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At least 577 records · Page 32
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

The black hole mass of NGC 4151. II. Stellar dynamical measurement from near-infrared integral field spectroscopy

We present a revised measurement of the mass of the central black hole (M{sub BH} ) in the Seyfert 1 galaxy NGC 4151. The new stellar dynamical mass measurement is derived by applying an axisymmetric orbit-superposition code to near-infrared integral field data obtained using adaptive optics with the Gemini Near-infrared Integral Field Spectrograph (NIFS). When our models attempt to fit both the NIFS kinematics and additional low spatial resolution kinematics, our results depend sensitively on how χ{sup 2} is computed—probably a consequence of complex bar kinematics that manifest immediately outside the nuclear region. The most robust results are obtained when only the high spatial resolution kinematic constraints in the nuclear region are included in the fit. Our best estimates for the black hole mass and H-band mass-to-light ratio are M{sub BH} ∼ 3.76 ± 1.15 × 10{sup 7} M{sub ☉} (1σ error) and Y{sub H} ∼ 0.34 ± 0.03 M{sub ☉}/L{sub ☉} (3σ error), respectively (the quoted errors reflect the model uncertainties). Our black hole mass measurement is consistent with estimates from both reverberation mapping (3.57{sub −0.37}{sup +0.45}×10{sup 7} M{sub ⊙}) and gas kinematics (3.0{sub −2.2}{sup +0.75}×10{sup 7} M{sub ⊙}; 1σ errors), and our best-fit mass-to-light ratio is consistent with the photometric estimate of Y{sub H} = 0.4 ± 0.2 M{sub ☉}/L{sub ☉}. The NIFS kinematics give a central bulge velocity dispersion σ{sub c} = 116 ± 3 km s{sup –1}, bringing this object slightly closer to the M{sub BH}-σ relation for quiescent galaxies. Although NGC 4151 is one of only a few Seyfert 1 galaxies in which it is possible to obtain a direct dynamical black hole mass measurement—and thus, an independent calibration of the reverberation mapping mass scale—the complex bar kinematics makes it less than ideally suited for this purpose.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Indirect drive ignition at the National Ignition Facility

This paper reviews scientific results from the pursuit of indirect drive ignition on the National Ignition Facility (NIF) and describes the program's forward looking research directions. In indirect drive on the NIF, laser beams heat an x-ray enclosure called a hohlraum that surrounds a spherical pellet. X-ray radiation ablates the surface of the pellet, imploding a thin shell of deuterium/tritium (DT) that must accelerate to high velocity (v > 350 km s –1 ) and compress by a factor of several thousand. Since 2009, substantial progress has been made in understanding the major challenges to ignition: Rayleigh Taylor (RT) instability seeded by target imperfections; and low-mode asymmetries in the hohlraum x-ray drive, exacerbated by laser-plasma instabilities (LPI). Requirements on velocity, symmetry, and compression have been demonstrated separately on the NIF but have not been achieved simultaneously. We now know that the RT instability, seeded mainly by the capsule support tent, severely degraded DT implosions from 2009–2012. Experiments using a 'high-foot' drive with demonstrated lower RT growth improved the thermonuclear yield by a factor of 10, resulting in yield amplification due to alpha particle heating by more than a factor of 2. Furthermore, large time dependent drive asymmetry in the LPI-dominated hohlraums remains unchanged, preventing further improvements. High fidelity 3D hydrodynamic calculations explain these results. Future research efforts focus on improved capsule mounting techniques and on hohlraums with little LPI and controllable symmetry. In parallel, we are pursuing improvements to the basic physics models used in the design codes through focused physics experiments.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Understanding asymmetries using integrated simulations of capsule implosions in low gas-fill hohlraums at the National Ignition Facility

