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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Geospace Plume and Its Impact on Dayside Magnetopause Reconnection Rate

The role a geospace plume in influencing the efficiency of magnetopause reconnection is an open question with two contrasting theories being debated. A local-control theory suggests that a plume decreases both local and global reconnection rates, whereas a global-control theory argues that the global reconnection rate is controlled by the solar wind rather than local physics. Observationally, limited numbers of point measurements from spacecraft cannot reveal whether a local change affects the global reconnection. A distributed observatory is hence needed to assess the validity of the two theories. We use THEMIS and Los Alamos National Laboratory spacecraft to identify the occurrence of a geospace plume and its contact with the magnetopause. Global evolution and morphology of the plume is traced using GPS measurements. SuperDARN is then used to monitor the distribution and the strength of dayside reconnection. Two storm-time geospace plume events are examined and show that as the plume contacts the magnetopause, the efficiency of reconnection decreases at the contact longitude. The amount of local decrease is 81% and 68% for the two events, and both values are consistent with the mass loading effect of the plume if the plume's atomic mass is ~4 amu. Reconnection in the surrounding is enhanced, and when the solar wind driving is stable, little variation is seen in the cross polar cap potential. This study illuminates a pathway to resolve the role of cold dense plasma on solar wind-magnetosphere coupling, and the observations suggest that plumes redistribute magnetopause reconnection activity without changing the global strength substantially.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Sympathetic cooling of positrons to cryogenic temperatures for antihydrogen production

The positron, the antiparticle of the electron, predicted by Dirac in 1931 and discovered by Anderson in 1933, plays a key role in many scientific and everyday endeavours. Notably, the positron is a constituent of antihydrogen, the only long-lived neutral antimatter bound state that can currently be synthesized at low energy, presenting a prominent system for testing fundamental symmetries with high precision. Here, we report on the use of laser cooled Be + ions to sympathetically cool a large and dense plasma of positrons to directly measured temperatures below 7 K in a Penning trap for antihydrogen synthesis. This will likely herald a significant increase in the amount of antihydrogen available for experimentation, thus facilitating further improvements in studies of fundamental symmetries.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Equation of State and Energy Loss of Hot and Dense Quark-Gluon matter from Holographic Black Holes

By using gravity/gauge correspondence, we construct a holographic model, constrained to mimic the lattice QCD equation of state at zero density, to investigate the temperature and baryon chemical potential dependence of the equation of state. We also obtained the energy loss of light and heavy partons within the hot and dense plasma represented by the heavy quark drag force, Langevin diffusion coefficients and jet quenching parameter at the critical point and across the first-order transition line predicted by the model.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Quantitative metrics for evaluating thermonuclear design codes and physics models applied to the National Ignition Campaign

In this study, physics models and design codes for hot dense plasmas undergoing thermonuclear burn are evaluated objectively using statistical metrics that compare the difference between calculations and data relative to the experimental uncertainties. The analysis is applied to the National Ignition Campaign (NIC) because it is relevant, comprehensive, and well documented. The statistics confirm that a key process afflicting NIC performance is mix driven by hydrodynamic instabilities as approximated here using the KL model [G. Dimonte and R. Tipton, Phys. Fluids 18, 085101 (2006)]. New physics models are also presented for instability-driven magnetic fields [B. Srinivasan et al., Phys. Rev. Lett. 108, 165002 (2012)] and the Coulomb logarithm for electron–ion thermal relaxation [G. Dimonte and J. Daligault, Phys. Rev. Lett. 101, 135001 (2008)]. The plasma-generated magnetic fields improve the agreement between code and data in a statistically significant manner by reducing the electron thermal conduction in the hot-spot via the Hall term. The Coulomb logarithm is presented in a numerically practical form that incorporates recent theoretical advances. However, it does not improve the agreement between the code and data because the thermal relaxation is so fast in non-ignited NIC plasmas that the typical 20% error does not change the tight coupling between electrons and ions. Even with these improved physics models, the one-dimensional simulations presented here are not able to describe the high-convergence NIC implosions in a statistically acceptable manner. Of the heroic multi-dimensional simulations of Clark et al. [Phys. Plasmas 23, 056302 (2016)], only those in three-dimensions satisfy the statistical acceptance criterion.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Demonstration of a laser-driven, narrow spectral bandwidth x-ray source for collective x-ray scattering experiments

