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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

COZMIC. III. Cosmological Zoom-in Simulations of Self-interacting Dark Matter with Suppressed Initial Conditions

We present eight cosmological dark matter (DM)-only zoom-in simulations of a Milky Way–like system that include suppression of the linear matter power spectrum P(k), and/or velocity-dependent DM self-interactions, as the third installment of the COZMIC suite. We consider a model featuring a massive dark photon that mediates DM self-interactions and decays into massless dark fermions. The dark photon and dark fermions suppress linear matter perturbations, resulting in dark acoustic oscillations in P(k), which ultimately affect dwarf galaxy scales. The model also features a velocity-dependent elastic self-interaction between DM particles (SIDM), with a cross section that can alleviate small-scale structure anomalies. For the first time, our simulations test the impact of P(k) suppression on gravothermal evolution in an SIDM scenario that leads to core collapse in (sub)halos with present-day virial masses below ≈10 9 M ⊙ . In simulations with P(k) suppression and self-interactions, the lack of low-mass (sub)halos and the delayed growth of structure reduce the fraction of core-collapsed systems relative to SIDM simulations without P(k) suppression. In particular, P(k) suppression that saturates current warm DM constraints almost entirely erases core collapse in isolated halos. Models with less extreme P(k) suppression produce core collapse in ≈20% of subhalos and ≈5% of isolated halos above 10 8 M ⊙ , and also increase the abundance of extremely low-concentration isolated low-mass halos relative to SIDM. These results reveal a complex interplay between early and late-Universe DM physics, revealing new discovery scenarios in the context of upcoming small-scale structure measurements.

dark matter↗
DOE OSTI2017

Technique for insulated and non-insulated metal liner X-pinch radiography on a 1 MA pulsed power machine

Broadband, high resolution X-pinch radiography has been demonstrated as a method to view the instability induced small scale structure that develops in near solid density regions of both insulated and non-insulated cylindrical metallic liners. In experiments carried out on a 1-1.2 MA 100-200 ns rise time pulsed power generator, μm scale features were imaged in initially 16 μm thick Al foil cylindrical liners. Better resolution and contrast were obtained using an X-ray sensitive film than with image plate detectors because of the properties of the X-pinch X-ray source. Here, we also discuss configuration variations that were made to the simple cylindrical liner geometry that appeared to maintain validity of the small-scale structure measurements while improving measurement quality.

47 OTHER INSTRUMENTATION↗
DOE OSTI2011

Dark atoms: asymmetry and direct detection

We present a simple UV completion of Atomic Dark Matter (aDM) in which heavy right-handed neutrinos decay to induce both dark and lepton number densities. This model addresses several outstanding cosmological problems: the matter/anti-matter asymmetry, the dark matter abundance, the number of light degrees of freedom in the early universe, and the smoothing of small-scale structure. Additionally, this realization of aDM may reconcile the CoGeNT excess with recently published null results and predicts a signal in the CRESST Oxygen band. We also find that, due to unscreened long-range interactions, the residual unrecombined dark ions settle into a diffuse isothermal halo.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Blob wakes in NSTX

Transient small-scale structures were identified in the wake of blobs movingpoloidally through the SOL of high-powered H-mode plasmas in NSTX, using the gaspuff imaging (GPI) diagnostic. These blob wakes had a poloidal wavelength in therange 3.5 cm, which is significantly smaller than the average blob scale of~12 cm, and the wakes had a poloidal velocity of 1.5 km/sec in theelectron diamagnetic direction, which is opposite to the blob poloidal velocity inthese shots. These wakes were radially localized 0-4 cm outside the separatrix andoccurred within ~50 microsec after the passage of a blob through the GPI field of view.The clearest wakes were seen when the GPI viewing angle was well aligned with thelocal B field line, as expected for such small-scale structures given the diagnosticgeometry. A plausible theoretical interpretation of the wakes is discussed: theobserved wakes share some features of drift waves and/or drift-Alfven waves whichcould be excited

blobs↗
DOE OSTI2019

Early Stage of the Explosion of Thin Flat Foils in a High-Current Diode at a Current of 40–80 kA

