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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Electron acceleration at oblique angles via stimulated Raman scattering at laser irradiance >10 16 W cm –2 μm 2

The generation of hot, directional electrons via laser-driven stimulated Raman scattering (SRS) is a topic of great importance in inertial confinement fusion (ICF) schemes. Little recent research has been dedicated to this process at high laser intensity, in which back, side, and forward scatter simultaneously occur in high energy density plasmas, of relevance to, for example, shock ignition ICF. In this paper, we present an experimental and particle-in-cell (PIC) investigation of hot electron production from SRS in the forward and near-forward directions from a single speckle laser of wavelength λ 0 = 1.053μm, peak laser intensities in the range I 0 = 0.2–1.0×10 17 Wcm –2 and target electron densities between ne = 0.3–1.6% n c , where n c is the plasma critical density. As the intensity and density are increased, the hot electron spectrum changes from a sharp cutoff to an extended spectrum with a slope temperature T = 34 ± 1 keV and maximum measured energy of 350 keV experimentally. Multidimensional PIC simulations indicate that the high energy electrons are primarily generated from SRS-driven electron plasma wave phase fronts with k vectors angled ~50° with respect to the laser axis. These results are consistent with analytical arguments that the spatial gain is maximized at an angle which balances the tendency for the growth rate to be larger for larger scattered light wave angles until the kinetic damping of the plasma wave becomes important. The efficiency of generated high energy electrons drops significantly with a reduction in either laser intensity or target electron density, which is a result of the rapid drop in growth rate of Raman scattering at angles in the forward direction.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

LaserNetUS at the Extreme Light Laboratory. Final report

This is the final report for LaserNetUS, Grant # DE-SC0019419. This project covered the first two annual cycles (2018-2020) of LaserNetUS experiments conducted at the Extreme Light Laboratory, University of Nebraska-Lincoln. The project provided students and scientists from four institutions (BYU, Stanford, UNR, and ARFL) with access to a world-class high-intensity laser facility. Experimental results were obtained on the topics of Nonlinear Thomson scattering, Relativistic vacuum acceleration, and electron beams in relativistic high-energy-density plasma to study x-ray line emission and radio frequencies of ultrashort relativistic electron beam interactions. Another benefit was the training of 10 students (undergraduate or graduate) and 6 young scientists (postdoc or associate/research professors) in critical areas to the future development of high energy density science and high-power laser technology.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Observation of a magneto-Rayleigh-Taylor instability in magnetically collimated plasma jets

We present the direct experimental observation of the formation of a diamagnetic cavity and magneto-Rayleigh-Taylor (MRT) instability in a β ≈ 1 high energy density plasma. Proton radiography is used to measure the two dimensional path-integrated magnetic field in a laser-produced plasma propagating parallel to a preimposed magnetic field. Flutelike structures, associated with the MRT instability, are observed to grow at the surface of the cavity, with a measured wavelength of 1.2 mm and growth time of 4 ns. These measurements are in good agreement with predictions of three dimensional magnetohydrodynamic simulations using the GORGON code. Published by the American Physical Society 2024

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

On numerical errors to the fields surrounding a relativistically moving particle in PIC codes

The particle-in-cell (PIC) method is widely used to model the self-consistent interaction between discrete particles and electromagnetic fields. It has been successfully applied to problems across plasma physics including plasma based acceleration, inertial confinement fusion, magnetically confined fusion, space physics, astrophysics, high energy density plasmas. In many cases the physics involves how relativistic particles (those with high relativistic γ factors) are generated and interact with plasmas. However, when relativistic particles stream across the grid, both in “vacuum” and in plasma, many numerical issues may arise which can lead to unphysical results. We present a detailed analysis of how discretized Maxwell solvers used in PIC codes can lead to numerical errors to the fields that surround particles that move at relativistic speeds across the grid. Expressions for the axial electric field as integrals in k space are presented that reveal two types of errors. The first arises from errors to the numerator of the integrand and leads to unphysical fields that are antisymmetric about the particle. Furthermore, the second arises from errors to the denominator of the integrand and lead to Cherenkov like radiation in “vacuum”. These fields are not anti-symmetric, extend behind the particle, and cause the particle to accelerate or decelerate depending on the solver and parameters. The unphysical fields are studied in detail for two representative solvers - the Yee solver and the FFT based solver. Although the Cherenkov fields are absent, the space charge fields are still present in the fundamental Brillouin zone for the FFT based solvers. In addition, the Cherenkov fields are present in higher order zones for the FFT based solvers. Comparison between the analytical solutions and PIC simulation results are presented. A solution for eliminating these unphysical fields by modifying the k operator in the axial direction is also presented. Using a customized finite difference solver, this solution was successfully implemented into OSIRIS [1]. Results from the customized solver are also presented. Additionally, this solution will be useful for a beam of particles that all move in one direction with a small angular divergence.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Ultra-intense femtosecond laser interactions with aligned nanostructures