Current capsule implosions at the National Ignition Facility (NIF) using high-density-carbon ablators and laser energies close to 2 MJ have shown neutron yields in excess of 50 kJ. Improving on this performance requires understanding of the different degradation mechanisms. For many NIF implosions, nuclear diagnostic signatures have inferred residual hot-spot velocities that correlate with fuel areal density variations consistent with a low-order mode-1 asymmetry. A current working hypothesis attributes these asymmetries to a combination of beam to beam variations in the laser delivery and possibly coupling to target features, such as the diagnostic holes needed for x-ray imaging. Recently, a new source has been identified, thickness variation in the ablator shell. To gain better understanding and eventually mitigate the causes of <ρR> asymmetries, 3D integrated simulations using the actual delivered laser powers are needed. To capture the effect of the diagnostic holes (DHs) using direct numerical simulation would require significantly large computational resources. Instead, our 3D simulations make use of a subgrid model developed using highly-resolved 2D simulations that include several details of the DH engineering complexity. Simulations of NIF shots using hohlraums without DHs, to isolate the effect of beam-to-beam variations, reproduce fairly well the observed nuclear diagnostic signatures. Similarly, reasonable agreement between data and simulations is also obtained in the presence of diagnostic holes. To account for the remaining discrepancies a sensitivity study of ablator thickness variation showed that 1% thickness asymmetries are comparable in effect to 1% peak drive mode-1 asymmetries. Furthermore, this study identified sensitivity to variations in the imbedded doped layer (needed to shield the DT ice from the high energy x-rays generated in the hohlraum) thickness even when the inner and outer surface of the ablator are perfectly spherical.

radiation hydrodynamics↗
DOE OSTI2018

From ICF to laboratory astrophysics: ablative and classical Rayleigh-Taylor Instability experiments in turbulent-like regimes

Rayleigh–Taylor instability (RTI) occurs whenever fluids of different densities are accelerated against the density gradient, as is the case for the target ablator in ICF implosions. The advent of megajoule class lasers, like the National Ignition Facility (NIF) or Laser Mégajoule, offers novel opportunities to study turbulent mixing flows in high energy density plasmas for fundamental hydrodynamics or laboratory astrophysics experiments. Here, we review different RTI experiments, performed either at the ablation front or at a classical embedded interface. A two-dimensional bubble-merger, bubble-competition regime was evidenced for the first time at the ablation front in indirect-drive on the NIF thanks to an unprecedented long x-ray drive. Similarly, a novel large-area, planar platform enables the capabilities to perform long duration direct drive hydrodynamics experiments on NIF. Starting from imprinted seeds, a three-dimensional bubble-merger regime was also observed in direct-drive, as larger bubbles overtook and merged with smaller bubbles. In the astrophysical context, RTI also plays a role in supernova (SN) explosions, either of Type Ia or II. We report on experiments performed on the LULI2000 facility studying RTI in scaled laboratory conditions relevant for the physics of young SN remnants. Finally, using a light CH foam as a deceleration medium, we measured, for the first time, the RTI mixing zone by PW transverse radiography.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Wetted foam liquid fuel ICF target experiments

We are developing a new NIF experimental platform that employs wetted foam liquid fuel layer ICF capsules. We will use the liquid fuel layer capsules in a NIF sub-scale experimental campaign to explore the relationship between hot spot convergence ratio (CR) and the predictability of hot spot formation. DT liquid layer ICF capsules allow for flexibility in hot spot CR via the adjustment of the initial cryogenic capsule temperature and, hence, DT vapor density. Our hypothesis is that the predictive capability of hot spot formation is robust and 1D-like for a relatively low CR hot spot (CR~15), but will become less reliable as hot spot CR is increased to CR>20. Simulations indicate that backing off on hot spot CR is an excellent way to reduce capsule instability growth and to improve robustness to low-mode x-ray flux asymmetries. In the initial experiments, we will test our hypothesis by measuring hot spot size, neutron yield, ion temperature, and burn width to infer hot spot pressure and compare to predictions for implosions with hot spot CR's in the range of 12 to 25. Larger scale experiments are also being designed, and we will advance from sub-scale to full-scale NIF experiments to determine if 1D-like behavior at low CR is retained as the scale-size is increased. The long-term objective is to develop a liquid fuel layer ICF capsule platform with robust thermonuclear burn, modest CR, and significant α-heating with burn propagation.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Absolute calibration of the continuum x-ray spectrometer (ConSpec) at the National Ignition Facility

