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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

A database and meta-analysis on the performance of exploding pusher implosions conducted at OMEGA

A database of 222 exploding pusher implosions conducted at the OMEGA Laser Facility is presented. The dataset consists of glass-shell capsules filled with varying pressures of D 2 , T 2 , and 3 He, which were imploded using square laser pulses with intensities ranging from 1 to 1 × 10 15 W/cm 2 . The database includes measurements of bang times, ion temperatures, and yields from the DD, D 3 He, and DT fusion reactions. A semi-analytic exploding pusher model is introduced, which effectively captures the observed trends in the data. This model predicts that the measurements scale according to a power-law relation based on the initial capsule and laser conditions. A generalized power-law scaling relation is directly fit to each dataset, providing a useful interpolation of the entire database. Overall, the database provides a valuable resource to estimating bang times, temperatures, and yields for the design of future experiments. Additionally, it provides a diverse set of data for validating more advanced implosion physics models.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

The physics of gain relevant to inertial fusion energy target designs

In inertial confinement fusion, pellets of deuterium tritium fuel are compressed and heated to the conditions where they undergo fusion and release energy. The target gain (ratio of energy released from the fusion reactions to the energy in the drive source) is a key parameter in determining the power flow and economics of an inertial fusion energy (IFE) power plant. In this study, the physics of gain is explored for laser-direct-drive targets with driver energy at the megajoule scale. This analysis is performed with the assumption of next-generation laser technologies that are expected to increase convergent drive pressures to over 200 Mbar. This is possible with the addition of bandwidth to the laser spectrum and by employing focal-spot zooming. Simple physics arguments are used to derive scaling laws that describe target gain as a function of laser energy, adiabat, ablation pressure, and implosion velocity. Scaling laws are found for the unablated mass, ablation pressure, areal density, implosion velocity, and in-flight aspect ratio. Furthermore, those scaling laws are then used to explore the design space for IFE targets.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Cross-beam energy transfer in conditions relevant to direct-drive implosions on OMEGA

In cross-beam energy transfer (CBET), the interference of two laser beams ponderomotively drives an ion-acoustic wave that coherently scatters light from one beam into the other. This redirection of laser beam energy can severely inhibit the performance of direct-drive inertial confinement fusion (ICF) implosions. To assess the role of nonlinear and kinetic processes in direct-drive-relevant CBET, the energy transfer between two laser beams in the plasma conditions of an ICF implosion at the OMEGA laser facility was modeled using particle-in-cell simulations. For typical laser beam intensities, the simulations are in excellent agreement with linear kinetic theory, indicating that nonlinear processes do not play a role in direct-drive implosions. At higher intensities, CBET can be modified by pump depletion, backward stimulated Raman scattering, or ion trapping, depending on the plasma density.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

A platform to measure isentropes from proton-heated warm dense matter on short pulse laser facilities

We describe the development of an experimental platform that measures the release isentrope of materials heated isochorically to temperatures of a few electron volts, using short-pulse laser-produced protons to heat the sample and long-pulse laser-produced x rays to perform streaked x-ray radiography. The density profiles derived from the radiography data are integrated to generate pressure–density isentropes, independent of prior knowledge of the equation of state of the sample material. In order to understand the sensitivities of isentrope extraction from radiography data, we analyze synthetic radiographs generated by a radiation hydrodynamics code. Noise reduction and high spatial resolution are critical for isentrope reconstruction, as demonstrated by the analysis of a proof-of-principle shot day on the OMEGA-EP facility. In conclusion, the data demonstrate the feasibility of the platform for characterizing isentropes, and we discuss the necessary improvements to enhance precision in differentiating between equation-of-state models.

Equations of state↗
DOE OSTI2020

Generation of focusing ion beams by magnetized electron sheath acceleration

Abstract We present the first 3D fully kinetic simulations of laser driven sheath-based ion acceleration with a kilotesla-level applied magnetic field. The application of a strong magnetic field significantly and beneficially alters sheath based ion acceleration and creates two distinct stages in the acceleration process associated with the time-evolving magnetization of the hot electron sheath. The first stage delivers dramatically enhanced acceleration, and the second reverses the typical outward-directed topology of the sheath electric field into a focusing configuration. The net result is a focusing, magnetic field-directed ion source of multiple species with strongly enhanced energy and number. The predicted improvements in ion source characteristics are desirable for applications and suggest a route to experimentally confirm magnetization-related effects in the high energy density regime. We additionally perform a comparison between 2D and 3D simulation geometry, on which basis we predict the feasibility of observing magnetic field effects under experimentally relevant conditions.

