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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Strongly Confined Bismuth Antimonide Quantum Dots

Bismuth antimonide (Bi 1−x Sb x ) has emerged as a highly promising material for quantum applications due to its complex band structure. In this study, spherical Bi 1−x Sb x quantum dots (QDs), with a diameter of around 8 ± 2 nm, were successfully synthesized by pulsed laser ablation in liquids. The energy bandgap was determined at 2.02 ± 0.27 eV, which is significantly higher than the bulk value (∼0.025 eV). The strong confinement nature of the dots was confirmed by the Raman peak shifts. The chemical composition of the Bi 1−x Sb x QDs was measured to be around 77 ± 2 at. % of Bi and 23 ± 2 at. % of Sb. The colloid containing the Bi 1−x Sb x QDs was classified as highly stable, displaying a zeta potential of −38 ± 18 mV. Finally, the Bi 1−x Sb x QDs exhibited an electron spin resonance (ESR) signal at room temperature and at cryogenic temperature (4.2 K); consequently, revealing the presence of paramagnetic states.

Alloys↗
DOE OSTI2021

Control of monodomain polymer-stabilized cuboidal nanocrystals of chiral nematics by confinement.

Liquid crystals are important components of optical technologies. Cuboidal crystals consisting of chiral liquid crystals-the so-called blue phases (BPs), are of particular interest due to their crystalline structures and fast response times, but it is critical that control be gained over their phase behavior as well as the underlying dislocations and grain boundaries that arise in such systems. Blue phases exhibit cubic crystalline symmetries with lattice parameters in the 100 nm range and a network of disclination lines that can be polymerized to widen the range of temperatures over which they occur. Here, we introduce the concept of strain-controlled polymerization of BPs under confinement, which enables formation of strain-correlated stabilized morphologies that, under some circumstances, can adopt perfect single-crystal monodomain structures and undergo reversible crystal-to-crystal transformations, even if their disclination lines are polymerized. We have used super-resolution laser confocal microscopy to reveal the periodic structure and the lattice planes of the strain and polymerization stabilized BPs in 3D real space. Our experimental observations are supported and interpreted by relying on theory and computational simulations in terms of a free energy functional for a tensorial order parameter. Simulations are used to determine the orientation of the lattice planes unambiguously. The findings presented here offer opportunities for engineering optical devices based on single-crystal, polymer-stabilized BPs whose inherent liquid nature, fast dynamics, and long-range crystalline order can be fully exploited.

confinement↗
DOE OSTI2020

Positron orbit effects during injection and confinement in a magnetic dipole trap

Lossless injection of positrons into a magnetic dipole trap and their subsequent confinement have been demonstrated. Here, we investigate by numerical single-particle simulations how the radial distribution of positrons in the trap is affected by the measurement itself, the choice of injection parameters, the asymmetry of the electric potential, and by elastic collisions. The results are compared to experimental data. A comprehensive understanding of these effects is a milestone on the road to creating an electron–positron plasma in a trap with a levitating superconducting coil.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Fill tube dynamics in inertial confinement fusion implosions with high density carbon ablators

Plasma jets, such as γ-ray burst jets, Herbig–Haro jets, μ-quasar jets, and active galactic nuclei jets, are found throughout the universe [S. Mendoza et al., Rev. Mex. Astron. Astrofis. 41, 453 (2005)]. Plasma jets are also present in indirect drive inertial confinement fusion experiments originating from the capsule's fill tube and occasionally from divots and voids in the capsules, particles on the exterior of the capsule, or from the tent holding the capsule in the target. This paper looks at two different gas-filled capsule implosions containing a plasma jet resulting from a capsule fill tube and fill channel, both of which utilized high density carbon ablators. Two models were developed, a drag and a snowplow model, which use the time-dependent motion of the injected mass through the hotspot to estimate the mass injected into the hotspot from the fill tube and channel, arriving at an average injected mass of ~84.5 ± 25.5 ng for the first experiment and 91 ± 20 ng for the second experiment. Furthermore, unlike previous methods to estimate fill tube injected mass, these techniques do not assume that the mixed mass is in thermal equilibrium with the hotspot or that the x-ray emission is only coming from within the hotspot itself. This paper also discusses the features seen in these experiments which include limb brightening in the shell for undoped ablators and flattening in the ablator from shadowing by the fill tube.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Magnetization around mix jets entering inertial confinement fusion fuel

