Engineering Papers⌕ Search

Engineering topics

Biener, J.

Publications and source records attributed to Biener, J..

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Increasing stagnation pressure and thermonuclear performance of inertial confinement fusion capsules by the introduction of a high-Z dopant

Inertial confinement fusion requires the inertia of the imploding mass to provide the necessary confinement such that the core reaches adequate high density, temperature, and pressure. Studies utilize low-Z capsules filled with hydrogenic fuel, which are subject to multiple instabilities at the interfaces during the implosion. To improve the stability of the fuel:capsule interface and narrow the imploding shell profile, capsules are doped with a small atomic percentage of a high-Z material. A series of recent indirect-drive experiments executed at the National Ignition Facility with tungsten-doped high density carbon capsules has demonstrated that the presence of this dopant serves to increase the in-flight aspect ratio of the shell and increase the compression and neutron yield performance of both gas-filled and deuterium-tritium cryogenically layered targets. These experiments definitively show that benefits accrued by the introduction of a high-Z dopant into the capsule can outweigh the detrimentally reduced stability of the ablation front, avoiding shell breakup or significant radiative cooling of the hot spot. Future experiments will utilize these types of capsules to additionally increase nuclear performance.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Hydrodynamic instabilities seeded by the X-ray shadow of ICF capsule fill-tubes [X-ray shadow imprint of hydrodynamic instabilities seeded by the fill-tube]

During the first few hundred picoseconds of indirect drive for inertial confinement fusion on the National Ignition Facility, x-ray spots formed on the hohlraum wall when the drive beams cast shadows of the fuel fill-tube on the capsule surface. Differential ablation at the shadow boundaries seeds perturbations which are hydrodynamically unstable under subsequent acceleration and can grow to impact capsule performance. Furthermore, we have characterized this shadow imprint mechanism and demonstrated two techniques to mitigate against it using (i) a reduced diameter fuel fill-tube, and (ii) a pre-pulse to blow down the fill-tube before the shadow forming x-ray spots from the main outer drive beams develop.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Fusion Energy Output Greater than the Kinetic Energy of an Imploding Shell at the National Ignition Facility

A series of cryogenic, layered deuterium-tritium (DT) implosions have produced, for the first time, fusion energy output twice the peak kinetic energy of the imploding shell. These experiments at the National Ignition Facility utilized high density carbon ablators with a three-shock laser pulse (1.5 MJ in 7.5 ns) to irradiate low gas-filled ( 0.3 mg / cc of helium) bare depleted uranium hohlraums, resulting in a peak hohlraum radiative temperature ~ 290 eV . The imploding shell, composed of the nonablated high density carbon and the DT cryogenic layer, is, thus, driven to velocity on the order of 380 km / s resulting in a peak kinetic energy of ~ 21 kJ , which once stagnated produced a total DT neutron yield of 1.9 × 10 16 (shot N170827) corresponding to an output fusion energy of 54 kJ. Time dependent low mode asymmetries that limited further progress of implosions have now been controlled, leading to an increased compression of the hot spot. Finally, it resulted in hot spot areal density ( ρr ~ 0.3 g / cm 2 ) and stagnation pressure ( ~ 360 Gbar ) never before achieved in a laboratory experiment.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Mitigation of X-ray shadow seeding of hydrodynamic instabilities on inertial confinement fusion capsules using a reduced diameter fuel fill-tube

We report a reduced X-ray shadow imprint of hydrodynamic instabilities on the high-density carbon ablator surface of inertial confinement fusion (ICF) capsules using a reduced diameter fuel fill tube on the National Ignition Facility (NIF). The perturbation seed mass from hydrodynamic instabilities was reduced by approximately an order of magnitude by reducing both the diameter and wall thickness of the fill tube by ~2×, consistent with analytical estimates. Overall, this work demonstrates a successful mitigation strategy for engineered features for ICF implosions on the NIF.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Measuring the shock impedance mismatch between high-density carbon and deuterium at the National Ignition Facility

Fine-grained diamond, or high-density carbon (HDC), is being used as an ablator for inertial confinement fusion (ICF) research at the National Ignition Facility (NIF). Accurate equation of state (EOS) knowledge over a wide range of phase space is critical in the design and analysis of integrated ICF experiments. Here in this paper, we report shock and release measurements of the shock impedance mismatch between HDC and liquid deuterium conducted during shock-timing experiments having a first shock in the ablator ranging between 8 and 14 Mbar. Using ultrafast Doppler imaging velocimetry to track the leading shock front, we characterize the shock velocity discontinuity upon the arrival of the shock at the HDC/liquid deuterium interface. Comparing the experimental data with tabular EOS models used to simulate integrated ICF experiments indicates the need for an improved multiphase EOS model for HDC in order to achieve a significant increase in neutron yield in indirect-driven ICF implosions with HDC ablators.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Variable convergence liquid layer implosions on the National Ignition Facility

