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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS2011

Models of the Solar Atmospheric Response to Flare Heating

I will present models of the solar atmospheric response to flare heating. The models solve the equations of non-LTE radiation hydrodynamics with an electron beam added as a flare energy source term. Radiative transfer is solved in detail for many important optically thick hydrogen and helium transitions and numerous optically thin EUV lines making the models ideally suited to study the emission that is produced during flares. I will pay special attention to understanding key EUV lines as well the mechanism for white light production. I will also present preliminary results of how the model solar atmosphere responds to Fletcher & Hudson type flare heating. I will compare this with the results from flare simulations using the standard thick target model.

Allred, Joel↗
DOE OSTI2022

Diagnosing the DARHT Electron Beam-Target Interaction and Hydrodynamic Expansion [Dissertation]

Quantitative electron beam-target interaction studies on the Dual-Axis Radiographic Hydrodynamic Test (DARHT) electron linear induction accelerators have only been performed recently. This includes characterization of the temperature, density, pressure, extent, and expansion velocity of the plasma plume. The results presented in this dissertation present a detailed and unified overview of the accelerator systems, target heating physics, beam transport, and diagnostic tools. Additional information includes calibration sources, radiation hydrodynamics, spectroscopic-quality radiation transport modeling, experimental measurements, and analyses of electron beam driven aluminum experiments. The first set of spatially and temporally resolved spectroscopic measurements of electron beam driven aluminum are presented. Contamination quantification analyses are used to understand the origin of the strong Na-I 3p-3s lines that are observed in absorption within the aluminum plasma continuum. These results inform the creation of the first spectroscopic-quality radiation transport model that links several atomic physics codes to interpret the conditions from which the Na-I lines originate. A good agreement is found between the surface analysis results and the model which confirms the concentration of the sodium present within the aluminum alloy foil material. It also demonstrates, for the first time on electron beam-driven target experiments, the ability to interpret plasma conditions from measured absorption lines. In a second experimental campaign which focuses on pure aluminum, the Al-I 3p-4s and 3p3d doublets are both measured in emission. A detailed analysis of the Al-I 3p-4s doublet reveals that the lines undergo moderate self-absorption. A simple model of the self-absorption effect is successfully used to match measured spectra at various temperature/density/plasma scale length combinations. These measurements led to the realization of the minimum density that can be resolved by the spectrometers for the Al-I 3p-4s lines due to the large slit width required to observe a signal on aluminum. These measurements also demonstrate the sensitivity of visible and long wave UV spectroscopy to minor changes in both temperature and density. The simple self-absorption model will be useful for analysis of other beam-target interaction experiments with spectra exhibiting either self-absorption or full self-reversal. Substantial headway has been made on the modeling front by linking together several codes needed to model both the energy deposition, hydrodynamic motion, and atomic kinetics to produce synthetic spectral calculations that are compared with experimental measurements. There exists ample space for improvement, especially with benchmarking the hydrodynamics codes and equation-of-state tables with experimental measurements. The X-ray diagnostics required to make these new measurements along with the simulation capabilities required to interpret the results are under development and will be the subject of future studies.

43 PARTICLE ACCELERATORS↗
DOE OSTI2020

C HIMERA : A Massively Parallel Code for Core-collapse Supernova Simulations

Herein we provide a detailed description of the C HIMERA code, a code developed to model core collapse supernovae (CCSNe) in multiple spatial dimensions. The CCSN explosion mechanism remains the subject of intense research. Progress to date demonstrates that it involves a complex interplay of neutrino production, transport, and interaction in the stellar core, three-dimensional stellar core fluid dynamics and its associated instabilities, nuclear burning, and the fundamental physics of the neutrino–stellar core weak interactions and the equations of state of all stellar core constituents—particularly, the nuclear equation of state associated with core nucleons, both free and bound in nuclei. C HIMERA , by incorporating detailed neutrino transport, realistic neutrino–matter interactions, three-dimensional hydrodynamics, realistic nuclear, leptonic, and photonic equations of state, and a nuclear reaction network, along with other refinements, can be used to study the role of neutrino radiation, hydrodynamic instabilities, and a variety of input physics in the explosion mechanism itself. It can also be used to compute observables such as neutrino signatures, gravitational radiation, and the products of nucleosynthesis associated with CCSNe. The code contains modules for neutrino transport, multidimensional compressible hydrodynamics, nuclear reactions, a variety of neutrino interactions, equations of state, and modules to provide data for post-processing observables such as the products of nucleosynthesis, and gravitational radiation. C HIMERA is an evolving code, being updated periodically with improved input physics and numerical refinements. We detail here the current version of the code, from which future improvements will stem, which can in turn be described as needed in future publications.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Cassio Simulations of X-ray Flow Over Lumps (XFOL) Experiments [Slides]