Engineering features are known to cause jets of ablator materials to enter the fuel hot-spot in inertial confinement fusion implosions. The Biermann battery mechanism wraps them in a self-generated magnetic field. Here we show that higher-Z jets have an additional thermoelectric magnetic source term that is not present for hydrogen jets, verified here through a kinetic simulation. It has similar magnitude to the Biermann term. We then include this in an extended magneto-hydrodynamic approach to post process an xRAGE radiation-hydrodynamic implosion simulation. The simulation includes an accurate model for the capsule fill tube, producing a dense carbon jet that becomes wrapped in a 4000 T magnetic field. A simple spherical carbon mix model shows that this insulates the electron heat conduction enough to cause contraction of the jet to an optically thick equilibrium. The denser magnetized jet hydrodynamics could change its core penetration and therefore the final mix mass, which is known to be well correlated with fusion yield degradation. Fully exploring this will require self-consistent magneto-hydrodynamic simulations. Experimental signatures of this self-magnetization may emerge in the high energy neutron spectrum.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Effect of cross-beam energy transfer on target-offset asymmetry in direct-drive inertial confinement fusion implosions

The unintentional mispositioning of inertial confinement fusion (ICF) capsules from the center of laser beam convergence has long been shown in simulations to generate large ℓ = 1 asymmetry and significantly degrade implosion symmetry and fusion yields. Experimental yields on the OMEGA Laser System, however, have shown much less sensitivity to this initial target offset. This paper presents simulations of offset ICF implosions improved by including a physics model of cross-beam energy transfer (CBET), a mechanism of laser energy scattering from one beam to another. Room-temperature OMEGA implosion experiments with prescribed target offsets are simulated with and without CBET, illustrating that CBET mitigates the ℓ = 1 implosion asymmetry from target offset. Here, comparison of simulations to multiple complementary experimental observables indicates the addition of CBET physics in offset simulations is necessary to match experimental results.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Transient magnetic field diffusion considerations relevant to magnetically assisted indirect drive inertial confinement fusion

We report application of a magnetic field to an indirect drive inertial confinement fusion target requires diffusion of the field through the high-Z and electrically conducting Hohlraum. The onset of the external field generates eddy currents in the Hohlraum wall that result in (1) a reduction of the peak field at the capsule, (2) heating of the Hohlraum wall through Ohmic dissipation, and (3) wall movement due to the inward force from the eddy current interacting with the field. Heating of the wall causes an increase in blackbody radiation which can preheat the capsule and frozen deuterium–tritium fuel, while wall motion leads to potential misalignment of the lasers at the Hohlraum wall. Limiting these detrimental effects sets requirements on the tolerable magnitude of each effect. We present a nonlinear model for B-field diffusion through an infinitely long thin-walled cylinder with a temperature dependent resistivity, to show that a 15 μm thick wall of pure gold fails to meet these requirements. A new Hohlraum material made from an alloy of Au and Ta has a measured resistivity of ≥60 times that of Au and is shown with the nonlinear model to meet the requirements for magnetization. We compare the nonlinear model to simulations of the actual Hohlraum target using a finite element code which includes temperature-dependent Hohlraum resistivity.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Time resolved ablator areal density during peak fusion burn on inertial confinement fusion implosions

Near peak compression, inertial confinement fusion implosions release both deuterium–tritium (DT) fusion gamma rays and neutron induced gamma rays from carbon from the areal density of the remaining ablator shell. The gamma reaction history diagnostic makes a time resolved measurement of both. Across many recent implosions, the carbon gamma ray peak arrives systematically 11 ± 10 ps later compared to DT fusion burn. The timing shift is consistent with the carbon areal density increasing throughout the peak of the fusion burn, implying that the carbon portion of the capsule continues to converge. A model finds that the observed timing shift is consistent with a 4π averaged carbon ablator inward velocity of 80 μm/ns for the contemporary National Ignition Facility implosions. In this work, the timing shift is possibly related to the energy balance of the implosion, with the expectation that a high performing, igniting capsule would see the carbon gamma rays arrive before the DT fusion peak.

Nuclear fusion↗
DOE OSTI2021

Mitigation of mode-one asymmetry in laser-direct-drive inertial confinement fusion implosions

Nonuniformities present in the laser illumination and target in laser-driven inertial confinement fusion experiments lead to an asymmetric compression of the target, resulting in an inefficient conversion of shell kinetic energy to thermal energy of the hot-spot plasma. In this paper, the effects of asymmetric compression of cryogenic deuterium tritium laser-direct-drive implosions are examined using a suite of nuclear and x-ray diagnostics on the OMEGA laser. The neutron-averaged hot-spot velocity (u → hs ) and apparent ion temperature (T i ) asymmetry are determined from neutron time-of-flight measurements of the primary deuterium tritium fusion neutron energy spectrum, while the areal density (ρR) of the compressed fuel surrounding the hot spot is inferred from measurements of the scattered neutron energy spectrum. Here, the low-mode perturbations of the hot-spot shape are characterized from x-ray self-emission images recorded along three quasi-orthogonal lines of sight. Implosions with significant mode-1 laser drive asymmetries show large hot-spot velocities (>100 km/s) in a direction consistent with the hot-spot elongation observed in x-ray images, measured T i asymmetry, and ρR asymmetry. Laser drive corrections have been applied through shifting the initial target location in order to mitigate the observed asymmetry. With the asymmetry corrected, a more-symmetric hot spot is observed with reduced u → hs , T i asymmetry, ρR asymmetry, and a 30% increase in the fusion yield.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Entropy generation from hydrodynamic mixing in inertial confinement fusion indirect-drive targets