Liquid layer implosions using the “wetted foam” technique, where the liquid fuel is wicked into a supporting foam, have been recently conducted on the National Ignition Facility for the first time [Olson et al., Phys. Rev. Lett. 117, 245001 (2016)]. In this paper, we report on a series of wetted foam implosions where the convergence ratio was varied between 12 and 20. Reduced nuclear performance is observed as convergence ratio increases. 2-D radiation-hydrodynamics simulations accurately capture the performance at convergence ratios (CR) ~ 12, but we observe a significant discrepancy at CR ~ 20. Finally, this may be due to suppressed hot-spot formation or an anomalous energy loss mechanism.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
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 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 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 OSTI2016

The near vacuum hohlraum campaign at the NIF: A new approach

The near vacuum campaign on the National Ignition Facility has concentrated its efforts over the last year on finding the optimum target geometry to drive a symmetric implosion at high convergence ratio (30x). As the hohlraum walls are not tamped with gas, the hohlraum is filling with gold plasma and the challenge resides in depositing enough energy in the hohlraum before it fills up. Hohlraum filling is believed to cause symmetry swings late in the pulse that are detrimental to the symmetry of the hot spot at high convergence. This paper describes a series of experiments carried out to examine the effect of increasing the distance between the hohlraum wall and the capsule (case to capsule ratio) on the symmetry of the hot spot. These experiments have shown that smaller Case to Capsule Ratio (CCR of 2.87 and 3.1) resulted in oblate implosions that could not be tuned round. Larger CCR (3.4) led to a prolate implosion at convergence 30x implying that inner beam propagation at large CCR is not impeded by the expanding hohlraum plasma. A Case to Capsule ratio of 3.4 is a promising geometry to design a round implosion but in a smaller hohlraum where the hohlraum losses are lower, enabling a wider cone fraction range to adjust symmetry.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Cryogenic tritium-hydrogen-deuterium and deuterium-tritium layer implosions with high density carbon ablators in near-vacuum hohlraums

High Density Carbon (or diamond) is a promising ablator material for use in near-vacuum hohlraums, as its high density allows for ignition designs with laser pulse durations of <10 ns. A series of Inertial Confinement Fusion (ICF) experiments in 2013 on the National Ignition Facility [Moses et al., Phys. Plasmas 16, 041006 (2009)] culminated in a deuterium-tritium (DT) layered implosion driven by a 6.8 ns, 2-shock laser pulse. This paper describes these experiments and comparisons with ICF design code simulations. Backlit radiography of a tritium-hydrogen-deuterium (THD) layered capsule demonstrated an ablator implosion velocity of 385 km/s with a slightly oblate hot spot shape. Other diagnostics suggested an asymmetric compressed fuel layer. A streak camera-based hot spot self-emission diagnostic (SPIDER) showed a double-peaked history of the capsule self-emission. Simulations suggest that this is a signature of low quality hot spot formation. Changes to the laser pulse and pointing for a subsequent DT implosion resulted in a higher temperature, prolate hot spot and a thermonuclear yield of 1.8 × 10{sup 15} neutrons, 40% of the 1D simulated yield.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

First high-convergence cryogenic implosion in a near-vacuum hohlraum

Recent experiments on the National Ignition Facility [M. J. Edwards et al., Phys. Plasmas 20, 070501 (2013)] demonstrate that utilizing a near-vacuum hohlraum (low pressure gas-filled) is a viable option for high convergence cryogenic deuterium-tritium (DT) layered capsule implosions. This is made possible by using a dense ablator (high-density carbon), which shortens the drive duration needed to achieve high convergence: a measured 40% higher hohlraum efficiency than typical gas-filled hohlraums, which requires less laser energy going into the hohlraum, and an observed better symmetry control than anticipated by standard hydrodynamics simulations. The first series of near-vacuum hohlraum experiments culminated in a 6.8 ns, 1.2 MJ laser pulse driving a 2-shock, high adiabat (α ~ 3.5) cryogenic DT layered high density carbon capsule. This resulted in one of the best performances so far on the NIF relative to laser energy, with a measured primary neutron yield of 1.8 X 10¹⁵ neutrons, with 20% calculated alpha heating at convergence ~27X.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

