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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Dynamics of femtosecond laser produced tungsten nanoparticle plumes

We investigated the expansion features of femtosecond laser generated tungsten nanoparticle plumes in vacuum. Fast gated images showed distinct two components expansion features, viz., plasma and nanoparticle plumes, separated by time of appearance. The persistence of plasma and nanoparticle plumes are ∼500 ns and ∼100 μs, respectively, and propagating with velocities differed by 25 times. The estimated temperature of the nanoparticles showed a decreasing trend with increasing time and space. Compared to low-Z materials (e.g., Si), ultrafast laser ablation of high-Z materials like W provides significantly higher nanoparticle yield. A comparison between the nanoparticle plumes generated by W and Si is also discussed along with other metals.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
NASA NTRS1971

Correlation between convection electric fields in the nightside magnetosphere and several wave and particle phenomena during two isolated substorms.

Correlation of several magnetoionospheric wave and particle phenomena previously linked observationally to magnetospheric substorms and inferred to involve convection electric fields with whistler measurements of convection activity during two relatively isolated substorms. The events occurred at about 0600 UT on July 15, 1965, and about 0500 UT on Oct. 13, 1965. The correlated phenomena include cross-L inward plasma drifts near midnight within the plasmaphere, diffuse auroral radar echoes observed near the dusk meridian, IPDP micropulsations (intervals of pulsations of diminishing period) in the premidnight sector, apparent contractions and expansions of the plasma sheet at about 20 earth radii in the magnetotail, and Pc 1/Pi 1 micropulsation events near or before midnight. Two new vlf phenomena occurred during the October 13 event - a noise band within the plasmasphere associated with a convecting whistler path, and ?hisslers,' falling-tone auroral-hiss forms repeated at intervals of about 2 sec.

Carpenter, D. L.↗
DOE OSTI2017

Detailed characterization of laser-produced astrophysically-relevant jets formed via a poloidal magnetic nozzle

We report that the collimation of astrophysically-relevant plasma ejecta in the form of narrow jets via a poloidal magnetic field is studied experimentally by irradiating a target situated in a 20 T axial magnetic field with a 40 J, 0.6 ns, 0.7 mm diameter, high-power laser. The dynamics of the plasma shaping by the magnetic field are studied over 70 ns and up to 20 mm from the source by diagnosing the electron density, temperature and optical self-emission. These show that the initial expansion of the plasma is highly magnetized, which leads to the formation of a cavity structure when the kinetic plasma pressure compresses the magnetic field, resulting in an oblique shock [A. Ciardi et al., Phys. Rev. Lett. 110, 025002 (2013)]. The resulting poloidal magnetic nozzle collimates the plasma into a narrow jet [B. Albertazzi et al., Science 346, 325 (2014)]. At distances far from the target, the jet is only marginally magnetized and maintains a high aspect ratio due to its high Mach-number (M~20) and not due to external magnetic pressure. The formation of the jet is evaluated over a range of laser intensities (10 12 –10 13 W/cm 2 ), target materials and orientations of the magnetic field. Lastly, plasma cavity formation is observed in all cases and the viability of long-range jet formation is found to be dependent on the orientation of the magnetic field.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1985

Evidence for gain on the C VI 182 A transition in a radiation-cooled selenium/Formvar plasma

Thin plastic foils coated with selenium have been irradiated using from 4 to 8 beams of the OMEGA laser in a line focus configuration. Spectra were recorded using a 3 meter spectrograph that viewed the plasma along the line focus. Based on a comparison of the intensities of the spectral lines from plasmas with lengths of 1.7, 3.4, 6.8, and 13.6 mm, the C VI n = 3 to 2 transition at 182 A was anomalously intense in the spectra from the longer plasmas. Calculations indicate that the carbon plasma was cooled by radiation from the highly-charged selenium plasma in a time that was smaller than the expansion time of the plasma. These plasma conditions are favorable for the occurrence of population inversions between the n = 2 and 3 levels of C VI resulting from recombination and cascading from higher levels. The measured gain coefficient for the C VI 182 A transition is 3/cm, and this corresponds to a gain-length product of 4 in the longest plasma.

