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At least 1,567 records · Page 87

Exotic Uses of Neutrons an X-rays as Probes for Chiral Magnets (Early Career Award) (Final Report)

This is the final report for Exotic Uses of Neutrons an X-rays as Probes for Chiral Magnets, an Early Career award to Prof. Dustin Gilbert, University of Tennessee, running 09/01/2020 - 08/31/2025. This project used neutron scattering as a unique tool to investigate magnetic chiral structures. Neutron scattering is a powerful technique in which the neutron wavepacket scatters from nuclear or magnetic structures, providing insight into the structure of a material and its magnetic features. In this work, we focused on chiral magnetic structures. Most magnetic materials are colinear ferro- or antiferromagnets, where the spin moments align parallel or anti-parallel with their neighbors. In some materials, the magnetic moments instead curl and can form closed loops. These structures, with the additional feature that the core and perimeter are oriented in opposite out-of-plane directions, exhibit a property called topology; these structures are known as skyrmions. Topology is a broadly used term, but here it refers to a magnetic configuration that cannot be created or destroyed through any continuous transformation. For these looped structures, the closed loop cannot be destroyed continuously, giving rise to unique properties such as collective dynamics and particle-like behavior. This also raises fundamental questions about how such structures form and evolve.

36 MATERIALS SCIENCE↗

The Magnetized Indirect Drive Project on the National Ignition Facility

A new project is underway at the National Ignition Facility with the goal of applying a seed magnetic field to the fusion fuel in an indirect drive hohlraum implosion and quantifying the effect on the hot-spot temperature, shape and neutron yield. Magnetizing fusion fuel is calculated to reduce heat loss from the implosion core by constraining the motion of electrons and fusion-generated alpha particles; this can improve the chances of achieving high-gain fusion in a laboratory plasma. Here, we describe the goals of this project and the significant scientific and technological challenges which must be overcome for this project to succeed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

OUTFLOWS AND DARK BANDS AT ARCADE-LIKE ACTIVE REGION CORE BOUNDARIES

Observations from the EUV Imaging Spectrometer (EIS) on board Hinode have revealed outflows and non-thermal line broadening in low intensity regions at the edges of active regions (ARs). We use data from Hinode's EIS, Solar Dynamic Observatory's Atmospheric Imaging Assembly and Helioseismic and Magnetic Imager, and the Transition Region and Coronal Explorer instrument to investigate the boundaries of arcade-like AR cores for NOAA ARs 11112, 10978, and 9077. A narrow, low intensity region that is observed at the core's periphery as a dark band shows outflows and increased spectral line broadening. This dark band is found to exist for days and appears between the bright coronal loop structures of different coronal topologies. We find a case where the dark band region is formed between the magnetic field from emerging flux and the field of the pre-existing flux. A magnetic field extrapolation indicates that this dark band is coincident with the spine lines or magnetic separatrices in the extrapolated field. This occurs over unipolar regions where the brightened coronal field is separated in connectivity and topology. This separation does not appear to be infinitesimal and an initial estimate of the minimum distance of separation is found to be Almost-Equal-To 1.5-3.5 Mm.

79 ASTRONOMY AND ASTROPHYSICS↗

Origin of the Sheared Magnetic Fields that Erupt in Flares and Coronal Mass Ejections

From a search of the Yohkoh/SXT whole-Sun movie in the years 2000 and 2001, we found 37 flare-arcade events for which there were full-disk magnetograms from SOHO/MDI, coronagraph movies from SOHO/LASCO, and before and after full-disk chromospheric images from SOHOBIT and/or from ground-based observatories. For each event, the observations show or strongly imply that the flare arcade was produced in the usual way by the eruption of sheared core field (as a flux rope) from along the neutral line inside a mature bipolar magnetic arcade. Two-thirds (25) of these arcades had the normal leading-trailing magnetic polarity arrangement of the active regions in the hemisphere of the arcade, but the other third (12) had reversed polarity, their leading flux being the trailing-polarity remnant of one or more old active regions and their trailing flux being the leading-polarity remnant of one or more other old active regions. From these observations, we conclude: (1) The sheared core field in a reversed-polarity arcade must be formed by processes in and above the photosphere, not by the emergence of a twisted flux rope bodily from below the photosphere. (2) The sheared core fields in the normal-polarity arcades were basically the same as those in the reversed-polarity arcades: both showed similar sigmoidal form and produced similar explosions (similar flares and CMEs). (3) Hence, the sheared core fields in normal-polarity mature arcades are likely formed mainly by the same processes as in reversed-polarity arcades. (4) These processes should be discernible in high-resolution magnetogram sequences and movies of the photosphere, chromosphere, and corona such those to come from Solar-B

