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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 937 records · Page 52
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Quantitative Determination of Wax Contamination in Polystyrene HIPE Foam Using Solid-State NMR

Differences in molecular mobility between polystyrene foam and Brij-78 wax results in vast differences in the 1 H nuclear magnetic resonance (NMR) linewidth. This allows for the convenient determination of wax content in the polystyrene foam components of inertial confinement fusion targets via solid-state NMR. Lastly, contamination levels as low as 0.1% are easily recognized and quantified, and the detection limit is calculated to be 0.02% even when only 32 transients are recorded.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Plasma Focused Ion Beam Milling of High-Aspect-Ratio Holes in Diamond

Plasma focused ion beam (PFIB) technology has a great potential for applications requiring rapid micro-machining of high-aspect-ratio features. Here, we use 30-keV Ar, Xe, and O 2 ion beams to study PFIB milling of high-aspect-ratio circular holes in polycrystalline diamond. Our results show that Xe and O 2 ion beams have the highest milling efficiency for low-aspect-ratio and high-aspect-ratio hole milling, respectively. Each ion beam species produces holes with its characteristic shape and wall surface morphology. In conclusion, based on these results, we demonstrate a “hybrid” hole milled in a two-step process with Xe and O 2 ion beams with the geometry and wall morphology attractive for the attachment of a fuel fill tube to the inertial confinement fusion capsule.

ICF targets↗
DOE OSTI2016

National direct-drive program on OMEGA and the National Ignition Facility

We report a major advantage of the laser direct-drive (DD) approach to ignition is the increased fraction of laser drive energy coupled to the hot spot and relaxed hot-spot requirements for the peak pressure and convergence ratios relative to the indirect-drive approach at equivalent laser energy. With the goal of a successful ignition demonstration using DD, the recently established national strategy has several elements and involves multiple national and international institutions. These elements include the experimental demonstration on OMEGA cryogenic implosions of hot-spot conditions relevant for ignition at MJ-scale energies available at the National Ignition Facility (NIF) and developing an understanding of laser-plasma interactions and laser coupling using DD experiments on the NIF. DD designs require reaching central stagnation pressures in excess of 100 Gbar. The current experiments on OMEGA have achieved inferred peak pressures of 56 Gbar (Regan et al 2016 Phys. Rev. Lett. 117 025001). Extensive analysis of the cryogenic target experiments and two- and three-dimensional simulations suggest that power balance, target offset, and target quality are the main limiting factors in target performance. In addition, cross-beam energy transfer (CBET) has been identified as the main mechanism reducing laser coupling. Reaching the goal of demonstrating hydrodynamic equivalence on OMEGA includes improving laser power balance, target position, and target quality at shot time. CBET must also be significantly reduced and several strategies have been identified to address this issue.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Alternative irradiation schemes for NIF and LMJ hohlraums

Here, we explore two alternative irradiation schemes for the large ('outer') and small ('inner') angle beams that currently illuminate National Ignition Facility (NIF) and Laser Mégajoule cavities. In the first, while the outer laser beams enter through the usual end laser entrance holes (LEH), the inner beams enter through slots along the cavity axis wall, illuminating the back wall of the cavity. This avoids the current interaction of the inner laser beams with the gold wall bubbles generated by the outer beams, which leads to large time-dependent changes in drive symmetry. Another scheme potentially useful for NIF uses only the outer beams. The radiative losses through the slots or from the use of outer beams only are compensated by using a smaller cavity and LEH.

