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DOE OSTI2018

Incoherent Scattering of Electromagnetic Waves by Langmuir Fluctuations Trapped in a Plasma Density Well

Incoherent scattering of a probing wave by Langmuir fluctuations trapped and enhanced near a local minimum of the electron density (plasma density well) in plasma with a parabolic density profile is considered. Steady-state amplitudes of fluctuations are calculated for arbitrary velocity distribution functions of plasma particles with allowance for electron collisions. It is shown that quasi-periodic oscillations with two characteristic scales can be present in the spectrum of the plasma line. The smaller scale is due to the wellknown effect of discretization of the spectrum of Langmuir fluctuations in a plasma density well. The larger scale is associated with the generation of scattered waves in two spatial regions and subsequent interference of these waves at the exit from the density well. Oscillations with this scale are more stable under unsteady plasma conditions and can be more often observed in experiments. The results of this work can be used to experimentally determine the plasma parameters, such as the electron collision frequency and the size and lifetime of the plasma density well.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2017

A complete basis of helicity operators for subleading factorization

Factorization theorems underly our ability to make predictions for many processes involving the strong interaction. Although typically formulated at leading power, the study of factorization at subleading power is of interest both for improving the precision of calculations, as well as for understanding the all orders structure of QCD. We use the SCET helicity operator formalism to construct a complete power suppressed basis of hard scattering operators for e + e - → dijets, e - p → e - jet, and constrained Drell-Yan, including the first two subleading orders in the amplitude level power expansion. We analyze the field content of the jet and soft function contributions to the power suppressed cross section for e + e - → dijet event shapes, and give results for the lowest order matching to the contributing operators. These results will be useful for studies of power corrections both in fixed order and resummed perturbation theory.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2018

Skyrmion Lattice Topological Hall Effect near Room Temperature

Magnetic skyrmions are stable nanosized spin structures that can be displaced at low electrical current densities. Because of these properties, they have been proposed as building blocks of future electronic devices with unprecedentedly high information density and low energy consumption. The electrical detection of an ordered skyrmion lattice via the Topological Hall Effect (THE) in a bulk crystal, has so far been demonstrated only at cryogenic temperatures in the MnSi family of compounds. Here, we report the observation of a skyrmion lattice Topological Hall Effect near room temperature (276 K) in a mesoscopic lamella carved from a bulk crystal of FeGe. This region coincides with the skyrmion lattice location revealed by neutron scattering. We provide clear evidence of a re-entrant helicoid magnetic phase adjacent to the skyrmion phase, and discuss the large THE amplitude (5 nΩ.cm) in view of the ordinary Hall Effect.

36 MATERIALS SCIENCE↗

DOE OSTI2019

Cosmology with stacked cluster weak lensing and cluster–galaxy cross-correlations

ABSTRACT Cluster weak lensing is a sensitive probe of cosmology, particularly the amplitude of matter clustering σ8 and matter density parameter Ωm. The main nuisance parameter in a cluster weak lensing cosmological analysis is the scatter between the true halo mass and the relevant cluster observable, denoted $\sigma _{\ln M_\mathrm{ c}}$. We show that combining the cluster weak lensing observable ΔΣ with the projected cluster–galaxy cross-correlation function wp,cg and galaxy autocorrelation function wp,gg can break the degeneracy between σ8 and $\sigma _{\ln M_\mathrm{ c}}$ to achieve tight, per cent-level constraints on σ8. Using a grid of cosmological N-body simulations, we compute derivatives of ΔΣ, wp,cg, and wp,gg with respect to σ8, Ωm, $\sigma _{\ln M_\mathrm{ c}}$, and halo occupation distribution (HOD) parameters describing the galaxy population. We also compute covariance matrices motivated by the properties of the Dark Energy Survey cluster and weak lensing survey and the BOSS CMASS galaxy redshift survey. For our fiducial scenario combining ΔΣ, wp,cg, and wp,gg measured over 0.3−30.0 h−1 Mpc, for clusters at z = 0.35−0.55 above a mass threshold Mc ≈ 2 × 1014 h−1 M⊙, we forecast a $1.4{{\ \rm per\ cent}}$ constraint on σ8 while marginalizing over $\sigma _{\ln M_\mathrm{ c}}$ and all HOD parameters. Reducing the mass threshold to 1 × 1014 h−1 M⊙ and adding a z = 0.15−0.35 redshift bin sharpens this constraint to $0.8{{\ \rm per\ cent}}$. The small-scale (rp < 3.0 h−1 Mpc) ‘mass function’ and large-scale (rp > 3.0 h−1 Mpc) ‘halo-mass cross-correlation’ regimes of ΔΣ have comparable constraining power, allowing internal consistency tests from such an analysis.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2017

