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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 667 records · Page 37
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Ionic Polymers Under Dynamic Conditions

Combining neutron scattering tools and exascale molecular dynamics simulations, research was carried out to resolve the structure and motion of ionic polymers under dynamic conditions. Ionizable polymers constitute a key component in current and potential transformative lightweight energy generation and storage devices. However, the inherent segregation of these polymers to ionic clusters and non-ionic domains, or clusters, that on one hand enables their function, confines the dynamics of the polymer chains, leading to the formation of far-from equilibrium states. These non-equilibrium states morph under in situ conditions, affecting the performance-longevity-safety-cost foundation that underlines the use of these polymers. On route to controlling the assemblies of ionizable polymers into stable functional materials, the research focused on a) understanding the inherent confinement of the polymer chains by the ionic clusters and b) resolving of the response of these polymers to flow fields that are integral to the processing and function of these macromolecules.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Transition from nonsequential to sequential double ionization in many-electron systems

Understanding strong-field double ionization of many-electron systems is an important fundamental problem with potential implications for molecular imaging within this regime. Using mid-IR radiation, we unambiguously identify the transition from nonsequential (e, 2e) to sequential double ionization in Xe at an intensity below 10 14 W/cm 2 . Ionization from excited orbitals is found to be decisive at low intensities, but we demonstrate that such mechanisms are unimportant in the sequential regime. We utilize these facts to successfully image a molecular dication using laser-induced electron diffraction. This methodology can be used to study molecular dynamics on unprecedented few-femtosecond time scales.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2023

Molecular Insight into the Effects of Clustering on the Dynamics of Ionomers in Solutions

Ionizable groups tethered to polymers enable their many current and potential applications. However, these functionalities drive the formation of physical networks through clustering of the ionic groups, resulting in constrained dynamics of the macromolecules. Understanding the molecular origin of this hindrance remains a critical fundamental question, whose solution will directly impact the processing of ionizable polymers from molecules to viable materials. Here, in this work, using quasielastic neutron scattering accompanied by molecular dynamics simulations, segmental dynamics of slightly sulfonated polystyrene is studied in solutions as the cohesion of the ionic assemblies is tuned. We find that in cyclohexane the ionic assemblies act as centers of confinement, affecting dynamics both on macroscopic lengths and in the vicinity of the ionic assemblies. Addition of a small amount of ethanol affects the packing of the ionizable groups within the assemblies, which in turn enhances the chain dynamics.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Azimuthal and axial structures in 3D particle-in-cell simulation of Penning discharge

We report the results of a 3D particle-in-cell simulation of cylindrical Penning discharge with the axial magnetic field in the so-called reflex configuration, where the cathode and anti-cathode are biased to the same negative potential. The discharge is supported by thermal electron emission from the cathode. Electron and ion collisions, including ionization, are fully accounted for. The emphasis is on a specific regime in which the plasma potential at the center of the discharge is positive with respect to the chamber walls, serving as an anode. Spatial and temporal scales of the observed azimuthal and axial fluctuations and structures are characterized. It is suggested that azimuthal structures are caused by the dissipative gradient-drift instability. We find that the axial fluctuations related to the plasma-beam instabilities are weakly correlated with the azimuthal perturbations of the density, so that the azimuthal modes rotate as a whole and do not show any axial shear. The behavior of the electric potential is more involved, demonstrating intermittent standing wave and propagating structures in the axial direction that modulate the electron transport, producing the standing wave pattern (along the z-direction) in the radial electron flux.

3D PIC simulation of discharge↗
DOE OSTI2016

Ionization equilibrium at the transition from valence-band to acceptor-band migration of holes in boron-doped diamond

