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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Novel focal point multipass cell for absorption spectroscopy on small sized atmospheric pressure plasmas

A novel focal point multipass cell (FPMPC) was developed, in which all laser beams propagate through a common focal point. It is exclusively constructed from standard optical elements. Main functional elements are two 90{sup ∘} off-axis parabolic mirrors and two retroreflectors. Up to 17 laser passes are demonstrated with a near-infrared laser beam. The number of laser passes is precisely adjustable by changing the retroreflector distance. At the focal point beams are constricted to fit through an aperture of 0.8 mm. This is shown for 11 beam passes. Moreover, the fast temporal response of the cell permits investigation of transient processes with frequencies up to 10 MHz. In order to demonstrate the applicability of the FPMPC for atmospheric pressure plasma jets, laser absorption spectroscopy on the lowest excited argon state (1s{sub 5}) was performed on a 1 MHz argon atmospheric pressure plasma jet. From the obtained optical depth profiles, the signal-to-noise ratio was deduced. It is shown that an elevation of the laser pass number results in an proportional increase of the signal-to-noise ratio making the FPMPC an appropriate tool for absorption spectroscopy on plasmas of small dimensions.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2017

Numerical study of the influence of surface reaction probabilities on reactive species in an rf atmospheric pressure plasma containing humidity

The quantification and control of reactive species (RS) in atmospheric pressure plasmas (APPs) is of great interest for their technological applications, in particular in biomedicine. Of key importance in simulating the densities of these species are fundamental data on their production and destruction. In particular, data concerning particle-surface reaction probabilities in APPs are scarce, with most of these probabilities measured in low-pressure systems. In this work, the role of surface reaction probabilities, γ, of reactive neutral species (H, O and OH) on neutral particle densities in a He–H 2 O radio-frequency micro APP jet (COST-$\mu $APPJ) are investigated using a global model. It is found that the choice of γ, particularly for low-mass species having large diffusivities, such as H, can change computed species densities significantly. Furthermore the importance of γ even at elevated pressures offers potential for tailoring the RS composition of atmospheric pressure microplasmas by choosing different wall materials or plasma geometries.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Atmospheric Pressure Plasma Treatment of Magnesium Alloy for Enhanced Coating Adhesion and Corrosion Resistance

Atmospheric pressure plasma (AP) treatment, using an open-air jet of ionized CO 2 , N 2 , or air, was applied to AZ91D Mg alloy surfaces to investigate its effects on primer coating adhesion and corrosion resistance. The CO 2 and air AP treatments formed an O- and C-rich surface layer (Mg-O-C) consisting of agglomerated nanoparticles and pits with a depth of a few microns and increasing the surface roughness by 6–8 times compared with the reference 600 grit-finished surface. Then, three commercial primers, zinc phosphate (ZnP), chromate-containing epoxy, and MIL23377, were applied on the treated surfaces to evaluate the corrosion resistance associated with the coating adhesion. Microscopic analysis demonstrated stronger interlocking between the primer layer and the nano-/microrough Mg-O-C surface compared to the untreated (600 grit-finished) surfaces, indicating improved coating adhesion and corrosion resistance. Crosscut tests of the MIL23377 primer on the CO 2 and air AP-treated surfaces showed the highest level of adhesion, ASTM class 5B. Salt spray corrosion tests showed that after 8 days of exposure, the primer coatings on air AP-treated surfaces had corrosion areas that were more than four times smaller than that of the 600 grit-finished surface. The N 2 AP treatment showed similar adhesion enhancement. The preliminary operation expenses for AP treatment using CO 2 , N 2 , and air were estimated at USD 30.62, USD 35.45, and USD 29.75 (from an air cylinder)/USD 0.66 (from an air compressor) per m 2 , respectively.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Effect of oxidation post treatments on TiO 2 coating manufactured using reactive very low-pressure plasma spraying (R-VLPPS)