Chiral extrapolations of the ρ ( 770 ) meson in N f = 2 + 1 lattice QCD simulations

Recent $N_f=2+1$ lattice data for meson-meson scattering in $p$-wave and isospin $I=1$ are analyzed using a unitarized model inspired by Chiral Perturbation Theory in the inverse-amplitude formulation for two and three flavors. We perform chiral extrapolations that postdict phase shifts extracted from experiment quite well. Additionally, the low-energy constants are compared to the ones from a recent analysis of $N_f=2$ lattice QCD simulations to check for the consistency of the hadronic model used here. Some inconsistencies are detected in the fits to $N_f=2+1$ data, in contrast to the previous analysis of $N_f=2$ data.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

NASA NTRS1975

The Forbush decrease of November 17, 1966

The Forbush decrease of November 17, 1966, takes place in two steps, a predecrease is followed by the main decrease. SSCs are observed on both occasions. The decrease is modest, short-lived, and is preceded and followed by an exceptionally steady level of the cosmic ray intensity. Preliminary results from a phenomenological study are presented. The observed changes in the cosmic ray intensity are correlated with interplanetary magnetic field direction at the onset of the predecrease and during part of the recovery phase. A simple explanation is given for the fact that the predecrease is not observed at the stations in the European-zone. It appears that a preferential recovery takes place from some directions in space, during the recovery phase of the Forbush decrease. Off-ecliptic scattering of lower energy cosmic rays is probably responsible for this. The same phenomena is probably also responsible for the difference between the amplitudes of the predecrease observed at different stations.

Ahluwalia, H. S.↗

NASA NTRS1981

Photoelectric lightcurves and rotation periods of the asteroids 46 Hestia and 115 Thyra

Results of photoelectric observations of the medium-sized minor planets 46 Hestia and 115 Thyra are presented. Thyra, with a rotational period of 7.241 plus or minus 0.001 hours, and a maxima and minima total amplitude of 0.20 mag, is classified as an S-type object. Hestia, with a rotation period of 21.04 plus or minus 0.01 hours, and an amplitude of 0.12 mag, has well-defined minima separated by long-duration flat maxima, and resemble an eclipsing binary system. Multiple scattering factors are found to be 0.054 plus or minus 0.003, and 0.058 plus or minus 0.002 for Hestia and Thyra, respectively. Results are compared with values found by Bowell and Lumme (1979), showing good agreement, although some discrepancy is found with Thyra's low value for the multiple-scattering factor.

Scaltriti, F.↗

NASA NTRS1982

Radar images of the earth from space

The operational principles and imagery available from microwave SAR radars for earth observations from aircraft, the Shuttle, and Seasat are explored. Using microwave frequencies is noted to offer imagery access in day or night, all-weather conditions. SAR radar functions by obtaining a series of reflected signals over a single path, with data processing combining the echoes into an image corresponding to what may be obtained with a large antenna. A stable, reference signal is added to the incoming signals in order to establish the phase and amplitude of echoes. Because the wavelengths of the images can be precisely controlled, Doppler shifts can be detected, thus allowing point by point scattering analysis in two-dimensions. The Shuttle SIR-A and the Seasat radar feature a ground resolution of 25 m. Applications of the satellite systems to terrain, ice mapping, and for a Venus radar mapper mission are described.

Elachi, C.↗

NASA NTRS1985

The local characteristic function of interplanetary particle propagation

An easily measurable intensity function which characterizes the interplanetary propagation of charged solar flare particles is presented. This function is nearly time invariant during a solar event despite the large variations of intensity and anisotropy, but varies from event to event. It characterizes the systematic and stochastic forces of the interplanetary magnetic field which focus and scatter the particles in pitch angle. The model of focused transport shows that this function is essentially determined by the local shape and amplitude of the pitch angle diffusion coefficient kappa (mu) and by the local value of the focusing length. The time profile of the solar particle injection is typically of negligible influence. The local characteristic function may be used as a powerful new tool for a systematic analysis of flare particle angular distributions, Examples are given.

Green, G.↗

NASA NTRS2006

Ultrasonication of Bismuth Telluride Nanocrystals Fabricated by Solvothermal Method

The objective of this study is to evaluate the effect of ultrasonication on bismuth telluride nanocrystals prepared by solvothermal method. In this study, a low dimensional nanocrystal of bismuth telluride (Bi2Te3) was synthesized by a solvothermal process in an autoclave at 180 C and 200 psi. During the solvothermal reaction, organic surfactants effectively prevented unwanted aggregation of nanocrystals in a selected solvent while controlling the shape of the nanocrystal. The atomic ratio of bismuth and tellurium was determined by energy dispersive spectroscopy (EDS). The cavitational energy created by the ultrasonic probe was varied by the ultrasonication process time, while power amplitude remained constant. The nanocrystal size and its size distribution were measured by field emission scanning electron microscopy (FESEM) and a dynamic light scattering system. When the ultrasonication time increased, the average size of bismuth telluride nanocrystal gradually increased due to the direct collision of nanocrystals. The polydispersity of the nanocrystals showed a minimum when the ultrasonication was applied for 5 min. Keywords: bismuth telluride, nanocrystal, low-dimensional, ultrasonication, solvothermal