A quasi-classical model of ionization equilibrium in the p-type diamond between hydrogen-like acceptors (boron atoms which substitute carbon atoms in the crystal lattice) and holes in the valence band (v-band) is proposed. The model is applicable on the insulator side of the insulator–metal concentration phase transition (Mott transition) in p-Dia:B crystals. The densities of the spatial distributions of impurity atoms (acceptors and donors) and of holes in the crystal are considered to be Poissonian, and the fluctuations of their electrostatic potential energy are considered to be Gaussian. The model accounts for the decrease in thermal ionization energy of boron atoms with increasing concentration, as well as for electrostatic fluctuations due to the Coulomb interaction limited to two nearest point charges (impurity ions and holes). The mobility edge of holes in the v-band is assumed to be equal to the sum of the threshold energy for diffusion percolation and the exchange energy of the holes. On the basis of the virial theorem, the temperature T{sub j} is determined, in the vicinity of which the dc band-like conductivity of holes in the v-band is approximately equal to the hopping conductivity of holes via the boron atoms. For compensation ratio (hydrogen-like donor to acceptor concentration ratio) K ≈ 0.15 and temperature T{sub j}, the concentration of “free” holes in the v-band and their jumping (turbulent) drift mobility are calculated. Dependence of the differential energy of thermal ionization of boron atoms (at the temperature 3T{sub j}/2) as a function of their concentration N is calculated. The estimates of the extrapolated into the temperature region close to T{sub j} hopping drift mobility of holes hopping from the boron atoms in the charge states (0) to the boron atoms in the charge states (−1) are given. Calculations based on the model show good agreement with electrical conductivity and Hall effect measurements for p-type diamond with boron atom concentrations in the range from 3 × 10{sup 17} to 3 × 10{sup 20 }cm{sup −3}, i.e., up to the Mott transition. The model uses no fitting parameters.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Creating localized plasma waves by ionization of doped semiconductors

Localized plasma waves can be generated by suddenly ionizing extrinsic semiconductors with spatially periodic dopant densities. The built-in electrostatic potentials at the metallurgical junctions, combined with electron density ripples, offer the exact initial condition for exciting long-lasting plasma waves upon ionization. This method can create plasma waves with a frequency between a few terahertz to subpetahertz without substantial damping. Here, the lingering plasma waves can seed backward Raman amplification in a wide range of resonance frequencies up to the extreme ultraviolet regime. Chirped wave vectors and curved wave fronts allow focusing the amplified beam in both longitudinal and transverse dimensions. The main limitation to this method appears to be obtaining sufficiently low plasma density from solid-state materials to avoid collisional damping.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Vibrational Spectroscopy for the Determination of Ionizable Group Content in Ionomer Materials

An approach based on vibrational spectral measurements is described for determining the ionizable group content of ion conducting polymer membrane materials. Aimed at supporting the assessment of membrane stability and wear characteristics, performance is evaluated for attenuated total reflection Fourier transform infrared (ATR FT-IR) spectroscopy, confocal Raman microscopy, and ATR FT-IR microscopy using perfluorinated ionomer membrane standards. One set of ionomer standards contained a sulfonic acid ionizable group and the other a sulfonyl imide group. The average number of backbone tetrafluoroethylene (TFE) units separating the ionizable-group containing side chains was in the range of 7.2–2.1 (sulfonic acid set) and 10.5–4.6 (sulfonyl imide set). A poly(tetrafluoroethylene) (PTFE) sample was included as a blank, representing the limit of zero ionizable group (and maximum TFE) content. Calibration relationships were derived from area-normalized vibrational spectra. For all three methods, calibration models applied to independent spectral measurements of samples predicted the ratio of backbone TFE groups to ionizable groups in the repeat unit ( m) with a standard error of ≤ ±0.3. The confocal Raman and ATR FT-IR microscopy techniques achieved ideal blank responses and the lowest prediction errors, down to m ± 0.1 at the 90% confidence level. With its relative simplicity, low sample size requirements, and potential for quantitative micron-scale spatial mapping of the ionizable group content within a membrane, the approach has application to advancing materials development, including exploratory synthesis, durability and wear assessment, and in situ studies of membrane process.

Korzeniewski, Carol↗
NASA NTRS1976

Calculations of molecular ionization energies using a self-consistent-charge Hartree-Fock-Slater method

A numerical-variational method for performing self-consistent molecular calculations in the Hartree-Fock-Slater (HFS) model is presented. Molecular wavefunctions are expanded in terms of basis sets constructed from numerical HFS solutions of selected one-center atomlike problems. Binding energies and wavefunctions for the molecules are generated using a discrete variational method for a given molecular potential. In the self-consistent-charge (SCC) approximation to the complete self-consistent-field (SCF) method, results of a Mulliken population analysis of the molecular eigenfunctions are used in each iteration to produce 'atomic' occupation numbers. The simplest SCC potential is then obtained from overlapping spherical atomlike charge distributions. Molecular ionization energies are calculated using the transition-state procedure; results are given for CO, H2O, H2S, AlCl, InCl, and the Ni5O surface complex. Agreement between experimental and theoretical ionization energies for the free-molecule valence levels is generally within 1 eV. The simple SCC procedure gives a reasonably good approximation to the molecular potential, as shown by comparison with experiment, and with complete SCF calculations for CO, H2O, and H2S.

