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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Pre-Ionization Controlled Laser Plasma Formation for Ignition Applications (Final Scientific/Technical Report)

This report consists of three grand funded papers. Abstracts for each follow. 1) In this work, we present experimental and modeling studies of air pre-ionization using ultraviolet (UV) laser pulses and its effect on laser breakdown of an overlapped near-infrared (NIR) pulse. Experimental studies are conducted with a 266 nm beam (fourth harmonic of Nd:YAG) for UV pre-ionization and an overlapped 1064 nm NIR beam (fundamental of Nd:YAG), both having pulse duration of 10 ns. Results show that the UV beam produces a pre-ionized volume which assists in breakdown of the NIR beam, leading to reduction in NIR breakdown threshold by factor of >2. Numerical modeling is performed to examine the ionization and breakdown of both beams. The modeled breakdown threshold of the NIR, including assist by pre-ionization, is in reasonable agreement with the experimental results. 2) The present contribution compares the energy absorption, optical emission, temperature, and fluid dynamics of ultraviolet (UV) λ = 266 nm and near infrared (NIR) λ = 1064 nm nanosecond laser induced plasmas in ambient air. For UV pulses at the conditions studied, energy absorption by the plasmas increases relatively gradually with laser pulse energy starting at delivered energy of E~8 mJ. Corresponding measurements of plasma luminosity show that the absorption of UV radiation does not necessarily result in visible plasma emission. For the NIR induced plasmas, the energy absorption profile is far more abrupt and begins at ~55 mJ. In contrast with UV, the absorption of NIR radiation is always accompanied by intense optical emission. The temperatures of both types of plasma have been measured with Rayleigh scattering thermometry (at times after the Thomson signal sufficiently diminishes). The UV plasmas can attain a wider range of temperatures, including lower temperatures, depending on the pulse energy (e.g., T ~400–2000K for E ~7–35 mJ at Δt = 10 μs after the pulse) while the NIR plasmas show only hotter temperatures (e.g., T ~ 12 000 K for E = 75 mJ at Δt = 10 μs after the pulse) as is consistent with the literature. Differences in the fluid dynamics for UV versus NIR pulses are shown with Schlieren imaging. In this work, the contrast in the UV and NIR plasma threshold behavior is attributed to differing roles of avalanche ionization and multiphoton ionization as is also illustrated by a simple numerical model. 3) The present contribution examines the impact of plasma dynamics and plasma-driven fluid dynamics on the flame growth of laser ignited mixtures and shows that a new dual-pulse scheme can be used to control the kernel formation process in ways that extend the lean ignition limit. We perform a comparative study between (conventional) single-pulse laser ignition (λ = 1064 nm) and a novel dual-pulse method based on combining an ultraviolet (UV) pre-ionization pulse (λ = 266 nm) with an overlapped near-infrared (NIR) energy addition pulse (λ = 1064 nm). We employ OH* chemiluminescence to visualize the evolution of the early flame kernel. For single-pulse laser ignition at lean conditions, the flame kernel separates through third lobe detachment, corresponding to high strain rates that extinguish the flame. In this work, we investigate the capabilities of the dual-pulse to control the plasma-driven fluid dynamics by adjusting the axial offset of the two focal points. In particular, we find there exists a beam waist offset whereby the resulting vorticity suppresses formation of the third lobe, consequently reducing flame stretch. With this approach, we demonstrate that the dual-pulse method enables reduced flame speeds (at early times), an extended lean limit, increased combustion efficiency, and decreased laser energy requirements.

Mechanical engineering↗
NASA NTRS2013

High Current Hollow Cathode Plasma Plume Measurements

Plasma plume measurements are reported for a hollow cathode assembly (HCA) oper-ated at discharge currents of 50, 70, and 100 A at xenon ow rates between 19 - 46 sccm.The HCA was centrally mounted in the annulus of the NASA-300MS Hall Thruster andwas operated in the spot and plume modes with additional data taken with an appliedmagnetic eld. Langmuir probes, retarding potential analyzers, and optical emission spec-troscopy were employed to measure plasma properties near the orice of the HCA and toassess the charge state of the near-eld plasma. Electron temperatures (2-6 eV) and plasmapotentials are consistent with probe-measured values in previous investigations. Operationwith an applied-eld yields higher discharge voltages, increased Xe III production, andincreased signals from the 833.5 nm C I line. While operating in plume mode and with anapplied eld, ion energy distribution measurements yield ions with energies signicantlyexceeding the applied discharge voltage. These ndings are correlated with high-frequencyoscillations associated with each mode.

