Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “IMPLOSIONS”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,315 records · Page 73
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Shock Ignition Laser-Plasma Interactions in Ignition-Scale Plasmas

Here, we use a subignition scale laser, the 30 kJ Omega, and a novel shallow-cone target to study laser-plasma interactions at the ablation-plasma density scale lengths and laser intensities anticipated for direct drive shock-ignition implosions at National Ignition Facility scale. Our results show that, under these conditions, the dominant instability is convective stimulated Raman scatter with experimental evidence of two plasmon decay (TPD) only when the density scale length is reduced. Particle-in-cell simulations indicate this is due to TPD being shifted to lower densities, removing the experimental back-scatter signature and reducing the hot-electron temperature. The experimental laser energy-coupling to hot electrons was found to be 1%–2.5%, with electron temperatures between 35 and 45 keV. Radiation-hydrodynamics simulations employing these hot-electron characteristics indicate that they should not preheat the fuel in MJ-scale shock ignition experiments.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Hot Spot Evolution Measured by High-Resolution X-Ray Spectroscopy at the National Ignition Facility

Evolution of the hot spot plasma conditions was measured using high-resolution x-ray spectroscopy at the National Ignition Facility. The capsules were filled with DD gas with trace levels of Kr and had either a high-density-carbon (HDC) ablator or a tungsten (W)-doped HDC ablator. Time-resolved measurement of the Kr He β spectra, absolutely calibrated by a simultaneous time-integrated measurement, allows inference of the electron density and temperature through observing Stark broadening and the relative intensities of dielectronic satellites. By matching the calculated hot spot emission using a collisional-radiative code to experimental observations, the hot spot size and areal density are determined. Here these advanced spectroscopy techniques further reveal the effect of W dopant in the ablator on the hot spot parameters for their improved implosion performance.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Optimization Methodology of Polar Direct-Drive Illumination for the National Ignition Facility

Improved laser illumination uniformity drives shocks and implosions to create more extreme high energy density environments. Predominantly, the geometry of experiments that can be performed is dictated by the layout of beams at laser facilities, limiting inter-facility and multiscale investigations. This Letter presents the first automated, algorithmic approach for generating illumination configurations for high energy density experiments. The method is demonstrated in comparison to a polar direct drive solid target experiment at the National Ignition Facility. The new illumination configuration is simulated to create greater than ×3 higher peak pressure and almost ×2 higher density by maintaining better shock uniformity. Furthermore, the optimization process is performed with reduced computational expense and isotropic plasma profiles, while accounting for the impact of cross-beam energy transfer.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Diagnostic and Power Feed Upgrades to the MAIZE Facility

The Michigan Accelerator for Inductive Z-pinch experiments (MAIZE) is a one stage, 1 MA, Linear Transformer Driver (LTD) at the University of Michigan. The MAIZE facility has been the site of various experimental studies, including wire array z-pinches for x-ray source development and cylindrical foil loads for implosion stability analysis. Here, in order to better understand and investigate these and other experiments, a 4- frame extreme ultraviolet (EUV) camera was implemented, the optical stability of a 12-frame laser shadowgraphy system was improved, B-dot probes were upgraded, and a Rogowski coil was constructed. New conical load hardware was also developed to reduce the inductance of the transmission line and thus improve the current delivered to the loads.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Identifying Entangled Physics Relationships Through Sparse Matrix Decomposition to Inform Plasma Fusion Design

We report a sustainable burn platform through inertial confinement fusion (ICF) has been an ongoing challenge for over 50 years. Mitigating engineering limitations and improving the current design involves an understanding of the complex coupling of physical processes. While sophisticated simulation codes are used to model ICF implosions, these tools contain necessary numerical approximation but miss physical processes that limit predictive capability. Identification of relationships between controllable design inputs to ICF experiments and measurable outcomes (e.g., neutron yield, neutron velocity, areal density) from performed experiments can help guide the future design of experiments and development of simulation codes, to potentially improve the accuracy of the computational models used to simulate ICF experiments. We use sparse matrix decomposition methods to identify clusters of a few related design variables. Sparse principal component analysis (SPCA) identifies groupings that are related to the physical origin of the variables (laser, hohlraum, and capsule). A variable importance analysis finds that in addition to variables highly correlated with neutron yield, such as picket power and laser energy, variables that represent a dramatic change of the ICF design, such as number of pulse steps, are also very important. The obtained sparse components are then used to train a random forest (RF) regression surrogate for predicting total yield. The RF performance on the training and testing data compares with the performance of the RF trained using all the design variables considered. This work is intended to inform design changes in future ICF experiments by augmenting the expert intuition and simulation results.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Ultrasonic Piezoelectric Atomizers: Electromechanical Modeling and Performance Testing

