for individual building customers, along with knowledge of pertinent building information (square footage, year built, number of floors, height of floors, wall construction type, and use type) available in county auditor databases, could be used to identify the best candidate buildings for recommissioning in terms of energy savings and simple payback. A study is completed for all natural gas customers of a utility in Montgomery and Clinton counties in Ohio. A total …

Metastability Of Free Cobalt And Iron Clusters: A Possible Precursor To Bulk Ferromagnetism, Xiaoshan Xu, Shuangye Yin, Ramiro Moro, Anthony Liang, John Bowlan, Walt A. De Heer

Xiaoshan Xu Papers

Homonuclear cobalt and iron clusters Co_N and Fe_N measured in a cryogenic molecular beam exist in two states with distinct magnetic moments (μ), polarizabilities, and ionization potentials, indicating distinct valences. The μ is approximately quantized: μ_N ~ 2Nμ_B in the ground states and μ_N* ~ Nμ_B in the excited states for Co; μ_N ~ 3N μ_B and μ_N * ~ Nμ_B for Fe. At a large size, the average μ of the two states converges to the bulk value with diminishing ionization potential differences. …

Modeling And Tuning Of Musical Percussive Beams, Eric Laukkanen

Summer Research

Standard vibraphone bars consist of aluminum beams which are traditionally tuned with an arched undercut, for the purpose of aligning the musical overtones harmonically. The acoustical effect of various progressions of undercuts on aluminum bars was studied using both an aluminum bar and a finite element computer model. The spectral signature of the aluminum bar was examined with a spectrum analyzer, and the corresponding eigenmodes were imaged with an electronic speckle pattern interferometer. These methods were used to analyze the changes in natural frequencies of the bar as matter was removed from various locations. Additionally, the aural character of each …

Targeting Residential Energy Reduction For City Utilities Using Historical Electrical Utility Data And Readily Available Building Data, Kevin P. Hallinan, J. Kelly Kissock, Robert J. Brecha, Austin Mitchell

Physics Faculty Publications

Energy use data for the eight-year period 2003–2010 was analyzed for over 1200 single family residences in Village of Yellow Springs, Ohio. Electricity, natural gas, residential building, and weather databases are merged to permit determination of the energy intensity of each home in the village. The energy use intensity for each home is disaggregated into weather independent and weather dependent electric and natural gas use. This use is compared to typical baseline, cooling, and heating energy use for the region. From this comparison, priority homes are identified for energy reduction investment. Collective potential low cost energy reduction is estimated for …

Colossal Negative Magnetoresistance In Dilute Fluorinated Graphene, X. Hong, S. -H. Cheng, C. Herding, J. Zhu

Xia Hong Publications

Adatoms offer an effective route to modify and engineer the properties of graphene. In this work, we create dilute fluorinated graphene using a clean, controlled, and reversible approach. At low carrier densities, the system is strongly localized and exhibits an unexpected, colossal negative magnetoresistance. The zero-field resistance is reduced by a factor of 40 at the highest field of 9 T and shows no sign of saturation. Unusual staircaselike field dependence is observed below 5 K. The magnetoresistance is highly anisotropic. These observations cannot be explained by existing theories, but likely require adatom-induced magnetism and/or a metal-insulator transition driven by …

Resonant Photoemission Of Rare Earth Doped Gan Thin Films, S. R. Mchale, J. W. Mcclory, J. C. Petrosky, J. Wu, R. Palai, Yaroslav B. Losovyj, Peter A. Dowben

Peter Dowben Publications

The 4d → 4f Fano resonances for various rare earth doped GaN thin films (RE = Gd, Er, Yb) were investigated using synchrotron photoemission spectroscopy. The resonant photoemission Fano profiles show that the major Gd and Er rare earth 4f weight is at about 5–6 eV below the valence band maximum, similar to the 4f weights in the valence band of many other rare earth doped semiconductors. For Yb, there is very little resonant enhancement of the valence band of Yb doped GaN, consistent with a largely 4f¹⁴ occupancy.

Schottky Barrier Formation At The Au To Rare Earth Doped Gan Thin Film Interface, S. R. Mchale, J. W. Mcclory, J. C. Petrosky, J. Wu, R. Palai, Yaroslav B. Losovyj, Peter A. Dowben

Peter Dowben Publications

The Schottky barriers formed at the interface between gold and various rare earth doped GaN thin films (RE = Yb, Er, Gd) were investigated in situ using synchrotron photoemission spectroscopy. The resultant Schottky barrier heights were measured as 1.68 ± 0.1 eV (Yb:GaN), 1.64 ± 0.1 eV (Er:GaN), and 1.33 ± 0.1 eV (Gd:GaN). We find compelling evidence that thin layers of gold do not wet and uniformly cover the GaN surface, even with rare earth doping of the GaN. Furthermore, the trend of the Schottky barrier heights follows the trend of the rare earth metal work function.