The initial stage of the nanosecond explosion of 1–15 μm-thick flat foils in a diode with a current of 40–80 kA is studied. Projection radiography is used to take images of exploded foils at a spatial resolution of 3–4 μm using the soft X-ray radiation (E = 2.5–5 keV) of a hybrid X-pinch and at a time resolution of 0.1 ns. Foil strips 0.3–2 mm wide and 0.5–7 mm long were introduced in the return circuit of the diode in a high-current BIN generator with a current amplitude of 270 kA and a current rise time of 100 ns; the main load of the generator is an X-pinch. The experiments demonstrate that small-scale structures, the shape and the size of which depend on the foil material and the current density and distribution in a foil, are formed in a foil. Possible scenarios of the structure formation are discussed.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Blob wakes in NSTX

Transient small-scale structures were identified in the wake of blobs moving poloidally through the scrape-off layer of high-powered H-mode plasmas in NSTX, using the gas puff imaging (GPI) diagnostic. These blob wakes had a poloidal wavelength in the range of λ pol = 3.5 ± 0.7 cm, which is significantly smaller than the average blob scale of L pol ~12 cm, and the wakes had a poloidal velocity of V pol = 1.5 ± 1.0 km/s in the electron diamagnetic direction, which is opposite to the blob poloidal velocity in these shots. These wakes were radially localized 0–4 cm outside the separatrix and occurred within ~50 μs after the passage of a blob through the GPI field of view. The clearest wakes were seen when the GPI viewing angle was well aligned with the local B field line, as expected for such small-scale structures given the diagnostic geometry. In conclusion, a plausible theoretical interpretation of the wakes is discussed: the observed wakes share some features of drift waves and/or drift-Alfvén waves which could be excited by the blobs.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Synthesis of aluminum nitride powders from a plasma-assisted ball milled precursor through carbothermal reaction

Highlights: • A novel and high efficiency synthesizing AlN powders method combining mechanical ball milling and DBDP has been developed. • The particle size, the crystallite size, the lattice distortion, the morphology of Al{sub 2}O{sub 3} powders, and the AlN conversion rate are investigated and compared under the ball milled Al{sub 2}O{sub 3} powders with DBDP and without DBDP. • The ball milled Al{sub 2}O{sub 3} powders with DBDP have small spherical structure morphology with very fine particles size and high specific surface area, which result in a higher chemical efficiency and a higher AlN conversion rate at lower thermal temperature. - Abstract: In this paper, aluminum nitride (AlN) powers have been produced with a novel and high efficiency method by thermal annealing at 1100–1600 °C of alumina (Al{sub 2}O{sub 3}) powders which were previously ball milled for various time up to 40 h with and without the assistant of dielectric barrier discharge plasma (DBDP). The ball milled Al{sub 2}O{sub 3} powders with DBDP and without DBDP and the corresponding synthesized AlN powers are characterized by X-ray diffraction, scanning electron microscope, and transmission electron microscopy. From the characteristics of the ball milled Al{sub 2}O{sub 3} powders with DBDP and without DBDP, it can be seen that the ball milled Al{sub 2}O{sub 3} powders with DBDP have small spherical structure morphology with very fine particles size and high specific surface area, which result in a higher chemical efficiency and a higher AlN conversion rate at lower thermal temperature. Meanwhile, the synthesized AlN powders can be known as hexagonal AlN with fine crystal morphology and irregular lump-like structure, and have uniform distribution with the average particle size of about between 500 nm and 1000 nm. This provides an important method for fabricating ultra fine powders and synthesizing nitrogen compounds.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Comparison of polystyrene scintillator fiber array and monolithic polystyrene for neutron imaging and radiography

The neutron imaging diagnostic at the National Ignition Facility has been operating since 2011 generating neutron images of deuterium-tritium (DT) implosions at peak compression. The current design features a scintillating fiber array, which allows for high imaging resolution to discern small-scale structure within the implosion. In recent years, it has become clear that additional neutron imaging systems need to be constructed in order to provide 3D reconstructions of the DT source and these additional views need to be on a shorter line of sight. As a result, there has been increased effort to identify new image collection techniques that improve upon imaging resolution for these next generation neutron imaging systems, such as monolithic deuterated scintillators. This work details measurements performed at the Weapons Neutron Research Facility at Los Alamos National Laboratory that compares the radiographic abilities of the fiber scintillator with a monolithic scintillator, which may be featured in a future short line of sight neutron imaging systems.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