Moore, Ronald L.↗

Quasi-Two-Dimensional Antiferromagnetic Spin Fluctuations in the Spin-Triplet Superconductor Candidate CeRh 2 As 2

The tetragonal heavy-fermion superconductor CeRh 2 ⁢As 2 (T c = 0.3 K) exhibits an exceptionally high critical field of 14 T for B ∥ c. It undergoes a field-driven first-order phase transition between superconducting states, potentially transitioning from spin-singlet to spin-triplet superconductivity. To further understand these superconducting states and the role of magnetism, we probe spin fluctuations in CeRh 2 ⁢As 2 using neutron scattering. Here, we find dynamic (π, π) antiferromagnetic (AFM) spin correlations with an anisotropic quasi-two-dimensional correlation volume. Our data place an upper limit of 0.31 μ B on the staggered magnetization of corresponding Néel orders at T = 0.08 K. Density functional theory calculations, treating Ce 4⁢ƒ electrons as core states, show that the AFM wave vector connects significant areas of the Fermi surface. Our findings indicate that the dominant excitations in CeRh 2 ⁢As 2 for ℏω⁢ < 1.2 meV are magnetic and suggest that superconductivity in CeRh 2⁢ As 2 is mediated by AFM spin fluctuations associated with a proximate quantum critical point.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Optical imagery and spectrophotometry of CTB 80

Narrow-band imagery and spectrophotometry of the central region of CTB 80 are presented. The images show weak forbidden O III and ubiquitous filamentary forbidden S II and H-alpha emission from the extended radio lobes in which the core is embedded. The data indicate that the extended component is shock heated. Balmer line-dominated emission is observed around the perimeter of the core. Assuming that the volume of the radio shell is similar to the volume of the thermal shell, it is found that a magnetic field of about 600 microG and a cosmic-ray proton-to-electron ratio of about 200 are required to explain the pressure and synchrotron volume emissivity in the radio shell. It is suggested that the optical emission form the core of CTB 80 arises behind shocks which are being driven into a magnetized thermal plasma by the confined relativistic wind from PSR 1951+32.

Hester, J. Jeff↗

Synthetic observations of wave propagation in a sunspot umbra

Spectropolarimetric temporal series from Fe I λ6301.5 Å and Ca II infrared triplet lines are obtained by applying the Stokes synthesis code NICOLE to a numerical simulation of wave propagation in a sunspot umbra from MANCHA code. The analysis of the phase difference between Doppler velocity and intensity core oscillations of the Fe I λ6301.5 Å line reveals that variations in the intensity are produced by opacity fluctuations rather than intrinsic temperature oscillations, except for frequencies between 5 and 6.5 mHz. On the other hand, the photospheric magnetic field retrieved from the weak field approximation provides the intrinsic magnetic field oscillations associated to wave propagation. Our results suggest that this is due to the low magnetic field gradient of our sunspot model. The Stokes parameters of the chromospheric Ca II infrared triplet lines show striking variations as shock waves travel through the formation height of the lines, including emission self-reversals in the line core and highly abnormal Stokes V profiles. Magnetic field oscillations inferred from the Ca II infrared lines using the weak field approximation appear to be related with the magnetic field strength variation between the photosphere and the chromosphere.

79 ASTRONOMY AND ASTROPHYSICS↗

TWO TIMESCALE DISPERSAL OF MAGNETIZED PROTOPLANETARY DISKS

Protoplanetary disks are likely to be threaded by a weak net flux of vertical magnetic field that is a remnant of the much larger fluxes present in molecular cloud cores. If this flux is approximately conserved its dynamical importance will increase as mass is accreted, initially by stimulating magnetorotational disk turbulence and subsequently by enabling wind angular momentum loss. We use fits to numerical simulations of ambipolar dominated disk turbulence to construct simplified one-dimensional evolution models for weakly magnetized protoplanetary disks. We show that the late onset of significant angular momentum loss in a wind can give rise to ''two timescale'' disk evolution in which a long phase of viscous evolution precedes rapid dispersal as the wind becomes dominant. The wide dispersion in disk lifetimes could therefore be due to varying initial levels of net flux. Magnetohydrodynamic (MHD) wind triggered dispersal differs from photoevaporative dispersal in predicting mass loss from small (<1 AU) scales, where thermal winds are suppressed. Our specific models are based on a limited set of simulations that remain uncertain, but qualitatively similar evolution appears likely if mass is lost from disks more quickly than flux, and if MHD winds become important as the plasma β decreases.

