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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Topography of bent crystals with microradian resolution in one dimension

Optimum performance in x-ray imaging and spectroscopy of plasmas with bent crystals is achievable only when the crystal reflects the x rays theoretically perfectly across its entire surface. However, typical thin quartz (101̄1) crystal samples kept flat by direct attachment to a flat substrate reflect 8 keV x rays differently across their surface, on a scale comparable to the ideal rocking curve. Additional processing improves the uniformity. Irradiation of flat crystals with collimated, monochromatic x rays in rocking curve topography shows such problems directly, with microradian resolution. Nonuniform x-ray reflection is more difficult to document for strongly bent crystals because, then, monochromatic, collimated x rays satisfy the Bragg condition only along a narrow stripe that may be too narrow to resolve with the available cameras. However, it can be resolved with a knife edge that moves through the reflected x rays with the necessary spatial precision as demonstrated here for a bent silicon crystal. This shows qualitatively similar imperfections in the reflection as flat quartz and as the bent quartz analyzers reported on previously with lower resolution.

Pereira, N. R. (ORCID:0000000290569596)↗
NASA NTRS1998

Coulomb Crystallization of Charged Microspheres Levitated in a Gas Discharge Plasma

The technical topic of the project was the experimental observation of Coulomb crystallization of charged microspheres levitated in a gas discharge plasma. This suspension, sometimes termed a dusty plasma, is closely analogous to a colloidal suspension, except that it has a much faster time response, is more optically thin, and has no buoyancy forces to suspend the particles. The particles are levitated by electric fields. Through their collective Coulomb repulsions, the particles arrange themselves in a lattice with a crystalline symmetry, which undergoes an order-disorder phase transition analogous to melting when the effective temperature of the system is increased. Due to gravitational sedimentation, the particles form a thin layer in the laboratory, so that the experimental system is nearly 2D, whereas in future microgravity experiments they are expected to fill a larger volume and behave like a 3D solid or liquid. The particles are imaged using a video camera by illuminating them with a sheet of laser light. Because the suspension is optically thin, this imaging method will work as well in a 3D microgravity experiment as it does in a 2D laboratory system.

Goree, John↗
DOE OSTI2026

Plasma-assisted atomic layer etching of single-crystal diamond

Applications of near-surface nitrogen-vacancy (NV) centers in diamond are often limited by surface defects created during processing. Understanding and controlling plasma-induced surface damage is important for preserving the optical and spin properties of diamond NV centers. We report molecular dynamics simulations of a novel form of plasma-aided atomic layer etching of diamond. In this proposed scheme, the initial surface modification step consists of Ar + ion bombardment. This creates an amorphous layer at the surface, the thickness of which is controlled by the ion energy. Amorphization is known to help smooth the surface, at least locally, and would also serve to sputter clean an initially contaminated surface. A second step impacts the amorphous carbon layer with O + between about 1 and 5 eV. Simulations show that this energy range will remove the amorphous carbon but will not etch the underlying diamond. Though this energy range is not trivial to achieve in a conventional low-temperature plasma, potential methods for creating these low-energy O + ions are discussed. In addition to a-C etching, the O + impacts are predicted to remove any isolated (100) diamond terraces by selectively attacking the edges of the terraces. The proposed atomic layer etching (ALE) approach reverses the conventional ALE sequence in which the surface modification step is usually chemical modification (oxidation in this case), followed by a removal step using Ar + impacts. This plasma ALE procedure is predicted to create a diamond surface that is atomically flat and defect free.