X-ray Thomson scattering (XRTS) is a powerful diagnostic technique that involves an x-ray source interacting with a dense plasma sample, resulting in a spectrum of elastically and inelastically scattered x-rays. Depending on the plasma conditions, one can measure a range of parameters from the resulting spectrum, including plasma temperature, electron density, and ionization state. To achieve sensitivity to collective electron oscillations, XRTS measurements require limited momentum transfer where the spectral separation of elastic and inelastic scattering is small. Such measurements require an x-ray probe source with a narrow bandwidth in order to reduce the spectral overlap between scattering contributions, allowing for the different features to be more precisely deconvolved. In this investigation, we discuss the theory behind how the bandwidth for a common XRTS probe, Zn He-α emission at 9 keV, can be reduced using a Cu K-edge filter.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Measuring characteristic differences between high- and low-performing discharges on the MegaJOuLe Neutron Imaging Radiography (MJOLNIR) DPF

A dense plasma focus (DPF) is a compact coaxial plasma gun, which completes its discharge as a Z-pinch, producing short (<100 ns) pulses of ions, x rays, and/or neutrons. Lawrence Livermore National Laboratory recently constructed and began operating a new device, the MJOLNIR (MegaJOuLe Neutron Imaging Radiography) DPF, which is designed for single-pulse flash neutron radiography. This device has achieved neutron yields of up to 4.1×10 11 neutrons/pulse at 3.3 MA peak current, and higher-current commissioning is under way. Like most DPFs, MJOLNIR exhibits variable yields in some configurations. Here, we present evidence of the role of parasitic current paths within the gun in stochastically influencing the yield. First through “conditioning shots,” where new hardware has been introduced, we show that increased run-down and run-in speeds correlate with higher yields. These observations are consistent with current being delivered to the electrodes but not to the main plasma sheath, degrading the implosion-driving force. Once nominal conditions are established, we correlate low-performing discharges with smaller current dip and associated voltage spike for a fixed machine configuration. A snow-plow model is able to recreate small-magnitude current dips through the introduction of a parasitic current path, and particle-in-cell simulations establish how parasitic current paths lower the ion beam energy available to produce neutrons. Finally, we observe an increased likelihood of shots with low yield and smaller current dip with increasing fill pressure.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

X-ray self-emission imaging with spherically bent Bragg crystals on the Z-machine

Here, an x-ray imaging scheme using spherically bent crystals was implemented on the Z-machine to image x rays emitted by the hot, dense plasma generated by a Magnetized Liner Inertial Fusion (MagLIF) target. This diagnostic relies on a spherically bent crystal to capture x-ray emission over a narrow spectral range (<15 eV), which is established by a limiting aperture placed on the Rowland circle. The spherical crystal optic provides the necessary high-throughput and large field-of-view required to produce a bright image over the entire, one-cm length of the emitting column of a plasma. The average spatial resolution was measured and determined to be 18 µm for the highest resolution configuration. With this resolution, the radial size of the stagnation column can be accurately determined and radial structures, such as bifurcations in the column, are clearly resolved. The success of the spherical-crystal imager has motivated the implementation of a new, two-crystal configuration for identifying sources of spectral line emission using a differential imaging technique.

47 OTHER INSTRUMENTATION↗
DOE OSTI2026

SALSAA: a statistical approach to line shapes from an average atom

Ion-Stark line broadening is a key density diagnostic for hot dense plasmas relevant to inertial fusion and astrophysics. It is caused by interactions of a radiating ion with nearby perturbing ions, whose electric microfields lead to changes in bound-bound transition energies. Ion-Stark broadening becomes increasingly difficult to compute for complex, many-electron ions with myriad transitions. In this paper, we propose a simplified approach to ion-Stark broadening based on self-consistent ion distributions and electronic structure from an average-atom model. We find that this approach reproduces the line shape predictions of one traditional method for high-n K-shell emission lines in aluminum ions with accuracy sufficient for density diagnostics in thermal plasmas with equal ion and electron temperatures. We expect that this approach can be extended to provide a reasonable picture of ion-Stark broadening in many-electron ions, enabling rapid calculations of line profiles in complex spectra.

average-atom↗
DOE OSTI2022

Hybrid Kohn-Sham+Thomas-Fermi scheme for high-temperature density functional theory

We report density functional theory has revolutionised our understanding of dense, strongly coupled systems in the condensed-matter limit. At elevated temperatures, such as those found in warm dense matter and dense plasma, the computational cost of calculating enough states to accurately describe a thermal ensemble of electrons is a major obstacle to practical Kohn-Sham calculations. This problem has recently been tackled from a number of approaches, including a plane-wave approximation for electrons at high energy. In this work, we demonstrate how the Thomas-Fermi density of states, equivalent to a local plane-wave approximation, can yield improved results for thermodynamic quantities, electron density profiles, and interatomic forces while requiring fewer states than existing methods.