Rosen, A.↗
DOE OSTI2018

Characterization and Analysis of Paper Spray Ionization of Organic Compounds

Paper spray ionization has arisen relatively recently as a complement and alternative to electro- and nanospray ionization with silica capillaries. A majority of the work in the present literature focuses on the chemical aspect of paper spray. In order to study the physical and phenomenological facet of its implementation, we measured current and voltage distributions of Taylor cones. To study transport phenomena on filter paper, we addressed the behavior of large, sparingly soluble tetraalkylammonium ions, which are usually used as mobility standards, in paper spray. The variation of intensity with time of monomers and dimers of these ions was measured with a differential mobility analyzer and compared with that produced by contamination in the paper. At the same time, we evaluated the proficiency of different paper spray techniques for protein analysis using nano spray as a reference. Experiments suggest that Taylor cones in paper spray are subject to hysteresis, whereas transport phenomena in the porous substrate notably affects the ionization of the sample. Additionally, we observed that paper spray tends to favor lower charge states in proteins. .

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1978

A semiclassical approach to collisional ionization with application to the Ar-He system

A semiclassical approach based on the propagation of classical trajectories on potential surfaces analytically continued into the complex plane, together with a discretization procedure, has been developed for the problem of collisional ionization. Based on Franck-Condon considerations the formalism is reduced to that of the two-state approximation. Preionization loss and tunnelling beyond turning points have not been considered. Calculated partial ionization cross sections for the Ar-He system show good agreement with a fully quantum mechanical treatment.

Lam, K.-S.↗
DOE OSTI2016

Polarity effects and apparent ion recombination in microionization chambers

Purpose: Microchambers demonstrate anomalous voltage-dependent polarity effects. Existing polarity and ion recombination correction factors do not account for these effects. As a result, many commercial microchamber models do not meet the specification of a reference-class ionization chamber as defined by the American Association of Physicists in Medicine. The purpose of this investigation is to determine the cause of these voltage-dependent polarity effects. Methods: A series of microchamber prototypes were produced to isolate the source of the voltage-dependent polarity effects. Parameters including ionization-chamber collecting-volume size, stem and cable irradiation, chamber assembly, contaminants, high-Z materials, and individual chamber components were investigated. Measurements were performed with electrodes coated with graphite to isolate electrode conductivity. Chamber response was measured as the potential bias of the guard electrode was altered with respect to the collecting electrode, through the integration of additional power supplies. Ionization chamber models were also simulated using COMSOL Multiphysics software to investigate the effect of a potential difference between electrodes on electric field lines and collecting volume definition. Results: Investigations with microchamber prototypes demonstrated that the significant source of the voltage-dependent polarity effects was a potential difference between the guard and collecting electrodes of the chambers. The voltage-dependent polarity effects for each prototype were primarily isolated to either the guard or collecting electrode. Polarity effects were reduced by coating the isolated electrode with a conductive layer of graphite. Polarity effects were increased by introducing a potential difference between the electrodes. COMSOL simulations further demonstrated that for a given potential difference between electrodes, the collecting volume of the chamber changed as the applied voltage was altered, producing voltage-dependent polarity effects in the chamber response. Ionization chamber measurements and COMSOL simulations demonstrated an inverse relationship between the chamber collecting volume size and the severity of voltage-dependent polarity effects on chamber response. The effect of a given potential difference on chamber polarity effects was roughly ten times greater for microchambers as compared to Farmer-type chambers. Stem and cable irradiations, chamber assembly, contaminants, and high-Z materials were not found to be a significant source of the voltage-dependent polarity effects. Conclusions: A potential difference between the guard and collecting electrodes was found to be the primary source of the voltage-dependent polarity effects demonstrated by microchambers. For a given potential difference between electrodes, the relative change in the collecting volume is smaller for larger-volume chambers, illustrating why these polarity effects are not seen in larger-volume chambers with similar guard and collecting electrode designs. Thus, for small-volume chambers, it is necessary to reduce the potential difference between the guard and collecting electrodes in order to reduce polarity effects for reference dosimetry measurements.