42 ENGINEERING↗
DOE OSTI2020

Fast electron transport dynamics and energy deposition in magnetized, imploded cylindrical plasma

Inertial confinement fusion approaches involve the creation of high-energy-density states through compression. High gain scenarios may be enabled by the beneficial heating from fast electrons produced with an intense laser and by energy containment with a high-strength magnetic field. Here, we report experimental measurements from a configuration integrating a magnetized, imploded cylindrical plasma and intense laser-driven electrons as well as multi-stage simulations that show fast electrons transport pathways at different times during the implosion and quantify their energy deposition contribution. The experiment consisted of a CH foam cylinder, inside an external coaxial magnetic field of 5 T, that was imploded using 36 OMEGA laser beams. Two-dimensional (2D) hydrodynamic modelling predicts the CH density reaches 9.0 g cm − 3 , the temperature reaches 920 eV and the external B-field is amplified at maximum compression to 580 T. At pre-determined times during the compression, the intense OMEGA EP laser irradiated one end of the cylinder to accelerate relativistic electrons into the dense imploded plasma providing additional heating. The relativistic electron beam generation was simulated using a 2D particle-in-cell (PIC) code. Finally, three-dimensional hybrid-PIC simulations calculated the electron propagation and energy deposition inside the target and revealed the roles the compressed and self-generated B-fields play in transport. During a time window before the maximum compression time, the self-generated B-field on the compression front confines the injected electrons inside the target, increasing the temperature through Joule heating. For a stronger B-field seed of 20 T, the electrons are predicted to be guided into the compressed target and provide additional collisional heating. This article is part of a discussion meeting issue ‘Prospects for high gain inertial fusion energy (part 2)’.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Observation of kinetic mix enhancement in thin-shell OMEGA implosions

Recent separated reactant experiments for thin-shell (6 µ⁢m) shock-driven implosions on OMEGA have demonstrated significant mix from a buried deuterated layer of the shell into the hot spot. Time resolved D 3 He-p reaction history data demonstrate a (50 ± 20)⁢ ps shift earlier in peak nuclear emission for separated reactant experiments relative to control, in contrast to past experimental data for thicker, 20 µ⁢m shells with no laser burn through that show a 75 ps delay due to the time required for hydrodynamic instabilities to develop. This contrast suggests that the mix mechanism was not hydrodynamic. Ion kinetic simulations utilizing fall line analyses show much closer agreement with mix yield and temperature than diffusion models, predicting a D 3 He-p mix yield of 1.7 × 10 9 as compared to the experimental value of 9.3⁢ (±2.1) × 10 8 . This is three orders of magnitude closer than the fall line analysis from a hydrodynamic simulation with an inline diffusive mix model, which suggests minimal mix and D 3 He-p yields of 5×10 5 . This makes kinetic mechanisms the only feasible explanation for the mix seen, demonstrating impact of a non-standard mix mechanism. An analytical model of this kinetic mix mechanism suggests that it can remain significant in situations when the shell expands significantly to low densities, and diffusive models predict negligible mix. Finally, kinetic mix will impact multiple types of high energy density, laser-driven fusion experiments including high-adiabat direct drive cryoexperiments, nuclear cross section experiments, and thin-shell polar direct drive experiments used to tune heat conduction models.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Understanding the deficiency in inertial confinement fusion hohlraum x-ray flux predictions using experiments at the National Ignition Facility

The predicted implosion performance of deuterium-tritium fuel capsules in indirect-drive inertial confinement fusion experiments relies on precise calculations of the x-ray drive in laser-heated cavities (hohlraums). This requires accurate, spectrally dependent simulations of laser to x-ray conversion efficiencies and x-ray absorption losses to the hohlraum wall. A set of National Ignition Facility experiments have identified a cause for the long-standing hohlraum “drive deficit” as the overprediction of gold emission at ~2.5 keV in nonlocal thermodynamic equilibrium coronal plasma regions within the hohlraum. Finally, reducing the emission and absorption opacity in this spectral region by ~20% brings simulations into agreement with measured x-ray fluxes and spectra.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

Observation of the stabilizing effect of a laminated ablator on the ablative Rayleigh-Taylor instability

A laminated ablator is explored as an alternative concept for stabilizing the ablative Rayleigh-Taylor instability which develops in inertial fusion targets. Experiments measuring the growth of the Rayleigh-Taylor instability of laminated planar foils are reported. Consistent with both theory and simulations, a significant reduction of the perturbation growth is experimentally observed for laminated ablators in comparison to what is observed for classical uniform ablators. Such an enhanced hydrodynamic stability opens opportunities for the design of high-gain inertial fusion targets.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2010