42 ENGINEERING↗
DOE OSTI2025

Laser-driven flash x-ray radiography of a shocked metallic foil

Characterizing hydrodynamic instability evolution in millimeter-scale, high-Z foils is crucial for understanding complex phenomena in high-energy-density physics. Here, we demonstrate a proof-of-concept, laser-driven flash x-ray radiography platform tailored for two-dimensional linear density mapping in shocked high-Z foils. Using chromium (Cr) foils with internal shockwaves (∼100 μm width), our platform achieves a spatial resolution of 59.8 ± 1.4 μm by employing a broadband x-ray source extending into the hundreds of keV range. The setup combines a compound parabolic concentrator cone with a tantalum wire target, a magnetic field to deflect residual transmitted electrons, and a copper casing to shield the sides and rear of the image plate pack. By varying the delay of the short-pulse beam driving the flash x-ray source, we resolve shockwave dynamics, specifically the velocity, position, width, and density profile, within the Cr foil. Reported experimental results are consistent with the corresponding hydrodynamics and radiation transport simulations, which accurately reproduce the measured electron and x-ray source terms. These developments enable the conversion of shockwave radiographs into two-dimensional density maps, enhancing interpretability for hydrodynamic instability evolution applications and validating the simulation approach.

36 MATERIALS SCIENCE↗
NASA NTRS1999

Solid Surface Combustion Experiment Yields Significant Observations

The spread of a flame over solid fuel is not only a fundamental textbook combustion phenomenon, but also the central element of destructive fires that cause tragic loss of life and property each year. Throughout history, practical measures to prevent and fight fires have been developed, but these have often been based on lessons learned in a costly fire. Since the 1960 s, scientists and engineers have employed powerful tools of scientific research to understand the details of flame spread and how a material can be rendered nonflammable. High-speed computers have enabled complex flame simulations, whereasand lasers have provided measurements of the chemical composition, temperature, and air velocities inside flames. The microgravity environment has emerged as the third great tool for these studies. Spreading flames are complex combinations of chemical reactions and several physical processes including the transport of oxygen and fuel vapor to the flame and the transfer of heat from the flame to fresh fuel and to the surroundings. Depending on its speed, air motion in the vicinity of the flame can affect the flame in substantially different ways. For example, consider the difference between blowing on a campfire and blowing out a match. On Earth, gravity induces air motion because of buoyancy (the familiar rising hot gases); this process cannot be controlled experimentally. For theoreticians, buoyant air motion complicates the problem modeling of flame spread beyond the capacity of modern computers to simulate. The microgravity environment provides experimental control of air motion near spreading flames, with results that can be compared with detailed theory. The Solid Surface Combustion Experiment (SSCE) was designed to obtain benchmark flame spreading data in quiescent test atmospheres--the limiting case of flames spreading. Professor Robert Altenkirch, Vice President for Research at Mississippi State University, proposed the experiment concept, and the NASA Lewis Research Center designed, built, and tested the SSCE hardware. It was the first microgravity science experiment built by Lewis for the space shuttle and the first combustion science experiment flown in space.

Sacksteder, Kurt R.↗
DOE OSTI2020

Laser propagation in a subcritical foam: Subgrid model

Here, we present a subgrid model for laser propagation in a subcritical foam. Our model describes the expansion of laser-irradiated foam elements that are below the resolution of the simulation grid and predicts the plasma conditions that result from burning down the foam. Our model can be included as a module within a larger multiphysics code, and we have implemented it within the code pF3D, which is used for simulating a laser-plasma interaction. The model predicts a reduced propagation velocity for a laser through a subcritical foam compared to simulating that foam as a homogeneous gas. This is attributed to the laser energy that goes into burning down the foam microstructure. We compare our model against experimental data by simulating a 2 mg/cc SiO 2 foam shot performed at the Janus laser facility at the Lawrence Livermore National Laboratory. pF3D simulations with the foam model predict hot ion temperatures. This leads to a reduction in the level of stimulated Brillouin scattering (SBS), bringing the simulated level of SBS into agreement with the data. Intensity fluctuations at the foam front due to laser speckles and refraction result in ion temperature fluctuations when the foam burns down. These drive long-lived electron density fluctuations on scales that are large compared to the pore size.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Evidence of non-isentropic release from high residual temperatures in shocked metals measured with ultrafast x-ray diffraction

