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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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All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Sub-keV design for the National Ignition Facility’s soft x-ray Opacity Spectrometer (OpSpec) and expansion plans for time-resolved measurements

When compared with the National Ignition Facility’s (NIF) original soft x-ray opacity spectrometer, which used a convex cylindrical design, an elliptically shaped design has helped to increase the signal-to-noise ratio and eliminated nearly all reflections from alternate crystal planes. The success of the elliptical geometry in the opacity experiments has driven a new elliptical geometry crystal with a spectral range covering 520–1100 eV. When coupled with the primary elliptical geometry, which spans 1000–2100 eV, the new sub-keV elliptical geometry helps to cover the full iron L-shell and major oxygen transitions important to solar opacity experimentation. The new design has been built and tested by using a Henke x-ray source and shows the desired spectral coverage. Additional plans are underway to expand these opacity measurements into a mode of time-resolved detection, ~1 ns gated, but considerations for the detector size and photometrics mean a crystal geometry redesign. Here, the new low-energy geometry, including preliminary results from the NIF opacity experiments, is presented along with the expansion plans into a time-resolved platform.

47 OTHER INSTRUMENTATION↗
DOE OSTI2022

2nd and 3rd order spectral energy corrections with penumbral de-blurring methodology for opacity platform used on the National Ignition Facility

The Opacity Spectrometer (OpSpec) used in the National Ignition Facility’s opacity experiments measures x-ray spectra from 0.9 to 2.1 keV from the different experimental regions: the backlight source, emission source, and the absorption region with the transmission calculated from these regions. The OpSpec designs have gone through several iterations to help improve the signal-to-noise ratio, remove alternate crystal plane reflections, and improve spectral resolution, which helps to increase the validity of the opacity measurements. However, the source spans well outside the current working spectral range, and higher-order reflections are intrinsic to the crystal, which increases the overall signal seen in the data regions. The recorded data are the convolution of 1st order transmission, higher-order reflections, and the penumbra blurring. In conclusion, this work represents the details for deconvolving the 2nd and 3rd order spectral energy corrections with a penumbral de-blurring to correct the relative measurement of x-ray intensity of different spectral energies and further analysis of datasets relevant to the opacity experiments.

47 OTHER INSTRUMENTATION↗
DOE OSTI2020

2021 Stewardship Science Academic Programs Annual

I am a staff scientist at Sandia National Laboratories (SNL). I work on multiple fundamental-science projects and lead modeling/data-analysis for the stellar opacity experiments. I also work with theorists to refine plasma material-property calculations to make NNSA simulations more predictable. These are challenging and important problems for national security. In fact, our experiments raised questions about “opacity”, the property of matter that controls energy transport inside stars. This work was published by Nature due to its serious implication over broad applications, and our team received NNSA Defense Program Award of Excellence, both in 2015. Work at SNL is collegial and full of learning through interactions with the world’s finest experimentalists and theorists. When I started my Ph.D. program, working at a national lab was a dream position. Today, I collaborate with top scientists to solve mission-critical problems. The Stewardship Science Academic Programs (SSAP) and National Laser Users’ Facility (NLUF) played a vital role in the efficient learning and seamless transition to SNL.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Development on the National Ignition Facility of a High Energy Density Opacity Platform

X-ray opacity is a crucial factor in all radiation-hydrodynamics calculations, yet it is one of the least validated of the material properties in simulation codes for high-energy-density plasmas. Recent opacity experiments at the Sandia Z-machine have shown up to factors of two discrepancies between theory and experiment for various mid-Z elements (Fe, Cr, Ni). These discrepancies raise doubts regarding the accuracy of the opacity models which are used in ICF and stewardship as well as in astrophysics. Therefore, a new experimental opacity platform has been developed on the National Ignition Facility (NIF), not only to verify the Z-machine experimental results, but also to extend the experiments to other temperatures and densities. Within the context of the national opacity strategy, the first NIF experiments were directed towards measuring the opacity of iron at a temperature of ~160 eV and an electron density of ~7xl021 cm-3(Anchor 1). The Z data agree with theory at these conditions, providing a reference point for validation of the NIF platform. Development shots on NIF have demonstrated the ability to create a sufficiently bright point backlighter using an imploding plastic capsule, and also a combined hohlraum, sample and laser drive able to produce iron plasmas at the desired conditions. Spectrometer qualification has been completed, albeit with additional improvements planned, and the first iron absorption spectra have now been obtained.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Go with the Radflow: Thermal radiation experiments in the high energy-density regime [Slides]