Laser-Driven Fast Electron Collimation in Targets with Resistivity Boundary

We demonstrate experimentally that the relativistic electron flow in a dense plasma can be efficiently confined and guided in targets exhibiting a high-resistivity-core-low-resistivity-cladding structure analogous to optical waveguides. The relativistic electron beam is shown to be confined to an area of the order of the core diameter (50 {mu}m), which has the potential to substantially enhance the coupling efficiency of electrons to the compressed fusion fuel in the Fast Ignitor fusion in full-scale fusion experiments.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

First Observation of Cross-Beam Energy Transfer Mitigation for Direct-Drive Inertial Confinement Fusion Implosions Using Wavelength Detuning at the National Ignition Facility

Cross-beam energy transfer (CBET) results from two-beam energy exchange via seeded stimulated Brillouin scattering, which detrimentally reduces ablation pressure and implosion velocity in direct-drive inertial confinement fusion. Direct-drive implosions at the National Ignition Facility were conducted to reduce CBET by detuning the laser-source wavelengths (±2.3 Å UV) of the interacting beams over the equatorial region of the target. For the first time, wavelength detuning was shown to increase the equatorial region velocity experimentally by 16% and to alter the in-flight shell morphology. These experimental observations are consistent with design predictions of radiation–hydrodynamic simulations that indicate a 10% increase in the average ablation pressure.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Electrical design analysis and breakdown voltage test aspects of indigenously developed electrical breaks at Cryo temperatures

Electrical insulation breaks are very critical component of large-scale fusion devices employing superconducting magnets and are used to insulate electrically the coil and the cryogenic supply line (kept at ground potential). The electrical insulation of breaks consists of the composites insulations, G-10 GFRP (Glass fiber reinforced plastic), cryogenic compatible epoxy and S-glass boron free fiber in air and helium environment under vacuum. To optimize the design parameters, the detailed electrical analysis have been carried out using the electrostatic solid axi-symmetric model by COMSOL 4.1 multiphysics software for electrodes separation, electrical field strength as well as flashover phenomenon between two electrodes with composite insulator material have been analyzed at different surfaces and contours along with by varying gaps between SS electrodes. We have carried out the high voltage breakdown test (0-35) kV, insulation resistance measurement at 0-5 kV test voltage in Paschen condition of (10{sup 3} -10{sup -5}) mbar in helium gas and air environment at 300 K and 77 K experimentally on in-house developed insulation breaks. (author)

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 OSTI2019

Design of a free-space image-relay optical time-domain reflectometer to measure fiber-optic time delays at inertial confinement fusion relevant wavelengths

Fiber optics are an integral part of data collection, often used to transport visible and UV light to streaked spectrometers and photodetectors. Precisely measuring fiber-optic time delay (FOTD) is necessary for absolute data timing or fiber replacement. An optical time domain reflectometer (OTDR) can be used to measure the fiber-optic time delay. Commercial OTDR’s measure only the fiber in telecommunications wavelengths in the IR. To measure fibers at relevant wavelengths for inertial confinement fusion experiments, a solution using a free-space image relay was devised at the University of Rochester’s Laboratory for Laser Energetics (LLE), where readily available equipment has been used to measure the FOTD to within 2 ps at 526.5 nm as well as 351 nm, which is an order of magnitude better than the timing jitter between LLE’s Hardware Timing System and second-harmonic (526.5-nm) fiducial laser pulses.