Shock experiments are widely used to understand the mechanical and electronic properties of matter under extreme conditions. However, after shock loading to a Hugoniot state, a clear description of the post-shock thermal state and its impacts on materials is still lacking. We used diffraction patterns from 100-fs x-ray pulses to investigate the temperature evolution of laser-shocked Al–Zr metal film composites at time delays ranging from 5 to 75 ns driven by a 120-ps short-pulse laser. We found significant heating of both Al and Zr after shock release, which can be attributed to heat generated by inelastic deformation. A conventional hydrodynamic model that employs (i) typical descriptions of Al and Zr mechanical strength and (ii) elevated strength responses (which might be attributed to an unknown strain rate dependence) did not fully account for the measured temperature increase, which suggests that other strength-related mechanisms (such as fine-scale void growth) could play an important role in thermal responses under shock wave loading/unloading cycles. Our results suggest that a significant portion of the total shock energy delivered by lasers becomes heat due to defect-facilitated plastic work, leaving less converted to kinetic energy. This heating effect may be common in laser-shocked experiments but has not been well acknowledged. High post-shock temperatures may induce phase transformation of materials during shock release. Another implication for the study is the preservability of magnetic records from planetary surfaces that have a shock history from frequent impact events.

42 ENGINEERING↗
DOE OSTI2020

Synthesis of precipitation-strengthened Al-Sc, Al-Zr and Al-Sc-Zr alloys via selective laser melting of elemental powder blends

Selective laser melting is used to create Al-1.5Sc, Al-1.5Zr and Al-0.75Sc-0.75Zr (at.%) alloys from blends of elemental Al, Sc, and Zr powders. This study investigates elemental alloying elements (Sc and Zr) which are high-melting and highly reactive, unlike previous work which focused on more concentrated elemental additions of lower-melting, lower-reactivity Cu and Si to aluminum. High-speed in situ synchrotron x-ray imaging and diffraction show that the 20–30 μm Al, Sc, and Zr powders fully melt and sufficiently mix in the molten state to create, on solidification, a homogeneous distribution of primary, micron-size L12 precipitates (Al 3 Sc, Al 3 Zr, and Al 3 (Sc,Zr), respectively) and nucleate micron-size Al matrix grains, as confirmed by SEM imaging of cross-sections. Here, a second laser pass, simulating a realistic additive-manufacturing build condition, fully remelts the initial volume which shows, after solidification, the same Al 3 (Sc,Zr) L1 2 primary micro-precipitates and very fine Al grains. After aging at 300–400°C, the alloys show large increases in hardness, consistent with an exceptionally high number density (1.4 × 10 24 m –3 ) and volume fraction (2.5%) of secondary Al 3 (Sc,Zr) nano-precipitates with a Sc-rich core and Zr-rich shell, as measured via atom-probe tomography.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Experimental and calculational investigation of laser-heated additive manufactured foams

Foam materials are starting to find application in laser-heated Hohlraums used to drive inertial confinement fusion implosions. Foams made using additive manufacturing (AM) techniques are now available and may have advantages over traditional chemical (aerogel) foams. Here, we present new experimental data on laser-heated AM foams. Samples of four different types of printed AM foams were heated using a single 527 nm laser beam at the Jupiter Laser Facility. The laser pulse was ∼180 J square pulse with an FWHM of 1.6 ns and a peak intensity of 3–4 × 1014 W/cm2. The foam densities ranged from 12 to 93 mg/cc (all supercritical for 527 nm light). We measured the backscattered light (power and spectrum), the transmitted light, side-on x-ray images, and the Ti K-shell emission that was used to infer the time-integrated temperature. The fraction of backscattered light was 6%–15% of the input laser energy. The pure carbon foam sample had less backscatter than a C8H9O3 foam of similar density, which was consistent with multi-fluid calculations that predicted less ion heating for the C8H9O3 foam. The level of backscatter and the thermal front speeds for the AM foams were similar to values measured for stochastic (aerogel) foams under similar conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2022

CoSyR: A novel beam dynamics code for the modeling of synchrotron radiation effects