Plasma diagnostics↗
NASA NTRS1989

Optical dispersion relations for diamondlike carbon films

Ellipsometric measurements on plasma deposited diamondlike amorphous carbon (a-C:H) films were taken in the visible, (E=1.75 to 3.5 eV). The films were deposited on Si and their properties were varied using high temperature (up to 750 C) anneals. The real (n) and imaginary (k) parts of the complex index of refraction N were obtained simultaneously. Following the theory of Forouhi and Bloomer, a least squares fit was used to find the dispersion relations n(E) and k(E). Reasonably good fits were obtained, showing that the theory can be used for a-C:H films. Moreover, the value of the energy gap (Eg) obtained in this way was compared to the Eg value using conventional Tauc plots and reasonably good agreement was obtained.

Alterovitz, Samuel A.↗
NASA NTRS1990

Optical dispersion relations for diamondlike carbon films

Ellipsometric measurements on plasma deposited diamondlike amorphous carbon (a-C:H) films were taken in the visible, (E = 1.75 to 3.5 eV). The films were deposited on Si and their properties were varied using high temperature (up to 750 C) anneals. The real (n) and imaginary (k) parts of the complex index of refraction, N, were obtained simultaneously. Following the theory of Forouhi and Bloomer, a least squares fit was used to find the dispersion relations n(E) and k(E). Reasonably good fits were obtained, showing that the theory can be used for a-C:H films. Moreover, the value of the energy gap, Eg, obtained in this way was compared the the Eg value using conventional Tauc plots and reasonably good agreement was obtained.

Alterovitz, Samuel A.↗
NASA NTRS1989

Optical dispersion relations for 'diamondlike' carbon films

Ellipsometric measurements on plasma deposited diamondlike amorphous carbon (a-C:H) films were taken in the visible, (E = 1.75 to 3.5 eV). The films were deposited on Si and their properties were varied using high temperature (up to 750 C) anneals. The real (n) and imaginary (k) parts of the complex index of refraction N were obtained simultaneously. Following the theory of Forouhi and Bloomer, a least squares fit was used to find the dispersion relations n(E) and k(E). Reasonably good fits were obtained, showing that the theory can be used for a-C:H films. Moreover, the value of the energy gap (Eg) obtained in this way was compared to the Eg value using conventional Tauc plots and reasonably good agreement was obtained.

Alterovitz, Samuel A.↗
DOE OSTI2022

Novel dual-reflection design applied for ITER core x-ray spectrometer

Here. a novel dual-reflection configuration is introduced for the International Tokamak Experimental Reactor (ITER) core x-ray spectrometer to fit the allocated space where it will be placed accompanied by moving the detectors backward to reduce the incident radiation dose. The highly oriented pyrolytic graphite, which has a mosaic structure of microscopic crystallites, is chosen for the front reflector motivated by higher x-ray throughput and stronger misalignment tolerance compared to the perfect crystal reflector. In the ITER core x-ray spectrometer, a combination of several reflector-deflected Lines of Sight (LOSs) and a direct LOS is proposed for the first time named X-Ray Crystal Spectroscopy Core (XRCS-Core). The system is optimized to observe lines from externally seeded xenon and the intrinsic tungsten impurity, meeting both port integration needs and measurement requirements. Its spectral performance is simulated using an analytical-raytracing mixed code——XRSA, showing good imaging quality with a spectral resolution higher than 8000. The XRCS-Core system is thought to be applicable in various ITER scenarios through the assessment taking into account the spectrometers’ specifications and the chosen lines’ emissivity in different plasma parameters.

47 OTHER INSTRUMENTATION↗
NASA NTRS1984

A solar spectral line list between 10 and 200 A modified for application to high spectral resolution X-ray astronomy

A spectral line list for the 10-200 A range is developed from existing solar spectra for application to high spectral resolution measurements of astrophysical plasmas. The solar spectral line lists are merged into a single comprehensive list. The effect of the solar emission measure distribution is removed from the line intensities, which results in a set of emission rates for the lines that can be applied to many optically thin, low density high temperature plasmas in ionization equilibrium. In addition to the measured solar lines, 250 theoretical lines are added to this list. These lines fall in wavelength regions where the existing solar lists have few lines because of limitations in instrumental sensitivity. Also, some lines have been added because the sun has very little plasma at temperatures of about one million K, and consequently these lines are weak or absent in solar spectra. The entire list contains about 600 lines. Finally, predicted spectra of the two RS CVn stars, alpha Aur (Capella) and UX Ari, are presented at 1 and 0.25 A spectral resolution. Also, the solar spectrum is shown at 1 A resolution, and the emission rate spectrum (spectrum not modified by an emission measure distribution) is shown at very high spectral resolution. The predicted spectra for Capella and UX Ari are based on results obtained from the Einstein and International Ultraviolet Explorer (IUE) spacecraft.