Mesoscale Flux-Closure Domain Formation In Single-Crystal Batio3, R. G.P. Mcquaid, L. J. Mcgilly, Pankaj Sharma, Alexei Gruverman, J. M. Gregg

Alexei Gruverman Publications

Over 60 years ago, Charles Kittel predicted that quadrant domains should spontaneously form in small ferromagnetic platelets. He expected that the direction of magnetization within each quadrant should lie parallel to the platelet surface, minimizing demagnetizing fields, and that magnetic moments should be configured into an overall closed loop, or flux-closure arrangement. Although now a ubiquitous observation in ferromagnets, obvious flux-closure patterns have been somewhat elusive in ferroelectric materials. This is despite the analogous behaviour between these two ferroic subgroups and the recent prediction of dipole closure states by atomistic simulations research. Here we show Piezoresponse Force Microscopy images of …

Analysis Of Hom Properties Of Superconducting Parallel-Bar Deflecting/Crabbing Cavities, Subashini De Silva, Jean R. Delayen

Physics Faculty Publications

The superconducting parallel-bar cavity is currently being considered for a number of deflecting and crabbing applications due to improved properties and compact design geometries. The 499 MHz deflecting cavity proposed for the Jefferson Lab 12 GeV upgrade and the 400 MHz crab cavity for the proposed LHC luminosity upgrade are two of the major applications. For high current applications the higher order modes must be damped to acceptable levels to eliminate any beam instabilities. The frequencies and R/Q of the HOMs and mode separation are evaluated and compared for different parallel-bar cavity designs.

Crab Crossing Schemes And Studies For Electron Ion Collider, S. Ahmed, Y. Derbenev, V. Morozov, A. Castilla, Geoffrey A. Krafft, B. Yunn, Subashini U. De Silva, Jean R. Delayen

Physics Faculty Publications

This report shows our progress in crab crossing consideration for future electron-ion collider envisioned at JLab. In this design phase, we are evaluating two crabbing schemes viz., the deflecting and dispersive. The mathematical formulations and lattice design for these schemes are discussed in this paper. Numerical simulations involving particle tracking through a realistic deflecting RF cavity and optics illustrate the desired crab tilt of 25 mrad for 1.35 MV. Evolution of beam propagation are shown which provides the physical insight of the crabbing phenomenon.

Design Of Superconducting Spoke Cavities For High-Velocity Applications, Jean R. Delayen, Subashini De Silva, C. S. Hopper

Physics Faculty Publications

Superconducting single- and multi-spoke cavities have been designed to-date for particle velocities from β₀ ~ 0.15 to β₀ ~ 0.65. Superconducting spoke cavities may also be of interest for higher-velocity, low-frequency applications, either for hadrons or electrons. We present the design of spoke cavities optimized for β₀ = 0.8 and β₀ = 1.

Design Of Superconducting Parallel Bar Cavities For Deflecting/Crabbing Applications, Jean R. Delayen, Subashini De Silva

Physics Faculty Publications

The superconducting parallel-bar cavity is a deflecting/ crabbing cavity with attractive properties, compared to other conventional designs, that is currently being considered for a number of applications. The new parallel-bar design with curved loading elements and circular or elliptical outer conductors have improved properties compared to the designs with rectangular outer conductors. We present the designs proposed as the deflecting cavities for the Jefferson Lab 12 GeV upgrade and for Project-X and crabbing cavities for the proposed LHC luminosity upgrade and electron-ion collider at Jefferson Lab.

Beam Dynamics Studies Of Parallel-Bar Deflecting Cavities, S. Ahmed, G. A. Krafft, K. Deitrick, Subashini U. De Silva, Jean R. Delayen, M. Spata, M. Tiefenback, A. Hofler, K. Beard

Physics Faculty Publications

We have performed three-dimensional simulations of beam dynamics for parallel-bar transverse electromagnetic mode (TEM) type RF separators: normal- and superconducting. The compact size of these cavities as compared to 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 eight 2-cell normal conducting cavities or a one- or two-cell superconducting structure are enough to produce the required vertical displacement at the Lambertson magnet. Both the normal and superconducting structures show very small emittance dilution due to the …

Fundamental And Hom Coupler Design Of The Superconducting Parallel-Bar Cavities, Subashini De Silva, Jean R. Delayen

Physics Faculty Publications

The superconducting parallel-bar cavity [1] is currently being considered as a deflecting system for the Jefferson Lab 12 GeV upgrade and as a crabbing cavity for a possible LHC luminosity upgrade. Currently the designs are optimized to achieve lower surface fields within the dimensional constraints for the above applications. A detailed analysis of the fundamental input power coupler design for the parallel-bar cavity is performed considering beam loading and the effects of microphonics. For higher beam loading the damping of the HOMs is vital to reduce beam instabilities generated due to the wake fields. An analysis of threshold impedances for …

Multipacting Analysis Of The Superconducting Parallel-Bar Cavity, Subashini De Silva, Jean R. Delayen

Physics Faculty Publications

The superconducting parallel-bar cavity [1] is a deflecting/crabbing cavity with attractive properties, compared to other conventional designs, that is being considered for a number of applications. Multipacting can be a limiting factor to the performance of in any superconducting structure. In the parallel-bar cavity the main contribution to the deflection is due to the transverse deflecting voltage, between the parallel bars, making the design potentially prone to multipacting. This paper presents the results of analytical calculations and numerical simulations of multipacting in the parallel-bar cavity with resonant voltage, impact energies and corresponding particle trajectories.