The self-consistent nonlinear dynamics of a relativistic charged particle beam interacting with its complete self-fields is a fundamental problem underpinning many of the accelerator design issues in high brightness beam applications, as well as the development of advanced accelerators. Particularly, synchrotron radiation induced effects in a magnetic dispersive beamline element can lead to collective beam instabilities and emittance growth. A novel beam dynamics code is developed based on a Lagrangian method for the calculation of the particles’ radiation near-fields using wavefront/wavelet meshes via the Green’s function of the Maxwell equations. These fields are then interpolated onto a moving mesh for dynamic update of the beam. This method allows radiation co-propagation and self-consistent interaction with the beam in 2D/3D simulations at greatly reduced numerical errors. Multiple levels of parallelisms are inherent in this method and implemented in our code CoSyR to enable at-scale simulations of nonlinear beam dynamics on modern computing platforms using MPI, multi-threading, and GPUs. Here, the current 2D implementation of CoSyR has been used to evaluate the transverse and longitudinal coherent radiation effects on the beam and to investigate beam optics designs proposed for mitigation of beam brightness degradation in a magnetic bunch compressor. In this paper, the design of CoSyR, as well as the benchmark with other coherent synchrotron radiation models, are described and discussed. Extension of the core algorithms to 3D is possible and planned.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRSDate not supplied

Simulating Micrometeoroid Bombardment on Mercury: Identifying New Space Weathering Features in the Laboratory

Airless bodies are continually exposed to the harsh interplanetary space environment, causing the alteration of their surfaces through a process known as space weathering (SW). SW is dominated by solar wind irradiation and micrometeoroid bombardment, which together alter the spectral, microstructural, and chemical characteristics of grains on the surface of airless bodies. The effects of SW are variable and depend on the heliocentric distance and the initial composition of the planetary surface, among other factors. On the Moon and S- type asteroids, it is well established that SW darkens and reddens the surface of these bodies and attenuates absorption bands across the Vis-NIR wavelengths. These spectral effects are largely the result of the production of metallic Fe nanoparticles (npFe). However, Mercury’s SW environment is unique compared to the Moon and S-type asteroids. Mercury is a geochemical endmember, with a surface composition low in Fe (<2 wt.%) and enriched in volatile components, including regions of the surface hypothesized to contain up to 4 wt.% graphite in the low reflectance material (LRM). In fact, the presence of graphite on Mercury has been hypothesized to act as a reducing agent for silicates during SW to produce Si-bearing Fe-rich metal. In addition, its location in the solar system exposes Mercury to an extreme SW environment, with the surface of the planet experiencing an intense solar wind flux and higher flux and velocity of micrometeoroid impactors compared to the Moon and S-type asteroids. The effects that such harsh SW has on materials with the unique compositional characteristics of Mercury are not well constrained. To better understand SW at Mercury, we must investigate these processes in the laboratory. Here, we present the results of our analyses of the spectral, microstructural and chemical characteristics of Mercury analog samples irradiated by pulsed laser to simulate the short duration, high temperature events associated with micrometeoroid impacts.

Nick Bott↗
DOE OSTI2021

Reconstructing 3D asymmetries in laser-direct-drive implosions on OMEGA

Three-dimensional reconstruction algorithms have been developed which determine the hot-spot velocity, hot-spot apparent ion temperature distribution, and fuel areal density distribution present in laser-direct-drive inertial con finement fusion implosions on the OMEGA laser. These reconstructions rely on multiple independent measurements of the neutron energy spectrum emitted from the fusing plasma. Measurements of the neutron energy spectrum on OMEGA are made using a suite of quasi-orthogonal neutron time-of-flight detectors and a magnetic recoil spectrometer. These spectrometers are positioned strategically around the OMEGA target chamber to provide unique 3-D measurements of the conditions of the fusing hot spot and compressed fuel near peak compression. Here, the uncertainties involved in these 3-D reconstructions are discussed and are used to identify a new nTOF diagnostic line of sight which when built will reduce the uncertainty in the hot-spot apparent ion temperature distribution from 0.7 to < 0.4 keV.

47 OTHER INSTRUMENTATION↗
NASA NTRS2024

Investigating Sulfur-Rich Mercury Analogs Exposed to Simulated Micrometeoroid Bombardment in the Laboratory