Seely, J. F.↗
NASA NTRS2010

Constraints on CME Evolution from in situ Observations of Ionic Charge States

We present a novel procedure for deriving the physical properties of Coronal Mass Ejections (CMES) in the corona. Our methodology uses in-situ measurements of ionic charge states of C, O, Si and Fe in the heliosphere and interprets them in the context of a model for the early evolution of ICME plasma, between 2 - 5 R-solar. We find that the data can be fit only by an evolution that consists of an initial heating of the plasma, followed by an expansion that ultimately results in cooling. The heating profile is consistent with a compression of coronal plasma due to flare reconnect ion jets and an expansion cooling due to the ejection, as expected from the standard CME/flare model. The observed frozen-in ionic charge states reflect this time-history and, therefore, provide important constraints for the heating and expansion time-scales, as well as the maximum temperature the CME plasma is heated to during its eruption. Furthermore, our analysis places severe limits on the possible density of CME plasma in the corona. We discuss the implications of our results for CME models and for future analysis of ICME plasma composition.

Gruesbeck, Jacob R.↗
NASA NTRS2017

Recent Progress in Laboratory Astrophysics and Astrochemistry Achieved with the COSmIC Facility

We describe the characteristics and the capabilities of the laboratory facility, COSmIC, that was developed at NASA Ames to generate, process and analyze interstellar, circumstellar and planetary analogs in the laboratory. COSmIC stands for "Cosmic Simulation Chamber" and is dedicated to the study of neutral and ionized molecules and nanoparticles under the low temperature and high vacuum conditions that are required to simulate various space environments such as diffuse interstellar clouds, circumstellar outflows and planetary atmospheres. COSmIC integrates a variety of state-of-the-art instruments that allow recreating simulated space conditions to generate, process and monitor cosmic analogs in the laboratory. The COSmIC experimental setup is composed of a Pulsed Discharge Nozzle (PDN) expansion, that generates a plasma in the stream of a free supersonic jet expansion, coupled to high-sensitivity, complementary in situ diagnostics: cavity ring down spectroscopy (CRDS) and laser induced fluorescence (LIF) systems for photonic detection, and Reflectron Time-Of-Flight Mass Spectrometer (ReTOF-MS) for mass detection. Recent results obtained using COSmIC will be highlighted. In particular, the progress that has been achieved in the domain of the diffuse interstellar bands (DIBs) and in monitoring, in the laboratory, the formation of circumstellar dust grains and planetary atmosphere aerosols from their gas-phase molecular precursors. Plans for future laboratory experiments on interstellar and planetary molecules and grains will also be addressed, as well as the implications of the studies underway for astronomical observations and past and future space mission data analysis.

Salama, Farid↗
DOE OSTI2021

The interplay between laser focusing conditions, expansion dynamics, ablation mechanisms, and emission intensity in ultrafast laser-produced plasmas

The interplay between ultrafast laser focusing conditions, emission intensity, expansion dynamics, and ablation mechanisms is critical to the detection of light isotopes relevant to nuclear energy, forensics, and geochemistry applications. Here, we study deuterium (2Hα) emission in plasmas generated from femtosecond laser ablation of a Zircaloy-4 target with a deuterium concentration of ≈37 at. %. Changes in emission intensity, plume morphology, crater dimensions, and surface modifications were investigated for varying focusing lens positions, where the laser was focused behind, at, and in front of the target. Spatially resolved optical emission spectroscopy and spectrally integrated plasma imaging were performed to investigate emission spectral features and plume morphology. Laser ablation crater dimensions and morphology were analyzed via optical profilometry and scanning electron microscopy. The 2Hα emission intensity showed significant reduction at the geometrical focal point or when the focal point is in front of the target. For all laser spot sizes, a two-component plume was observed but with different temporal histories. At the best focal point, the plume was spherical. When the laser was focused behind the target, the plume was elongated and propagated to farther distances than for the best focal position. In contrast, when the laser was focused in front of the target, filaments were generated in the beam path, and filament-plasma coupling occurred. By focusing the laser behind the target, the amount of material removal in the laser ablation process can be significantly reduced while still generating a plasma with a sufficient 2Hα emission signal for analysis.