TiO 2 coatings manufactured using reactive very low-pressure plasma spraying (R-VLPPS) were analyzed in different regions related to their position compared to the plasma flame. For that, a screen was used in order to hide an area of the substrate from the direct plasma flux. The coating morphology changed from quasi lamellar structure to highly vapor structure and coatings exhibited obvious modifications in terms of phases and mechanical properties. The effect of oxidation post treatment on the as sprayed coating was then studied by selecting two methods: in situ oxidation post treatment and classical thermal treatment. The two post treatments provided an increase of the main rutile phase and a decrease of both the size and the contents of porosity simultaneously.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Interaction of Long-lived Reactive Species from Cold Atmospheric Pressure Plasma with Polymers: Chemical Modification by Ozone and Reactive Oxygen-Nitrogen Species

Atmospheric pressure plasma (APP) sources are able to generate a variety of reactive species that have different effects on materials, such as functionalization, etching and deposition. In this article, we study the effect of long-lived reactive neutral species on polymers using a model plasma-surface interaction (PSI) system that consists of ultra-thin (~10 nm) polystyrene (PS) films and a surface micro-discharge (SMD) reactor operated with various N 2 /O 2 working gas mixtures. We characterized and quantified the reactive species generated by SMD using IR and UV absorption, and we found that O 3 , N 2 O 5 , N 2 O and HNO 3 are the dominant long-lived reactants near the target surface. When exposing PS films to these reactive species, we observed material responses including film thickness expansion, surface and bulk oxidation, and surface organic nitrate formation. The quantity of these changes varied with the N 2 /O 2 working gas composition. By correlating material response with gas phase species, we find that the chemical modification of PS strongly depends on the density of O 3 in the gas phase, which is indicative of an essential role of O 3 in the remote APP treatment of polymers. Our results show that O 3 causes polymer surface oxidation, participates in the diffusion-reaction process in the polymer bulk, and results in aromatic ring cleavage and the formation of carbonyl groups. In contrast, we did not find a correlation between surface organic nitrate and individual long-lived reactive species mentioned above. This indicates that surface organic nitrate formation on polymer surfaces might result from the interaction of multiple reactive species, including O 3 and nitrogen containing species. A model for the interphase mass transfer of reactive species from gas to solid was also described.

36 MATERIALS SCIENCE↗
DOE OSTI2018

A Planar Source of Atmospheric-Pressure Plasma Jet

In a single-barrier discharge with voltage sharpening and low gas consumption (up to 1 L/min), plane atmospheric pressure plasma jets with a width of up to 3 cm and length of up to 4 cm in air are formed in the slit geometry of the discharge zone. The energy, temperature, and spectral characteristics of the obtained jets have been measured. The radiation spectrum contains intense maxima corresponding to vibrational transitions of the second positive system of molecular nitrogen N{sub 2} (C{sup 3}Π{sub u} → B{sup 3}Π{sub g}) and comparatively weak transition lines of the first positive system of the N{sub 2}{sup +} ion (B{sup 2}Σ{sub u}{sup +} → X{sup 2}Σ{sub g}). By an example of inactivation of the Staphylococcus aureus culture (strain ATCC 209), it is shown that plasma is a source of chemically active particles providing the inactivation of microorganisms.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Experimental and Modeling of Low Pressure Plasma as a Complementary Process for Thermal Waste Treatment - 19270

Polymeric waste contaminated with radionuclides is a challenging wasteform in its raw state. This waste is characterized by its high volume to weight ratio, together with the hazard of its radiolysis and consequently, the generation of flammable and explosive gases (e.g. H2 and light hydrocarbons). Thus, minimizing waste volumes together with stabilizing the wasteform are of high significance in the treatment of contaminated polymers. Thermal decomposition of polymeric waste results in gas products, mainly hydrocarbon molecules (C2-C6), which cannot be released to the atmosphere for environmental reasons. Here, we study a secondary gas treatment reactor, using plasma formed by inductive radio-frequency (13.56 MHz RF), in order to decompose the hydrocarbon gas products into smaller molecules. As a case study, we compare the plasma treatment of gases from two sources: a mixed gaseous product collected from the pyrolytic decomposition of high-density polyethylene (HDPE), and industrial butane gas. We also examine the effects of systematic addition of Ar, N{sub 2} and Ar+N{sub 2} mixtures to the treated gases. In this work, we utilize optical emission spectroscopy (OES) to obtain in situ data from the region in the center of the inductive RF coil. The main emissions from discharges in the gases or their mixtures occur in the 200-700 nm spectral region. Their relative intensities depend strongly on the plasma excitation mode, N{sub 2} flow rate, and gas feed composition. The addition of N{sub 2} to the input gas enhanced hydrocarbon decomposition as compared to the addition of pure Ar. This can be attributed to decomposition by free-radical reactions rather than by particles collisions processes. We performed preliminary modeling of the plasma behavior from ignition to steady state, which takes less than 0.01 s under these conditions. These simulations will help us to better understand and optimize a variety of decomposition reactions. The results of this study suggest that coupling low pressure plasma to conventional thermal decomposition techniques can provide an effective treatment process for contaminated solid plastic waste. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
NASA NTRS1995