Space weathering (SW) continually alters the spectral, microstructural, and chemical characteristics of the surface of airless bodies across the solar system. The effects of SW vary depending on the heliocentric distance and the initial composition of the target surface. While SW on the Moon and S-type asteroids is well documented, our understanding of how this process affects Mercury is at an early stage. Mercury’s interplanetary environment is harsh, with the surface of the planet experiencing an intense solar wind flux as well as a higher flux and velocity of micrometeoroid impactors compared to the Moon and S-type asteroids. In addition, Mercury is also a geochemical endmember, with a surface composition low in Fe (<2 wt.%) and enriched in volatile components, such as sulfur (up to 4 wt.% in the low reflectance material (LRM)). These volatile components are thought to play a major role in the formation of hollows via their sublimation. Sulfur has been hypothesized to occur at the surface of Mercury as sulfide minerals (MgS, CaS) based on its correlation with Mg and Ca in remote sensing data. However, recent observations of chaotic terrains in the north polar area of Mercury and of glacier-like features at lower latitudes indicated that octasulfur (S 8 , elemental sulfur) is another likely constituent of a volatile-rich layer in Mercury’s crust. Its behavior on Mercury may result in a complex cycle of enrichment and depletion. While S is often depleted on small body surfaces, Mercury’s gravity could result in ejected S subsequently returning to the surface and coating regolith grains. Further, the reaction of reduced S-rich gas with glasses of a Mercury-like composition also produced S-rich coatings. However, the precise behavior and evolution of S-rich species exposed to the harsh SW on Mercury remains poorly understood and needs to be further investigated in the laboratory. Here, we present the results of our analyses of the spectral, microstructural, and chemical characteristics of S-rich Mercury analogs irradiated by pulsed laser to simulate the short duration, high temperature events associated with micrometeoroid impacts.

N Bott↗
DOE OSTI2021

Unabsorbed light beamlets for diagnosing coronal density profiles and absorption nonuniformity in direct-drive implosions on OMEGA

Laser light scattered from a target is the most-direct measurement for diagnosing laser absorption in a direct-drive implosion. The 3ωGOI (gated optical imager) beamlets diagnostic images unabsorbed light from all 60 OMEGA beams as distinct “beamlet” spots for each beam. The implosion can be diagnosed using the position and intensity of these beamlets. The position of each beamlet in the image is determined by refraction and can be used to fit the coronal plasma density profile of the implosion. The inferred plasma density profiles are comparable to profiles predicted by the 1-D hydrodynamics code LILAC but suggest the predictions underestimate the density farther out in the corona. The intensity of light in each spot depends on the cumulative effects of absorption and cross-beam energy transfer along the beamlet’s path through the corona. Furthermore, the measured variation in intensity and polarization between similar spots indicates that absorption during OMEGA implosions is less uniform than previously known.

47 OTHER INSTRUMENTATION↗
DOE OSTI2021

Cross-beam energy transfer saturation by ion trapping-induced detuning

The performance of direct-drive inertial confinement fusion implosions relies critically on the coupling of laser energy to the target plasma. Cross beam energy transfer (CBET), the resonant exchange of energy between intersecting laser beams mediated by ponderomotively driven ion-acoustic waves (IAW), inhibits this coupling by scattering light into unwanted directions. Furthermore, the variety of beam intersection angles and varying plasma conditions in an implosion results in IAWs with a range of phase velocities. Here we show that CBET saturates through a resonance detuning that depends on the IAW phase velocity and that results from trapping-induced modifications to the ion distribution functions. For smaller phase velocities, the modifications to the distribution functions can rapidly thermalize in the presence of mid-Z ions, leading to a blueshift in the resonant frequency. For larger phase velocities, the modifications can persist, leading to a redshift in the resonant frequency. Ultimately, these results may reveal pathways towards CBET mitigation and inform reduced models for radiation hydrodynamics codes to improve their predictive capability.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Hot electron preheat in hydrodynamically scaled direct-drive inertial confinement fusion implosions on the NIF and OMEGA

Hot electron preheat has been quantified in warm, directly driven inertial confinement fusion implosions on OMEGA and the National Ignition Facility (NIF), to support hydrodynamic scaling studies. These CH-shell experiments were designed to be hydrodynamically equivalent, spanning a factor of 40 in laser energy and a factor of 3.4 in spatial and temporal scales, while preserving the incident laser intensity of 10 15 W/cm 2 . Experiments with similarly low levels of beam smoothing on OMEGA and NIF show a similar fraction (~0.2%) of laser energy deposited as hot electron preheat in the unablated shell on both OMEGA and NIF and similar preheat per mass (~2 kJ/mg), despite the NIF experiments generating a factor of three more hot electrons (~1.5% of laser energy) than on OMEGA (~0.5% of laser energy). This is plausibly explained by more absorption of hot electron energy in the ablated CH plasma on NIF due to larger areal density, as well as a smaller solid angle of the imploding shell as viewed from the hot electron generating region due to the hot electrons being produced at a larger standoff distance in lower-density regions by stimulated Raman scattering, in contrast to in higher-density regions by two-plasmon decay on OMEGA. Finally, the results indicate that for warm implosions at intensities of around 10 15 W/cm 2 , hydrodynamic equivalence is not violated by hot electron preheat, though for cryogenic implosions, the reduced attenuation of hot electrons in deuterium–tritium plasma will have to be considered.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