Draney, J. S. [Princeton University, NJ (United St↗
NASA NTRS1986

The low cycle fatigue behavior of a plasma-sprayed coating material

Single crystal nickel-base superalloys employed in turbine blade applications are often used with a plasma spray coating for oxidation and hot corrosion resistance. These coatings may also affect fatigue life of the superalloy substrate. As part of a large program to understand the fatigue behavior of coated single crystals, fully reversed, total strain controlled fatigue tests were run on a free standing NiCoCrAlY coating alloy, PWA 276, at 0.1 Hz. Fatigue tests were conducted at 650 C, where the NiCoCrAlY alloy has modest ductility, and at 1050 C, where it is extremely ductile, showing tensile elongation in excess of 100 percent. At the lower test temperature, deformation induced disordering softened the NiCoCrAlY alloy, while at the higher test temperature cyclic hardening was observed which was linked to gradual coarsening of the two phase microstructure. Fatigue life of the NiCoCrAlY alloy was significantly longer at the higher temperature. Further, the life of the NiCoCrAlY alloy exceeds that of coated, /001/-oriented PWA 1480 single crystals at 1050 C, but at 650 C the life of the coated crystal is greater than that of the NiCoCrAlY alloy on a total strain basis.

Gayda, J.↗
NASA NTRS1986

Low cycle fatigue behaviour of a plasma-sprayed coating material

Single crystal nickel-base superalloys employed in turbine blade applications are often used with a plasma spray coating for oxidation and hot corrosion resistance. These coatings may also affect fatigue life of the superalloy substrate. As part of a large program to understand the fatigue behavior of coated single crystals, fully reversed, total strain controlled fatigue tests were run on a free standing NiCoCrAlY coating alloy, PWA 276, at 0.1 Hz. Fatigue tests were conducted at 650 C, where the NiCoCrAlY alloy has modest ductility, and at 1050 C, where it is extremely ductile, showing tensile elongation in excess of 100 percent. At the lower test temperature, deformation induced disordering softened the NiCoCrAlY alloy, while at the higher test temperature cyclic hardening was observed which was linked to gradual coarsening of the two phase microstructure. Fatigue life of the NiCoCrAlY alloy was significantly longer at the higher temperature. Further, the life of the NiCoCrAlY alloy exceeds that of coated, /001/-oriented PWA 1480 single crystals at 1050 C but at 650 C the life of the coated crystal is greater than that of the NiCoCrAlY alloy on a total strain basis.

Gayda, J.↗
DOE OSTI2022

Preservation of a Dust Crystal as it Falls in an Afterglow Plasma

In an experiment, the power that sustains a plasma was extinguished, so that microspheres, which had been levitated, fell downward toward a lower electrode. At the beginning of their fall, the microspheres were self-organized with a crystalline structure. This structure was found to be preserved as the microspheres accelerated all the way to the lower electrode. Although microspheres had, in this afterglow plasma, large positive charges of 12,500 e, their interparticle repulsion was unable to significantly alter the crystalline arrangement of the microspheres, as they fell. After their impact on the lower electrode, the microspheres bounced upward, and only then was the crystalline structure lost.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

94 GHz microplasma sustained by a photonic crystal

A photonic crystal (PhC) with a single vacancy sustains an argon microplasma at 94 GHz. The PhC consists of a 7 × 13 array of small alumina rods, each 250 μm in radius. The PhC has a forbidden bandgap from 70–105 GHz. The vacancy creates an internal electromagnetic resonance at 94 GHz that intensifies the electric field of an incident wave to 5 × 10 5 V m –1 . Breakdown of low-pressure argon gas (80 mbar) occurs and forms a stable, ellipsoidal plasma inside the crystal. The central core of the microplasma is probed using a 200 μm optical fiber inserted into the PhC. The rotational temperature of the CH molecule is estimated from a numerical fit of the plasma emission and is found to increase from 450–650 K with both pressure (200–1000 mbar) and incident wave power (100 mW–1100 mW). Under these conditions, the electron density increases with both power and pressure from 0.5–1.5 × 10 20 m –3 . Furthermore, this plasma density range brackets the electron plasma frequency at 94 GHz. The results are compared with a similar microplasma operating at 44 GHz.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Metastable argon dynamics in a pulsed microplasma at 43 GHz

