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At least 595 records · Page 33
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

CHAOS. III. GAS-PHASE ABUNDANCES IN NGC 5457

We present Large Binocular Telescope observations of 109 H ii regions in NGC 5457 (M101) obtained with the Multi-Object Double Spectrograph. We have robust measurements of one or more temperature-sensitive auroral emission lines for 74 H ii regions, permitting the measurement of “direct” gas-phase abundances. Comparing the temperatures derived from the different ionic species, we find: (1) strong correlations of T [N ii] with T [S iii] and T [O iii], consistent with little or no intrinsic scatter; (2) a correlation of T [S iii] with T [O iii], but with significant intrinsic dispersion; (3) overall agreement between T [N ii], T [S ii], and T [O ii], as expected, but with significant outliers; (4) the correlations of T [N ii] with T [S iii] and T [O iii] match the predictions of photoionization modeling while the correlation of T [S iii] with T [O iii] is offset from the prediction of photoionization modeling. Based on these observations, which include significantly more observations of lower excitation H ii regions, missing in many analyses, we inspect the commonly used ionization correction factors (ICFs) for unobserved ionic species and propose new empirical ICFs for S and Ar. We have discovered an unexpected population of H ii regions with a significant offset to low values in Ne/O, which defies explanation. We derive radial gradients in O/H and N/O which agree with previous studies. Our large observational database allows us to examine the dispersion in abundances, and we find intrinsic dispersions of 0.074 ± 0.009 in O/H and 0.095 ± 0.009 in N/O (at a given radius). We stress that this measurement of the intrinsic dispersion comes exclusively from direct abundance measurements of H ii regions in NGC 5457.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Response of CR-39 nuclear track detectors to protons with non-normal incidence

This paper presents data from experiments with protons at non-normal incidence to CR-39 nuclear track detectors, analyzing the properties of detection efficiency, proton track diameter, track contrast, and track eccentricity. Understanding the CR-39 response to protons incident at an angle is important for designing charged particle detectors for inertial confinement fusion (ICF) applications. This study considers protons with incident energies less than 3 MeV. In this regime, an incident angle of 10° has no effect on CR-39 detection efficiency, and >85% detection efficiency is preserved up through 25° in the range of 1.0 MeV–2.1 MeV. For ICF applications, incident angles above 30° are deemed impractical for detector design due to significant drops in proton detection at all energies. We observe significant reductions in detection efficiency compared to theoretical predictions, particularly at low energies where proton tracks are etched away. The proton track diameter measured by the scan system is observed to decrease with higher incident angles. The track diameters are analyzed with two fitting models, and it is shown that the diameter–energy relation can be fit with the existing models at angles up to 30°. The optical contrast of the tracks tends to increase with the angle, meaning that the tracks are fainter, and a larger increase is observed for higher energies. Eccentricity, a measure of how elongated proton tracks are, increases with the incident angle and drops after the critical angle. The lowest energy tracks remain nearly circular even at higher angles.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

Using millimeter-sized carbon-deuterium foils for high-precision deuterium-tritium neutron spectrum measurements in direct-drive inertial confinement fusion at the OMEGA laser facility

Millimeter-sized CD foils fielded close (order mm) to inertial confinement fusion (ICF) implosions have been proposed as a game-changer for improving energy resolution and allowing time-resolution in neutron spectrum measurements using the magnetic recoil technique. This paper presents results from initial experiments testing this concept for direct drive ICF at the OMEGA laser facility. While the foils are shown to produce reasonable signals, inferred spectral broadening is seen to be high (~5 keV) and signal levels low (by ~20%) compared to expectation. Before this type of foil is used for precision experiments, the foil mount must be improved, oxygen uptake in the foils better characterized, and impact of uncontrolled foil motion prior to detection investigated.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Impact of asymmetries on fuel performance in Inertial Confinement Fusion

Low-mode asymmetries prevent effective compression, confinement and heating of the fuel in inertial confinement fusion (ICF) implosions and their control is essential to achieving ignition. Ion temperatures (Tion) in ICF experiments are inferred from the broadening of primary neutron spectra. Directional motion (flow) of the fuel at burn also impacts broadening and will lead to artificially inflated “Tion” values. Flow due to low-mode asymmetries is expected to give rise to line-of-sight variations in measured Tion. We report on intentionally asymmetrically driven experiments at the OMEGA laser facility designed to test the ability to accurately predict and measure line-of-sight differences in apparent Tion due to low-mode asymmetry-seeded flows. Contrasted to Chimera and xRAGE simulations, the measurements demonstrate how all asymmetry seeds have to be considered to fully capture the flow field in an implosion. In particular, flow induced by the stalk that holds the target is found to interfere with the seeded asymmetry. A substantial stalk-seeded asymmetry in the areal density of the implosion is also observed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