We illustrate the absolute calibration of the continuum x-ray spectrometer (ConSpec), designed to measure the hot-spot electron temperature of inertial confinement fusion (ICF) implosions at the National Ignition Facility (NIF). The spectrometer measures emission from photon energies of 20 to 30 keV where opacity effects in ICF implosions at the NIF are negligible and provides spatial resolution to separate the hot-spot emission from other x-ray sources, such as the gold emission from the hohlraum wall. Using a combination of x-ray ray tracing and calibration data taken using a well characterized x-ray source, we measure the dispersion, spatial resolution, and absolute sensitivity of the instrument. Finally, we present an example spectrum measured at the NIF and demonstrate the ability to measure the hot-spot electron temperature with uncertainty under 10%.

47 OTHER INSTRUMENTATION↗
DOE OSTI2026

Measurement of the 75 As ⁢(𝑛, 2⁢𝑛) cross section at 14.1 MeV at the National Ignition Facility

Here, a new measurement of the 75 As (𝑛, 2⁢𝑛) measurement was performed using the 14.1 MeV neutron pulse produced by fusion experiments at the National Ignition Facility (NIF). The target material consisted of GaAs foils encapsulated in aluminum irradiation containers, along with Au monitor foils, and positioned in the NIF chamber during high neutron yield shots. After irradiation, the GaAs and Au foils were counted with high purity germanium detectors to assess the production of (𝑛, 2⁢𝑛) activation products to determine the flux and the cross section of interest. The measured cross section was 966 ± 71 mb at 14.1 ± 0.37 MeV. This work provides a proof of concept for a platform for performing “ride-along” cross section measurements at NIF to contribute to existing nuclear data as well as measure new cross sections in the future.

and nuclear chemistry↗
DOE OSTI2020

Multibeam absolute stimulated Raman scattering and two-plasmon decay

Multibeam absolute instability thresholds for stimulated Raman scattering (SRS) and two-plasmon decay (TPD) are calculated in three dimensions for conditions relevant to direct-drive inertial confinement fusion experiments on the OMEGA laser and at the National Ignition Facility (NIF). Although multibeam effects are found to be significant for both instabilities, SRS is found to have less efficient multibeam coupling than TPD. The results are consistent with the observation of a TPD-dominated regime on the OMEGA laser and a SRS-dominated regime on the NIF despite the single-beam SRS threshold being lower than the single-beam TPD threshold on both facilities. The minimum instability threshold for NIF plasma parameters occurs for SRS near quarter-critical densities with a shared electromagnetic wave propagating along the beam axis.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Core conditions for alpha heating attained in direct-drive inertial confinement fusion

It is shown that direct-drive implosions on the OMEGA laser have achieved core conditions that would lead to significant alpha heating at incident energies available on the National Ignition Facility (NIF) scale. The extrapolation of the experimental results from OMEGA to NIF energy assumes only that the implosion hydrodynamic efficiency is unchanged at higher energies. This approach is independent of the uncertainties in the physical mechanism that degrade implosions on OMEGA, and relies solely on a volumetric scaling of the experimentally observed core conditions. It is estimated that the current best-performing OMEGA implosion [Regan et al., Phys. Rev. Lett. 117, 025001 (2016)] extrapolated to a 1.9 MJ laser driver with the same illumination configuration and laser-target coupling would produce 125 kJ of fusion energy with similar levels of alpha heating observed in current highest performing indirect-drive NIF implosions.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

First Liquid Layer Inertial Confinement Fusion Implosions at the National Ignition Facility

