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All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Plasma Assisted Catalytic Conversion of Carbon Dioxide (CO2) and Propane to Propylene and Carbon Monoxide (CO)

Presented at the NETL Project Review Meetings in 2022, the presentation summary includes the following status updates: -Feasibility of the CO2-ODH reaction with plasma demonstrated at much lower temperatures than conventional processes -Presence of CO2 enhances propane conversion in the plasma reactor -Ce doped, 5 wt.%/CexZr1-xO2 catalyst demonstrated enhanced selectivity and stability for propylene production via CO2-ODH process under thermal conditions -Comprehensive characterization coupled with designed catalytic experiments identified Cr3+ as the active site CO2-ODH proceeds via dehydrogenation route -Coke formation, which causes catalyst deactivation, inhibited by both Ce and CO2

Zhou, S. James↗
DOE OSTI2024

Collaborative Research Proposal: Time Resolved Optical Emissions Spectroscopy and Laser Induced Fluorescence Spectroscopy of Nanosecond Pulsed Discharges in a Gas-Liquid Water Film Reactor

Electrical discharge plasma formed in contact with liquid water is of interest for a wide range of applications in chemical, biomedical, agricultural, electrical, and materials science and engineering. Such plasma reactors are of very timely importance since they also have significant disinfection capability by inactivating bacteria, viruses and other pathogens. Many types of plasma sources including those driven by AC, DC, RF, microwave, and pulsed electrical power supplies coupled to a wide range of different electrode configurations and reactor designs have been developed and explored which contact the plasma with liquid water. Recent roadmaps have recommended that further work is needed to develop our understanding of the fundamental chemical and physical process which occur at the interface of non-thermal plasma with liquid water solutions in order to advance this large diversity of applications which ultimately depend upon efficient production of key reactive chemical species. There is a wide range of interacting factors that affect the chemical reactions that occur in the plasma, in the liquid phase, and at the interface. These factors ultimately govern the key reactive chemical species formed and used in the various applications and they include a) the reactor design and input parameters, b) the discharge and transport processes, c) the plasma properties, and d) the resulting chemical reactions. For pulsed discharges, the power supply design and output parameters control the applied voltage, frequency, rise time, and width (duration) of the applied pulses. The reactor design involves specification of the gas-liquid contacting methods, electrode gap distance, reactor volume and shape, and gas and liquid flow rates achievable. The gas and liquid compositions as well as the liquid properties such as pH and conductivity are also of key importance in determination of the resulting chemical reactions. In addition, the important plasma properties include plasma gas temperature, electron density, electron energy (distribution), and size of the plasma channels which are all affected by the discharge and transport properties. Many studies have focused on specific aspects of these various processes. Of particular important and relevance to the proposed work is the utilization of nanosecond pulses to generate plasma in gas-liquid systems, liquid bubbles, underwater, and in gases. Recent advances in nanosecond pulses provide significant advantages in utilization with liquid water. For example, fast rise time and short pulses are less sensitive to water conductivity, such short pulses may provide advantages in fast temporal quenching of the plasma, and fundamental analysis of pulse properties, including pulse shape and width, may be facilitated by investigation of single filamentary fast pulses. Many studies have also dealt with the role of the gas composition on formation of reactive oxygen species (ROS) (i.e., hydroxyl radicals – ·OH, hydrogen peroxide – H 2 O 2 , various atomic oxygen species, ozone-O 3 , hydroperoxyl radicals HO 2 ·) and reactive nitrogen species (RNS) (i.e., nitrogen oxides – NO, NO 2 , N 2 O - collectively termed NO X , nitrite-NO 2 - , nitrate-NO 3 - , peroxynitrite-ONOO - ). The hydroxyl radical is the critical species in many chemical oxidation reactions for chemical degradation of toxic compounds in water and gases and for synthesis of some compounds. The mixture of various nitrogen oxide species is important for many biochemical and biological processes involved in biomedical and agricultural applications including disinfection and fertilizer production. The present proposal focuses on determination of the effects of time resolved electron density and hydroxyl radicals on plasma chemical reactions through collaboration with the Princeton Collaborative Low Temperature Plasma Research Facility (PCRF) at the Princeton Plasma Physics Laboratory (PPPL). In order to further investigate the role of the plasma generated electrons and hydroxyl radicals on the overall formation of the key species including hydrogen peroxide, hydroxyl radicals, and nitrogen oxides, the proposed work, thus seeks to determine high resolution time resolved electron density by optical emissions spectroscopy and time resolved hydroxyl radicals using laser induced fluorescence in the nanosecond discharge reactor. The combination of data on electron density and hydroxyl radical concentration will be utilized in the present work to more fully characterize the chemical reaction processes in this system and to advance the design, development, and operation of such chemical reactors for a wide range of applications.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Ground state rotational and kinetic temperatures of C 2 molecules in a laser-produced plasma