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. 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 OSTI2018

A novel method to recover DD fusion proton CR-39 data corrupted by fast ablator ions at OMEGA and the National Ignition Facility

CR-39 detectors are used routinely in inertial confinement fusion (ICF) experiments as a part of nuclear diagnostics. CR-39 is filtered to stop fast ablator ions which have been accelerated from an ICF implosion due to electric fields caused by laser-plasma interactions. In some experiments, the filtering is insufficient to block these ions and the fusion-product signal tracks are lost in the large background of accelerated ion tracks. A technique for recovering signal in these scenarios has been developed, tested, and implemented successfully. The technique involves removing material from the surface of the CR-39 to a depth beyond the endpoint of the ablator ion tracks. The technique preserves signal magnitude (yield) as well as structure in radiograph images. The technique is effective when signal particle range is at least 10 um deeper than the necessary bulk material removal.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Investigation of ion kinetic effects in direct-drive exploding-pusher implosions at the NIF

Measurements of yield, ion temperature, areal density (rhoR), shell convergence, and bang time have been obtained in shock-driven, D2 and D3He gas-filled “exploding-pusher” inertial confinement fusion (ICF) implosions at the National Ignition Facility (NIF) to assess the impact of ion kinetic effects. These measurements probed the shock convergence phase of ICF implosions, a critical stage in hot-spot ignition experiments. The data complement previous studies of kinetic effects in shock-driven implosions. Ion temperature and fuel rhoR inferred from fusion-product spectroscopy are used to estimate the ion-ion mean free path in the gas. A trend of decreasing yields relative to the predictions of 2D draco hydrodynamics simulations with increasing Knudsen number (the ratio of ion-ion mean free path to minimum shell radius) suggests that ion kinetic effects are increasingly impacting the hot fuel region, in general agreement with previous results. The long mean free path conditions giving rise to ion kinetic effects in the gas are often prevalent during the shock phase of both exploding pushers and ablatively-driven implosions, including ignition-relevant implosions.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Top-level physics requirements and simulated performance of the MRSt on the National Ignition Facility

The time-resolving Magnetic Recoil Spectrometer (MRSt) for the National Ignition Facility (NIF) has been identified by the US National Diagnostic Working Group as one of the transformational diagnostics that will reshape the way inertial confinement fusion (ICF) implosions are diagnosed. The MRSt will measure the time-resolved neutron spectrum of an implosion, from which the time-resolved ion temperature, areal density, and yield will be inferred. Top-level physics requirements for the MRSt were determined based on simulations of numerous ICF implosions with varying degrees of alpha heating, P2 asymmetry, and mix. Synthetic MRSt data were subsequently generated for different configurations using Monte–Carlo methods to determine its performance in relation to the requirements. The system was found to meet most requirements at current neutron yields at the NIF. This work was supported by the DOE and LLNL.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1982

Inertial Confinement fusion targets

Inertial confinement fusion (ICF) targets are made as simple flat discs, as hollow shells or as complicated multilayer structures. Many techniques were devised for producing the targets. Glass and metal shells are made by using drop and bubble techniques. Solid hydrogen shells are also produced by adapting old methods to the solution of modern problems. Some of these techniques, problems, and solutions are discussed. In addition, the applications of many of the techniques to fabrication of ICF targets is presented.

Hendricks, C. D.↗
NASA NTRS1983

A technique for thick polymer coating of inertial-confinement-fusion targets

A technique to coat a stalk-mounted inertial-confinement fusion (ICF) target with a thick polymer layer has been successfully demonstrated. The polymer solution is first atomized, allowed to coalesce into a droplet, and positioned in a stable acoustic levitating field. The stalk-mounted ICF target is then moved into the acoustic field by manipulating a 3-D positioner to penetrate the surface membrane of the droplet, thus immersing the target in the levitated coating solution. The target inside the droplet is maintained at the center of the levitated liquid using the 3-D positional information provided by two orthogonally placed TV cameras until the drying process is completed. The basic components of the experimental apparatus, including an acoustic levitator, liquid sample deployment device, image acquisition instrumentation, and 3-D positioner, are briefly described.