Kautz, Elizabeth J. (ORCID:0000000263389223)↗
DOE OSTI2015

Non-gated laser-induced breakdown spectroscopy in bulk water by position-selective detection

Temporal and spatial evolutions of the laser-induced plasma in bulk water are investigated using fast imaging and emission spectroscopic techniques. By tightly focusing a single-pulse nanosecond Nd: YAG laser beam into the bulk water, we generate a strongly expanded plasma with high reproducibility. Such a strong expanding plasma enables us to obtain well-resolved spectral lines by means of position-selective detection; hence, the time-gated detector becomes abdicable. The present results suggest not only a possible non-gated approach for underwater laser-induced breakdown spectroscopy but also give an insight into the plasma generation and expansion in bulk water.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

Wave steepening and shock formation in ultracold neutral plasmas

We present observations of wave steepening and signatures of shock formation during expansion of ultracold neutral plasmas formed with an initial density distribution that is centrally peaked and decays exponentially with distance. The plasma acceleration and velocity decrease at large distance from the plasma center, leading to central ions overtaking ions in the outer regions and the development of a steepening front that is narrow compared to the size of the plasma. The density and velocity change dramatically across the front, and significant heating of the ions is observed in the region of steepest gradients. For a reasonable estimate of electron temperature, the relative velocity of ions on either side of the front modestly exceeds the local sound speed (Mach number M≳1). This indicates that by sculpting steep density gradients, it is possible to create the conditions for shock formation, or very close to it, opening a new avenue of research for ultracold neutral plasmas.

Computational fluid dynamics↗
NASA NTRS1989

The POLAR code wake model - Comparison with in situ observations

Measurements made by the plasma diagnostics package during Spacelab 2 are discussed and compared with predictions made with the Air Force Geophysics Laboratory POLAR wake code. This code uses a complex geometric model of the orbiter and the self-similar solution of the expansion of a plasma into a vacuum as its model basis. Excellent qualitative and quantitative agreement is found at distances greater than about 30 m. At least to the first order, the model's approximations are justified.

Murphy, G.↗
DOE OSTI2017

Evolution of uranium monoxide in femtosecond laser-induced uranium plasmas

We report on the observation of uranium monoxide (UO) emission following fs laser ablation (LA) of a uranium metal sample. The formation and evolution of the molecular emission are studied under various ambient air pressures. Observation of UO emission spectra at a rarefied residual air pressure of ~1 Torr indicates that the UO molecule is readily formed in the expanding plasma with trace concentrations of oxygen present within the vacuum chamber. Furthermore, the persistence of the UO emission exceeded that of the atomic emission; however, the molecular emission was delayed in time compared to the atomic emission due to the necessary cooling and expansion of the plasma before the UO molecules can form.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
NASA NTRS1981

Substorm-related plasma sheet motions as determined from differential timing of plasma changes at the ISEE satellites

From an ISEE survey of substorm dropouts and recoveries during the period February 5 to May 25, 1978, 66 timing events observed by the Los Alamos Scientific Laboratory/Max-Planck-Institut Fast Plasma Experiments were studied in detail. Near substorm onset, both the average timing velocity and the bulk flow velocity at the edge of the plasma sheet are inward, toward the center. Measured normal to the surface of the plasma sheet, the timing velocity is 23 + or - 18 km/s and the proton flow velocity is 20 + or - 8 km/s. During substorm recovery, the plasma sheet reappears moving outward with an average timing velocity of 133 + or - 31 km/s; however, the corresponding proton flow velocity is only 3 + or - 7 km/s in the same direction. It is suggested that the difference between the average timing velocity for the expansion of the plasma sheet and the plasma bulk flow perpendicular to the surface of the sheet during substorm recovery is most likely the result of surface waves moving past the position of the satellites.