36 MATERIALS SCIENCE↗
DOE OSTI2022

First-principles study of L -shell iron and chromium opacity at stellar interior temperatures

Recently developed free-energy density functional theory (DFT)-based methodology for optical property calculations of warm dense matter has been applied for studying L-shell opacity of iron and chromium at T = 182 eV. We use Mermin–Kohn–Sham density functional theory with a ground-state and a fully temperature-dependent generalized gradient approximation exchange-correlation (XC) functionals. It is demonstrated that the role of XC at such a high-T is negligible due to the total free-energy of interacting system being dominated by the noninteracting free-energy term in agreement with estimations for the homogeneous electron gas. Furthermore, our DFT predictions are compared to the radiative emissivity and opacity of dense plasmas model, to the real-space Greens function method, and to experimental measurements. Good agreement is found between all three theoretical methods, and in the bound–continuum region for Cr when compared to the experiment, while the discrepancy between direct DFT calculations and the experiment for Fe remains essentially the same as for plasma-physics models.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Optimizing MeV photon dose generation in laser-solid interactions via stable beam propagation

Bremsstrahlung MeV x rays with high doses are essential for radiography of dense objects. Intense, short-pulse laser-driven MeV x-ray sources offer a promising solution, but understanding how the dose scales with laser intensity is crucial for their development. While theory predicts a square root scaling with laser intensity, experimental verification has been hindered by significant shot-to-shot variations, often exacerbated by long preplasma scale lengths from low laser contrast. Here, we demonstrate low shot-to-shot dose variation and confirm the theoretical scaling using high-contrast OMEGA EP laser interactions with millimeter-thick tantalum foils, achieving MeV x-ray doses up to 5.4 rad at 1 m for E photon > 500 keV. Simulations reveal that the unique focal spot of the OMEGA EP laser enables efficient x-ray generation and reduced variability by facilitating deeper laser penetration into dense plasma, even with shorter preplasma scale lengths. Published by the American Physical Society 2025

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

DIII-D Electron Cyclotron Heating and Current Drive System Status and Plans

The DIII-D 110 GHz Electron Cyclotron Heating and Current Drive (ECH/ECCD) System supports a wide range of experiments at the DIII-D National Fusion Facility and is pioneering innovative new techniques for future fusion reactors. Here, the system currently includes 8 sockets with 4 installed gyrotrons, 31.75 mm circular corrugated transmission lines, four dual real time steerable launchers plus two Top Launchers. After the successful testing of the first Top Launcher, that injects the EC waves downward nearly parallel to the resonance layer with double current drive efficiency and a long absorption path, a second new Top Launcher was designed and installed with an upgraded design. Some of the operational limitations encountered for the 110 GHz X-mode second harmonic resonance scenario launched in over-dense plasmas were overcome with the alternative use of O-mode second harmonic launch. Two new gyrotrons in a new series manufactured by CPI were installed and tested, bringing up the total installed power to 3 MW. The installation of repaired and new gyrotrons will increase the number of installed gyrotrons to 7 in 2023. An addition to the DIII-D building will be completed in early 2022 to provide the space to expand the ECH/ECCD system to ten gyrotron systems, plus an extra gyrotron test socket.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Chasing ghosts: characterization of artifact generation in coded aperture decoding due to experimental implementation

Coded aperture imaging is a form of lensless aperture imaging that projects multiple overlapping images of the source onto the detector, enhancing signal strength, which is advantageous for low-flux sources or high-resolution imaging. This technique requires decoding of the detector signal to reconstruct the original source, which involves convolving the detector data with the aperture pattern. When the signal is from a centered point source, the reconstructed source image is known as the point spread function (PSF). A clean PSF without artifacts is a Dirac delta function [Appl. Opt. 20, 1858 (1981)]. This paper examines the robustness of the decoding process against variations in experimental tolerances by analyzing artifact growth in the reconstructed PSF. We illustrate the effects of incorrect magnification, rotation, and detector size and find that aperture–detector rotational misalignment about the imaging axis is the most sensitive parameter, with significant artifact generation occurring with angular offsets of less than one degree. We discuss compensation methods for imperfect aperture placement, finding that small detector sizes produce uncompensatable artifact generation, and compare theoretical predictions with experimental PSF measurements of a rank , 6.8 mm thick (less than one mean free path) coded aperture with a 3.5 mm cell size, conducted at the MegaJOuLe Neutron Imaging Radiography dense plasma focus [IEEE Trans. Plasma Sci. 49, 3299 (2021)] using a 2.45 MeV neutron source. Based on our findings, we recommend using magnified coded apertures in the under-sampled regime, which allows for the inclusion of fiducial markers to characterize aperture–detector rotational offsets and the addition of mechanical coupling, where possible, to constrain rotational and magnification offsets.