Los Alamos National Laboratory is a nuclear weapons laboratory supporting our nation's defense. In support of the mission is a high energy-density physics program in which we design and execute experiments to study radiation-hydrodynamics phenomena and improve the predictive capability of our large-scale multi-physics software codes on our supercomputers. The Radflow Project is maturing a unique spectroscopic measurement that yields a spatially dependent supersonic radiation wavefront profile. The spectroscopic measurement is much more constraining than the typically used radiography, which measures the density changes due to the shock as the radiation wave goes subsonic. Recently, the spectroscopic measurement has been applied to advanced targets with a detailed heterogeneity representing a single realization of a stochastic medium. The Radflow Project also conducts opacity experiments to explain the current conundrum of the experimental iron opacity differing from theory, which is important in modeling the sun. More than that, though, we need to be able to answer these science questions and be able to validate our theory and codes.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Opacity on NIF: Anchor 2 Iron (Level 2 Milestone 7118 Report)

In FY2020 we fulfilled the exit criteria of milestone 7118. We fielded iron opacity experiments at higher densities and temperatures approaching anchor 2 conditions and made good progress on overcoming the problems that we found. This report describes in detail the progress that has been made. We presented the results in a LANL seminar on August 10 and we gave two talks on our results to the National Opacity Workshop Series, one on July 9 and the other on September 14. Before discussing the anchor 2 measurements, we present an update of the NIF anchor 1 data. We did a new analysis of the anchor 1 data and compared the results to a series of calculations using the LANL ATOMIC code. Figures 1 and 2 compare the data with the best-fit to calculations. This result is significantly improved over the result published in Atoms. The differences are small for the iron quasi-continuum between 8-9.5 Å and for the Mg Heα and Lyα lines. The opacities near the centers of the iron bound-bound features also match fairly well in the 9.5-12.5 Å range. However, the opacity windows between the large iron bound-bound features are deeper in the Atomic predictions than the measurement. Furthermore, large discrepancies exist for the Mg He β, γ, and δ lines and for the short-wavelength quasicontinuum. The experiment and analysis refinements described below have set the stage for unraveling these discrepancies. Specifically, we can repeat the Anchor 1 experiments using improved backlighter, hohlraum, and spectrometers to obtain reduced backgrounds and better spectral resolution. Exploiting the AlMg calibration experiments and repeating the Anchor 1 measurements multiple times will enable formal and rigorous uncertainty determination. This well-defined path gives us confidence that high quality opacity data can be obtained on NIF.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

How transient effects can change the inferred plasma temperatures when using K-shell sulfur line ratios in a time dependent iron sulfide plasma

This paper describes how the steady state atomic kinetics approximation can underestimate the electron temperature determined from K-shell lines in ps-time-scale transient plasmas. In particular, we model the temperature determination of solid FeS targets used in opacity experiments at the Orion laser facility from the ratio of sulfur He-α to Ly-α lines. Such experiments use short-pulse lasers to heat a thin microdot of FeS buried in a plastic target to temperatures of more than 1 keV and densities of approximately 1–2 g/cm 3 . Using atomic kinetics calculations based on a temperature history from a radiation hydrodynamic simulation of the target evolution, the peak temperature inferred from the sulfur line ratios is 1.29 keV at 3.1 ps as compared with the input peak temperature of 1.41 keV at 2.0 ps. There is a time lag of 1.2 ps at the peak, and an overall 0.5 ps time lag in the temporal history of the temperature as the plasma cools over the next 10 ps.

Rilloraza, Francisco↗
DOE OSTI2021

National Opacity Program: Analysis of Opacity-relevant X-ray Emission Spectra (Milestone Report ID 7121)