High-density carbon capsule experiments on the national ignition facility

Indirect-drive implosions with a high-density carbon (HDC) capsule were conducted on the National Ignition Facility (NIF) to test HDC properties as an ablator material for inertial confinement fusion. In this study, a series of five experiments were completed with 76-μm-thick HDC capsules using a four-shock laser pulse optimized for HDC. The pulse delivered a total energy of 1.3 MJ with a peak power of 360 TW. The experiment demonstrated good laser to target coupling (~90 %) and excellent nuclear performance. Lastly, a deuterium and tritium gas-filled HDC capsule implosion produced a neutron yield of 1.6×10 15 ± 3×10 13 , a yield over simulated in one dimension of 70%.

42 ENGINEERING↗
DOE OSTI2014

Optimizing supercapacitor electrode density: achieving the energy of organic electrolytes with the power of aqueous electrolytes

The value of electrode density is often overlooked in the pursuit of impressive supercapacitor metrics. Low-density electrodes deliver the best performance in terms of gravimetric energy and power densities when only the mass of the electrodes is considered. However, energy and power values with respect to the total system mass (electrode + electrolyte) or volume are more meaningful for practical application. Low-density electrodes are impractical due to both large mass contributions by the electrolyte and large system volumes. In this work, we use highly compressible graphene aerogel electrodes (up to 87.5% volumetric compression) to systematically characterize the effects of electrode density on energy and power metrics. The results reveal that electrode density is similar to electrode thickness in that both parameters have a squared effect on power. Accounting for the aqueous electrolyte's mass lowered the gravimetric energy and power by almost an order of magnitude for 0.144 g cm –3 dense carbon electrodes but only by a factor of 1.5 when the electrode density was increased to 1.15 g cm –3 through compression. The high-density electrodes achieve 8 W h kg –1 , 70 000 W kg –1 , and 144 F cm –3 in a symmetric electrode setup after factoring in the aqueous electrolyte's mass. Therefore, in the pursuit of high energy per mass, it can be just as effective to lower the system's mass with smaller electrolyte fractions as it is to use electrolytes with larger voltage ranges. High electrode densities allow aqueous electrolyte supercapacitors to attain energy densities per the system mass comparable to those of commercially-available organic electrolyte supercapacitors while maintaining 10–100× greater power.

25 ENERGY STORAGE↗
DOE OSTI2014

Incipient plasticity of single-crystal tantalum as a function of temperature and orientation

The nanocontact plastic behavior of single-crystalline Ta (1 0 0), Ta (1 1 0) and Ta (1 1 1) was studied as a function of temperature and indentation rate. Tantalum, a representative body centred cubic (BCC) metal, reveals a unique deformation behavior dominated by twinning and the generation of stacking faults. Experiments performed at room temperature exhibit a single pop-in event, while at 200 °C, above the critical temperature, a transition to multiple pop-ins was observed. The experimental results are discussed with respect to the orientation as well as temperature and correlated to the defect structures using both anisotropic finite element and MD simulations. In addition, the serrated flow observed at 200 °C is related to differences in the quasi-elastic reloading originating from changes in the defect mechanism.

36 MATERIALS SCIENCE↗
DOE OSTI2014

High-density carbon ablator experiments on the National Ignition Facility

High Density Carbon (HDC) is a leading candidate as an ablator material for Inertial Confinement Fusion (ICF) capsules in x-ray (indirect) drive implosions. HDC has a higher density (3.5 g/cc) than plastic (CH, 1 g/cc), which results in a thinner ablator with a larger inner radius for a given capsule scale. This leads to higher x-ray absorption and shorter laser pulses compared to equivalent CH designs. This paper will describe a series of experiments carried out to examine the feasibility of using HDC as an ablator using both gas filled hohlraums and lower density, near vacuum hohlraums. These experiments have shown that deuterium (DD) and deuterium-tritium gas filled HDC capsules driven by a hohlraum filled with 1.2 mg/cc He gas, produce neutron yields a factor of 2× higher than equivalent CH implosions, representing better than 50% Yield-over-Clean (YoC). In a near vacuum hohlraum (He = 0.03 mg/cc) with 98% laser-to-hohlraum coupling, such a DD gas-filled capsule performed near 1D expectations. A cryogenic layered implosion version was consistent with a fuel velocity = 410 ± 20 km/s with no observed ablator mixing into the hot spot.

01 COAL, LIGNITE, AND PEAT↗