47 OTHER INSTRUMENTATION↗
DOE OSTI2010

Analysis of direct-drive capsule compression experiments on the Iskra-5 laser facility

We have analyzed and numerically simulated our experiments on the compression of DT-gas-filled glass capsules under irradiation by a small number of beams on the Iskra-5 facility (12 beams) at the second harmonic of an iodine laser ({lambda} = 0.66 {mu}m) for a laser pulse energy of 2 kJ and duration of 0.5 ns in the case of asymmetric irradiation and compression. Our simulations include the construction of a target illumination map and a histogram of the target surface illumination distribution; 1D capsule compression simulations based on the DIANA code corresponding to various target surface regions; and 2D compression simulations based on the NUTCY code corresponding to the illumination conditions. We have succeeded in reproducing the shape of the compressed region at the time of maximum compression and the reduction in neutron yield (compared to the 1D simulations) to the experimentally observed values. For the Iskra-5 conditions, we have considered targets that can provide a more symmetric compression and a higher neutron yield.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Simple model of the indirect compression of targets under conditions close to the national ignition facility at an energy of 1.5 MJ

The possibility of the analysis and interpretation of the reported experiments with the megajoule National Ignition Facility (NIF) laser on the compression of capsules in indirect-irradiation targets by means of the one-dimensional RADIAN program in the spherical geometry has been studied. The problem of the energy balance in a target and the determination of the laser energy that should be used in the spherical model of the target has been considered. The results of action of pulses differing in energy and time profile (“low-foot” and “high-foot” regimes) have been analyzed. The parameters of the compression of targets with a high-density carbon ablator have been obtained. The results of the simulations are in satisfactory agreement with the measurements and correspond to the range of the observed parameters. The set of compared results can be expanded, in particular, for a more detailed determination of the parameters of a target near the maximum compression of the capsule. The physical foundation of the possibility of using the one-dimensional description is the necessity of the closeness of the last stage of the compression of the capsule to a one-dimensional process. The one-dimensional simulation of the compression of the capsule can be useful in establishing the boundary behind which two-dimensional and three-dimensional simulation should be used.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2010

High-power electromagnetic wave in a magnetically insulated transmission line of the ANGARA-5-1 facility

Studies of physical phenomena in magnetically insulated transmission lines (MITLs) of high-power pulsed current generators, analysis of operation of existing megavolt generators, and designing of new high-current generators with a power of up to {approx}10 TW require creating an efficient numerical code for modeling the propagation of a high-power electromagnetic pulse in an MITL. This paper presents basic theoretical concepts of MITL operation in the framework of telegraph equations with allowance for electron leakage and variations in the electrode emissivity and analyzes propagation of an electromagnetic wave in the MITLs of the ANGARA-5-1 eight-module facility toward a dynamic load installed in the central unit with a matrix inductance.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

Theoretical and experimental studies of the radiative properties of matter at high energy densities and their application to the problems of inertial confinement fusion

The paper presents the results of theoretical and experimental studies of the radiative properties of plasmas produced by heating and compression of various materials to high energy densities. The specific features of the theoretical plasma model known as the ion model, which is used to calculate the radiative characteristics of plasmas of complex chemical composition, are discussed. The theoretical approach based on this model is applied to the plasma produced during the explosion of the X-pinch wires. The theoretical estimate of the radiation efficiency is compared with the experimental data on the total energy yield from an X-pinch made of two different wires (NiCr and Alloy 188). The radiative characteristics of (C12 H16 O8) and (C8 H12 O6) plasmas are calculated for the temperature diagnostics of plasmas produced from porous targets employed in inertial confinement fusion experiments with the use of laser radiation and heavy-ion beams.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

Magneto-inertial fusion with laser compression of a magnetized spherical target

The paper is devoted to the principles of magneto-inertial fusion and laser-plasma methods of generation of a Megagauss field during spherical implosion of a magnetized target. A model based on a magnetic confinement system, namely, a cusp configuration with inertial compression of the target by a laser driver, is developed. The dynamics of plasma in a cusp compressed under the effect of laser beams is precalculated. Analytical and numerical estimates of the particle number and magnetic field intensity during magneto-inertial plasma compression are obtained. The problems of irradiation of a spherically closed volume by a high-energy laser pulse are discussed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