Homogeneous media is not a good approximation for stochastic media with large clump sizes and therefore not valid for our experiments. The media created for these experiments is not Markovian distributed. Stochastic media transport methods don’t work well with non-Markovian mixtures. Sphere at various axial locations in the dmain encounter very different radflow characteristics and therefore result in different spectroscopic signatures. Ongoing analysis of tally surfaces will allow for better characterization of the radiation flow in radiation hydrodynamics simulations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Classical-quantum simulation of non-equilibrium Marshak waves

In the radiation hydrodynamic simulations used to design inertial confinement fusion (ICF) and pulsed power experiments, nonlinear radiation diffusion tends to dominate CPU time. This raises the interesting question of whether a quantum algorithm can be found for nonlinear radiation diffusion which provides a quantum speedup. Recently, such a quantum algorithm was introduced based on a quantum algorithm for solving systems of nonlinear partial differential equations (PDEs) which provides a quadratic quantum speedup. Here, we apply this quantum PDE (QPDE) algorithm to the problem of a non-equilibrium Marshak wave propagating through a cold, semi-infinite, optically thick target, where the radiation and matter fields are not assumed to be in local thermodynamic equilibrium. The dynamics is governed by a coupled pair of nonlinear PDEs which are solved using the QPDE algorithm, as well as two standard PDE solvers: (i) Python's py-pde solver; and (ii) the KULL ICF simulation code developed at Lawrence-Livermore National Laboratory. We compare the simulation results obtained using the QPDE algorithm and the standard PDE solvers and find excellent agreement.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Using tabulated NLTE data for Hohlraum simulations

Non-local thermodyamic equilibrium (NLTE) atomic kinetics is necessary in inertial confinement fusion Hohlraum simulations for adequately modeling high-Z walls and dopants but is computationally very expensive. We present here an approach for tabulating NLTE material data in an economical manner. Material properties for an arbitrary radiation field are provided through tabulated data for a limited set of radiation fields plus derivatives with respect to components of those radiation fields. We have implemented this method in a radiation-hydrodynamics code and compare Hohlraum simulations done with inline NLTE calculations with those done with tables constructed from the same atomic data. The results demonstrate that NLTE tables can replace inline calculations in Hohlraum simulations without a significant loss of accuracy.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Improving Predictive Capability in REHEDS Simulations with Fast, Accurate, and Consistent Non-Equilibrium Material Properties

Predictive design of REHEDS experiments with radiation-hydrodynamic simulations requires knowledge of material properties (e.g. equations of state (EOS), transport coefficients, and radiation physics). Interpreting experimental results requires accurate models of diagnostic observables (e.g. detailed emission, absorption, and scattering spectra). In conditions of Local Thermodynamic Equilibrium (LTE), these material properties and observables can be pre-computed with relatively high accuracy and subsequently tabulated on simple temperature-density grids for fast look-up by simulations. When radiation and electron temperatures fall out of equilibrium, however, non-LTE effects can profoundly change material properties and diagnostic signatures. Accurately and efficiently incorporating these non-LTE effects has been a longstanding challenge for simulations. At present, most simulations include non-LTE effects by invoking highly simplified inline models. These inline non-LTE models are both much slower than table look-up and significantly less accurate than the detailed models used to populate LTE tables and diagnose experimental data through post-processing or inversion. Because inline non-LTE models are slow, designers avoid them whenever possible, which leads to known inaccuracies from using tabular LTE. Because inline models are simple, they are inconsistent with tabular data from detailed models, leading to ill-known inaccuracies, and they cannot generate detailed synthetic diagnostics suitable for direct comparisons with experimental data. This project addresses the challenge of generating and utilizing efficient, accurate, and consistent non-equilibrium material data along three complementary but relatively independent research lines. First, we have developed a relatively fast and accurate non-LTE average-atom model based on density functional theory (DFT) that provides a complete set of EOS, transport, and radiative data, and have rigorously tested it against more sophisticated first-principles multi-atom DFT models, including time-dependent DFT. Next, we have developed a tabular scheme and interpolation methods that compactly capture non-LTE effects for use in simulations and have implemented these tables in the GORGON magneto-hydrodynamic (MHD) code. Finally, we have developed post-processing tools that use detailed tabulated non-LTE data to directly predict experimental observables from simulation output.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Thermal transport modeling of laser-irradiated spheres