The interaction of ultrafast laser pulses of relativistic intensity with high aspect ratio nanostructures can efficiently and volumetrically heat matter to an ultra-high-energy-density regime encountered in the center of stars and within the core of fusion capsules compressed by the world’s largest lasers. It also generates gigantic quasi-static electromagnetic fields that accelerate particles to very high energy. Here, we present an overview of the physics and applications of these dense relativistic plasmas that can be created with pulses of relatively modest energy from lasers that can operate at a high repetition rate. Recent nanowire array experiments produced near-solid density plasmas with an extreme degree of ionization (e.g., Au +72 ), converted ultrafast pulses of laser light into intense x-ray flashes with record efficiency, and accelerated ions to MeV energies, efficiently driving micro-scale fusion reactions that generate flashes of quasi-monoenergetic neutrons. These plasmas also serve as a platform for advancing the understanding of atomic processes in extreme environments and open a new pathway to laser-driven fusion energy. The irradiation of nanostructures at intensities of > 1 x 10 22 W cm –2 is predicted to lead to an extreme ultra-high energy density plasma regime characterized by terabar pressures that is virtually unexplored.

Optics↗
DOE OSTI2024

Toward electron temperature profiles in hot-dense plasmas from x-ray spectral ensembles

High repetition rate laser systems enable new strategies for diagnosing plasma behavior with large datasets. Here, we define an ensemble technique that relies on randomized targeting of x-ray tracer micro-stripes. On each shot, a high-intensity laser pulse is focused on a solid target with Ti tracer stripes embedded in an Al foil, randomly targeting a micro-stripe, a portion of a stripe, or a gap between stripes. High-resolution, time-integrated x-ray spectrometers capture line emission from the portion of the micro-stripe that is heated to sufficiently high electron temperatures. Accumulation of many such cases is used to construct ensemble distributions of x-ray line intensities that encompass all relative offsets of the laser focus to the micro-stripe centers. Synthetic intensity distributions are likewise generated using collisional-radiative modeling. Bayesian fitting of modeled to measured intensity distributions establishes the most likely radial temperature profiles, enabling comparison to hydrodynamic models and calling into question the cylindrical symmetry of these micro-stripe-embedded systems. Ensemble techniques have significant potential for high-energy-density plasma diagnostics, especially with the advent of high repetition rate experiments.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

LaserNetUS at the Extreme Light Laboratory

This is the final report for LaserNetUS, Grant # DE-SC0019419. This project covered the first two annual cycles (2018-2020) of LaserNetUS experiments conducted at the Extreme Light Laboratory, University of Nebraska-Lincoln. The project provided students and scientists from four institutions (BYU, Stanford, UNR, and ARFL) with access to a world-class high-intensity laser facility. Experimental results were obtained on the topics of Nonlinear Thomson scattering, Relativistic vacuum acceleration, and electrons beams in relativistic high-energy-density plasma to study x-ray line emission and radio frequencies of ultrashort relativistic electron beam interactions. Another benefit was the training of 10 students (undergraduate or graduate) and 6 young scientists (postdocs or associate/research professors) in areas that are key to the future development of high energy density science and high-power laser technology.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1970

Laser heating of ionized helium

High energy density plasma generation by heating He gas to high temperatures with electric discharge and focused ruby laser beam