Radial energy transport by magnetospheric ULF waves: Effects of magnetic curvature and plasma pressure

The 'radial' transport of energy by internal ULF waves, stimulated by dayside magnetospheric boundary oscillations, is analyzed in the framework of one-fluid magnetohydrodynamics. (the term radial is used here to denote the direction orthogonal to geomagnetic flux surfaces.) The model for the inhomogeneous magnetospheric plasma and background magnetic field is axisymmetric and includes radial and parallel variations in the magnetic field, magnetic curvature, plasma density, and low but finite plasma pressure. The radial mode structure of the coupled fast and intermediate MHD waves is determined by numerical solution of the inhomogeneous wave equation; the parallel mode structure is characterized by a Wentzel-Kramer-Brillouin (WKB) approximation. Ionospheric dissipation is modeled by allowing the parallel wave number to be complex. For boudnary oscillations with frequencies in the range from 10 to 48 mHz, and using a dipole model for the background magnetic field, the combined effects of magnetic curvature and finite plasma pressure are shown to (1) enhance the amplitude of field line resonances by as much as a factor of 2 relative to values obtained in a cold plasma or box-model approximation for the dayside magnetosphere; (2) increase the energy flux delivered to a given resonance by a factor of 2-4; and (3) broaden the spectral width of the resonance by a factor of 2-3. The effects are attributed to the existence of an 'Alfven buoyancy oscillation,' which approaches the usual shear mode Alfven wave at resonance, but unlike the shear Alfven mode, it is dispersive at short perpendicular wavelengths. The form of dispersion is analogous to that of an internal atmospheric gravity wave, with the magnetic tension of the curved background field providing the restoring force and allowing radial propagation of the mode. For nominal dayside parameters, the propagation band of the Alfven buoyancy wave occurs between the location of its (field line) resonance and that of the fast mode cutoff that exists at larger radial distances.

Kouznetsov, Igor↗
NASA NTRS2016

Atmospheric Pressure Plasma Jet as a Dry Alternative to Inkjet Printing in Flexible Electronics

We have developed an atmospheric pressure plasma jet printing system that works at room temperature to 50 deg C unlike conventional aerosol assisted techniques which require a high temperature sintering step to obtain desired thin films. Multiple jets can be configured to increase throughput or to deposit multiple materials, and the jet(s) can be moved across large areas using a x-y stage. The plasma jet has been used to deposit carbon nanotubes, graphene, silver nanowires, copper nanoparticles and other materials on substrates such as paper, cotton, plastic and thin metal foils.

Printable electronics↗
DOE OSTI2016

Electrical and optical properties of Ar/NH{sub 3} atmospheric pressure plasma jet

Inspired by the Penning effect, we obtain a glow-like plasma jet by mixing ammonia (NH{sub 3}) into argon (Ar) gas under atmospheric pressure. The basic electrical and optical properties of an atmospheric pressure plasma jet (APPJ) are investigated. It can be seen that the discharge mode transforms from filamentary to glow-like when a little ammonia is added into the pure argon. The electrical and optical analyses contribute to the explanation of this phenomenon. The discharge mode, power, and current density are analyzed to understand the electrical behavior of the APPJ. Meanwhile, the discharge images, APPJ's length, and the components of plasma are also obtained to express its optical characteristics. Finally, we diagnose several parameters, such as gas temperature, electron temperature, and density, as well as the density number of metastable argon atoms of Ar/NH{sub 3} APPJ to help judge the usability in its applications.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Tomographic optical emission spectroscopy of an atmospheric pressure plasma jet and surface ionization waves on planar and structured surfaces

