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At least 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Partially Ionized Plasma Physics and Technological Applications

Partially ionized plasma physics has attracted increased attention recently due to numerous technological applications made possible by the increased sophistication of computer modelling, the depth of the theoretical analysis, and the technological applications to a vast field of manufacturing for computer components. Partially ionized plasma is characterized by a significant presence of neutral particles in contrast to the fully ionized plasma. The theoretical analysis is based upon solutions of the kinetic Boltzmann equation, yielding the non-Maxwellian electron energy distribution function (EEDF), thereby emphasizing the difference with a fully ionized plasma. The impact of the effect on discharges in inert and molecular gases is described in detail, yielding the complex nonlinear phenomena resulting in plasma selforganization. A few examples of such phenomena are given, including the non-monotonic EEDFs in the discharge afterglow in a mixture of argon with the molecular gas NF3; the explosive generation of cold electron populations in capacitive discharges, hysteresis of EEDF in inductively coupled plasmas. Recently, highly advanced computer codes were developed in order to address the outstanding challenges in plasma technology. These developments are briefly described in general terms.

non-Maxwellian electron energy distribution functi↗
DOE OSTI2016

HEATING OF THE WARM IONIZED MEDIUM BY LOW-ENERGY COSMIC RAYS

In light of evidence for a high ionization rate due to low-energy cosmic rays (LECR) in diffuse molecular gas in the solar neighborhood, we evaluate their heat input to the warm ionized medium (WIM). LECR are much more effective at heating plasma than they are at heating neutrals. We show that the upper end of the measured ionization rates corresponds to a local LECR heating rate sufficient to maintain the WIM against radiative cooling, independent of the nature of the ionizing particles or the detailed shape of their spectrum. Elsewhere in the Galaxy the LECR heating rates may be higher than those measured locally. In particular, higher fluxes of LECR have been suggested for the inner Galactic disk, based on the observed hard X-ray emission, with correspondingly larger heating rates implied for the WIM. We conclude that LECR play an important and perhaps dominant role in the thermal balance of the WIM.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

The connection between reddening, gas covering fraction, and the escape of ionizing radiation at high redshift

Using a large sample of spectroscopically confirmed z∼3 galaxies, we establish an empirical relationship between reddening (E(B−V)), neutral gas covering fraction (f{sub cov}(H I)), and the escape of ionizing (Lyman continuum, LyC) photons. Our sample includes 933 galaxies at z∼3,121 of which have deep spectroscopic observations (≳7 hr) at 850≲λ{sub rest}≲1300 Å with the Low Resolution Imaging Spectrograph on Keck. The high covering fraction of outflowing optically thick H I indicated by the composite spectra of these galaxies implies that photoelectric absorption, rather than dust attenuation, dominates the depletion of LyC photons. By modeling the composite spectra as the combination of an unattenuated stellar spectrum including nebular continuum emission with one that is absorbed by H I and reddened by a line-of-sight extinction, we derive an empirical relationship between E(B−V) and f{sub cov}(H I). Galaxies with redder UV continua have larger covering fractions of H I characterized by higher line-of-sight extinctions. We develop a model which connects the ionizing escape fraction with E(B−V), and which may be used to estimate the ionizing escape fraction for an ensemble of galaxies. Alternatively, direct measurements of the escape fraction for our sample allow us to constrain the intrinsic LyC-to-UV flux density ratio to be 〈S(900 A-ring )/S(1500 A-ring )〉{sub int}≳0.20, a value that favors stellar population models that include weaker stellar winds, a flatter initial mass function, and/or binary evolution. Last, we demonstrate how the framework discussed here may be used to assess the pathways by which ionizing radiation escapes from high-redshift galaxies.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Turbulent dynamo in a conducting fluid and a partially ionized gas

By following the Kazantsev theory and taking into account both microscopic and turbulent diffusion of magnetic fields, we develop a unified treatment of the kinematic and nonlinear stages of a turbulent dynamo process, and we study the dynamo process for a full range of magnetic Prandtl number P {sub m} and ionization fractions. We find a striking similarity between the dependence of dynamo behavior on P {sub m} in a conducting fluid and R (a function of ionization fraction) in a partially ionized gas. In a weakly ionized medium, the kinematic stage is largely extended, including not only exponential growth but a new regime of dynamo characterized by a linear-in-time growth of magnetic field strength, and the resulting magnetic energy is much higher than the kinetic energy carried by viscous-scale eddies. Unlike the kinematic stage, the subsequent nonlinear stage is unaffected by microscopic diffusion processes and has a universal linear-in-time growth of magnetic energy with the growth rate as a constant fraction 3/38 of the turbulent energy transfer rate, showing good agreement with earlier numerical results. Applying the analysis to the first stars and galaxies, we find that the kinematic stage is able to generate a field strength only an order of magnitude smaller than the final saturation value. But the generation of large-scale magnetic fields can only be accounted for by the relatively inefficient nonlinear stage and requires longer time than the free-fall time. It suggests that magnetic fields may not have played a dynamically important role during the formation of the first stars.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