79 ASTRONOMY AND ASTROPHYSICS↗

Progress on HL-LHC Nb 3 Sn Magnets

The high-luminosity Large Hadron Collider (HL-LHC) project aims at allowing to increase the collisions in the LHC by a factor of ten in the decade 2025-2035. One essential element is the superconducting magnet around the interaction region points, where the large aperture magnets will be installed to allow to further reduce the beam size in the interaction point. The core of this upgrade is the Nb 3 Sn triplet, made up of 150-mm aperture quadrupoles in the range of 7-8 m. The project is being shared between the European Organization for Nuclear Research and the US Accelerator Upgrade Program, based on the same design, and on the two strand technologies. The project is ending the short model phase, and entering the prototype construction. We will report on the main results of the short model program, including the quench performance and field quality. A second important element is the 11 T dipole that replaces a standard dipole making space for additional collimators. The magnet is also ending the model development and entering the prototype phase. A critical point in the design of this magnet is the large current density, allowing increase of the field from 8 to 11 T with the same coil cross section as in the LHC dipoles. This is also the first two-in-one Nb 3 Sn magnet developed so far. We will report the main results on the test and the critical aspects.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Magnetic moments of A = 3 nuclei obtained from chiral effective field theory operators

Chiral effective field theory (χEFT) provides a framework for obtaining internucleon interactions in a systematically improvable fashion from first principles, while also providing for the derivation of consistent electroweak current operators. In this study, we apply consistently derived interactions and currents towards calculating the magnetic dipole moments of the A = 3 systems 3 H and 3 He. We focus here on LENPIC interactions obtained using semilocal coordinate-space (SCS) regularization. Starting from the momentum-space representation of the LENPIC χEFT vector current, we derive the SCS-regularized magnetic dipole operator up through next-to-next-to-leading order (N 2 LO). We then carry out no-core shell-model calculations for 3 H and 3 He systems using the SCS LENPIC interaction at N 2 LO in χEFT and evaluate the magnetic dipole moments obtained using the consistently derived one-nucleon and two-nucleon electromagnetic currents. As anticipated by prior results with χEFT currents, the current corrections through N 2 LO provide improved, but not yet complete, agreement with experiment for the 3 H and 3 He magnetic dipole moments.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

Electronic structure of the (Nd{sub 1−x}Dy{sub x}){sub 2}Fe{sub 14}B (0 ≤ x ≤ 1) system studied by X-ray photoelectron spectroscopy

Systematic characterization of electronic structures in the (Nd{sub 1−x}Dy{sub x}){sub 2}Fe{sub 14}B system, especially the 4f behavior, provides an insight to the physical nature of the evolution of magnetic properties. A series of X-ray photoelectron spectroscopy (XPS) core-level and valence-band spectra were used to study the electronic structures. It was found that substitution of Dy for Nd in Nd{sub 2}Fe{sub 14}B results in a nonlinear variation in the evolution of electronic structures. Only the finite coupling between the Nd 4f states and the Fe 3d states is found at both the Nd-rich regime and the Dy-rich regime. When the Dy concentration and the Nd concentration approach to be equal, a strong coupling between the Nd 4f states and the Fe 3d states is found, which results in a bonding state between them. Additionally, the 4f components in the (Nd{sub 1−x}Dy{sub x}){sub 2}Fe{sub 14}B system are ascribed to three parts: 1) the individual contribution of the Dy 4f states, which emerges just after the Dy-substitution; 2) the contribution of the coupling between the Nd 4f states and the Dy 4f states, which arises only when 0.4 ≤ x ≤ 0.6; 3) the associated contributions of the Nd 4f states and the Dy 4f states, where the contribution of the Nd 4f states and that of the Dy 4f states are prominent in the Nd-rich regime and Dy-rich regime, respectively.