Here in this paper, an approach for 3D plasma structure diagnostics using tomographic optical emission spectroscopy (Tomo-OES) of a nanosecond pulsed atmospheric pressure plasma jet (APPJ) is presented. In contrast to the well-known Abel inversion, Tomo-OES does not require cylindrical symmetry to recover 3D distributions of plasma light emission. Instead, many 2D angular projections are measured with intensified cameras and the multiplicative algebraic reconstruction technique is used to recover the 3D distribution of light emission. This approach solves the line-of-sight integration problem inherent to optical diagnostics, allowing recovery of localized OES information within the plasma that can be used to better infer plasma parameters within complex plasma structures. Here, Tomo-OES was applied to investigate an APPJ operated with helium in ambient air and impinging on planar and structured dielectric surfaces. Surface charging caused the guided streamer from the APPJ to transition to a surface ionization wave (SIW) that propagated along the surface. The SIW experienced variable geometrical and electrical material properties as it propagated, leading to 3D configurations that were non-symmetric and spatially complex. Light emission from He, N$_2^+$, and N2 were imaged at ten angular projections and the respective time-resolved 3D emission distributions in the plasma were then reconstructed. The spatial resolution of each tomographic reconstruction was 7.4 µm and the temporal resolution was 5 ns, sufficient to observe the guided streamer and the effects of the structured surface on the SIW. Emission from He showed the core of the jet and emission from N$_2^+$ and N2 indicated effects of entrainment of ambient air. Penning ionization of N2 created a ring or outer layer of N$_2^+$ that spatially converged to form the 'plasma bullet' or spatially diverged across a surface as part of a SIW. The SIW entered trenches of size 150 µm, leading to decreases in plasma light emission in regions above the trenches. The plasma light emission was higher in some regions with trenches, possibly due to effects of field enhancement.

plasma interactions with complex surfaces↗
DOE OSTI2024

Experiments and gyrokinetic simulations of the nonlinear interaction between spinning magnetized plasma pressure filaments

A set of experiments using controlled, skin depth-sized plasma pressure filaments in close proximity have been carried out in a large linear magnetized plasma device. Two- and three-filament configurations have been used to determine the scale of cross field nonlinear interaction. When the filaments are separated by a distance of approximately five times the size of a single filament or less, a significant transfer of charge and energy occurs, leading to the generation of inter-filament electric fields. This has the effect of rotating the filaments and influencing the merging dynamics. Nonlinear gyrokinetic simulations using seeded filaments confirm the presence of unstable drift-Alfvén modes driven by the steep electron temperature gradient. When the filaments are within a few collisionless electron skin depths (separations twice the size of a single filament), the unstable perturbations drive the convective mixing of the density and temperature and rearrange the gradients such that they maximize in the region surrounding the filament bundle.

Sydora, R. D. (ORCID:0000000192543149)↗
DOE OSTI2020

Spatially resolved absolute densities of reactive species and positive ion flux in He-O 2 RF-driven atmospheric pressure plasma jet: touching and non-touching with dielectric substrate

Atmospheric pressure plasma jets (APPJs) are operating in direct contact with dielectric substrates for many applications. Nonetheless, many studies have been focusing on free jets. In this letter, we report spatially resolved measurements of reactive species including neutral and ionic species in an He + 1% O 2 RF-driven APPJ by molecular beam mass spectrometry equipped with a dielectric sampling plate, enabling to detect species densities for APPJ operating remotely or in direct contact with a substrate. Here, the spatially resolved distribution of O, O 2 (a 1 Δ g ) and O 3 is dominated by convection and, remarkably, shows minimum differences between touching and non-touching conditions.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2017

Atmospheric-Pressure Plasma Jet Surface Treatment for Use in Improving Adhesion

Atmospheric-pressure plasma jets (APPJs) are a method of plasma treatment that plays an important role in material processing and modifying surface properties of materials, especially polymers. Gas plasmas react with polymer surfaces in numerous ways such as oxidation, radical formation, degradation, and promotion of cross-linking. Because of this, gas and plasma conditions can be explored for chosen processes to maximize desired properties. The purpose of this study is to investigate plasma parameters in order to modify surface properties for improved adhesion between aluminum and epoxy substrates using two types of adhesives. The background, results to date, and future work will be discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Atmospheric pressure plasma treatment of skin: penetration into hair follicles