Doschek, G. A.↗
DOE OSTI2021

Measurement of neutral gadolinium oscillator strengths using dual-comb absorption spectroscopy in laser-produced plasmas

The oscillator strengths of 43 transitions of neutral gadolinium from 530 to 535 nm were determined based on high-resolution absorption spectra measured by probing a laser-produced plasma (LPP) using time-resolved dual-comb spectroscopy (DCS). Absorption spectra were measured at various time delays, ranging from 33 to 252 µs after the onset of the plasma formation, over which the temperature and number density varied as the ablation plume evolved. A Boltzmann analysis was used to determine the excitation temperature and column density of Gd in the ablation plume, based on measured absorption from 20 Gd I spectral lines with known oscillator strengths. Oscillator strengths were then determined for additional dipole-allowed Gd I transitions identified in the absorption spectra, 19 of which were previously unreported. Oscillator strengths of all measured transitions were compared with literature values when available and show good agreement in most cases. Time-resolved measurement of atomic absorption in the cooling plasma provides access to a range of excitation temperatures and optical densities for the atoms in the ablation plume, allowing repeated measurements under different conditions, thereby improving confidence in the results. The high spectral bandwidth and resolution capabilities of DCS make it well-suited to measuring the dense optical spectrum of Gd, and the technique is applicable to other elements, especially lanthanides and actinides.

(280.4788) Optical Sensing, (280.5395) Plasma Diag↗
DOE OSTI2020

Topological controls on aluminosilicate glass dissolution: Complexities induced in hyperalkaline aqueous environments

Abstract Fly ash, an aluminosilicate composite consisting of disordered (major) and crystalline (minor) compounds, is a low‐carbon alternative that can partially replace ordinary portland cement (OPC) in the binder fraction of concrete. Therefore, understanding the reactivity of fly ash in the hyperalkaline conditions prevalent in concrete is critical to predicting concrete's performance; including setting and strength gain. Herein, temporal measurements of the solution composition (using inductively coupled plasma‐optical emission spectrometry: ICP‐OES) are used to assess the aqueous dissolution rate of monophasic synthetic aluminosilicate glasses analogous to those present in technical fly ashes, under hyperalkaline conditions (10 ≤ pH ≤ 13) across a range of temperatures (25°C ≤ T≤45°C). The dissolution rate is shown to depend on the average number of topological constraints per atom within the glass network (n c , unitless), but this dependence weakens with increasing pH (>10). This is postulated to be on account of: (a) time‐dependent changes in the glass’ surface structure, that is, the number of topological constraints; and/or (b) a change in the dissolution mechanism (eg from network hydrolysis to transport control). The results indicate that the topological description of glass dissolution is most rigorously valid only at very short reaction times (ie at high undersaturations), especially under conditions of hyperalkalinity. These findings provide an improved basis to understand the underlying factors that affect the initial and ongoing reactivity of aluminosilicate glasses such as fly ash in changing chemical environments, for example, when such materials are utilized in cementitious composites.

Oey, Tandré↗
NASA NTRS1987

A study of the Io-associated plasma and neutral sodium cloud

Narrow-band interference filter images were obtained for the Io torus at the S II wavelengths of 6716, 6731 and at the wavelenght of the S III, 9532 spectrum. The purpose of these observations is to study the short term temporal behavior of the torus and to gain a better understanding of the systematic morphology of the torus. From these images, estimates were obtained for the electron and ion densities and ion temperatures as a function of longitude, latitude, radius from Jupiter, and time. From the analysis of images taken in 1983 and 1984, extremely sharp longitudinal variations in plasma density were detected, subcorotational velocities were measures in the torus plasma, the presence of an optical east-west brightness asymmetry was confirmed in the ion emissions, and longitudinal variations were detected in torus ion temperatures.

Pilcher, Carl B.↗
DOE OSTI2025

Optical Imaging of Laser-Driven Fast Electron Weibel-like Filamentation in Overcritical Density Plasma

We report on the measurement of filamented transport of laser-generated fast electron beams in near-critical density plasma. A relativistic intensity long-wave-infrared laser irradiated a hydrodynamically shaped helium gas flow at an electron density n e ≃ 10 25 m − 3 , generating a large flux of fast electrons that propagated beyond the critical surface. The beam-to-background electron density ratio was sufficiently high to drive growth of Weibel-like filamentation, which was measured by optical probing to extend up to 800 μ m with radii ∼ 10 μ m . Particle-in-cell simulations reproduce the main features of the filamentation generation, suggesting that collisionless processes are dominant in these interactions. Expansion of the filaments after formation infers a fast electron heated plasma temperature ∼ 400 eV in the overcritical density plasma. Published by the American Physical Society 2025

43 PARTICLE ACCELERATORS↗
NASA NTRS1974

Temperature dependence of emission measure in solar X-ray plasmas. 1: Non-flaring active regions