The first cryogenic deuterium and deuterium-tritium liquid layer implosions at the National Ignition Facility (NIF) demonstrate D 2 and DT layer Inertial Confinement Fusion (ICF) implosions that can access low-to-moderate hot spot convergence ratio (12 30) DT ice layer implosions. Although high CR is desirable in an idealized 1D sense, it amplifies the deleterious effects of asymmetries. To date, these asymmetries prevented the achievement of ignition at the NIF and are the major cause of simulation-experiment disagreement. In the initial liquid layer experiments, high neutron yields were achieved with CR’s of 12-17, and the hot spot formation is well understood, demonstrated by good agreement between the experimental data and the radiation hydrodynamic simulations. These initial experiments open a new NIF experimental capability that provides an opportunity to explore the relationship between hot-spot convergence ratio and the robustness of hot-spot formation during ICF implosions.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Particle-in-cell simulations of burning inertial confinement fusion capsule implosions

Anomalies observed in the neutron spectral shift of high-yield shots at the National Ignition Facility (NIF) suggest the presence of suprathermal ions [E. P. Hartouni et al., Nat. Phys. 19, 72 (2023)], implying that kinetic effects play a significant role in burning inertial confinement fusion (ICF) plasmas. Furthermore, recent measurements of reaction-in-flight (RIF) neutrons offer a direct probe of the stopping power in the burning fuel region of high-energy alpha particles and up-scattered fuel ions. We have developed the particle-in-cell code PICNIC, an exactly energy-conserving particle-in-cell Monte-Carlo collision (PIC-MCC) code to simulate the burn stage in ICF. We present results from 1D spherical simulations of NIF shot N210808, which was the first to exceed the Lawson criterion for laser fusion. We find that the suprathermal ions generated by large-angle Rutherford and nuclear elastic scattering (NES) with fusion alphas produce an alpha knock-on neutron (AKN) signal consistent with the extent and relative yield of the AKN spectrum identified in ignition experiments at the NIF. Furthermore, we also find that the inclusion of large-angle scattering physics does not explain the anomalously large spectral shift observed in the experiment.

High-energy-density plasmas↗
DOE OSTI2024

Repair strategy for fused silica wedged focus lens with high-density filamentary damage

The National Ignition Facility (NIF) is intentionally operated with the final fused silica glass (SiO2) optics exposed to fluences and intensities with the potential to induce damage that will grow with additional laser exposure. Therefore, the NIF operates a recycle loop to refurbish final optics by mitigating any initiated surface damage to arrest its growth. However, the morphology of filamentary damage, caused by local self-focusing in the bulk of a silica optic, adds complexity to optics mitigation and provides a limitation to optic reusability. Here, we evaluate techniques for mitigating isolated and clustered filamentary damage. Optical microscopy before and after installation on NIF was used to determine the efficacy of filamentary mitigation after a series of high fluence and intensity laser exposures. The challenges and success rate of the methods are compared for various filamentary damage mitigation strategies.

National Ignition Facility↗
DOE OSTI2025

Optimizing fused silica debris shield use in the National Ignition Facility

The National Ignition Facility (NIF) deliberately and routinely operates with its final optics exposed to fluences likely to induce and grow damage. This choice has enabled the NIF to operate at energies previously unachievable at the expense of limitations to delivered power and energy contingent on the ability to repair damage on the final optics. Prior to the introduction of the fused silica debris shield (FSDS), the grating debris shield (GDS) was the optic type on the NIF most prone to damage and hence a primary limiter to the delivered energy. The introduction of the FSDS has reduced the damage initiation rate on the GDS by about two orders of magnitude to date. Despite the FSDS being a disposable optic, it is important to understand how the FSDS damages and when its damage requires it to be exchanged to maximize the FSDS lifetime while still protecting the GDS from damage. We will define the FSDS exchange criteria and evaluate the damage initiation mechanisms of the FSDS. The surface damage morphologies provide insight into the impact of the various damage mechanisms that limit the FSDS lifetime. These results are utilized in our analysis to optimize the FSDS exchange criteria to further extend the GDS lifetime.