Lee, M. C.↗
NASA NTRS1987

Transport vehicle for manned Mars missions powered by inertial confinement fusion

Inertial confinement fusion (ICF) is an ideal engine power source for manned spacecraft to Mars because of its inherently high power-to-mass ratios and high specific impulses. In this paper a concept is produced for a vehicle powered by ICF and utilizing a magnetic thrust chamber to avoid plasma thermalization with wall structures and the resultant degradation of specific impulse, that are unavoidable with the use of mechanical thrust chambers. This vehicle is capable of 100-day manned Mars missions with a 100-metric-ton payload and a total vehicle launch mass near 6000 metric tons, based on advanced technology assumed to be available by A.D. 2020.

Orth, Charles D.↗
NASA NTRS1994

Uniform hydrogen fuel layers for inertial fusion targets by microgravity

A critical concern in the fabrication of targets for inertial confinement fusion (ICF) is ensuring that the hydrogenic (D(sub 2) or DT) fuel layer maintains spherical symmetry. Solid layered targets have structural integrity, but lack the needed surface smoothness. Liquid targets are inherently smooth, but suffer from gravitationally induced sagging. One method to reduce the effective gravitational field environment is freefall insertion into the target chamber. Another method to counterbalance field gravitational force is to use an applied magnetic field combined with a gradient field to induce a magnetic dipole force on the liquid fuel layer. Based on time dependent calculations of the dynamics of the liquid fuel layer in microgravity environments, we show that it may be possible to produce a liquid layered ICF target that satisfies both smoothness and symmetry requirements.

Parks, P. B.↗
NASA NTRS2002

Magnetized Target Fusion Driven by Plasma Liners

Magnetized target fusion is an emerging, relatively unexplored approach to fusion for electrical power and propulsion application. The physical principles of the concept are founded upon both inertial confinement fusion (ICF) and magnetic confinement fusion (MCF). It attempts to combine the favorable attributes of both these orthogonal approaches to fusion, but at the same time, avoiding the extreme technical challenges of both by exploiting a fusion regime intermediate between them. It uses a material liner to compress, heat and contain the fusion reacting plasma (the target plasma) mentally. By doing so, the fusion burn could be made to occur at plasma densities as high as six orders of magnitude higher than conventional MCF such as tokamak, thus leading to an approximately three orders of magnitude reduction in the plasma energy required for ignition. It also uses a transient magnetic field, compressed to extremely high intensity (100's T to 1000T) in the target plasma, to slow down the heat transport to the liner and to increase the energy deposition of charged-particle fusion products. This has several compounding beneficial effects. It leads to longer energy confinement time compared with conventional ICF without magnetized target, and thus permits the use of much lower plasma density to produce reasonable burn-up fraction. The compounding effects of lower plasma density and the magneto-insulation of the target lead to greatly reduced compressional heating power on the target. The increased energy deposition rate of charged-particle fusion products also helps to lower the energy threshold required for ignition and increasing the burn-up fraction. The reduction in ignition energy and the compressional power compound to lead to reduced system size, mass and R&D cost. It is a fusion approach that has an affordable R&D pathway, and appears attractive for propulsion application in the nearer term.

Thio, Y. C. Francis↗
NASA NTRS2004

Calibration Software for Use with Jurassicprok

The Jurassicprok Interferometric Calibration Software (also called "Calibration Processor" or simply "CP") estimates the calibration parameters of an airborne synthetic-aperture-radar (SAR) system, the raw measurement data of which are processed by the Jurassicprok software described in the preceding article. Calibration parameters estimated by CP include time delays, baseline offsets, phase screens, and radiometric offsets. CP examines raw radar-pulse data, single-look complex image data, and digital elevation map data. For each type of data, CP compares the actual values with values expected on the basis of ground-truth data. CP then converts the differences between the actual and expected values into updates for the calibration parameters in an interferometric calibration file (ICF) and a radiometric calibration file (RCF) for the particular SAR system. The updated ICF and RCF are used as inputs to both Jurassicprok and to the companion Motion Measurement Processor software (described in the following article) for use in generating calibrated digital elevation maps.