This study presents an experimental comparison between rotational and kinetic temperatures of molecular species in a laser-produced plasma, utilizing tunable laser absorption spectroscopy. We analyzed high-resolution and time-resolved absorption spectra of 31 rotational transitions within the Phillips A 1 II u –X 1 Σ g 3-0 band of the C 2 molecule, measured from a laser-produced graphite plasma in ~2 Torr argon, within the 771–781 nm spectral range. Spectral fitting provided quantitative state column densities of C 2 rotational energy levels in the ground electronic and vibrational states. Boltzmann analysis revealed thermalized rotational distributions showing rotational temperatures decreasing from 3000 to 600 K within 5–500 μs following the onset of the laser plasma. The measured kinetic and rotational temperatures of C 2 molecules are comparable, suggesting that collisional processes in the laser-produced plasma are sufficient to maintain thermal equilibrium between the C 2 molecules and the Ar background gas.

Absorption spectroscopy↗
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↗
DOE OSTI2022

Modelling general-relativistic plasmas with collisionless moments and dissipative two-fluid magnetohydrodynamics

ABSTRACT Relativistic plasmas are central to the study of black hole accretion, jet physics, neutron star mergers, and compact object magnetospheres. Despite the need to accurately capture the dynamics of these plasmas and the implications for relativistic transients, their fluid modelling is typically done using a number of (overly) simplifying assumptions, which do not hold in general. This is especially true when the mean free path in the plasma is large compared to the system size, and kinetic effects start to become important. Going beyond common approaches used in the literature, we describe a fully relativistic covariant 14-moment based two-fluid system appropriate for the study of electron–ion or electron–positron plasmas. This generalized Israel-Stewart-like system of equations of motion is obtained directly from the relativistic Boltzmann–Vlasov equation. This new formulation can account for non-ideal effects, such as anisotropic pressures and heat fluxes, not present in previous formulations of two-fluid magnetohydrodynamics. We show that a relativistic two-fluid plasma can be recast as a single fluid coupled to electromagnetic fields with (potentially large) out-of-equilibrium corrections. We keep all electron degrees of freedom, which provide self-consistent evolution equations for electron temperature and momentum. The out-of-equilibrium corrections take the form of a collisional 14-moment closure previously described in the context of viscous single fluids. The equations outlined in this paper are able to capture the full two-fluid character of collisionless plasmas found in black hole accretion and flaring processes around compact objects, as well Braginskii-like two-fluid magnetohydrodynamics applicable to weakly collisional plasmas inside accretion discs.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2002

Etching of Silicon in HBr Plasmas for High Aspect Ratio Features

Etching in semiconductor processing typically involves using halides because of the relatively fast rates. Bromine containing plasmas can generate high aspect ratio trenches, desirable for DRAM and MEMS applications, with relatively straight sidewalk We present scanning electron microscope images for silicon-etched trenches in a HBr plasma. Using a feature profile simulation, we show that the removal yield parameter, or number of neutrals removed per incident ion due to all processes (sputtering, spontaneous desorption, etc.), dictates the profile shape. We find that the profile becomes pinched off when the removal yield is a constant, with a maximum aspect ratio (AR) of about 5 to 1 (depth to height). When the removal yield decreases with increasing ion angle, the etch rate increases at the comers and the trench bottom broadens. The profiles have ARs of over 9:1 for yields that vary with ion angle. To match the experimentally observed etched time of 250 s for an AR of 9:1 with a trench width of 0.135 microns, we find that the neutral flux must be 3.336 x 10(exp 17)sq cm/s.