42 ENGINEERING↗
DOE OSTI2023

Expression of V-nitrogenase and Fe-nitrogenase in Methanosarcina acetivorans is controlled by molybdenum, fixed nitrogen, and the expression of Mo-nitrogenase

ABSTRACT All nitrogen-fixing bacteria and archaea (diazotrophs) use molybdenum (Mo) nitrogenase to reduce dinitrogen (N 2 ) to ammonia, with some also containing vanadium (V) and iron-only (Fe) nitrogenases that lack Mo. Among diazotrophs, the regulation and usage of the alternative V-nitrogenase and Fe-nitrogenase in methanogens are largely unknown. Methanosarcina acetivorans contains nif , vnf , and anf gene clusters encoding putative Mo-nitrogenase, V-nitrogenase, and Fe-nitrogenase, respectively. This study investigated nitrogenase expression and growth by M. acetivorans in response to fixed nitrogen, Mo/V availability, and CRISPRi repression of the nif , vnf , and/or anf gene clusters. The availability of Mo and V significantly affected growth of M. acetivorans with N 2 but not with NH 4 Cl. M. acetivorans exhibited the fastest growth rate and highest cell yield during growth with N 2 in medium containing Mo, and the slowest growth in medium lacking Mo and V. qPCR analysis revealed the transcription of the nif operon is only moderately affected by depletion of fixed nitrogen and Mo, whereas vnf and anf transcription increased significantly when fixed nitrogen and Mo were depleted, with removal of Mo being key. Immunoblot analysis revealed Mo-nitrogenase is detected when fixed nitrogen is depleted regardless of Mo availability, while V-nitrogenase and Fe-nitrogenase are detected only in the absence of fixed nitrogen and Mo. CRISPRi repression studies revealed that V-nitrogenase and/or Fe-nitrogenase are required for Mo-independent diazotrophy, and unexpectedly that the expression of Mo-nitrogenase is also required. These results reveal that alternative nitrogenase production in M. acetivorans is tightly controlled and dependent on Mo-nitrogenase expression. IMPORTANCE Methanogens and closely related methanotrophs are the only archaea known or predicted to possess nitrogenase. Methanogens play critical roles in both the global biological nitrogen and carbon cycles. Moreover, methanogens are an ancient microbial lineage and nitrogenase likely originated in methanogens. An understanding of the usage and properties of nitrogenases in methanogens can provide new insight into the evolution of nitrogen fixation and aid in the development nitrogenase-based biotechnology. This study provides the first evidence that a methanogen can produce all three forms of nitrogenases, including simultaneously. The results reveal components of Mo-nitrogenase regulate or are needed to produce V-nitrogenase and Fe-nitrogenase in methanogens, a result not seen in bacteria. Overall, this study provides a foundation to understand the assembly, regulation, and activity of the alternative nitrogenases in methanogens.

Biotechnology & Applied Microbiology↗
DOE OSTI2017

Control and Information Systems for the National Ignition Facility

Orchestration of every National Ignition Facility (NIF) shot cycle is managed by the Integrated Computer Control System (ICCS), which uses a scalable software architecture running code on more than 1950 front-end processors, embedded controllers, and supervisory servers. The ICCS operates laser and industrial control hardware containing 66 000 control and monitor points to ensure that all of NIF’s laser beams arrive at the target within 30 ps of each other and are aligned to a pointing accuracy of less than 50 μm root-mean-square, while ensuring that a host of diagnostic instruments record data in a few billionths of a second. NIF’s automated control subsystems are built from a common object-oriented software framework that distributes the software across the computer network and achieves interoperation between different software languages and target architectures. A large suite of business and scientific software tools supports experimental planning, experimental setup, facility configuration, and post-shot analysis. Standard business services using open-source software, commercial workflow tools, and database and messaging technologies have been developed. An information technology infrastructure consisting of servers, network devices, and storage provides the foundation for these systems. Thus, this work is an overview of the control and information systems used to support a wide variety of experiments during the National Ignition Campaign.