Scherrer, V. E.↗
DOE OSTI2023

An investigation of shock formation vs shock mitigation of colliding plasma jets

Here, this work studies the interaction between colliding plasma jets to understand regimes in which jet merging results in shock formation vs regimes in which the shock formation is mitigated due to the collisionless interpenetration of the jets. A kinetic model is required for this study because fluid models will always produce a shock upon the collision of plasma jets. The continuum-kinetic, Vlasov–Maxwell–Dougherty model with one velocity dimension is used to accurately capture shock heating, along with a novel coupling with a moment equation to evolve perpendicular temperature for computational efficiency. As a result, this relatively inexpensive simulation can be used for detailed scans of the parameter space toward predictions of shocked vs shock-mitigated regimes, which is of interest for several fusion concepts such as plasma-jet-driven magneto-inertial fusion, high-energy-density plasmas, astrophysical phenomena, and other laboratory plasmas. The initial results obtained using this approach are in agreement with the preliminary outcomes of the plasma liner experiment.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Proof-of-concept Talbot–Lau x-ray interferometry with a high-intensity, high-repetition-rate, laser-driven K-alpha source

Talbot–Lau x-ray interferometry is a grating-based phase-contrast technique, which enables measurement of refractive index changes in matter with micrometric spatial resolution. The technique has been established using a variety of hard x-ray sources, including synchrotron, free-electron lasers, and x-ray tubes, and could be used in the optical range for low-density plasmas. The tremendous development of table-top high-power lasers makes the use of high-intensity, laser-driven K-alpha sources appealing for Talbot–Lau interferometer applications in both high-energy-density plasma experiments and biological imaging. To this end, we present the first, to the best of our knowledge, feasibility study of Talbot–Lau phase-contrast imaging using a high-repetition-rate laser of moderate energy (100 mJ at a repetition rate of 10 Hz) to irradiate a copper backlighter foil. The results from up to 900 laser pulses were integrated to form interferometric images. A constant fringe contrast of 20% is demonstrated over 100 accumulations, while the signal-to-noise ratio continued to increase with the number of shots. Phase retrieval is demonstrated without prior ex-situ phase stepping. Instead, correlation matrices are used to compensate for the displacement between reference acquisition and the probing of a PMMA target rod. The steps for improved measurements with more energetic laser systems are discussed. The final results are in good agreement with the theoretically predicted outcomes, demonstrating the applicability of this diagnostic to a range of laser facilities for use across several disciplines.

Bouffetier, V. (ORCID:0000000160791260)↗
DOE OSTI2020

Saturn-ring proton backlighters for the National Ignition Facility

Proton radiography is a well-established technique for measuring electromagnetic fields in high-energy-density plasmas. Fusion reactions producing monoenergetic particles, such as D 3 He, are commonly used as a source, produced by a capsule implosion. Using smaller capsules for radiography applications is advantageous as the source size decreases, but on the National Ignition Facility (NIF), this can introduce complications from increasing blow-by light, since the phase plate focal spot size is much larger than the capsules. In this article, we report a demonstration of backlighter targets where a “Saturn” ring is placed around the capsule to block this light. The nuclear performance of the backlighters is unperturbed by the addition of a ring. We also test a ring with an equatorial cutout, which severely affects the proton emission and is not viable for radiography applications. These results demonstrate the general viability of Saturn ring backlighter targets for use on the NIF.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Impact of penetrating collisions of plasma ions on spectral line shapes

Spectral-line-broadening models have been moving towards including full Coulomb interactions between the atom and plasma, replacing the commonly used dipole approximation. The effects of the full Coulomb interaction have been thoroughly explored for plasma electrons, resulting in redshifts of spectral lines in high-energy-density plasmas. We explore the impact of a full Coulomb treatment on ion broadening. Penetrating collisions due to ions do not significantly impact the linewidths. The most significant aspect is the appearance of quasimolecular resonances in the far line wings, such as those previously observed in white-dwarf spectra. We identify several problems with the existing models. The most direct implementation causes the quasimolecular features to appear at the wrong photon energies. It is possible to include the detailed molecular structure, but this currently requires the Anderson-Talman approximation, which ignores the N-body properties of the plasma. We find that N-body effects can substantially broaden these quasimolecular features and even shift them, depending on the plasma conditions. We conclude that penetration of ions into the spatial extent of the radiator wave function does not strongly affect the usual diagnostics and may have a moderate to weak effect on opacity. Furthermore, the Rosseland mean opacity is weighted towards low-opacity regions of a spectrum, where these quasimolecular features are found.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Symmetric Set of Transport Coefficients for Collisional Magnetized Plasma