Thermal transport of uniformly laser-irradiated spheres of various materials is investigated computationally. One-dimensional simulations of low- to mid-Z materials (Be, Al, and Cu) are performed to evaluate the impact of nonlocal electron transport on experimental observables under laser intensities of relevance to direct-drive inertial confinement fusion. Here we compare thermal transport models of different levels of fidelity: flux-limited Spitzer–Harm diffusion, the Schurtz–Nicolai–Busquet (SNB) reduced-order nonlocal model, and a Fokker–Planck description. Spitzer–Harm diffusion with different flux-limiter factors are compared with different implementations of the SNB model in the HYDRA radiation hydrodynamics code. Under the conditions of interest, the peak heat flux in the thermal front with the SNB model shows good agreement with Fokker–Planck calculations, with the largest errors below 10% at 10 15 W/cm 2 laser intensity. From HYDRA-SNB simulations, two experimentally relevant effects are observed from nonlocal heat transport when compared to flux-limited Spitzer–Harm modeling: coronal temperatures are cooler due to reduced heat fluxes in the expanding plasma and (for mid-Z materials) x-ray emissions are enhanced due to preheating in the dense plasma.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2026

Constraining hydrodynamic models of inertial confinement fusion implosions using capsule surrogate experiments

We conduct capsule surrogate experiments at the National Ignition Facility to calibrate radiation hydrodynamic simulations to infer hydrodynamic conditions that are not observable in indirect drive ignition implosions. We tune the simulations by applying laser power and cross beam energy transfer (CBET) saturation multipliers to match the observables from capsule surrogate experiments. Shock timing, velocity, and symmetry are measured in liquid D 2 filled Keyhole capsule surrogate experiments and implosion trajectory, stagnation time, and shape time history are measured in in-flight 2D backlit x-ray radiography experiments (“2DConA”) of D 2 gas filled capsule implosions. Calibrated simulations suggest that the N210808 ignition implosion (fusion target gain = 0.7) had a shell mass remaining at stagnation of less than the nominal %5 (3.8%) and resulted in less confinement. For N221204, the shell was made 5.75 μm thicker to trade implosion velocity for increased confinement and resulted in a target gain = 1.5 with a shell mass remaining of 5.7%. Furthermore, a single adjusted model can reproduce all shock timing data as changes are made to shell thickness (79–85 μm) and laser wavelength separation (1.8–4.0 Å). However, for the 2DConA implosions, a 5% variation in the peak power laser multipliers and a 30% variation in late-time CBET between experiments are needed to match the observed stagnation times, in-flight $P_2$ shape, and hot-spot $P_2$ shape. While progress is being made to improve the models in simulations using focused experiments, capsule surrogate experiments will continue to be needed to optimize future ignition designs.

Lasers↗
DOE OSTI2024

Impact of moment-based, energy integrated neutrino transport on microphysics and ejecta in binary neutron star mergers

We present an extensive study of the effects of neutrino transport in three-dimensional general relativistic radiation hydrodynamics (GRHD) simulations of binary neutron star (BNS) mergers using our moment-based, energy-integrated neutrino radiation transport (M1) scheme. Here, we consider a total of eight BNS configurations, while varying equation of state models, mass ratios, and grid resolutions, for a total of 16 simulations. We find that M1 neutrino transport is crucial in modeling the local absorption of neutrinos and the deposition of lepton number throughout the medium. We provide an in-depth look at the effects of neutrinos on the fluid dynamics and luminosity during the late inspiral and postmerger phases, the properties of ejecta and outflow, and the postmerger nucleosynthesis. The simulations presented in this work comprise an extensive study of the combined effect of the equation of state and M1 neutrino transport in GRHD simulations of BNS mergers, and establish that the solution provided by our M1 scheme is robust across system properties.

150 ≤ A ≤ 18959 ≤ A ≤ 8990 ≤ A ≤ 149↗
NASA NTRS1992

Shock breakout in SN 1987A

Detailed models for the UV burst from SN 1987A are calculated using a two-temperature radiation hydrodynamics code. The sequence of events which occur during shock breakout is described, including the formation of a radiative precursor, the disappearance of the shock, and the growth of a thin, dense shell above the photosphere which gives rise to a new viscous, isothermal shock. Continuum spectra are calculated under the assumption that the emergent radiation is a dilute blackbody with a color temperature equal to the radiation temperature at the thermalization depth. This color temperature is 2-3 times higher than the effective temperature. Light-travel-time corrections have been included in the light curves and the spectra. Quantities most relevant to accurate modeling of the fluorescing ring around SN 1987A are highlighted.