Ultrasonic atomization of bulk liquids has received extensive attention in the past few decades due to the ability to produce controlled droplet sizes, a necessity for many industries such as spray coating and aerosol drug delivery. Despite the increase in attention, one novel application of this technology has been overlooked until recently, and that is the moisture removal capabilities of atomization. The first ever ultrasonic dryer, created by researchers at Oak Ridge National Lab in 2016, applies the mechanisms of atomization to mechanically remove moisture from clothing. The process utilizes the ultrasonic vibrations created by a piezoelectric transducer in direct contact with a wet fabric to rupture the liquid-vapor boundary of the retained water. Once ruptured, smaller droplets are ejected from the bulk liquid and are actively removed from the fabric pores. The mechanisms of droplet ejection from this event are related to both capillary waves forming on the liquid surface (Capillary Wave Theory), as well as the implosion of cavitation bubbles formed from the hydraulic shocks propagating from the transducer (Cavitation Theory). In this work, we present an analytical model for predicting the moisture removal rate of a wet fabric exposed to ultrasonic vibrations, and connect the atomization events to a global variable, acceleration, in order to decouple the nondeterministic relationship between the transducer and applied voltage. The acceleration governing atomization is predicted using a verified numerical model. The numerical model is shown to assist in developing ultrasonic drying by means of efficiently evaluating transducer design changes.

Dupuis, Eric D.↗
DOE OSTI2018

Lens design challenges for scintillator-based neutron imaging

Neutron imaging is an important diagnostic to study inertial confinement fusion (ICF) implosions at the National Ignition Facility (NIF) using neutrons emitted in the fusion reactions. Analysis of time-gated images of the primary fusion (14.1 MeV) and down-scattered (6-12 MeV) neutrons based on their time-of-flight allows for the reconstruction of the burning hot spot undergoing fusion and the surrounding cold fuel. The Los Alamos National Laboratory (LANL) Advanced Imaging team has been providing these images since 2011. Currently, two additional lines of sight are being designed and built for NIF to allow three-dimensional reconstructions. Neutron imaging relies on the conversion of neutrons into light to be captured by an imaging system through the use of a scintillator. Although the current neutron imaging system utilizes a fiber scintillator array, a newly designed imaging system will consist of a thick monolithic scintillator and custom-designed lenses to collect the light. The custom lens has to resolve an image produced in the thick volume of the scintillator and therefore needs a large depth of field.

42 ENGINEERING↗
DOE OSTI2019

In-tank, on-shot characterization of the OMEGA laser system focal spot

Direct-drive fusion implosion experiments using the 60-beam OMEGA Laser System require ~1% rms uniformity on target. Measurements from laser diagnostics indicate that beam-to-beam power variation has been sufficiently reduced such that the uniformity nearly meets this requirement; however, experimental results suggest otherwise. To better understand this discrepancy, a full-beam-in-tank diagnostic has been developed to characterize the on-shot, full-energy focal spot of a single beam inside the target chamber using a small sample of the beam from the final optic assembly. In this paper, we describe the diagnostic and present the results of commissioning experiments.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Nanofabrication and inspection of fuel capsules for inertial confinement fusion