Short pulses of millimeter wave (MMW) radiation at 43 GHz create microplasma within a photonic crystal for pressures from 40 to 600 Torr (1.3 × 10 3 –8.0 × 10 4 Pa). Gas breakdown occurs within a photonic crystal, which acts as an electromagnetic resonator to create a strong initial electric field. The time response of the argon metastable density is experimentally determined during the pulse and in the afterglow using laser absorption. The metastable density overshoots the steady-state condition at the beginning of the pulse and during the afterglow. Modeling is presented to understand these observations. The overproduction of argon 1s5 at the beginning of each pulse is due to a concurrent overshoot in the MMW electric field within the photonic crystal. This field overheats the plasma electrons and enhances the production of excited states. The burst of argon metastables observed in the afterglow is due to the pooled energy of the plasma stored in electrons, ions, and excited states of argon. As a result, understanding metastable production is an important intermediate step to ionization and is also critical in the study of diode-pumped rare gas lasers.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1981

A Solution in Search of Problems

Ferrofluids offered vast-problem solving potential. Under license for the NASA technology, Dr. Ronald Moskowitz and Dr. Ronald Rosensweig formed Ferrofluids Corporation. First problem they found a solution for was related to the manufacture of semiconductor "chips" for use in electronic systems. They developed a magnetic seal composed of ferrofluid and a magnetic circuit. Magnetic field confines the ferrofluid in the regions between the stationary elements and the rotary shaft of the seal. Result is a series of liquid barriers that totally bar passage of contaminants. Seal is virtually wear-proof and has a lifetime measured in billions of shaft revolutions. It has reduced maintenance, minimizes "downtime" of production equipment, and reduces the cost of expensive materials that had previously been lost through seal failures. Products based on ferrofluid are exclusion seals for computer disc drives and inertia dampers for stepper motors. Uses are performance-improving, failure-reducing coolants for hi-fi loudspeakers. Other applications include analytical instrumentation, medical equipment, industrial processes, silicon crystal growing furnaces, plasma processes, fusion research, visual displays, and automated machine tools.

Source record↗
DOE OSTI2026

Supramolecular Assembly of Multielement Ribbon-like Structures Derived from Halide Perovskites

Halide perovskites are crucial materials with broad applications owing to their exceptional optoelectronic properties. Vacancy-ordered double perovskites, featuring highly tunable transition metal sites, enable controllable optoelectronic properties through multielement compositional design. Here, in this study, we introduced 18-crown-6 into the vacancy-ordered double perovskites system and developed two-dimensional ribbon-like single crystals (18C6@K) 2 {PtSnTeIrRe} 1 Cl 6 via an antisolvent supramolecular assembly method, demonstrating morphology modulation through multielement composition design. The crystals crystallize in the centrosymmetric space group $P\bar{1}$. The dumbbell-shaped structural units (crown ether@A)2MX6 pack along a and b axes to form a 2-dimensional (2D) monolayer, and these monolayers further stack along the c axis to generate the ribbon-like single crystals. Energy-dispersive X-ray spectroscopy (EDX) qualitatively confirmed the uniform distribution of the five transition metals throughout the crystal, while inductively coupled plasma atomic emission spectroscopy (ICP–AES) quantitatively verified their atomic ratios. We further investigated the origin of the morphology, distinct from the previously reported cube-like single crystals with the $R\bar{3}$ space group. When acetonitrile was used as the solvent, three-dimensional crystals with $R\bar{3}$ symmetry were obtained, whereas dimethylformamide (DMF) was essential for forming two-dimensional ribbon-like single crystals. The essential role of DMF could be ascribed to its capability to maintain a higher concentration of the building blocks. Moreover, Ir 4+ and Pt 4+ cations also played critical roles in inducing the two-dimensional ribbon-like morphology. The three-element (18C6@K) 2 {PtSnTe}1Cl 6 single crystals exhibited bright yellow emission under 375 nm laser excitation, demonstrating the tunability of optoelectronic properties of this class of material.