The highly ionized circumgalactic medium is kinematically uniform around galaxies

The circumgalactic medium (CGM) traced by O vi λλ1031,1037 doublet absorption has been found to concentrate along the projected major and minor axes of the host galaxies. This suggests that O vi traces accreting and outflowing gas, respectively, which are key components of the baryon cycle of galaxies. We investigate this further by examining the kinematics of 29 O vi absorbers associated with galaxies at 0.13<z{sub gal}<0.66 as a function of galaxy color, inclination, and azimuthal angle. Each galaxy was imaged with the Hubble Space Telescope (HST), and the absorption was detected in COS/HST spectra of nearby (D<200 kpc) background quasars. We use the pixel-velocity two-point correlation function to characterize the velocity spread of the absorbers, which is a method used previously for a sample of Mg ii absorber–galaxy pairs. The absorption velocity spread for O vi is more extended than Mg ii, which suggests that the two ions trace differing components of the CGM. Again, in contrast to Mg ii, the O vi absorption velocity spreads are similar regardless of galaxy color, inclination, and azimuthal angle. This indicates that the kinematics of the high-ionization gas is not strongly influenced by the current star formation activity in the galaxy. The kinematic homogeneity of O vi absorption and its tendency to be observed mainly along the projected galaxy major and minor axes is likely due to varying ionization conditions and gas densities about the galaxy. Gas in intermediate azimuthal angles may be ionized out of the O vi phase, possibly resulting in an azimuthal angle dependence of the distribution of gas in higher ionization states.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

HST/COS observations of ionized gas accretion at the disk-halo interface of M33

We report the detection of accreting ionized gas at the disk–halo interface of the nearby galaxy M33. We analyze Hubble Space Telescope/Cosmic Origins Spectrograph absorption-line spectra of seven ultraviolet-bright stars evenly distributed across the disk of M33. We find Si iv absorption components consistently redshifted relative to the bulk M33's ISM absorption along all the sightlines. The Si iv detection indicates an enriched, disk-wide, ionized gas inflow toward the disk. This inflow is most likely multi-phase as the redshifted components can also be observed in ions with lower ionization states (e.g., S ii, P ii, Fe ii, Si ii). Kinematic modeling of the inflow is consistent with an accreting layer at the disk–halo interface of M33, which has an accretion velocity of 110{sub −20}{sup +15} km s{sup −1} at a distance of 1.5{sub −1.0}{sup +1.0} kpc above the disk. The modeling indicates a total mass of ∼3.9 × 10{sup 7} M {sub ⊙} for the accreting material at the disk–halo interface on the near side of the M33 disk, with an accretion rate of ∼2.9 M {sub ⊙} yr{sup −1}. The high accretion rate and the level of metal enrichment suggest the inflow is likely to be the fallback of M33 gas from a galactic fountain and/or the gas pulled loosed during a close interaction between M31 and M33. Our study of M33 is the first to unambiguously reveal the existence of a disk-wide, ionized gas inflow beyond the Milky Way, providing a better understanding of gas accretion in the vicinity of a galaxy disk.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Multi-fluid Approach to High-frequency Waves in Plasmas. II. Small-amplitude Regime in Partially Ionized Media

The presence of neutral species in a plasma has been shown to greatly affect the properties of magnetohydrodynamic waves. For instance, the interaction between ions and neutrals through momentum transfer collisions causes the damping of Alfvén waves and alters their oscillation frequency and phase speed. When the collision frequencies are larger than the frequency of the waves, single-fluid magnetohydrodynamic approximations can accurately describe the effects of partial ionization, since there is a strong coupling between the various species. However, at higher frequencies, the single-fluid models are not applicable and more complex approaches are required. Here, we use a five-fluid model with three ionized and two neutral components, which takes into consideration Hall’s current and Ohm’s diffusion in addition to the friction due to collisions between different species. We apply our model to plasmas composed of hydrogen and helium, and allow the ionization degree to be arbitrary. By analyzing the corresponding dispersion relation and numerical simulations, we study the properties of small-amplitude perturbations. We discuss the effect of momentum transfer collisions on the ion-cyclotron resonances and compare the importance of magnetic resistivity, and ion–neutral and ion–ion collisions on the wave damping at various frequency ranges. Applications to partially ionized plasmas of the solar atmosphere are performed.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Which Stars Are Ionizing the Orion Nebula?