3D nanofabrication via Two-Photon Polymerization (TPP) provides a unique capability of flexibly fabricating complex structures over 1D-3D dimensions and µm-cm scales with resolutions below 100 nm. In the past years, the Laser-Assisted Nano Engineering (LANE) Group at the University of Nebraska-Lincoln (UNL) has been working closely with the Laboratory of Laser Energetics (LLE) in developing practical TPP approaches to fabricating various target structures for Inertial Confinement Fusion (ICF). At the same time, fuel capsules for ICF experiments should be inspected for surface and wall-embedded defects. Plastics materials [e.g., for example polystyrene (PS)] are the common materials used to make fuel capsules. However, during their manufacturing, capsules usually contain defects (vacuoles) embedded inside the shell walls, which may distort the implosion processes and influence the ICF performance of the capsules. The size of vacuoles is usually in a range from 100 to 2000 nm. Coherent anti-Stokes Raman scattering (CARS) microscope offers the capabilities of inspecting and characterizing the capsule defects. Furthermore, cryo-CARS microscopy was developed to explore how fuel isotope distributed inside target when icing that could not be diagnosed before.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Study of the expansion dynamics of the plasma of a thin aluminum foil under the action of soft X-ray emission

Results are presented from experiments on the irradiation of thin aluminum foils by an intense soft X-ray (SXR) source on the basis of the Z-pinch formed during the implosion of a tungsten wire array at the Angara-5-1 facility. The state of the foil target is examined by taking two-dimensional X-ray frames. The expansion velocity of the plasma formed under the action of pulsed SXR emission on the front (irradiated) and back sides of the foil and the glow intensity of aluminum plasma on the back side are found from the spatial distribution of the radiation intensity of the plasma of the irradiated foil. The time at which the foil plasma becomes transparent to Z-pinch radiation is determined from the increase in the intensity of transmitted SXR emission.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Stability of compression of the inner array plasma in nested arrays

The implosion of nested fiber/wire arrays was studied experimentally at the Angara-5-1 facility. The outer array consisted of kapron fibers, while the inner array was made of tungsten wires. The experiments were carried out at a discharge current of 3 MA. Stable compression of the inner array plasma was achieved by increasing the number of fibers in the outer array. In this case, a compact Z-pinch formed at the array axis. Near the pinch, no trailing plasma produced from the high-Z material of the inner array and capable of scattering and reradiating X-ray photons was observed. The trailing edge of the X-ray pulse was found to shorten in the absence of the trailing plasma around the pinch.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Inertial Confinement Fusion: Status and Challenges

While a variety of laboratory-based fusion schemes have been studied for decades, the only fusion scheme yet to demonstrate fusion ignition and significant energy gain has been X-ray-driven inertially confined fusion. Ignition was demonstrated to occur at the thermodynamic conditions where it had long been expected, but the energy required for the implosion system to reach these conditions was more than projected years ago. This short review gives a status update on the three principal inertial confinement fusion schemes and research challenges going forward.

gain↗
DOE OSTI2017

Materials Selection for Heavy Ion Fusion Hohlraums

The hohlraum surrounds the fuel capsule in a heavy ion fusion (HIF) target. The hohlraum absorbs ion beam driver energy and emits this energy uniformly around the capsule in the form of X-rays. High-atomic-number materials are necessary in the walls of the hohlraum to contain the X-ray energy around the capsule during the implosion process. These high-atomic-number hohlraum materials affect many aspects of an HIF power plant operation. A systematic review of available information for all high-atomic-number elements was conducted to select candidate hohlraum materials. The effects of materials on target fabrication, energy cost, target gain, radioactivity, chemical toxicity, and potential for recycle were considered. Lead and tungsten are the lowest-cost acceptable materials in the primary coolant. The combination of lead and tungsten provide better target gain than either material alone. Seeding the primary coolant with submicron-sized tungsten particles can minimize tungsten growth in small openings in power plant components such as vacuum tritium disengagers. In conclusion, concerns remain for possible tungsten particle agglomeration, settling, or erosion caused by tungsten particles. Tungsten could be replaced by several lanthanide elements if tungsten proves unacceptable.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Technique for Forming Solid D2 and D-T Layers for Shock Timing Experiments at the National Ignition Facility

Capsule implosion experiments on the National Ignition Facility (NIF) are driven with a carefully tailored laser pulse that delivers a sequence of shocks to the ablator and fuel. In order to ensure the shocks converge at the desired position, the shock strength and velocity are measured in experimental platforms referred to as keyhole targets. We made shock measurements on capsules completely filled with liquid deuterium for the solid deuterium tritide (D-T) layer campaigns. Modeling has been used to extend these results to form an estimate of the shock properties in solid D-T layers. Furthermore, to verify and improve the surrogacy of the liquid-filled keyhole measurements, we have developed a technique to form a solid layer inside the keyhole capsule. The layer is typically uniform over a 400-μm-diameter area. This is sufficient to allow direct measurement of the shock velocity. This layering technique has been successfully applied to 13 experiments on the NIF. The technique may also be applicable to fast-igniter experiments since some proposed designs resemble keyhole targets. We discuss our method in detail and give representative results.