The increase in entropy from the physical mixing of two adjacent materials in inertial confinement fusion (ICF) implosions and gas-filled hohlraums is analytically assessed. An idealized model of entropy generation from the mixing of identical ideal-gas particles across a material interface in the presence of pressure and temperature gradients is applied. Physically, mix-driven entropy generation refers to the work done by the gases in expanding into a larger common volume from atomic mixing under the condition of no internal energy change, or work needed to restore the initial unmixed state. Furthermore, the effect of a mix-generated entropy increase is analytically shown to lead to less compression of the composite ICF fluid under adiabatic conditions. The amount of entropy generation is estimated to be ~10 J for a Rayleigh–Taylor-induced micrometer-scale annular mixing layer between the solid deuterium–tritium fuel and (undoped) high-density carbon pusher of an imploding capsule at the National Ignition Facility (NIF). This level of entropy generation is consistent with lower-than-expected fuel compressions measured on the NIF [Hurricane et al., Phys. Plasmas 26, 052704 (2019)]. The degree of entropy increase from mixing of high-Z hohlraum wall material and low-Z, moderate- to high-density gas fills is estimated to lead to ~100 kJ of heat generation for NIF-scale experiments [Moody et al., Phys. Plasmas 21, 056317 (2014)]. This value represents a significant fraction of the inferred missing x-ray drive energy based on observed delays in capsule implosion times compared with mainline simulations [Jones et al., Phys. Plasmas 19, 056315 (2012)].

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Experimental characterization of hot-electron emission and shock dynamics in the context of the shock ignition approach to inertial confinement fusion

We report on planar target experiments conducted on the OMEGA-EP laser facility performed in the context of the shock ignition (SI) approach to inertial confinement fusion. The experiment aimed at characterizing the propagation of strong shock in matter and the generation of hot electrons (HEs), with laser parameters relevant to SI (1-ns UV laser beams with I ~10 16 W/cm 2 ). Time-resolved radiographs of the propagating shock front were performed in order to study the hydrodynamic evolution. The hot-electron source was characterized in terms of Maxwellian temperature, T h , and laser to hot-electron energy conversion efficiency η using data from different x-ray spectrometers. The post-processing of these data gives a range of the possible values for T h and η [i.e., T h [keV] ϵ (20, 50) and η ϵ (2%, 13%)]. These values are used as input in hydrodynamic simulations to reproduce the results obtained in radiographs, thus constraining the range for the HE measurements. According to this procedure, we found that the laser converts ~10% ± 4% of energy into hot electrons with T h = 27 ± 8 keV. The paper shows how the coupling of different diagnostics and numerical tools is required to sufficiently constrain the problem, solving the large ambiguity coming from the post-processing of spectrometers data. The effect of the hot electrons on the shock dynamics is then discussed, showing an increase in the pressure around the shock front. Furthermore, the low temperature found in this experiment without pre-compression laser pulses could be advantageous for the SI scheme, but the high conversion efficiency may lead to an increase in the shell adiabat, with detrimental effects on the implosion.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

A polar direct drive liquid deuterium–tritium wetted foam target concept for inertial confinement fusion

We propose a new approach to inertial confinement fusion (ICF) that could potentially lead to ignition and propagating thermonuclear burn at the National Ignition Facility (NIF). The proposal is based upon a combination of two concepts, referred to as polar direct drive and liquid deuterium–tritium wetted foam capsules. With this new concept, 2D radiation hydrodynamic simulations indicate that ICF ignition and propagating thermonuclear burn are possible with the laser power and energy capabilities available today on the NIF.