WIMP and SIMP dark matter from the spontaneous breaking of a global group

We propose and study a scalar extension of the Standard Model which respects a ℤ{sub 3} symmetry remnant of the spontaneous breaking of a global U(1){sub DM} symmetry. Consequently, this model has a natural dark matter candidate and a Goldstone boson in the physical spectrum. In addition, the Higgs boson properties are changed with respect to the Standard Model due to the mixing with a new particle. We explore regions in the parameter space taking into account bounds from the measured Higgs properties, dark matter direct detection as well as measurements of the effective number of neutrino species before recombination. The dark matter relic density is determined by three classes of processes: the usual self-annihilation, semi-annihilation and purely dark matter 3→2 processes. The latter has been subject of recent interest leading to the so-called ‘Strongly Interacting Massive Particle’ (SIMP) scenario. We show under which conditions our model can lead to a concrete realization of such scenario and study the possibility that the dark matter self-interactions could address the small scale structure problems. In particular, we find that in order for the SIMP scenario to work, the dark matter mass must be in the range 7−115 MeV, with the global symmetry energy breaking scale in the TeV range.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Production of dark-matter bound states in the early universe by three-body recombination

The small-scale structure problems of the universe can be solved by self-interacting dark matter that becomes strongly interacting at low energy. A particularly predictive model for the self-interactions is resonant short-range interactions with an S-wave scattering length that is much larger than the range. The velocity dependence of the cross section in such a model provides an excellent fit to self-interaction cross sections inferred from dark-matter halos of galaxies and clusters of galaxies if the dark-matter mass is about 19 GeV and the scattering length is about 17 fm. Such a model makes definite predictions for the few-body physics of weakly bound clusters of the dark-matter particles. The formation of the two-body bound cluster is a bottleneck for the formation of larger bound clusters. We calculate the production of two-body bound clusters by three-body recombination in the early universe under the assumption that the dark matter particles are identical bosons, which is the most favorable case. If the dark-matter mass is 19 GeV and the scattering length is 17 fm, the fraction of dark matter in the form of two-body bound clusters can increase by as much as 4 orders of magnitude when the dark-matter temperature falls below the binding energy, but its present value remains less than 10 -6 . The present fraction can be increased to as large as 10 -3 by relaxing the constraints from small-scale structure and decreasing the mass of the dark matter particle.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Structure and dynamics of small van der Waals complexes

We illustrate computational aspects of the calculation of the potential energy surfaces of small (up to five atoms) van der Waals complexes with high-level quantum chemistry techniques such as the CCSD(T) method with extended basis sets. We discuss the compromise between the required accuracy and the computational time. Further, we show how these potential energy surfaces can be fitted and used in dynamical calculations such as non-reactive inelastic scattering.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Computer simulation structure and vibrations of small metal cluster on the Cu (111) surface

Vibrational properties of the small tetrahedral cluster of Co on the Cu (111) surface are studied by using tight-binding second moment approximation interatomic interaction potentials. It was shown that interaction of the clusters with substrate leads to arising of frustrated translation and frustrated rotation in-plane polarized vibrational modes localized on the cluster atoms. The Co{sub 4} cluster on the surface the high frequency modes remain strongly localized and mixed with the nearest neighbor atoms vibrations.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Modeling ablator grain structure impacts in ICF implosions

High-density carbon is a leading ablator material for inertial confinement fusion (ICF). This and some other ablator materials have grain structure which is believed to introduce very small-scale (~nm) density inhomogeneity. In principle, such inhomogeneity can affect key ICF metrics like fuel compression and yield, by, for example, acting as a seed for instabilities and inducing mix between ablator and fuel. However, assessments of such effects are uncertain due to the difficulty of modeling this small-scale structure in ICF simulations, typically requiring reduced-resolution modeling that scales these features. We present a grain model and show both the impact of de-resolving grains and the complex mixing dynamics such structures can induce. We find that different methods for de-resolving grains can yield both different total deposition of kinetic energy perturbations and different fuel–ablator mixing. We then show a simple-to-implement approach for approximately conserving the deposition of perturbed kinetic energy and demonstrate that, for the present grain model and test cases, this approach yields a reasonably matched time history of mix width between less and more resolved grain models. The simulations here also demonstrate the complex interaction history between grain-induced mixing and instability around the fuel–ablator interface, showing, for example, that the grain-induced perturbations typically trigger instability of conduction-driven density gradients in the DT fuel, enhancing mix penetration early in the acceleration of the shell. Furthermore simulating both microscale and nanoscale grains, we find initial evidence for larger mixing in the microscale case of the present model, despite smaller deposited kinetic energy perturbation.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