36 MATERIALS SCIENCE↗

FEEDBACK EFFECTS ON LOW-MASS STAR FORMATION

Protostellar feedback, both radiation and bipolar outflows, dramatically affects the fragmentation and mass accretion from star-forming cores. We use ORION, an adaptive mesh refinement gravito-radiation-hydrodynamics code, to simulate low-mass star formation in a turbulent molecular cloud in the presence of protostellar feedback. We present results of the first simulations of a star-forming cluster that include both radiative transfer and protostellar outflows. We run four simulations to isolate the individual effects of radiation feedback and outflow feedback as well as the combination of the two. We find that outflows reduce protostellar masses and accretion rates each by a factor of three and therefore reduce protostellar luminosities by an order of magnitude. This means that, while radiation feedback suppresses fragmentation, outflows render protostellar radiation largely irrelevant for low-mass star formation above a mass scale of 0.05 M{sub Sun }. We find initial fragmentation of our cloud at half the global Jeans length, around 0.1 pc. With insufficient protostellar radiation to stop it, these 0.1 pc cores fragment repeatedly, forming typically 10 stars each. The accretion rate in these stars scales with mass as predicted from core accretion models that include both thermal and turbulent motions; the accretion rate does not appear to be consistent with either competitive accretion or accretion from an isothermal sphere. We find that protostellar outflows do not significantly affect the overall cloud dynamics, in the absence of magnetic fields, due to their small opening angles and poor coupling to the dense gas. The outflows reduce the mass from the cores by 2/3, giving a core to star efficiency, {epsilon}{sub core} {approx_equal} 1/3. The simulations are also able to reproduce many observation of local star-forming regions. Our simulation with radiation and outflows reproduces the observed protostellar luminosity function. All of the simulations can reproduce observed core mass functions, though we find they are sensitive to telescope resolution. We also reproduce the two-point correlation function of these observed cores. Lastly, we reproduce the initial mass function itself, including the low-mass end, when outflows are included.

79 ASTRONOMY AND ASTROPHYSICS↗

Self-Assembled TiN-Metal Nanocomposites Integrated on Flexible Mica Substrates towards Flexible Devices

The integration of nanocomposite thin films with combined multifunctionalities on flexible substrates is desired for flexible device design and applications. For example, combined plasmonic and magnetic properties could lead to unique optical switchable magnetic devices and sensors. In this work, a multiphase TiN-Au-Ni nanocomposite system with core–shell-like Au-Ni nanopillars embedded in a TiN matrix has been demonstrated on flexible mica substrates. The three-phase nanocomposite film has been compared with its single metal nanocomposite counterparts, i.e., TiN-Au and TiN-Ni. Magnetic measurement results suggest that both TiN-Au-Ni/mica and TiN-Ni/mica present room-temperature ferromagnetic property. Tunable plasmonic property has been achieved by varying the metallic component of the nanocomposite films. The cyclic bending test was performed to verify the property reliability of the flexible nanocomposite thin films upon bending. This work opens a new path for integrating complex nitride-based nanocomposite designs on mica towards multifunctional flexible nanodevice applications.

42 ENGINEERING↗

Platinum dendritic nanoparticles with magnetic behavior

Magnetic nanoparticles have attracted increasing attention for biomedical applications in magnetic resonance imaging, high frequency magnetic field hyperthermia therapies, and magnetic-field-gradient-targeted drug delivery. In this study, three-dimensional (3D) platinum nanostructures with large surface area that features magnetic behavior have been demonstrated. The well-developed 3D nanodendrites consist of plentiful interconnected nano-arms ∼4 nm in size. The magnetic behavior of the 3D dendritic Pt nanoparticles is contributed by the localization of surface electrons due to strongly bonded oxygen/Pluronic F127 and the local magnetic moment induced by oxygen vacancies on the neighboring Pt and O atoms. The magnetization of the nanoparticles exhibits a mixed paramagnetic and ferromagnetic state, originating from the core and surface, respectively. The 3D nanodendrite structure is suitable for surface modification and high amounts of drug loading if the transition temperature was enhanced to room temperature properly.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

6.5% Silicon Steel Core Material (Non-Grain Oriented Electrical Steel) (Rev.01)

6.5% (Non-Grain-Oriented) Silicon Steel is a soft magnetic material that is best used in electrical rotating machinery, such as motors and generators. It has a high silicon content up to 6.5 mass %, which reduces the alloy magnetostriction to nearly zero, but causes brittleness and other associated manufacturing challenges. Due to its more random texture compared to 3% (grain-oriented) silicon steel, 6.5% (non-grain-oriented) silicon steel is used for primarily for rotating applications, i.e. motors and generators. Typical operating frequencies of 6.5% Silicon Steel is 400 Hz (hertz). A variety of forms can be manufactured, including lamination, toroidal and C-cores, as well as glued block cores of various shapes by cutting or pressing.