Forbes, T. G.↗
NASA NTRS1999

Source Distributions of Substorm Ions Observed in the Near-Earth Magnetotail

This study employs Geotail plasma observations and numerical modeling to determine sources of the ions observed in the near-Earth magnetotail near midnight during a substorm. The growth phase has the low-latitude boundary layer as its most important source of ions at Geotail, but during the expansion phase the plasma mantle is dominant. The mantle distribution shows evidence of two distinct entry mechanisms: entry through a high latitude reconnection region resulting in an accelerated component, and entry through open field lines traditionally identified with the mantle source. The two entry mechanisms are separated in time, with the high-latitude reconnection region disappearing prior to substorm onset.

Ashour-Abdalla, M.↗
DOE OSTI2014

Development and Benchmarking of a Hybrid PIC Code For Dense Plasmas and Fast Ignition (Final Report)

Radiation processes play an important role in the study of both fast ignition and other inertial confinement schemes, such as plasma jet driven magneto-inertial fusion, both in their effect on energy balance, and in generating diagnostic signals. In the latter case, warm and hot dense matter may be produced by the convergence of a plasma shell formed by the merging of an assembly of high Mach number plasma jets. This innovative approach has the potential advantage of creating matter of high energy densities in voluminous amount compared with high power lasers or particle beams. An important application of this technology is as a plasma liner for the flux compression of magnetized plasma to create ultra-high magnetic fields and burning plasmas. HyperV Technologies Corp. has been developing plasma jet accelerator technology in both coaxial and linear railgun geometries to produce plasma jets of sufficient mass, density, and velocity to create such imploding plasma liners. An enabling tool for the development of this technology is the ability to model the plasma dynamics, not only in the accelerators themselves, but also in the resulting magnetized target plasma and within the merging/interacting plasma jets during transport to the target. Welch pioneered numerical modeling of such plasmas (including for fast ignition) using the LSP simulation code. Lsp is an electromagnetic, parallelized, plasma simulation code under development since 1995. It has a number of innovative features making it uniquely suitable for modeling high energy density plasmas including a hybrid fluid model for electrons that allows electrons in dense plasmas to be modeled with a kinetic or fluid treatment as appropriate. In addition to in-house use at Voss Scientific, several groups carrying out research in Fast Ignition (LLNL, SNL, UCSD, AWE (UK), and Imperial College (UK)) also use LSP. A collaborative team consisting of HyperV Technologies Corp., Voss Scientific LLC, FAR-TECH, Inc., Prism Computational Sciences, Inc. and Advanced Energy Systems Inc. joined efforts to develop new physics and numerical models for LSP in several key areas to enhance the ability of LSP to model high energy density plasmas (HEDP). This final report details those efforts. Areas addressed in this research effort include: adding radiation transport to LSP, first in 2D and then fully 3D, extending the EMHD model to 3D, implementing more advanced radiation and electrode plasma boundary conditions, and installing more efficient implicit numerical algorithms to speed complex 2-D and 3-D computations. The new capabilities allow modeling of the dominant processes in high energy density plasmas, and further assist the development and optimization of plasma jet accelerators, with particular attention to MHD instabilities and plasma/wall interaction (based on physical models for ion drag friction and ablation/erosion of the electrodes). In the first funding cycle we implemented a solver for the radiation diffusion equation. To solve this equation in 2-D, we used finite-differencing and applied the parallelized sparse-matrix solvers in the PETSc library (Argonne National Laboratory) to the resulting system of equations. A database of the necessary coefficients for materials of interest was assembled using the PROPACEOS and ATBASE codes from Prism. The model was benchmarked against Prism's 1-D radiation hydrodynamics code HELIOS, and against experimental data obtained from HyperV's separately funded plasma jet accelerator development program. Work in the second funding cycle focused on extending the radiation diffusion model to full 3-D, continued development of the EMHD model, optimizing the direct-implicit model to speed up calculations, add in multiply ionized atoms, and improved the way boundary conditions are handled in LSP. These new LSP capabilities were then used, along with analytic calculations and Mach2 runs, to investigate plasma jet merging, plasma detachment and transport, restrike and advanced jet accelerator design. In addition, a strong linkage to diagnostic measurements was made by modeling plasma jet experiments on PLX to support benchmarking of the code. A large number of upgrades and improvements advancing hybrid PIC algorithms were implemented in LSP during the second funding cycle. These include development of fully 3D radiation transport algorithms, new boundary conditions for plasma-electrode interactions, and a charge conserving equation of state that permits multiply ionized high-Z ions. The final funding cycle focused on 1) mitigating the effects of a slow-growing grid instability which is most pronounced in plasma jet frame expansion problems using the two-fluid Eulerian remap algorithm, 2) extension of the Eulerian Smoothing Algorithm to allow EOS/Radiation modeling, 3) simulations of collisionless shocks formed by jet merging, 4) simulations of merging jets using high-Z gases, 5) generation of PROPACEOS EOS/Opacity databases, 6) simulations of plasma jet transport experiments, 7) simulations of plasma jet penetration through transverse magnetic fields, and 8) GPU PIC code development. The tools developed during this project are applicable not only to the study of plasma jets, but also to a wide variety of HEDP plasmas of interest to DOE, including plasmas created in short-pulse laser experiments performed to study fast ignition concepts for inertial confinement fusion.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