Ensman, Lisa↗
DOE OSTI2025

Demonstration of x-ray fluorescence spectroscopy as a sensitive temperature diagnostic for high-energy-density physics experiments

We present the use of x-ray fluorescence spectroscopy (XFS) to a sensitive temperature diagnostic in shocked foams at temperatures of 30–75 eV. Cobalt-doped foams were shock compressed using a planar drive at the OMEGA laser facility and photo-pumped with a Zn He⁢𝛼 x-ray source. Analysis of the resulting cobalt 𝐾⁢𝛽 x-ray fluorescence spectra using collisional radiative codes allows the temperature to be determined in the shocked foams. Furthermore, this method provides a sensitive and robust technique to determine temperatures in high-energy-density physics experiments in the tens of electronvolts temperature range. In these experiments, we find that radiation hydrodynamic simulations predict a lower temperature in the shocked foams compared to analysis of the XFS data using collisional radiative models. Although additional experiments with an independent temperature diagnostic to absolutely calibrate XFS spectra for these conditions will be required to resolve this discrepancy, these results demonstrate the excellent temperature sensitivity of XFS spectra for high-energy-density physics experiments.

Atomic spectra↗
DOE OSTI2020

Characterizing laser preheat for laser-driven magnetized liner inertial fusion using soft x-ray emission

Laser heating of a gas in a cylindrical liner held in by a thin foil window is a critical process in the MagLIF (magnetized liner inertial fusion) concept. Window burn-through and gas heating for OMEGA scale MagLIF cylinders as a function of time have been determined using spectrally integrated soft x-ray diagnostics. Window laser absorption is classified in terms of the emitted x-rays from the window plasma as a function of laser energy, and shows that laser energy absorbed is weakly dependent on incident intensity. Radiation-hydrodynamic simulations overestimate the amount of laser energy absorbed by the window as evidenced by the increase in x-ray radiation across several photon energy bands compared to experiments. Gas temperatures inferred from soft x-ray emission from the front 1 mm of the liner are shown to evolve in time in a similar manner to simulation predictions. In conclusion, soft x-ray emission from the gas within the region of the liner that is normally imploded is shown to meet the 100 eV requirements set by the initial point design for laser-driven MagLIF.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Achieving record hot spot energies with large HDC implosions on NIF in HYBRID-E

HYBRID-E is an inertial confinement fusion implosion design that increases energy coupled to the hot spot by increasing the capsule scale in cylindrical hohlraums while operating within the current experimental limits of the National Ignition Facility. HYBRID-E reduces the hohlraum scale at a fixed capsule size compared to previous HYBRID designs, thereby increasing the hohlraum efficiency and energy coupled to the capsule, and uses the cross-beam energy transfer (CBET) to control the implosion symmetry by operating the inner (23° and 30°) and outer (44° and 50°) laser beams at different wavelengths (Δλ> 0). Small case to capsule ratio designs can suffer from insufficient drive at the waist of the hohlraum. We show that only a small amount of wavelength separation between the inner and outer beams (Δλ1-2 Å) is required to control the symmetry in low-gas-filled hohlraums (0.3 mg/cm3 He) with enough drive at the waist of the hohlraum to symmetrically drive capsules 1180 μm in outer radius. This campaign is the first to use the CBET to control the symmetry in 0.3 mg/cm3 He-filled hohlraums, the lowest gas fill density yet fielded with Δλ> 0. We find a stronger sensitivity of hot spot P2 in μm per Angstrom (40–50 μm/Å wavelength separation) than observed in high-gas-filled hohlraums and previous longer pulse designs that used a hohlraum gas fill density of 0.6 mg/cm3. There is currently no indication of transfer roll-off with increasing Δλ, indicating that even longer pulses or larger capsules could be driven using the CBET in cylindrical hohlraums. We show that the radiation flux symmetry is well controlled during the foot of the pulse, and that the entire implosion can be tuned symmetrically in the presence of the CBET in this system, with low levels of laser backscatter out of the hohlraum and low levels of hot electron production from intense laser–plasma interactions. Radiation hydrodynamic simulations can accurately represent the early shock symmetry and be used as a design tool, but cannot predict the late-time radiation flux symmetry during the peak of the pulse, and semi-empirical models are used to design the experiments. Deuterium–tritium (DT)-layered tests of 1100 μm inner radius implosions showed performance close to expectations from simulations at velocities up to ~360 km/s, and record yields at this velocity, when increasing the DT fuel layer thickness to mitigate hydrodynamic mixing of the ablator into the hot spot as a result of defects in the ablator. However, when the implosion velocity was increased, mixing due to these defects impacted performance. The ratio of measured to simulated yield for these experiments was directly correlated with the level of observed mixing. These simulations suggest that reducing the mixing, e.g., by improving the capsule defects, could result in higher performance. In addition, future experiments are planned to reduce the coast time at this scale, delay between the peak compression and the end of the laser, to increase the hot spot convergence and pressure. To reduce the coast time by several hundred ps compared to the 1100 μm inner radius implosions, HYBRID-E has also fielded 1050 μm inner radius capsules, which resulted in higher hot spot pressure and a fusion energy yield of ~170 kJ.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