We have produced high energy density iron plasmas at temperatures above 1 keV and electron densities exceeding 1023 cm -3 (~ 1 g/cm 3 ) using the Orion laser at the Atomic Weapons Establishment. These plasmas were created by irradiating 50 µm diameter layered targets with frequency doubled (λ = 527 nm), 1 ps laser pulses focused to a 100 µm diameter producing an irradiance of ~ 2 x 10 18 W/cm 2 . The buried layer targets consist of 160 nm iron sulfide (FeS), 60 nm potassium chloride (KCl), and 15 nm carbon. The combined layers are tamped on both sides with 3 µm of parylene-N. The x-ray emission from the plasma was measured using two time-resolved, and four time-integrated Bragg crystal spectrometers, as well as one time-integrated imaging system. One time-resolved x-ray spectrometer measured emission from L-shell transitions in highly charged iron, the other from K-shell transitions in helium-like S 14+ and hydrogen-like S 15+ . The time-integrated spectrometers are intensity-calibrated and measured emission from K-shell transitions in sulfur, potassium, chlorine, and both K-shell and L-shell transitions in iron. The density and temperature of the plasma were determined by modeling the x-ray spectra using different spectral and hydrodynamic modeling packages. A brief overview of the uncertainties associated with the measurements and models are presented. We also give an overview of our 1-D HYDRA-DCA radiation-hydrodynamics model and improvements for future work. Our results aid in assessing experimental uncertainties associated with plasma uniformity and with x-ray emission employed as diagnostics in opacity experiments at temperatures and densities not achievable elsewhere and represent a significant step in creating and diagnosing plasmas near LTE. These results are summarized as part of the completion requirements for milestone 7121

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Error Budgeting

We calculate opacity from k (hn)=-ln[T(hv)]/pL, where T(hv) is the transmission for photon energy hv, p is sample density, and L is path length through the sample. The density and path length are measured together by Rutherford backscatter. Δk = $\partial k$\ $\partial T$ ΔT + $\partial k$\ $\partial (pL)$. We can re-write this in terms of fractional error as Δk/k = Δ1n(T)/T + Δ(pL)/(pL). Transmission itself is calculated from T=(U-E)/(V-E)=B/B0, where B is transmitted backlighter (BL) signal and B 0 is unattenuated backlighter signal. Then ΔT/T=Δln(T)=ΔB/B+ΔB 0 /B 0 , and consequently Δk/k = 1/T (ΔB/B + ΔB$_0$/B$_0$ + Δ(pL)/(pL). Transmission is measured in the range of 0.2<T<0.6 so that 1.5<1/T<5.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Accelerating the rate of discovery: toward high-repetition-rate HED science

As high-intensity short-pulse lasers that can operate at high-repetition-rate (HRR) (>10 H z ) come online around the world, the high energy density (HED) science they enable will experience a radical paradigm shift. The >10 3 increase in shot rate over today's shot-per-hour drivers translates into dramatically faster data acquisition, more experiments, and the ability to exploit machine learning, and thus the potential to significantly accelerate the advancement of HED science. A wide range of HED experiments, from opacity investigations to secondary source generation to plasma nuclear physics, will benefit from the increased statistics, precision, and exploration of phase space. Besides increasing the rate at which scientific experiments can be performed, HRR also allows for the rapid delivery of optimal experiments supported by simulations and modeling augmented by close coupling to empirical data. To fully realize such an HRR framework, numerous subsystems must be developed and brought together, including feedback laser control loops, high-throughput targetry and diagnostics, cognitive simulation, enhanced HED codes, and advanced data analytics. This paper describes the vision for an integrated HRR laser experimental HED system and outlines some of the major considerations and challenges for realizing it.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Oxygen Opacity Measurements at High-Energy-Density Conditions

We present the first benchmark measurements of oxygen opacity at high-energy-density, crucial for understanding stellar interiors. A 3–5−μm thick SiO 2 sample was heated using a Z facility x-ray source, and opacity was measured in the 5–19.5 Å range with multiple spectrometers. The electron temperature and density inferred from Si 𝐾-shell spectra were 148 ± 4 eV and 8.6 ±1.4 × 10 21 cm −3 , respectively. Six experiments showed opacity reproducibility within ±15% and 5%–25% opacity uncertainty. Measured oxygen opacity and seven different opacity models exhibit extraordinary overall agreement. Discrepancies near the H-like photon ionization threshold and in certain spectral lines suggest the need for model refinements.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

National Ignition Facility Opacity Time Resolved Spectrometer Systems Engineering Final Project