Hwang, Helen H.↗
NASA NTRS2018

Microgravity Experiments of Solid Waste Conversion into Useful Commodities

This Summer I participated in two projects at Kennedy Space Center in Cape Canaveral, Florida. The projects focus on the NASA's Deep Space Gateway applications for future Mars travel. All of these projects use recycling technology to use resources found on Earth and on other planets for fuel and other environmental applications. The first project I took the lead on is “Plasma Arc Gasification.” Plasma is a high temperature and very efficient way to process waste to create usable byproducts. The plasma chamber in temperature is comparable to that of the sun and this energy will help create an environment in which the waste can be recycled properly for not only plant support, but also for possible fuel application as well. I preformed the tests in a quartz tube, which is used to hold the waste (cotton, plastics, nylon, paper and a human waste simulant) and the waste is then combusted using O2 (present in air) into gases such as H2, H2O, CH4 and CO2. I determined which gases are present using a Fourier-transform infrared spectroscopy (FTIR) machine, which analyzes the peaks of the gases using liquid nitrogen. Problems arose in the beginning from the reactor emitting electromagnetic waves (EMI) that interfered with the technology of the experiment, specifically the thermocouples. This was solved through multiple tests with the positioning of the thermocouple power supply further away from the plasma reactor. I worked with another intern, Daniel Santander, who developed a space plant chamber which uses CO2 and H2O (harvested from the plasma reactor) to grow plants in space. The chamber possess a CO2 monitor, which controls the amount of gas that enters the chamber, along with a water integration system to supply the amount of water needed for proper plan growth. This technology will then be used for plant growth in space for the Astronauts on future space flights and possibly on the International Space Station (ISS). The second project I worked on is the “Orbital Syngas / Commodity Augmentation Reactor (OSCAR)” which focuses on the issues experienced in long-duration space flight regarding waste disposal. In previous space flight missions, waste was stored on board and returned to Earth for disposal. This technique is not applicable to long space flight missions to Mars due to the rocket being months away from Earth. OSCAR is using microgravity waste disposal techniques to produce fuels from the recycled waste. The waste is converted to syngas through a thermal degradation process. This process helps create an environmentally friendly way to dispose and reuse trash on board the space craft. Currently waste is being tested in the form of cotton and plastics. OSCAR is designed as a microgravity reactor that is currently being tested in a drop tower rig at Glenn Research Center. I helped design the 3D model for the insulation that will line the reactor. The first few trials, I dissolved the plastic of the mold in acetone. This method worked, but was very costly. I then received a silicone material to construct the mold from Swamp Works here at Kennedy. Through multiple trials with the silicone, this method worked best for developing the end pieces of the insulation for the chamber.

Plasma↗
NASA NTRS1974

Applications of plasma core reactors to terrestrial energy systems

Plasma core reactors offer several new options for future energy needs in addition to space power and propulsion applications. Power extraction from plasma core reactors with gaseous nuclear fuel allows operation at temperatures higher than conventional reactors. Highly efficient thermodynamic cycles and applications employing direct coupling of radiant energy are possible. Conceptual configurations of plasma core reactors for terrestrial applications are described. Closed-cycle gas turbines, MHD systems, photo- and thermo-chemical hydrogen production processes, and laser systems using plasma core reactors as prime energy sources are considered. Cycle efficiencies in the range of 50 to 65 percent are calculated for closed-cycle gas turbine and MHD electrical generators. Reactor advantages include continuous fuel reprocessing which limits inventory of radioactive by-products and thorium-U-233 breeder configurations with about 5-year doubling times.-

Latham, T. S.↗
NASA NTRS1980

IMP-8. Volume 2: Scientific section

Results of the analysis of the IMP-8 data, which was collected during the first six and one-half years after launch of the IMP-8 spacecraft are presented. The plasma wave experiment data were processed and are available in an easily accessible summary form. These data continue to provide a valuable source for comparative studies with plasma wave experiments on other spacecraft operating in the solar wind and within the Earth's magnetosphere.