3D printing↗
DOE OSTI2021

Self-organized confinement in whole-device modeling of laboratory magnetospheres

Turbulent self-organization driven by global ideal interchange modes in a dipole-confined plasma is explored with self-consistent, whole-plasma simulations using a flux-tube averaged magnetohydrodynamic model in dipole magnetic geometry. We show the existence of robust particle pinch driven by ideal interchange-mode fluctuations, in which the particles are transported up the density gradient. It is found that the plasma profiles in a dipole field spontaneously relax to a marginally stable state as centrally peaked pressure and density are created by global interchange-mode transport.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Instability seeding mechanisms due to internal defects in inertial confinement fusion targets

Performance degradation in laser-driven inertial confinement fusion (ICF) implosions is caused by several effects, one of which is Rayleigh–Taylor instability growth. Defects in ICF targets, such as internal voids and surface roughness, create instability seeds in the shell as shocks propagate through the target. A comprehensive understanding of seeding mechanisms is essential to characterize the impact of target defects on inflight shell integrity and mass injection into the central, lower-density vapor region. An analysis of early-time behavior of both single-mode shell mass modulations and isolated voids is performed by examining the evolution of the acoustic waves launched by these target imperfections. A systematic study of localized perturbation growth as a function of defect placement and size is presented. Furthermore, the use of low-density ablator materials (such as foams) is suggested as a potential mitigation strategy to improve target robustness against the impact of defect-initiated growth.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Three-dimensional electron temperature measurement of inertial confinement fusion hotspots using x-ray emission tomography

Here we present a novel approach to reconstruct three-dimensional (3D) electron temperature distributions of inertially confined fusion plasma hotspots at the National Ignition Facility. Using very limited number of two-dimensional (2D) x-ray imaging lines of sight, we perform 3D reconstructions of x-ray emission distributions from different x-ray energy channels ranging from 20 to 30 keV. 2D time-integrated x-ray images are processed using the algebraic reconstruction technique to reconstruct a 3D hotspot x-ray emission distribution that is self-consistent with the input images. 3D electron temperatures are computed using the energy channel ratios. We demonstrate the high accuracy and applicability of this method with different complex hotspot geometries in both synthetic and experimental results.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Transfer learning driven design optimization for inertial confinement fusion

Transfer learning is a promising approach to create predictive models that incorporate simulation and experimental data into a common framework. In this technique, a neural network is first trained on a large database of simulations and then partially retrained on sparse sets of experimental data to adjust predictions to be more consistent with reality. Previously, this technique has been used to create predictive models of Omega [Humbird et al., IEEE Trans. Plasma Sci. 48, 61–70 (2019)] and NIF [Humbird et al., Phys. Plasmas 28, 042709 (2021); Kustowski et al., Mach. Learn. 3, 015035 (2022)] inertial confinement fusion (ICF) experiments that are more accurate than simulations alone. Here, in this work, we conduct a transfer learning driven hypothetical ICF campaign in which the goal is to maximize experimental neutron yield via Bayesian optimization. The transfer learning model achieves yields within 5% of the maximum achievable yield in a modest-sized design space in fewer than 20 experiments. Furthermore, we demonstrate that this method is more efficient at optimizing designs than traditional model calibration techniques commonly employed in ICF design. Such an approach to ICF design could enable robust optimization of experimental performance under uncertainty.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

The Vacuum Cherenkov Detector (VCD) for γ-ray measurements in inertial confinement fusion experiments

Inertial confinement fusion experiments at both the National Ignition Facility (NIF) and the Laboratory for Laser Energetics OMEGA laser facility currently utilize Cherenkov detectors, with fused silica as the Cherenkov medium. At the NIF, the Quartz Cherenkov Detectors improve the precision of neutron time-of-flight measurements; and at OMEGA, the Diagnostic for Areal Density provides measurements of capsule shell areal densities. An inherent property of fused silica is the radiator’s relatively low energy threshold for Cherenkov photon production (E threshold < 1 MeV), making it advantageous over gas-based Cherenkov detectors for experiments requiring low-energy γ detection. The Vacuum Cherenkov Detector (VCD) has been specifically designed for efficient detection of low energy γ’s. Its primary use is in implosion experiments, which will study reactions relevant to stellar and big-bang nucleosynthesis, such as T( 4 He,γ) 7 Li, 4 He( 3 He,γ) 7 Be, and 12 C(p,γ) 13 N. Further, the VCD is compatible with LLE’s standard Ten-Inch Manipulator diagnostic insertion module. This work will outline the design and characterization of the VCD as well as provide results from recent experiments conducted at the OMEGA laser facility.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Design of multi neutron-to-gamma converter array for measuring time resolved ion temperature of inertial confinement fusion implosions

The ion temperature varying during inertial confinement fusion implosions changes the amount of Doppler broadening of the fusion products, creating subtle changes in the fusion neutron pulse as it moves away from the implosion. A diagnostic design to try to measure these subtle effects is introduced—leveraging the fast time resolution of gas Cherenkov detectors along with a multi-puck array that converts a small amount of the neutron pulse into gamma-rays, one can measure multiple snapshots of the neutron pulse at intermediate distances. Further, precise measurements of the propagating neutron pulse, specifically the variation in the peak location and the skew, could be used to infer time-evolved ion temperature evolved during peak compression.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