Braginskii extended magnetohydrodynamics is used to model transport in collisional astrophysical and high energy density plasmas. We show that commonly used approximations to the α ⊥ and β ⊥ transport coefficients [e.g., Epperlein and Haines, Phys. Fluids 29 , 1029 (1986) ] have a subtle inaccuracy that causes significant artificial magnetic dissipation and discontinuities. This is because magnetic transport actually relies on β ∥ - β ⊥ and α ⊥ - α ∥ , rather than α ⊥ and β ⊥ themselves. We provide fit functions that rectify this problem and thus resolve the discrepancies with kinetic simulations in the literature. Furthermore, then implemented in the g orgon code, they reduce the predicted density asymmetry amplitude at laser ablation fronts. Recognizing the importance of α ⊥ - α ∥ and β ∥ - β ⊥ , we recast the set of coefficients. This makes explicit the symmetry of the magnetic and thermal transport, as well as the symmetry of the coefficients themselves.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

X-Ray Diffraction of Ramp-Compressed Silicon to 390 GPa

Silicon (Si) exhibits a rich collection of phase transitions under ambient-temperature isothermal and shock compression. This report describes in-situ diffraction measurements of ramp compressed Si between 40 and 389 GPa. Angle-dispersive x-ray scattering reveals that Si assumes an hexagonal close-packed (hcp) structure between 40 and 93 GPa, and, at higher pressure, a face-centered cubic (fcc) structure which persists to at least 389 GPa, the highest pressure for which the crystal structure of Si has been investigated. Furthermore, the range of hcp stability extends to higher pressures and temperatures than predicted by theory.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Implementation of Talbot–Lau x-ray deflectometry in the pulsed power environment using a copper X-pinch backlighter

A Talbot–Lau x-ray deflectometer can map electron density gradients in high energy density plasmas, as well as provide information about plasma elemental composition through single-image x-ray refraction and attenuation measurements. A new adaptation to a pulsed power environment used backlighting from copper X-pinches, allowing for electron density mapping of a low-Z object. Even though the X-pinch backlighter is not properly optimized for emitting x-rays in terms of source size and photon fluence, Moire fringe patterns with contrast up to 14% and fringe shift due to refraction on a beryllium object are obtained. Due to the proximity of the deflectometer with the X-pinch (~6 cm), it is shown that a protective filter is required to avoid damage in the closest (i.e., source) grating due to both plasma debris and mechanical shock. Regarding grating survival, these did not show any damage due to the intense magnetic field or heating induced by plasma radiation. Electron density on beryllium was measured with a difference lower than 16%. The areal electron density mapping of the sample was limited by source size characteristics, in similarity to transmission radiography. These results show the potential of plasma electron density as well as material mapping through Talbot–Lau x-ray deflectometry in a pulsed power environment.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Experimental Measurements of Ion Diffusion Coefficients and Heating in a Multi-Ion-Species Plasma Shock

Collisional plasma shocks generated from supersonic flows are an important feature in many astrophysical and laboratory high-energy-density plasmas. Compared to single-ion-species plasma shocks, plasma shock fronts with multiple ion species contain additional structure, including interspecies ion separation driven by gradients in species concentration, temperature, pressure, and electric potential. We present time-resolved density and temperature measurements of two ion species in collisional plasma shocks produced by head-on merging of supersonic plasma jets, allowing determination of the ion diffusion coefficients. Here our results provide the first experimental validation of the fundamental inter-ion-species transport theory. The temperature separation, a higher-order effect reported here, is valuable for advancements in modeling HED and ICF experiments.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Performance of a hardened x-ray streak camera at Lawrence Livermore National Laboratory’s National Ignition Facility

Electron tubes continue to provide the highest speeds possible for recording dynamics of hot high-energy density plasmas. Standard streak camera drive electronics and CCD readout are not compatible with the radiation environment associated with high DT fusion yield inertial confinement fusion experiments >10 13 14 MeV DT neutrons or >10 9 n cm -2 ns -1 . Here, we describe a hardened x-ray streak camera developed for the National Ignition Facility and present preliminary results from the first experiment on which it has participated, recording the time-resolved bremsstrahlung spectrum from the core of an inertial confinement fusion implosion at more than 40× the operational neutron yield limit of the previous National Ignition Facility x-ray streak cameras.

47 OTHER INSTRUMENTATION↗