Sterilization of skin prior to surgery is challenged by the reservoir of bacteria that resides in hair follicles. Atmospheric pressure plasma jets (APPJs) have been proposed as a method to treat and deactivate these bacteria as atmospheric plasmas are able to penetrate into structures and crevices with dimensions similar to those found in hair follicles. In this paper, we discuss results from a computational investigation of an APPJ sustained in helium flowing into ambient air, and incident onto a layered dielectric similar to human skin in which there are idealized hair follicles. We found that, depending on the location of the follicle, the bulk ionization wave (IW) incident onto the skin, or the surface IW on the skin, are able to launch IWs into the follicle. The uniformity of treatment of the follicle depends on the location of the first entry of the plasma into the follicle on the top of the skin. Typically, only one side of the follicle is treated on for a given plasma pulse, with uniform treatment resulting from rastering the plasma jet across the follicle over many pulses. Plasma treatment of the follicle is sensitive to the angle of the follicle with respect to the skin, width of the follicle pocket, conductivity of the dermis and thickness of the underlying subcutaneous fat layer, the latter due to the change in capacitance of the tissue.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2024

Generation of Large-Volume High-Pressure Plasma by Spatio-Temporal Control of Space Charge

Due to the fundamental limitations of scaling, very little progress has been made towards achieving a large-volume dense non-equilibrium plasma near atmospheric pressures. Commercially available state-of-the art glow-like atmospheric plasma devices for industrial applications are either narrow tubes or wide slits with narrow openings. Often multiple sources are put together in various configurations to process larger surfaces. The traditional methods of exciting electrodes create spatially fixed electric fields. As a result, the space charge at atmospheric pressure tends to be spatially confined resulting in non-uniformity which eventually leads to instability as the discharge is scaled. Theoretical work done under this project showed that it is possible to generate a spatially rotating electric field by exciting a set of electrodes with phase staggered sinusoidal waveforms. The modeling and simulations were done using plasma fluid models. It was shown that such a field can produce a uniform plasma. At the conclusion of the project, experimental proof of concept with an eight-electrode system in various gases (Air, Helium and Argon) was demonstrated. Power measurements and spectral investigation show that the concept can be used to generate a uniform stable plasma. This plasma source has the potential of opening new applications of nonthermal plasma including combustion of carbon-free fuel. The current limitation of the proposed method in scaling to higher volume and pressure is the need for multiple high voltage amplifiers.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Molecular admixtures and impurities in atmospheric pressure plasma jets

A more complete understanding of reactive chemistry generated by atmospheric pressure plasma jets (APPJs) is critical to many emerging medical, agricultural, and water treatment applications. Adding molecular gases to the noble working gas which flows through the jet is a common method to tailor the resulting production of reactive oxygen and nitrogen species (RONS). In this paper, results are discussed from a computational investigation of the consequences of H 2 O and O 2 admixtures on the reactive chemistry of He APPJs flowing into humid air. This investigation, performed with a 2-dimensional plasma hydrodynamics model, addresses the RONS that are initially produced and the evolution of that chemistry on longer time scales. Without an admixture, the impurities in 99.999% pure helium are a major source of RONS. The addition of H 2 O decreases the production of reactive nitrogen species (RNS) and increases the production of reactive oxygen species (ROS). The addition of O 2 significantly decreases the production of RNS, as well as hydrogen-containing ROS, but increases the production of ROS without hydrogen. This selectivity comes from the lower ionization energy of O 2 compared to N 2 and H 2 O, which then allows for charge exchange reactions. These charge exchange reactions change the RONS which are produced in the afterglow by dissociative recombination. The consequences of impurities were also examined. Humid air impurities as low as 10 ppm in the helium can account for 79%-98% of the production of most RONS in the absence of an intentional admixture. The degree to which the impurities affect the RONS production depends on the electrode configuration and can be reduced by molecular admixtures.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