42 ENGINEERING↗
DOE OSTI2017

Quantitative Defect Analysis of Ablator Capsule Surfaces Using a Leica Confocal Microscope and a High-Density Atomic Force Microscope

High-density carbon (HDC) is being evaluated as an alternative to the current National Ignition Facility (NIF) point-design ablator material (glow discharge plasma, or GDP, plastic) due to its high density and optimal opacity, which leads to a higher implosion velocity. Chemical-vapor-deposition-coated HDC capsules have a near perfect surface figure but a microscopically rough surface. After polishing, the surface becomes smooth at nanometer scales but has numerous micron-sized surface pits, whose volumes, morphology, and distribution must be quantified to guide NIF target selection. Traditional metrology tools for GDP surface defects, such as the atomic force microscope (AFM) based Spheremapper and a phase-shifting differential interferometer, lack the resolution to characterize these localized features. In this paper, we describe how this metrology challenge is met by developing automated surface metrology solutions based on a high-density (HD) AFM and a Leica confocal microscope. Furthermore, these tools are complementary in nature. HD-AFM has a 0.1-μm spatial resolution and determines the overall shape distortion and pit statistics by tracing great circles on a capsule with high throughput.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Optical characterization of the on-target OMEGA focal spot at high energy using the full-beam in-tank diagnostic

The full-beam in-tank (FBIT) diagnostic has been deployed to directly measure the target-plane beam fluence profile, when operated at high energy, of the OMEGA Laser System at the University of Rochester’s Laboratory for Laser Energetics. This article presents the results of early measurements taken with this diagnostic and discusses an improvement that has overcome performance limitations discovered during the initial testing. The diagnostic gives new insight into the ability of the OMEGA Laser System to provide uniform fluence profiles that are consistent across all 60 beams in the laser. Overall, the ultimate goal of the FBIT diagnostic is to allow accurate assessment of the fluence uniformity on a spherical target in 60-beam implosion experiments

47 OTHER INSTRUMENTATION↗
DOE OSTI2022

Design of proton deflectometry with in situ x-ray fiducial for magnetized high-energy-density systems

We report a design and implementation of proton deflectometry with an in situ reference x-ray image of a mesh to precisely measure non-uniform magnetic fields in expanding plasmas at the OMEGA and OMEGA EP laser facilities. The technique has been developed with proton and x-ray sources generated from both directly driven capsule implosions and short pulse laser–solid interactions. The accuracy of the measurement depends on the contrast of both the proton and x-ray images. Here we present numerical and analytic studies to optimize the image contrast using a variety of mesh materials and grid spacings. Our results show clear enhancement of the image contrast by factors of four to six using a high Z mesh with large grid spacing. This leads to further improvement in the accuracy of the magnetic field measurement using this technique in comparison with its first demonstration at the OMEGA laser facility [Rev. Sci. Instrum. 93, 023502 (2022) [CrossRef]].

47 OTHER INSTRUMENTATION↗
DOE OSTI2017

Simplified model of pinhole imaging for quantifying systematic errors in image shape

In this paper, we examine systematic errors in x-ray imaging by pinhole optics for quantifying uncertainties in the measurement of convergence and asymmetry in inertial confinement fusion implosions. We present a quantitative model for the total resolution of a pinhole optic with an imaging detector that more effectively describes the effect of diffraction than models that treat geometry and diffraction as independent. This model can be used to predict loss of shape detail due to imaging across the transition from geometric to diffractive optics. We find that fractional error in observable shapes is proportional to the total resolution element we present and inversely proportional to the length scale of the asymmetry being observed. Finally, we have experimentally validated our results by imaging a single object with differently sized pinholes and with different magnifications.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