Chu, Sang-Hyon↗

DOE OSTI2020

Detection, monitoring, and determination of location of changes in metallic structures using multimode acoustic signals

Methods for detection, monitoring, and determination of location of changes in rigid structures with arbitrarily complex geometries are described. Implementations include locating acoustic transducers that generate and receive acoustic signals at multiple locations along a surface of the rigid structure, wherein longitudinal spacing between the transducer locations define measurement zones. Acoustic signals with chosen amplitude-time-frequency characteristics excite multiple vibration modes in the structure within each zone. Small mechanical changes in the inspection zones lead to scattering and attenuation of broadband acoustic signals, which are detectable as changes in received signal characteristics as part of a through-transmission technique. Additional use of short, narrowband pulse acoustic signals as part of a pulse-echo technique allows determination of the relative location of the mechanical change within each zone based on the differential delay profiles.

42 ENGINEERING↗

DOE OSTI2023

Manipulation of Scattering Spectra with Topology of Light and Matter

Structured lights, including beams carrying spin and orbital angular momenta, radially and azimuthally polarized vector beams, as well as spatiotemporal optical vortices, have attracted significant interest due to their unique amplitude, phase front, polarization, and temporal structures, enabling a variety of applications in optical and quantum communications, micromanipulation, and super-resolution imaging. In parallel, structured optical materials, metamaterials, and metasurfaces consisting of engineered unit cells—meta-atoms, opened new avenues for manipulating the flow of light and optical sensing. While several studies explored structured light effects on the individual meta-atoms, their shapes are largely limited to simple spherical geometries. However, the synergy of the structured light and complex-shaped meta-atoms has not been fully explored. Here, in this paper, the role of the helical wavefront of Laguerre–Gaussian beams in the excitation and suppression of higher-order resonant modes inside all-dielectric meta-atoms of various shapes, aspect ratios, and orientations, is demonstrated and the excitation of various multipolar moments that are not accessible via unstructured light illumination is predicted. The presented study elucidates the role of the complex phase distribution of the incident light in shape-dependent resonant scattering, which is of utmost importance in a wide spectrum of applications ranging from remote sensing to spectroscopy.

42 ENGINEERING↗

DOE OSTI2015

Broadband surface-wave transformation cloak

Guiding surface electromagnetic waves around disorder without disturbing the wave amplitude or phase is in great demand for modern photonic and plasmonic devices, but is fundamentally difficult to realize because light momentum must be conserved in a scattering event. A partial realization has been achieved by exploiting topological electromagnetic surface states, but this approach is limited to narrow-band light transmission and subject to phase disturbances in the presence of disorder. Recent advances in transformation optics apply principles of general relativity to curve the space for light, allowing one to match the momentum and phase of light around any disorder as if that disorder were not there. This feature has been exploited in the development of invisibility cloaks. An ideal invisibility cloak, however, would require the phase velocity of light being guided around the cloaked object to exceed the vacuum speed of light—a feat potentially achievable only over an extremely narrow band. In this paper, we theoretically and experimentally show that the bottlenecks encountered in previous studies can be overcome. We introduce a class of cloaks capable of remarkable broadband surface electromagnetic waves guidance around ultrasharp corners and bumps with no perceptible changes in amplitude and phase. These cloaks consist of specifically designed nonmagnetic metamaterials and achieve nearly ideal transmission efficiency over a broadband frequency range from 0 + to 6 GHz. Finally, this work provides strong support for the application of transformation optics to plasmonic circuits and could pave the way toward high-performance, large-scale integrated photonic circuits.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2015

Parametric generation of broadband biphotons in a periodic sequence of thin crystals

Collinear parametric scattering of light under type-II phase matching is considered in a periodic sequence of nonlinear cells made of BBO crystals. The possibilities of reducing the duration of the wave packets of biphotons and increasing their intensity under monochromatic pumping are studied. The analysis is based on the account of dispersion of the refractive indices using Sellmeier equations. The obtained results allow one to conclude that at an appropriate choice of the crystal thicknesses and the number of cells, it is possible to significantly increase the flux of broadband biphotons and obtain extremely short quantum packets. It is shown that for sufficiently small thicknesses of individual crystals (layers), this system exhibits a fine structure in the spectrum of biphotons: with an increase in the number of cells (layers) the broadband spectrum is divided into a number of narrow bands and the number of these bands increases. When use is made of a nonlinear BBO crystal, this method allows one to obtain ultrashort packets of biphotons with duration τ{sub 0} ≈ 2 fs. Compared with a different method of generation of broadband biphotons, which is based on the use of quasi-phase-matched periodically poled crystals, the method studied in this paper does not necessitate the need for the phase modulation of a biphoton to be converted into the amplitude modulation. (nonlinear optical phenomena)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2020