ALEGRA/Sceptre Code Coupling [Brief]

Researchers at Sandia have developed an advanced radiation hydrodynamic simulation capability by coupling the ALEGRA and Sceptre codes.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2022

Double cylinder target design for study of hydrodynamic instabilities in multi-shell ICF

Cylindrical implosions are used to study hydrodynamic instability growth for inertial confinement fusion (ICF) applications, as the cylindrical geometry allows for easier diagnostic access while retaining convergence effects. In this work, we use the established cylindrical implosion platform [Palaniyappan et al., Phys. Plasmas 27, 042708 (2020)] to inform the double shell ICF campaign [Montgomery et al., Phys. Plasmas 25, 092706 (2018)]. We present a design for a double cylindrical target as an analogue to the double shell ICF capsule in order to study hydrodynamic instability growth on the high-Z inner shell. Our design work is done with two-dimensional (2D) Eulerian radiation-hydrodynamics simulations, considering the axial uniformity of the implosion and feasibility of measuring the instability growth of pre-seeded single mode sinusoidal perturbations. We discuss in depth the design for a target to be directly driven at the OMEGA laser facility [Boehly et al., Opt. Commun. 133, 495 (1997)]. We evaluate the design for axial implosion symmetry and visibility of instability growth using synthetic radiographs constructed from the simulations, as the instability growth on the inner cylinder is experimentally measured using x-ray radiography of the implosion. We find that the seeded perturbation growth on the inner cylinder should be visible in an experiment, even with axial implosion asymmetry and preheat. We compare our 2D simulations with linear theory predictions for perturbation growth and show that a cylinder with lower azimuthal mode number (mode-20) perturbations compares more favorably with linear theory, while a cylinder with higher azimuthal mode number (mode-40) perturbations at the same starting amplitude saturates and is over-predicted by linear theory.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS2011

Using Models for How Energetic Electrons Heat the Atmosphere During Flares

Using models for how energetic electrons heat the atmosphere during flares, we simulate the radiative-hydrodynamic response of the lower solar atmosphere to flare heating. The simulations account for much of the non-LTE, optically thick radiative transfer that occurs in the chromosphere. Our models predict an increase in white light continuum during the flare on the order of 20%, but this is highly sensitive to the electron beam flux used in the simulation. We find that a majority of the white light continuum originates in the chromosphere as a result of Balmer and Paschen recombinations, but a significant portion also forms in the photosphere which has been heated by radiative backwarming.

Allred, Joel↗
DOE OSTI2025

Hydrodynamic expansion and near-infrared absorption of x-ray heated aluminum plasmas

We use x-ray pulses from dense argon plasmas at the Z Machine (Sandia National Laboratories) to generate hypersonic aluminum plasmas akin to material ejecta during proposed planetary defense missions, fusion reactor wall excursions, and other high-energy density processes. Near-infrared absorption is used to diagnose the controlled expansion of the plasmas through cylindrical cavities following their generation from x-ray heating of solid aluminum 7075 alloy. The data are compared to multidimensional radiation hydrodynamics simulations utilizing the ALEGRA multiphysics code, accounting for the dynamics of radiation scattering, material phase change, plasma expansion, thermal re-irradiation, and interactions with the cavity and with the infrared beams. To allow for accurate simulation, density functional theory is used to apply the Hagen–Rubens relation for the far-infrared and is adjoined with a detailed configuration accounting model using the Propaceos code, producing opacities spanning 10 −1 –10 4 eV photon energy for aluminum 7075 alloy, and in comparison with pure aluminum. The model is found to agree with experimental data in the higher-fluence regime when the Hagen–Rubens relation is applied. The ejected material, which is observed to travel up to 55 km/s, is comprised of a strongly ionized, non-LTE plasma front at ∼10 eV temperature followed by a weakly ionized LTE gas at higher density. The present findings lend some confidence to the broad-range equation of state and infrared opacity models for weakly ionized aluminum plasmas while demonstrating an approach to their future refinement, with potential application to astrophysical plasmas and other extreme processes.

Adiabatic process↗