Mechanical Study Of Superconducting Parallel-Bar Deflecting/Crabbing Cavities, Hyekyoung Park, Jean R. Delayen, Subashini De Silva

Physics Faculty Publications

The superconducting parallel-bar deflecting/crabbing cavities have improved properties compared to conventional cavity structures. It is currently being considered for number of applications. The mechanical design analysis is performed on two designs of the 499 MHz parallel-bar deflecting cavity for the Jefferson Lab 12 GeV upgrade. The main purpose of the mechanical study is to examine the structural stability of the cavities under the operating conditions in the accelerators. The study results will suggest the need for additional structural strengthening. Also the study results will help to develop a concept of the tuning method. If the cavity is to be installed …

Design Of Low-Frequency Superconducting Spoke Cavities For High-Velocity Applications, Jean R. Delayen, C. S. Hopper, R. G. Olave

Physics Faculty Publications

Superconducting single- and multi-spoke cavities have been designed to-date for particle velocities from β~0.15 to β~0.65. Superconducting spoke cavities may also be of interest for higher-velocity, low-frequency applications, either for hadrons or electrons. We present the design of 325 and 352 MHz spoke cavities optimized for β=0.8 and β=1.

Design Of Superconducting Multi-Spoke Cavities For High Velocity Applications, C. S. Hopper, Jean R. Delayen

Physics Faculty Publications

Superconducting spoke cavities have been designed and tested for particle velocities up to β₀ ~ 0.6 and are currently being designed for velocities up to β₀ = 1. We present the electromagnetic designs for two-spoke cavities operating at 325 MHz for β₀ = 0.82 and β₀ = 1.

Higher Order Mode Properties Of Superconducting Two-Spoke Cavities, C. S. Hopper, Jean R. Delayen, R. G. Olave

Physics Faculty Publications

Multi-Spoke cavities lack the cylindrical symmetry that many other cavity types have, which leads to a more complex Higher Order Mode (HOM) spectrum. In addition, spoke cavities offer a large velocity acceptance which means we must perform a detailed analysis of the particle velocity dependence for each mode's R/Q. We present here a study of the HOM properties of two-spoke cavities designed for high-velocity applications. Frequencies, R/Q and field profiles of HOMs have been calculated and are reported.

Conceptual Design Of A Polarized Medium Energy Electron-Ion Collider At Jlab, S. Ahmed, A. Bogacz, Ya. Derbenev, A. Hutton, Geoffrey Krafft, R. Li, V. Morozov, F. Pilat, R. Rimmer, Y. Roblin, T. Satogata, M. Spata, B. Terzić, M. Tiefenback, H. Wang, B. Yunn, Y. Zhang, P. Chetsov, Jean R. Delayen, Subashini Desilva, Hisham Sayed, V. Dudnikov, R. Johnson, F. Marhauser, M. Sullivan, S. Manikonda, P. N. Ostroumov, S. Abeyratne, B. Erdelyi, Y. Kim, A. Kondratenko

Physics Faculty Publications

A medium energy electron-ion collider is envisioned as the primary future of the JLab nuclear science program beyond the 12 GeV upgraded CEBAF. The present conceptual design selects a ring-ring collider option, covers a CM energy range up to 65 GeV for collisions of polarized electrons with polarized light ions or unpolarized light to heavy ions, and reaches a luminosity at above 10³⁴ cm^-2s^-1 per detector over multiple interaction points. This paper presents a brief description of the current conceptual design of the accelerator.

Optical Cell For Combinatorial In Situ Raman Spectroscopic Measurements Of Hydrogen Storage Materials At High Pressures And Temperatures, Jason R. Hattrick-Simpers, Wilbur S. Hurst, Sesha S. Srinivasan, James E. Maslar

Faculty Publications

An optical cell is described for high-throughput backscattering Raman spectroscopic measurements of hydrogen storagematerials at pressures up to 10 MPa and temperatures up to 823 K. High throughput is obtained by employing a 60 mm diameter × 9 mm thick sapphire window, with a corresponding 50 mm diameter unobstructed optical aperture. To reproducibly seal this relatively large window to the cell body at elevated temperatures and pressures, a gold o-ring is employed. The sample holder-to-window distance is adjustable, making this cell design compatible with optical measurement systems incorporating lenses of significantly different focal lengths, e.g., microscope objectives and single element …