60 APPLIED LIFE SCIENCES↗
NASA NTRS2004

The Effect of Salts on Electrospray Ionization of Amino Acids in the Negative Mode

The continued search for organics on Mars will require the development of simplified procedures for handling and processing of soil or rock core samples prior to analysis by onboard instrumentation. Extraction of certain organic molecules such as amino acids from rock and soil samples using a liquid solvent (H2O) has been shown to be more efficient (by approximately an order of magnitude) than heat extraction methods. As such, liquid extraction (using H2O) of amino acid molecules from rock cores or regolith material is a prime candidate for the required processing. In this scenario, electrospray ionization (ESI) of the liquid extract would be a natural choice for ionization of the analyte prior to interrogation by one of a variety of potential analytical separation techniques (mass spectroscopy, ion mobility spectroscopy, etc.). Aside from the obvious compatibility of ESI and liquid samples, ESI offers simplicity and a soft ionization capability. In order to demonstrate that liquid extraction and ESI can work as part of an in situ instrument on Mars, we must better understand and quantify the effect salts have on the ESI process. In the current work, we have endeavored to investigate the feasibility and limitations of negative mode ESI of Martian surface samples in the context of sample salt content using ion mobility spectroscopy (IMS).

H I Kim↗
DOE OSTI2018

Probing periodic potential of crystals via strong-field re-scattering

Strong-field ionization and re-scattering phenomena have been used to image angstrom-scale structures of isolated molecules in the gas phase. These methods typically make use of the anisotropic response of the participating molecular orbital. Recently, an anisotropic strong-field response has also been observed in high-order harmonic generation (HHG) from bulk crystals. In a (100) cut magnesium oxide crystal, extreme ultraviolet high-harmonics are found to depend strongly on the crystal structure and inter-atomic bonding. Here, we extend these measurements to other two important crystal orientations: (111) and (110). We find that HHG from these orientations is also strongly anisotropic. The underlying dynamics is understood using a real-space picture, where high-harmonics are produced via coherent collision of strong-field driven electrons from the atomic sites, including from the nearest neighbor atoms. We find that harmonic efficiency is enhanced when semi-classical electron trajectories connect to the concentrated valence charge distribution regions around the atomic cores. Similarly, the efficiency is suppressed when the trajectories miss the atomic cores. Furthermore, these results further support the real-space picture of HHG with implications for retrieving the periodic potential of the crystal, if not the wavefunctions in three-dimensions.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2016

The prevalence of gas outflows in type 2 AGNs

To constrain the nature and fraction of the ionized gas outflows in active galactic nuclei (AGNs), we perform a detailed analysis on gas kinematics as manifested by the velocity dispersion and shift of the [O III] λ5007 emission line, using a large sample of ∼39,000 type 2 AGNs at z < 0.3. First, we confirm a broad correlation between [O III] and stellar velocity dispersions, indicating that the bulge gravitational potential plays a main role in determining the [O III] kinematics. However, [O III] velocity dispersion is on average larger than stellar velocity dispersion by a factor of 1.3–1.4 for AGNs with double Gaussian [O III], suggesting that the non-gravitational component, i.e., outflows, is almost comparable to the gravitational component. Second, the increase of the [O III] velocity dispersion (after normalized by stellar velocity dispersion) with both AGN luminosity and Eddington ratio suggests that non-gravitational kinematics are clearly linked to AGN accretion. The distribution in the [O III] velocity–velocity dispersion diagram dramatically expands toward large values with increasing AGN luminosity, implying that the launching velocity of gas outflows increases with AGN luminosity. Third, the majority of luminous AGNs present the non-gravitational kinematics in the [O III] profile. These results suggest that ionized gas outflows are prevalent among type 2 AGNs. On the other hand, we find no strong trend of the [O III] kinematics with radio luminosity, once we remove the effect of the bulge gravitational potential, indicating that ionized gas outflows are not directly related to radio activity for the majority of type 2 AGNs.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Influence of the electrode gap separation on the pseudospark-sourced electron beam generation