Chapin, Elaine↗
DOE OSTI2011

INERTIAL FUSION DRIVEN BY INTENSE HEAVY-ION BEAMS

Intense heavy-ion beams have long been considered a promising driver option for inertial-fusion energy production. This paper briefly compares inertial confinement fusion (ICF) to the more-familiar magnetic-confinement approach and presents some advantages of using beams of heavy ions to drive ICF instead of lasers. Key design choices in heavy-ion fusion (HIF) facilities are discussed, particularly the type of accelerator. We then review experiments carried out at Lawrence Berkeley National Laboratory (LBNL) over the past thirty years to understand various aspects of HIF driver physics. A brief review follows of present HIF research in the US and abroad, focusing on a new facility, NDCX-II, being built at LBNL to study the physics of warm dense matter heated by ions, as well as aspects of HIF target physics. Future research directions are briefly summarized.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

Control System For Cryogenic THD Layering At The National Ignition Facility

The National Ignition Facility (NIF) is the world largest and most energetic laser system for Inertial Confinement Fusion (ICF). In 2010, NIF began ignition experiments using cryogenically cooled targets containing layers of the tritium-hydrogen-deuterium (THD) fuel. The 75 {micro}m thick layer is formed inside of the 2 mm target capsule at temperatures of approximately 18 K. The ICF target designs require sub-micron smoothness of the THD ice layers. Formation of such layers is still an active research area, requiring a flexible control system capable of executing the evolving layering protocols. This task is performed by the Cryogenic Target Subsystem (CTS) of the NIF Integrated Computer Control System (ICCS). The CTS provides cryogenic temperature control with the 1 mK resolution required for beta-layering and for the thermal gradient fill of the capsule. The CTS also includes a 3-axis x-ray radiography engine for phase contrast imaging of the ice layers inside of the plastic and beryllium capsules. In addition to automatic control engines, CTS is integrated with the Matlab interactive programming environment to allow flexibility in experimental layering protocols. The CTS Layering Matlab Toolbox provides the tools for layer image analysis, system characterization and cryogenic control. The CTS Layering Report tool generates qualification metrics of the layers, such as concentricity of the layer and roughness of the growth boundary grooves. The CTS activities are automatically coordinated with other NIF controls in the carefully orchestrated NIF Shot Sequence.

42 ENGINEERING↗
DOE OSTI2012

Reduced Variance for Material Sources in Implicit Monte Carlo

Implicit Monte Carlo (IMC), a time-implicit method due to Fleck and Cummings, is used for simulating supernovae and inertial confinement fusion (ICF) systems where x-rays tightly and nonlinearly interact with hot material. The IMC algorithm represents absorption and emission within a timestep as an effective scatter. Similarly, the IMC time-implicitness splits off a portion of a material source directly into the radiation field. We have found that some of our variance reduction and particle management schemes will allow large variances in the presence of small, but important, material sources, as in the case of ICF hot electron preheat sources. We propose a modification of our implementation of the IMC method in the Jayenne IMC Project. Instead of battling the sampling issues associated with a small source, we bypass the IMC implicitness altogether and simply deterministically update the material state with the material source if the temperature of the spatial cell is below a user-specified cutoff. We describe the modified method and present results on a test problem that show the elimination of variance for small sources.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

Uniform DT 3T burn: computations and sensitivities

A numerical model was developed in C to integrate the nonlinear deutrium-tritium (DT) burn equations in a three temperature (3T) approximation for spatially uniform test problems relevant to Inertial Confinement Fusion (ICF). Base model results are in excellent agreement with standard 3T results. Data from NDI, SESAME, and TOPS databases is extracted to create fits for the reaction rate parameter, the Planck opacity, and the coupling frequencies of the plasma temperatures. The impact of different fits (e.g., TOPS versus SESAME opacity data, higher order polynomial fits ofNDI data for the reaction rate parameter) were explored, and sensitivity to several model inputs are presented including: opacity data base, Coulomb logarithm, and Bremsstrahlung. Sensitivity to numerical integration time step size, and the relative insensitivity to the discretized numerics and numerical integration method was demonstrated. Variations in the IC for densities and temperatures were explored, showing similar DT burn profiles in most cases once ignition occurs. A coefficient multiplying the Compton coupling term (default, A = 1) can be adjusted to approximate results from more sophisticated models. The coefficient was reset (A = 0.4) to match the maximum temperatures resulting from standard multi-group simulations of the base case test problem. Setting the coefficient to a larger value, (A = 0.6) matches maximum ion temperatures in a kinetic simulation of a high density ICF-like regime. Matching peak temperatures does not match entire temperature-time profiles, indicating the Compton coefficient is density and time dependent as the photon distribution evolves. In the early time burn during the ignition of the DT, the present model with modified Compton coupling provides a very simple method to obtain a much improved match to the more accurate solution from the multi-group radiation model for these DT burn regimes.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