36 MATERIALS SCIENCE↗

Electronic structure and x-ray magnetic circular dichroism in YbAgCu4 and YbInCu4

X-ray absorption and magnetic circular dichroism spectra at the L-3 edge of Yb have been studied theoretically in the mixed-valent compounds YbAgCu4 and YbInCu4 using the fully relativistic Dirac linear muffin-tin orbital band structure method. The effect of the spin-orbit (SO) interaction and Coulomb repulsion U on the electronic structure of YbAgCu4 and YbInCu4 is examined in the frame of the local spin-density approximation (LSDA)+SO+U method. The core-hole effect in the final states as well as the effect of the electric quadrupole E-2 and magnetic dipole M-1 transitions have been investigated. The calculated results are compared with available experimental data.

Antonov, VN↗

Computed Tomography Scanning and Geophysical Measurements of Appalachian Basin Core from the Jones and Laughlin #1 Well, Beaver County, PA

The computed tomography (CT) facilities and the Multi-Sensor Core Logger (MSCL) at the National Energy Technology Laboratory (NETL) in Morgantown, West Virginia, were used to characterize Appalachian Basin core from Beaver County, Pennsylvania. The primary impetus of this work is a collaboration between the U.S. Department of Energy (DOE) and the Pennsylvania Geological Survey to characterize and make publicly available core information from the Onondaga-Huntersville formations of the Appalachian Basin. This stratigraphic well and the core data produced in this report will aid in understanding the structural complexities of the Onondaga-Huntersville formations. The resultant datasets are presented in this report and can be accessed from NETL's Energy Data eXchange (EDX) online system using the following link: https://edx.netl.doe.gov/dataset/jonesandlaughlin1well. All equipment and techniques used were non-destructive, enabling future examinations and analyses to be performed on these cores. Fractures, discontinuities, and millimeter-scale features were readily detectable with imaging performed with the NETL medical CT scanner over the entire core. Qualitative analysis of the medical CT images, coupled with X-ray fluorescence (XRF), and magnetic susceptibility measurements from the MSCL were useful in identifying zones of interest for further study. Targeted higher resolution CT scanning of select sections was performed with NETL’s micro-CT scanner. The combination of methods used provides a multiscale analysis of the core; the resulting macro and micro descriptions are relevant to many subsurface energy related examinations traditionally performed at NETL.

58 GEOSCIENCES↗

Final Report for Project. Quark matter under extreme conditions

The results obtained in the two years of the grant have served to shine new light on several important questions about the phases of quantum chromodynamics (QCD) under extreme conditions that include quark matter at high density, as well quark-gluon plasma at high temperatures, both in the presence of strong magnetic fields. The interest in including an external magnetic field on these studies is motivated by the generation of large magnetic fields in off-central heavy-ion collisions and by their common presence in astrophysical compact objects, the two scenarios where the physics of quark matter becomes relevant. The tasks carried out in this DOE project led us, among other things, to discover the first connection between the physics of very dense quark matter and novel materials as for instance topological insulators and Weyl semimetals; they allowed us to find a physical explanation for and a solution to a standing puzzle in the apparent effect of a magnetic field on the critical temperature of the QCD chiral transition; and they led us to establish by the first time that the core of the observed two-solar-mass neutron stars could be made up of quark matter in certain inhomogeneous chiral phases in a magnetic field and that this was consistent with current astrophysical observations. A major goal established by the Nuclear Science Advisory committee in its most recent report “Reaching for the Horizon” has been “to truly understand how nuclei and strongly interacting matter in all its forms behave and can predict their behavior in new settings.” The results found in this DOE project have all contributed to address this goal, and thus they are important for advancing fundamental knowledge in the area of nuclear physics and for enhancing our understanding of the role of strong magnetic fields in the two settings where they are most relevant, neutron stars and heavy-ion collisions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