Source record↗
NASA NTRS2007

Large-Area Permanent-Magnet ECR Plasma Source

A 40-cm-diameter plasma device has been developed as a source of ions for material-processing and ion-thruster applications. Like the device described in the immediately preceding article, this device utilizes electron cyclotron resonance (ECR) excited by microwave power in a magnetic field to generate a plasma in an electrodeless (noncontact) manner and without need for an electrically insulating, microwave-transmissive window at the source. Hence, this device offers the same advantages of electrodeless, windowless design - low contamination and long operational life. The device generates a uniform, high-density plasma capable of sustaining uniform ion-current densities at its exit plane while operating at low pressure [<10(exp -4) torr (less than about 1.3 10(exp -2) Pa)] and input power <200 W at a frequency of 2.45 GHz. Though the prototype model operates at 2.45 GHz, operation at higher frequencies can be achieved by straightforward modification to the input microwave waveguide. Higher frequency operation may be desirable in those applications that require even higher background plasma densities. In the design of this ECR plasma source, there are no cumbersome, power-hungry electromagnets. The magnetic field in this device is generated by a permanent-magnet circuit that is optimized to generate resonance surfaces. The microwave power is injected on the centerline of the device. The resulting discharge plasma jumps into a "high mode" when the input power rises above 150 W. This mode is associated with elevated plasma density and high uniformity. The large area and uniformity of the plasma and the low operating pressure are well suited for such material-processing applications as etching and deposition on large silicon wafers. The high exit-plane ion-current density makes it possible to attain a high rate of etching or deposition. The plasma potential is <3 V low enough that there is little likelihood of sputtering, which, in plasma processing, is undesired because it is associated with erosion and contamination. The electron temperature is low and does not vary appreciably with power.

Foster, John E.↗
DOE OSTI2021

Development and Use of an Ultra-High Resolution Electron Scattering Apparatus

In this LDRD project, we developed a versatile capability for high-resolution measurements of electron scattering processes in gas-phase molecules, such as ionization, dissociation, and electron attachment/detachment. This apparatus is designed to advance fundamental understanding of these processes and to inform predictions of plasmas associated with applications such as plasma-assisted combustion, neutron generation, re-entry vehicles, and arcing that are critical to national security. We use innovative coupling of electron-generation and electron-imaging techniques that leverages Sandia’s expertise in ion/electron imaging methods. Velocity map imaging provides a measure of the kinetic energies of electrons or ion products from electron scattering in an atomic or molecular beam. We designed, constructed, and tested the apparatus. Tests include dissociative electron attachment to O2 and SO2, as well as a new method for studying laser-initiated plasmas. This capability sets the stage for new studies in dynamics of electron scattering processes, including scattering from excited-state atoms and molecules.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1995

Electric conductivity of plasma in solar wind

One of the most important parameters in MHD description of the solar wind is the electric conductivity of plasma. There exist now two quite different approaches to the evaluation of this parameter. In the first one a value of conductivity taken from the most elaborated current theory of plasma should be used in calculations. The second one deals with the empirical, phenomenological value of conductivity. E.g.: configuration of interplanetary magnetic field, stretched by the expanding corona, depends on the magnitude of electrical conductivity of plasma in the solar wind. Knowing the main empirical features of the field configuration, one may estimate the apparent phenomenological value of resistance. The estimations show that the electrical conductivity should be approximately 10(exp 13) times smaller than that calculated by Spitzer. It must be noted that the empirical value should be treated with caution. Due to the method of its obtaining it may be used only for 'large-scale' description of slow processes like coronal expansion. It cannot be valid for 'quick' processes, changing the state of plasma, like collisions with obstacles, e.g., planets and vehicles. The second approach is well known in large-scale planetary hydrodynamics, stemming from the ideas of phenomenological thermodynamics. It could formulate real problems which should be solved by modern plasma physics, oriented to be adequate for complicated processes in space.

Chertkov, A. D.↗
NASA NTRS1990

Monitoring Coating Thickness During Plasma Spraying

High-resolution video measures thickness accurately without interfering with process. Camera views cylindrical part through filter during plasma spraying. Lamp blacklights part, creating high-contrast silhouette on video monitor. Width analyzer counts number of lines in image of part after each pass of spray gun. Layer-by-layer measurements ensure adequate coat built up without danger of exceeding required thickness.