Zhu, Heqing [University of California, Berkeley, C↗
DOE OSTI2025

Relativistic Laser Plasma Interactions At The Highest Intensities

High energy density science (HEDS) explores the nature of matter under extreme conditions of temperature and pressure. It is of fundamental importance and has many applications such as facilitating imaging with ions, neutrons, x-rays, and gamma rays with new applications being developed, including materials processing and medical therapies. In this project, we used high power, ultrashort pulse lasers to reach HEDS conditions. We have shown that low-cost, liquid crystal film based, double plasma mirror systems can be used to greatly improve laser pulse contrast while still maintaining high power and excellent spatial mode.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Illuminating White Dwarf Spectra through Laboratory Experiments at Cosmic Conditions

We establish the work on white dwarf stars in the larger context of the experiments of the Wootton Center for Astrophysical Plasma Properties (WCAPP); these experiments are conducted at the plasma conditions found in the cosmos, without the need for scaling. We briefly summarize the results of these experiments to-date and their astrophysical and physical import, before focusing on the white dwarf experiments. Over 97% of stars either are, or will become, white dwarf stars, giving them broad relevance. We describe the astrophysical and physical problems associated with white dwarf photospheres, the plasma where the observed light arises. Here, the astrophysical questions include the age of the universe, the age and history of star formation in our Galaxy's varied morphological components and the evolution of stars. The compact nature of these ubiquitous stars means that the atomic physics is not well constrained even in the outermost layers. Further, it suggests that many important processes, including crystallization in dense Coulomb plasma, occur and have a significant effect on the evolution and structure of these stars and thus all their many applications.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Design and expected performance of a variable-radii sinusoidal spiral x-ray spectrometer for the National Ignition Facility

A novel high-resolution x-ray spectrometer for point-like emission sources has been developed using a crystal shape having both a variable major and a variable minor radius of curvature. This variable-radii sinusoidal spiral spectrometer (VR-Spiral) allows three common spectrometer design goals to be achieved simultaneously: 1. reduction of aberrations and improved spectral (energy) resolution, 2. reduction of source size broadening, and 3. use of large crystals to improve total throughput. The VR-Spiral concept and its application to practical spectrometer design are described in detail. This concept is then used to design a spectrometer for an extreme extended x-ray absorption fine structure experiment at the National Ignition Facility looking at the Pb L 3 absorption edge at 13.0352 keV. The expected performance of this VR-Spiral spectrometer, both in terms of energy resolution and spatial resolution, is evaluated through the use of a newly developed raytracing tool, xicsrt. Finally, the expected performance of the VR-Spiral concept is compared to that of spectrometers based on conventional toroidal and variable-radii toroidal crystal geometries showing a greatly improved energy resolution.

47 OTHER INSTRUMENTATION↗
DOE OSTI2022

Argon metastable density and temperature of a 43 GHz microplasma

Argon (1s 5 ) metastable density and translational gas temperature are experimentally measured using laser diode absorption spectroscopy within a 43 GHz microplasma. The plasma is initiated and sustained within a photonic crystal constructed from a rectangular array of alumina rods, each 1 mm in diameter. This configuration generates stable microplasma from 10 to 600 Torr using millimeter wave power from 100 to 1200 mW. The metastable density is in the order of 10 18 m –3 at low pressure. However, Ar(1s 5 ) density decreases to undetectable levels with increasing pressure and wave power. The gas temperature is extracted from the Lorentzian line shape of the absorption profile at 811.53 nm. The gas temperature increases from approximately 400 K at low pressure to 2000 K at 320 Torr (427 mbar, 4.27 × 10 4 Pa). Furthermore, these data are compared with previous results and suggest that the microplasma has a dense core of electrons that depletes the metastable density at high gas pressure and wave power.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