The National Ignition Facility (NIF) is the world’s largest and most energetic laser facility. The NIF system is designed to produce high energy density (temperature and pressure) conditions through the application of its 192 laser beams. One of the users of NIF is the opacity platform developed to study the opacities at temperatures and densities relevant to the solar interior and stellar evolution. The platform was developed to study iron (Fe) opacity at temperatures relevant to the solar interior. The opacity campaign uses spectrometers to gather data. Spectrometers utilize crystals to produce x-ray spectra that are recorded on time-integrated and time-resolved detectors. The opacity spectrometer (OpSpec) currently fielded and in use at NIF uses a time integrated film channel to collect data. The opacity spectrometer time resolved (OpSpecTR) will utilize novel hCMOS detectors to capture time resolved images of spectra of interest. The key stakeholders identified for OpSpecTR included the physicists responsible for OpSpec and OpSpecTR, the Target Area Science and Engineering (TASE) department at NIF, the NIF and Photon Science (NIF & PS) Opacity program, the Nevada National Security Site (NNSS) Physics and Engineering program, the Sandia hCMOS manufacturing and testing program, and the Los Alamos National Laboratory (LANL) program sponsor. The Target and Experimental Operations (TEXOPS) was identified as a key stakeholder because the group includes the individuals that will physically interact with the OpSpecTR system as it participates in NIF experiments. The opacity platform collects data in a unique orientation relative to the existing diagnostics fielded at NIF. The existing infrastructure at NIF uses a diagnostic manipulator (DIM) to insert the diagnostic near the target chamber center to collect data during a NIF shot. Existing diagnostics collect data through the center line of the DIM axis and collect relevant data perpendicular to this axis. The opacity platform requires crystals mounted in a specific orientation which requires data collection parallel to the DIM axis. This deviation from standard NIF practices was a key factor in developing requirements.

42 ENGINEERING↗
DOE OSTI2021

Opacity Table Generation

Radiation opacity is a key property of material systems which describes the absorption and scattering of photons. Such processes are an important part of energy transport, diagnostics, and astrophysical phenomena. Recent experiments in iron opacity and continuum lowering have sparked renewed interest in and careful vetting of opacity models. Even within the local thermodynamic equilibrium approximation, opacity varies over a large parameter space: material, temperature, density, and energy. Opacity tables that span wide regimes of this parameter space are of prime importance to radiation-hydrodynamics codes. Accurate opacity calculations cannot be achieved inline during a radiation hydrodynamics simulation since they involve accounting for all possible electron transitions of all important atomic states of a thermal ensemble. Livermore’s current framework utilizes precalculated tables at many densities, temperatures, and energies. Last year, the opacity theory team completed an L2 milestone concerning the development of a new code, Opus, which served the dual purpose of creating a modern code infrastructure and version control as well as the basis for training new members of that team, a critical need as key members near or are passed retirement. For the current L2 milestone, we exercised and validated Opus on three elements: boron, carbon, and nitrogen, which have few enough electrons to allow a careful convergence study over many input parameters. Here, we report on the production of new tables, show their convergence with respect to important parameters, state some of their limitations, and document a mostly automated production process. In this section, we address the milestone completion criteria, found on the title page and the subsection headings. In section 2, we validate Opus against Tycho and compare with TabOp and Atomic. Section 3 details some of the physics implemented in Opus and relevant to this report. We then cover details of the density-temperature grid in section 4 and do a spectral comparison between different parameter settings and different codes in section 5. After summarizing these results in section 6, we give instructions how to run the opacity table scripts in appendix A and document the scripts and input/output files in appendix B.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

DANTE as a primary temperature diagnostic for the NIF iron opacity campaign

The Opacity Platform on the National Ignition Facility (NIF) has been developed to measure iron opacities at varying densities and temperatures relevant to the solar interior and to verify recent experimental results obtained at the Sandia Z-machine, that diverge from theory. The first set of NIF experiments collected iron opacity data at ∼150 eV to 160 eV and an electron density of ∼7 × 1021 cm−3, with a goal to study temperatures up to ∼210 eV, with electron densities of up to ∼3 × 1022 cm−3. Among several techniques used to infer the temperature of the heated Fe sample, the absolutely calibrated DANTE-2 filtered diode array routinely provides measurements of the hohlraum conditions near the sample. However, the DANTE-2 temperatures are consistently low compared to pre-shot LASNEX simulations for a range of laser drive energies. We have re-evaluated the estimated uncertainty in the reported DANTE-2 temperatures and also the error generated by varying channel participation in the data analysis. An uncertainty of ±5% or better can be achieved with appropriate spectral coverage, channel participation, and metrology of the viewing slot.