42 ENGINEERING↗
DOE OSTI2016

Fabrication, characterization, and modeling of comixed films for NXS calibration targets [Fabrication and metrology of the NXS calibration targets]

In 2014/2015 at the Omega laser facility, several experiments took place to calibrate the National Ignition Facility (NIF) X-ray spectrometer (NXS), which is used for high-resolution time-resolved spectroscopic experiments at NIF. The spectrometer allows experimentalists to measure the X-ray energy emitted from high-energy targets, which is used to understand key data such as mixing of materials in highly compressed fuel. The purpose of the experiments at Omega was to obtain information on the instrument performance and to deliver an absolute photometric calibration of the NXS before it was deployed at NIF. The X-ray emission sources fabricated for instrument calibration were 1-mm fused silica spheres with precisely known alloy composition coatings of Si/Ag/Mo, Ti/Cr/Ag, Cr/Ni/Zn, and Zn/Zr, which have emission in the 2- to 18-keV range. Critical to the spectrometer calibration is a known atomic composition of elements with low uncertainty for each calibration sphere. This study discusses the setup, fabrication, and precision metrology of these spheres as well as some interesting findings on the ternary magnetron-sputtered alloy structure.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Fresnel zone plate development for x-ray radiography of hydrodynamic instabilities at the National Ignition Facility

The study of Rayleigh–Taylor (RT) and Richtmyer–Meshkov (RM) instabilities in a planar geometry at high energy densities at the National Ignition Facility (NIF) requires high spatial resolution imaging. We demonstrate the potential of Fresnel zone plates (FZPs) to achieve resolution that would unlock such studies. FZPs are circular aperiodic gratings that use diffraction to focus x rays and produce an image with high spatial resolution. Taking into account the NIF’s challenging environment, we have designed a specific array of five FZPs for a zinc backlighter to take a radiograph of a target with 9 keV x rays. We measured a mean resolution for the FZP of 1.9µm±0.5µm and a ±1mm depth of focus at an x-ray calibration facility as well as a 2.3µm±0.4µm resolution on a resolution wire mesh shot on the NIF. We also performed an in-depth analysis of the image quality to assess the capability to resolve the small features present in RT and RM instabilities.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Impact of increased smoothing by spectral dispersion bandwidth on stimulated Brillouin scattering in laser driven Hohlraums

Experiments were conducted at the National Ignition Facility (NIF) to investigate the impact of increased smoothing by spectral dispersion (SSD) bandwidth on the production of stimulated Brillouin scattering (SBS) within an indirect-drive inertial confinement fusion (ICF) Hohlraum. This was done in a subscale gold Hohlraum driven by 192 laser beams depositing 1.1 MJ of energy. The laser bandwidth was increased from 45 to 118 GHz (before frequency tripling) on the 30° and 50° cones, where backscatter could be measured using the Full Aperture Backscatter Station (FABS). It was expected that this 2.6-fold increase in bandwidth would suppress SBS generated within the Hohlraum plasma and lower the backscattered SBS energy on the 50° cones by over a factor of four. Experimental results, however, show that this SSD change only reduced the 50° cone SBS during the main capsule drive by -18±31% and -4.5±7.8% over the entire pulse. This is small compared to expected shot-to-shot SBS reproducibility (∼30%), such that the result can be considered within normal performance fluctuations. New 3D parallel paraxial code (pF3D) simulations, accounting for beam refractive intensification reproduce this result, suggesting that closer to 300 GHz of bandwidth would have been required to mitigate SBS to the expected level. Delivering such a high bandwidth is not feasible at NIF when operating at high peak power and would potentially prevent NIF’s ability to use cross-beam energy transfer (CBET) for implosion symmetry tuning.

Physics↗