Selwood, M. P. [Lawrence Livermore National Labora↗
DOE OSTI2020

NDSE Static Series V & VI Test Results

The purpose for the Neutron-Diagnosed Subcritical Experiment (NDSE) Static Test Series at the Nevada National Security Site (NNSS) Area 11 is to develop and validate the capability to make precise and accurate measurements of k eff for Special Nuclear Material (SNM) targets with k eff ~ 0.95.1 The series has now completed six sets of measurements using the deuterium-tritium (DT) Dense Plasma Focus (DPF) neutron source, with a Rocky-Flats-Shells Highly Enriched Uranium (RF HEU) target, to measure the gamma die-away to this purpose. The last of these series, Series V and VI, are the subject of this report. Both series were performed on a target comprised of the Object IV HEU + CH 2 configuration, which is identical to Object II but with smaller DPF collimators that limit the incident neutron flux to the HEU radius.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2020

Single-Crystal X-Ray Spectropolarimeter

X-ray spectropolarimetry is a diagnostics technique suitable for measuring intense electron beams and strong magnetic fields in hot, dense plasmas. To increase the accuracy achievable, we investigated the possibility of measuring both orthogonal components of linear polarization simultaneously using a single crystal. We demonstrated experimentally for the first time that crystals with cubic symmetry can be used as polarizing beam splitters. We also found that the polarization-splitting planes in cubic crystals can be accessed in two crystal orientations, a property that can be used to decrease the clutter in polarized spectra. In parallel, we developed a ray-tracing code and are working to add the crystal reflectivity to instrument modeling codes, to help us interpret the spectra and to design spectroscopic and spectropolarimetric instruments. This work is motivated by the need to perform measurements of important quantities in difficult experimental conditions, such as the axial magnetic field at stagnation in magnetized liner inertial fusion loads.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2022

High-Fidelity Dynamic Neutron Imaging and Radiography for Subcritical Experiments and Other Applications (Final Report)

This project aims to advance neutron technologies that support subcritical experiments (SCEs) and other dynamic material applications. In previous years, there were three main thrusts for this project. The first and main effort focused on imaging the source of neutrons on a dense plasma focus (DPF). The second portion focused on improving the neutron yield from a DPF. The source developed on the Nevada National Security Site (NNSS) Gemini DPF yielded ~8 × 10 11 deuterium-deuterium (DD) neutrons/pulse in relatively short pulse widths of approximately 100 ns FWHM.

47 OTHER INSTRUMENTATION↗
DOE OSTI2023

Flash Neutron Imaging [Poster]

The NNSS has extensive historical experience with high-fidelity flash neutron imaging which may be applicable to the needs of NA-22. In recent neutron imaging tests, a dense plasma focus (DPF) discharges a capacitor bank across a hydrogen-filled diode to create a flash of fusion neutrons emitted from a point, which can be used for active interrogation. Object inspection may include both radiography transmission imaging as well as emission imaging of the subject via an aperture. A scintillator screen (coupled to a low-Z converter when necessary) converts deposited energy to visible light, which is relayed through optics to an ultra-sensitive visible imager contained in a light-tight box. Flash photon imaging, utilizing bremsstrahlung emission instead of fusion neutrons, is also available and is more mature.

98 NUCLEAR DISARMAMENT, SAFEGUARDS, AND PHYSICAL P↗
DOE OSTI2024

Modeling Competing Line-broadening Mechanisms in Neutron Star Atmospheres: Interference between Motional Stark and Ion Broadening

Neutron star surfaces have extremely high magnetic fields. In the atmosphere, the broadening of spectral lines will be substantial from the dense plasma as well as from the magnetic field. One broadening mechanism of note is due to the motional Stark effect (MSE)—an additional electric field that arises from the motion of the atom in the magnetic field. However, approximate formulae are often used to construct atmosphere models, and the MSE is assumed to be the dominant line-broadening mechanism even in ions. Detailed pressure-broadening models in these extreme magnetic fields are now currently being developed. In these more detailed models, it was suggested that the MSE may not be as large as previously predicted. If correct, this hypothesis implies that neutron star line widths might be dominated by pressure broadening rather than by motional Stark broadening. We find that, in the absence of plasma perturbations, for typical magnetic fields (B = 10 12 G), mid-Z elements, such as oxygen, have motional Stark widths of order 1 eV for transitions between dipole-allowed transitions from the ground state, though higher temperatures and transitions to higher-energy states are expected to have more broadening. The MSE also breaks down selection rules, giving rise to forbidden transitions, which have much larger widths. When plasma perturbations are included, we find that the plasma perturbation and motional Stark processes are not independent and, as a result, the spectral lines become narrow in a nontrivial way and display harmonics of the ion cyclotron frequency.

74 ATOMIC AND MOLECULAR PHYSICS↗