Opachich, Y. P. (ORCID:0000000314323989)↗
DOE OSTI2024

FY2024 Q4 L2 Milestone 8237 for Opacity-on-NIF

This document addresses parts 2 and 3 of the original milestone request. In the following writeup, the development of OpSpecTR at LLNL by LLNL and NNSS personnel will be detailed first, followed by a write-up of the development of Vme-resolved simulaVons of the opacity-on-NIF experiment. Capsule backlight simulaVons, hohlraum simulaVons, and sample simulaVons from CASSIO are combined to produce the line of sight from the capsule to an effecVve OpSpec posiVon. Spectra are generated by post-processing these simulaVons from either Spect3D, a commercial software by Prism ComputaVonal Sciences, or FESTR (Finite Element Spectroscopic Transport of RadiaVon), a LANL code. While the simulaVons do not at this stage proceed late enough to include the worst of the backgrounds generated from the hohlraum experimentally and each post-processing simulaVon includes only one ray for each spectrometer channel, these efforts represent proof of concept for a new capability to complete Vme-resolved and Vmegated simulaVons for the complete line of sight of the complex opacity-on-NIF geometry. Future work will be discussed at the end of the report for both efforts.

42 ENGINEERING↗
DOE OSTI2025

Sequential spectral line analysis for accurate density and temperature diagnosis of laboratory opacity measurements

The accuracy of iron opacity calculated in stellar interiors has been questioned since the discovery of the “solar problem” and the discrepancies between the measured and modeled iron opacity reported in 2015. Experimental opacity benchmarks require accurate temperature and density measurements, which were inferred by analyzing tracer magnesium spectra in those experiments. Could the observed discrepancy be explained by insufficient accuracy in the inferred temperature, density, and their uncertainties? Previous analyses may have yielded biased results due to three limitations: (1) simultaneous multi-line fitting, (2) approximations in line-shape models, and (3) exclusion of certain spectral lines due to insufficient background characterization. Notably, the first issue is a common concern for many inversion methods, including Bayesian inferences. We present a refined analysis method that overcomes these limitations, applied to three categories of iron opacity experiments (Anchor 1, 2, and 3). In particular, the sequential fitting method yields unbiased results with more realistic uncertainties by accounting for line inconsistencies in the parameter uncertainties. The average electron temperature and density values are 162 ± 6 eV and (7.0 ± 1.9) × 10 21 cm −3 for six Anchor 1 experiments, 189 ± 7 eV and (3.4 ± 0.3) × 10 22 cm −3 for 21 Anchor 2 experiments, and 201 ± 6 eV and (4.8 ± 1.1) × 10 22 cm −3 for nine Anchor 3 experiments. These results show ∼4% temperature and ∼20% density reproducibility over a decade, which also aligns with the inferred parameter uncertainties. In conclusion, the resulting temperature and density uncertainties lead to a quasi-continuum iron opacity variation of ±4%–7% for wavelengths below 9.5 Å, which is insufficient to explain the significant model-data discrepancies reported in 2015.

Absorption spectroscopy↗
NASA NTRS1990

Application of high stability oscillators to radio science experiments using deep space probes

The microwave telecommunication links between the earth and deep space probes have long been used to conduct radio science experiments which take advantage of the phase coherency and stability of these links. These experiments measure changes in the phase delay of the signals to infer electrical, magnetic and gravitational properties of the solar system environment and beyond through which the spacecraft and radio signals pass. The precision oscillators, from which the phase of the microwave signals are derived, play a key role in the stability of these links and therefore the sensitivity of these measurements. These experiments have become a driving force behind recent and future improvements in the Deep Space Network and spacecraft oscillators and frequency and time distribution systems. Three such experiments which are key to these improvements are briefly discussed and relationship between their sensitivity and the signal phase stability is described. The first is the remote sensing of planetary atmospheres by occultation in which the radio signal passes through the atmosphere and is refracted causing the signal pathlength to change from which the pressure and the temperature of the atmosphere can be derived. The second experiment is determination of the opacity of planetary rings by passage of the radio signals through the rings. The third experiment is the research for very low frequency gravitational radiation. The fractional frequency variation of the signal is comparable to the spatial strain amplitude the system is capable of detecting. A summary of past results and future possibilities for these experiments are presented.

Kursinski, Emil R.↗