Scattering Observables from One- and Two-body Densities: Formalism and Application to $\pmb \gamma $ ${}^3\hbox {He}$ Scattering

We introduce the transition-density formalism, an efficient and general method for calculating the interaction of external probes with light nuclei. One- and two-body transition densities that encode the nuclear structure of the target are evaluated once and stored. They are then convoluted with an interaction kernel to produce amplitudes, and hence observables. Here, by choosing different kernels, the same densities can be used for any reaction in which a probe interacts perturbatively with the target. The method therefore exploits the factorisation between nuclear structure and interaction kernel that occurs in such processes. We study in detail the convergence in the number of partial waves for matrix elements relevant in elastic Compton scattering on 3 He. The results are fully consistent with our previous calculations in Chiral Effective Field Theory. But the new approach is markedly more computationally efficient, which facilitates the inclusion of more partial-wave channels in the calculation. We also discuss the usefulness of the transition-density method for other nuclei and reactions. Calculations of elastic Compton scattering on heavier targets like 4 He are straightforward extensions of this study, since the same interaction kernels are used. And the generality of the formalism means that our 3 He densities can be used to evaluate any 3 He elastic-scattering observable with contributions from one- and two-body operators.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2019

Multiquark matrix elements in the proton and three gluon exchange for exclusive $η_c$ production in photon-proton diffractive scattering

Exclusive production of a η c pseudoscalar meson in γ ( * ) + p → η c + p scattering at high energies involves a C -odd exchange in the t -channel. We formulate the description of this process within the high-energy framework of eikonal dipole scattering. We obtain expressions for the light-cone wave function of the η c required in this framework as well as for the C -odd amplitudes due to exchange of a single photon, of a photon plus two gluons, and of three gluons. We relate these amplitudes to correlators of the plus component of the quark current in the light-cone wave function of the proton. For high transverse momenta, these correlators correspond to (leading twist) generalized parton distributions given by diagrams where all exchanged gauge bosons attach to a single quark in the proton. Diagrams involving multiquark matrix elements potentially sensitive to correlations screen infrared singularities. Moreover, they are numerically important for configurations where the exchanged bosons nearly share the total momentum transfer. Using two simple models for the three-quark Fock state of the proton at x ≃ 0.1 , we find that single photon exchange dominates for | t | < 1.5 GeV 2 . Here, the quark generalized parton distribution could be measured cleanly in γ ( * ) + p → η c + p via single photon exchange. For higher momentum transfer, three-gluon (“Odderon”) exchange is dominant.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2014

Scattering and bound states of fermions in a mixed vector–scalar smooth step potential

The scattering of a fermion in the background of a smooth step potential is considered with a general mixing of vector and scalar Lorentz structures with the scalar coupling stronger than or equal to the vector coupling. Charge-conjugation and chiral-conjugation transformations are discussed and it is shown that a finite set of intrinsically relativistic bound-state solutions appears as poles of the transmission amplitude. It is also shown that those bound solutions disappear asymptotically as one approaches the conditions for the realization of the so-called spin and pseudospin symmetries in a four-dimensional space–time. - Highlights: • Scattering and bound states of fermions in a kink-like potential. • No pair production despite the high localization. • No bounded solution under exact spin and pseudospin symmetries.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2023

Probing the Boundary between Classical and Quantum Mechanics by Analyzing the Energy Dependence of Single-Electron Scattering Events at the Nanoscale

The relation between the energy-dependent particle and wave descriptions of electron–matter interactions on the nanoscale was analyzed by measuring the delocalization of an evanescent field from energy-filtered amplitude images of sample/vacuum interfaces with a special aberration-corrected electron microscope. The spatial field extension coincided with the energy-dependent self-coherence length of propagating wave packets that obeyed the time-dependent Schrödinger equation, and underwent a Goos–Hänchen shift. The findings support the view that wave packets are created by self-interferences during coherent–inelastic Coulomb interactions with a decoherence phase close to Δφ = 0.5 rad. Due to a strictly reciprocal dependence on energy, the wave packets shrink below atomic dimensions for electron energy losses beyond 1000 eV, and thus appear particle-like. Consequently, our observations inevitably include pulse-like wave propagations that stimulate structural dynamics in nanomaterials at any electron energy loss, which can be exploited to unravel time-dependent structure–function relationships on the nanoscale.

36 MATERIALS SCIENCE↗