Miller, Robert A.↗
NASA NTRS1985

Correlated observations of substorm effects in the near-earth region and the deep magnetotail

Simultaneous observations of energetic particle measurements from the geosynchronous satellite 1982-019 and magnetic field, electron plasma, and energetic proton and electron measurements obtained with ISEE 3 in the deep tail are presented. The data are supplemented by ground magnetograms. A substorm occurred on March 22, 1983, close to 0300 UT as identified in the ground magnetograms and by a particle injection at geosynchronous orbit. About 10 min later, ISEE 3 observed (at a distance of approximately 130 RE in the deep tail) magnetic field, plasma, and energetic particle signatures consistent with the passage of a plasmoid. After the passage of the plasmoid the satellite enters shortly into a lobelike environment, in which an energetic proton beam is observed. High-resolution magnetic field data are indicative of small-scale structures in the postplasmoid plasma sheet. From the plasma sheet flow speed during the plasmoid's passage it is concluded that the 0300 UT substorm is responsible for its origin. This allows an approximate timing of the plasmoid release at a near-earth neutral line and of the plasma sheet recovery after substorm onset, and it indicates a close relationship between processes in the near-earth plasma sheet and the deep tail during substorms.

Scholer, M.↗
NASA NTRS1979

Is the galactic corona produced by galactic flares?

The effect of the differential rotation of the disk of the Galaxy on magnetic field which penetrates the disk is considered. The magnetic field will be progressively distorted from a potential (current-free) form and will at some stage become unstable. It is expected that an MHD instability, a resistive instability, or a combination of the two, will result in the release of the excess magnetic energy and that part of the released energy will be converted into heat. By estimating the energy release and the rate at which this process will occur and by assuming that this energy input is balanced by radiation, estimates were obtained of the parameters of the resulting plasma. It appears that this process alone can heat a galactic corona to temperatures of order 10 to the 6th power K.

Sturrock, P. A.↗
NASA NTRS1980

Is the galactic corona produced by galactic flares

The effect of the differential rotation of the disk of the galaxy on magnetic field which penetrates the disk is considered. The magnetic field will be progressively distorted from a potential (current-free) form and will at some stage become unstable. We expect, from knowledge of solar flares, that an MHD instability, a resistive instability, or a combination of the two, will result in the release of the excess magnetic energy, and that part of the released energy will be converted into heat. By estimating the energy release and the rate at which this process will occur and by assuming that this energy input is balanced by radiation, we obtain estimates of the parameters of the resulting plasma. It appears that this process alone can heat a galactic corona to temperatures of order one-million K.

Sturrock, P. A.↗
NASA NTRS1997

Global Kinetic Modeling of Banded Electron Structures in the Plasmasphere

Significant fluxes of 10 eV to 30 keV electrons have been detected in the plasmasphere, appearing as banded structures in energy with broad spatial extents and slowly evolving over several days. It is thought that these populations are decaying plasma sheet electrons injected into the corotating region of near-Earth space. This capture can occur when the convective electric field drops rapidly and the Alfven boundary suddenly outward, trapping the inner edge of the plasma sheet along closed drift paths. Our bounce-averaged kinetic model of superthermal electron transport is able to simulate this capture and the subsequent drift, diffusion, and decay of the plasma cloud. Results of this simulation will be shown and discussed, from the initial injection during the elevated convection to the final loss of the particles. It is thought that not only Coulomb collisions but also wave-particle interactions play a significant role in altering the plasma cloud. Quasilinear diffusion is currently being incorporated into the model and the importance of this mechanism will be examined. Also, the high anisotropy of the trapped population could be unstable and generate plasma waves. These and other processes will be investigated to determine the final fate of the cloud and to quantify where, how, and when the energy of the plasma cloud is deposited. Comparisons with CRRES observations of these events are shown to verify the model and explain the data.

Liemohn, M. W.↗
NASA NTRS1984

Arguments for fundamental emission by the parametric process L yields T + S in interplanetary type III bursts

Observations of low frequency ion acoustic-like waves associated with Langmuir waves present during interplanetary Type 3 bursts are used to study plasma emission mechanisms and wave processes involving ion acoustic waves. It is shown that the observed wave frequency characteristics are consistent with the processes L yields T + S (where L = Langmuir waves, T = electromagnetic waves, S = ion acoustic waves) and L yields L' + S proceeding. The usual incoherent (random phase) version of the process L yields T + S cannot explain the observed wave production time scale. The clumpy nature of the observed Langmuir waves is vital to the theory of IP Type 3 bursts. The incoherent process L yields T + S may encounter difficulties explaining the observed Type 3 brightness temperatures when Langmuir wave clumps are incorporated into the theory. The parametric process L yields T + S may be the important emission process for the fundamental radiation of interplanetary Type 3 bursts.

Cairns, I. H.↗