Pseudospark-sourced electron beam is a self-focused intense electron beam which can propagate without any external focusing magnetic field. This electron beam can drive a beam-wave interaction directly or after being post-accelerated. It is especially suitable for terahertz radiation generation due to the ability of a pseudospark discharge to produce small size in the micron range and very high current density and bright electron beams. In this paper, a single-gap pseudospark discharge chamber has been built and tested with several electrode gap separations to explore the dependence of the pseudospark-sourced electron beam current on the discharge voltage and the electrode gap separation. Experimental results show that the beam pulses have similar pulse width and delay time from the distinct drop of the applied voltage for smaller electrode gap separations but longer delay time for the largest gap separation used in the experiment. It has been found that the electron beam only starts to occur when the charging voltage is above a certain value, which is defined as the starting voltage of the electron beam. The starting voltage is different for different electrode gap separations and decreases with increasing electrode gap separation in our pseudospark discharge configuration. The electron beam current increases with the increasing discharge voltage following two tendencies. Under the same discharge voltage, the configuration with the larger electrode gap separation will generate higher electron beam current. When the discharge voltage is higher than 10 kV, the beam current generated at the electrode gap separation of 17.0 mm, is much higher than that generated at smaller gap separations. The ionization of the neutral gas in the main gap is inferred to contribute more to the current increase with increasing electrode gap separation.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Hydrodynamic model of a dielectric-barrier discharge in pure chlorine

A one-dimensional hydrodynamic model of a dielectric-barrier discharge (DBD) in pure chlorine is developed, and the properties of the discharge are modeled. The discharge is excited in an 8-mm-long discharge gap between 2-mm-thick dielectric quartz layers covering metal electrodes. The DBD spatiotemporal characteristics at gas pressures of 15–100 Torr are modeled for the case in which a 100-kHz harmonic voltage with an amplitude of 8 kV is applied to the electrodes. The average power density deposited in the discharge over one voltage period is 2.5–5.8 W/cm{sup 3}. It is shown that ions and electrons absorb about 95 and 5% of the discharge power, respectively. In this case, from 67 to 97% of the power absorbed by electrons is spent on the dissociation and ionization of Cl{sub 2} molecules. Two phases can be distinguished in the discharge dynamics: the active (multispike) phase, which follows the breakdown of the discharge gap, and the passive phase. The active phase is characterized by the presence of multiple current spikes, a relatively high current, small surface charge density on the dielectrics, and large voltage drop across the discharge gap. The passive phase (with no current spikes) is characterized by a low current, large surface charge density on the dielectrics, and small voltage drop across the discharge gap. The peak current density in the spikes at all pressures is about 4 mA/cm{sup 2}. In the multispike phase, there are distinct space charge sheaths with thicknesses of 1.5–1.8 mm and a mean electron energy of 4.3–7 eV and the central region of quasineutral plasma with a weak electric field and a mean electron energy of 0.8–3 eV. The degree of ionization of chlorine molecules in the discharge is ~0.02% at a pressure of 15 Torr and ~0.01% at 100 Torr. The DBD plasma is electronegative due to the fast attachment of electrons to chlorine atoms: e + Cl{sub 2} → Cl + Cl{sup –}. The most abundant charged particles are Cl{sub 2}{sup +} and Cl{sup −} ions, and the degree of ionization during current spikes in the active phase is (4.1–5.5) × 10{sup –7}. The mechanism of discharge sustainment is analyzed. The appearance of a series of current spikes in the active phase of the discharge is explained.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Spatially resolved absolute quantitation in thin tissue by mass spectrometry

Mass spectrometry (MS) has become the de facto tool for routine quantitative analysis of biomolecules. MS is increasingly being used to reveal the spatial distribution of proteins, metabolites, and pharmaceuticals in tissue and interest in this area has led to a number of novel spatially resolved MS technologies. Most spatially resolved MS measurements are qualitative in nature due to a myriad of potential biases, such as sample heterogeneity, sampling artifacts, and ionization effects. As applications of spatially resolved MS in the pharmacological and clinical fields increase, demand has become high for quantitative MS imaging and profiling data. As a result, several varied technologies now exist that provide differing levels of spatial and quantitative information. Furthermore, this review provides an overview of MS profiling and imaging technologies that have demonstrated quantitative analysis from tissue. Focus is given on the fundamental processes affecting quantitative analysis in an array of MS imaging and profiling technologies and methods to address these biases.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