X-ray and ultraviolet line emission from hot, optically thin material forming coronal active regions on the sun may be described in terms of an emission measure distribution function, Phi (T). A relationship is developed between line flux and Phi (T), a theory which assumes that the electron density is a single-valued function of temperature. The sources of error involved in deriving Phi (T) from a set of line fluxes are examined in some detail. These include errors in atomic data (collisional excitation rates, assessment of other mechanisms for populating excited states of transitions, element abundances, ion concentrations, oscillator strengths) and errors in observed line fluxes arising from poorly - known instrumental responses. Two previous analyses are discussed in which Phi (T) for a non-flaring active region is derived. A least squares method of Batstone uses X-ray data of low statistical significance, a fact which appears to influence the results considerably. Two methods for finding Phi (T) ab initio are developed. The coefficients are evaluated by least squares. These two methods should have application not only to active-region plasmas, but also to hot, flare-produced plasmas.

Phillips, K. J. H.↗
DOE OSTI2022

Multimodal study of the impact of stimulation pH on shale pore structure, with an emphasis on organics behavior in alkaline environments

The tight nature of shale formations calls for hydraulic fracturing techniques able of altering the pore architecture to facilitate the production of hydrocarbon resources. The composition, pH, salinity, density and chemistry of Hydraulic Fracturing Fluids (HFF) vary substantially depending on reservoir characteristics. pH is among the most important stimulation fluid properties, ranging from very acidic, for carbonate reservoirs, to basic, in the case of clay-rich formations. pH regulates what geochemical reactions take place between the stimulation fluid and shale, as well as pore architecture alteration. The dissolution of carbonates and pyrite, and the precipitation of common minerals such as barite, gypsum and iron oxides in acidic environments have been extensively documented. In contrast, alkali stimulation environments and the role of organic components have received less attention. This research provides insight into the role of both minerals and organic components during alkaline stimulation, and the resulting pore architecture alterations. Here, a set of reactive experiments are performed using three different shales, with varying organic matter (OM) content, at different pH (3, 6, 8, 10, 12). The analysis of pore architecture alteration induced by the reaction was performed via nitrogen (N2) gas adsorption and Time-Domain Nuclear Magnetic Resonance (TD-NMR). Inductively Coupled Plasma - Optical Emission Spectrometry (ICP-OES) was used to measure the composition of the stimulation fluid post-reaction. The system with a larger impact on the pore architecture (pH 12) underwent a more extensive analysis through the application of Focused Ion Beam Scanning Electron Microscopy (FIB-SEM) and x-ray Diffraction (XRD). Results show that mineral dissolution contributed to the creation of secondary porosity, mainly through dissolution of clays and silicates. We show that the abundance and distribution of organic matter both play a significant role in changes in pore architecture. Most samples showed an increase in inter-organic porosity, likely due to the organic acids within kerogen reacting with the stimulation fluid. Samples with a larger amount and more widespread distribution of organic matter show the most significant alterations. Finally, we also highlight the dissolution process of iron-rich minerals, including framboidal pyrite, as another important source of secondary porosity.

04 OIL SHALES AND TAR SANDS↗
DOE OSTI2022

Novel design for a polarizing DUV spectrometer using a Wollaston prism and its application as a diagnostic for measuring Thomson scattering data in the presence of strong self-emission backgrounds

We present a novel design for an optical spectrometer for use in ultraviolet Thomson scattering measurements of plasma parameters in high energy density (HED) inertial confinement fusion experiments on large-scale high-energy laser facilities. In experiments investigating high-Z plasmas, the fidelity of measurements is commonly limited by signal/background ratios approaching or exceeding unity. An alpha barium borate Wollaston prism can provide both spectral dispersion and polarization channel separation, allowing simultaneous measurement of both the Thomson scattering signal and plasma self-emission along a single line of sight and in a single experiment, which should greatly improve data quality and reduce the opportunity cost of taking high quality measurements. Here, we present a basic discussion of the design and a worked example of an instrument designed to take fourth harmonic electron plasma wave measurements in HED experiments at the OMEGA laser facility.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1991

Effect of an arcjet plume on satellite reflector performance

The effect of an arcjet plume on the performance of satellite reflector antennas is studied. The arcjet plume is modeled as a weakly ionized plasma. The spatial permittivity distribution of the plume is approximated using the measured electron density profile and a cold plasma model. Geometrical optics is applied to determine the ray paths as well as the transmitted fields through the inhomogeneous plume. The ray optics results are compared against several exact solutions for scattering from inhomogeneous dielectrics, and good agreement is observed for sufficiently large scatterer size. The far-field antenna patterns of the reflector in the presence of the plume are calculated from the transmitted ray fields using a ray-tube integration scheme. For arcjet prototypes in the 1-kW class, the plume effect on the antenna performance is small. As the electron density increases, the main beam and sidelobe level gradually degrade. The main beam also tends to squint away from the plume region.

Ling, Hao↗