An implicit particle code with exact energy and charge conservation for studies of dense plasmas in axisymmetric geometries

A collisional particle code based on implicit energy- and charge-conserving methods in axisymmetric geometries is presented. A new particle pusher for axisymmetric systems is introduced that is compatible with exact energy and charge conservation and yields improved accuracy compared to other methods. How to appropriately treat all aspects of the algorithm near the r = 0 axis of symmetry is described in detail. Here, the axisymmetric model is verified by simulating the free expansion of a plasma sphere in 2D cylindrical and 1D spherical geometries. The algorithm's ability to study the dynamic compression of a dense plasma is illustrated by simulating the dynamic Z-pinch in 1D cylindrical geometry.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1984

The laboratory simulation of unmagnetized supernova remnants Absence of a blast wave

Supernova remnants are experimentally simulated by irradiating spherical targets with eight-beam carbon dioxide laser in a chamber containing finite amounts of neutral gas, the gas being ionized by radiation from the hot target. The expansion velocities of the target plasmas are approximately the same as the expansion velocities of supernova ejecta and the experiment is successfully scaled to the case of a supernova remnant in an unmagnetized, low-density, interstellar medium. No sweep-up of the ambient plasma is detected, indicating that no hydrodynamic shock wave is formed to couple the target ejecta to the ambient gas. The experiment implies that if supernova ejecta couple to the interstellar medium, magnetic-field effects may be crucial to the physical description.

Borovsky, J. E.↗
DOE OSTI2014

Asymptotic theory of double layer and shielding of electric field at the edge of illuminated plasma

The method of matched asymptotic expansions is applied to the problem of a collisionless plasma generated by UV illumination localized in a central part of the plasma in the limiting case of small Debye length λ{sub D}. A second-approximation asymptotic solution is found for the double layer positioned at the boundary of the illuminated region and for the un-illuminated plasma for the plane geometry. Numerical calculations for different values of λ{sub D} are reported and found to confirm the asymptotic results. The net integral space charge of the double layer is asymptotically small, although in the plane geometry it is just sufficient to shield the ambipolar electric field existing in the illuminated region and thus to prevent it from penetrating into the un-illuminated region. The double layer has the same mathematical nature as the intermediate transition layer separating an active plasma and a collisionless sheath, and the underlying physics is also the same. In essence, the two layers represent the same physical object: a transonic layer.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