The common assumption that θ{sup 1} Ori C is the dominant ionizing source for the Orion Nebula is critically examined. This assumption underlies much of the existing analysis of the nebula. In this paper we establish through comparison of the relative strengths of emission lines with expectations from Cloudy models and through the direction of the bright edges of proplyds that θ{sup 2} Ori A, which lies beyond the Bright Bar, also plays an important role. θ{sup 1} Ori C does dominate ionization in the inner part of the Orion Nebula, but outside of the Bright Bar as far as the southeast boundary of the Extended Orion Nebula, θ{sup 2} Ori A is the dominant source. In addition to identifying the ionizing star in sample regions, we were able to locate those portions of the nebula in 3D. This analysis illustrates the power of MUSE spectral imaging observations to identify sources of ionization in extended regions.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

A Theoretical Study of the Outer Layers of Eight Kepler F-stars: The Relevance of Ionization Processes

We have analyzed the theoretical model envelopes of eight Kepler F-stars by computing the phase shift of the acoustic waves, α(ω), and its related function, β(ω). The latter is shown to be a powerful probe of the external stellar layers since it is particularly sensitive to the partial ionization zones located in these upper layers. We found that these theoretical envelopes can be organized into two groups, each of which is characterized by a distinct β(ω) shape that we show to reflect the differences related to the magnitudes of ionization processes. Since β(ω) can also be determined from the experimental frequencies, we compared our theoretical results with the observable β(ω). Using the function β(ω), and with the purpose of quantifying the magnitude of the ionization processes occurring in the outer layers of these stars, we define two indexes, Δβ{sub 1} and Δβ{sub 2}. These indexes allow us to connect the microphysics of the interior of the star with macroscopic observable characteristics. Motivated by the distinct magnetic activity behaviors of F-stars, we studied the relation between the star’s rotation period and these indexes. We found a trend, in the form of a power-law dependence, that favors the idea that ionization is acting as an underlying mechanism, which is crucial for understanding the relation between rotation and magnetism and even observational features such as the Kraft break.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1996

Clusters of DNA induced by ionizing radiation: formation of short DNA fragments. I. Theoretical modeling

We have developed a general theoretical model for the interaction of ionizing radiation with chromatin. Chromatin is modeled as a 30-nm-diameter solenoidal fiber comprised of 20 turns of nucleosomes, 6 nucleosomes per turn. Charged-particle tracks are modeled by partitioning the energy deposition between primary track core, resulting from glancing collisions with 100 eV or less per event, and delta rays due to knock-on collisions involving energy transfers >100 eV. A Monte Carlo simulation incorporates damages due to the following molecular mechanisms: (1) ionization of water molecules leading to the formation of OH, H, eaq, etc.; (2) OH attack on sugar molecules leading to strand breaks: (3) OH attack on bases; (4) direct ionization of the sugar molecules leading to strand breaks; (5) direct ionization of the bases. Our calculations predict significant clustering of damage both locally, over regions up to 40 bp and over regions extending to several kilobase pairs. A characteristic feature of the regional damage predicted by our model is the production of short fragments of DNA associated with multiple nearby strand breaks. The shapes of the spectra of DNA fragment lengths depend on the symmetries or approximate symmetries of the chromatin structure. Such fragments have subsequently been detected experimentally and are reported in an accompanying paper (B. Rydberg, Radiat, Res. 145, 200-209, 1996) after exposure to both high- and low-LET radiation. The overall measured yields agree well quantitatively with the theoretical predictions. Our theoretical results predict the existence of a strong peak at about 85 bp, which represents the revolution period about the nucleosome. Other peaks at multiples of about 1,000 bp correspond to the periodicity of the particular solenoid model of chromatin used in these calculations. Theoretical results in combination with experimental data on fragmentation spectra may help determine the consensus or average structure of the chromatin fibers in mammalian DNA.

Non-NASA Center↗
DOE OSTI2015

Investigation of the initial and volume recombination losses in gamma versatile cylindrical ionization chamber VGIC developed for gamma ray dosimetry

A versatile Gamma ionization chambers are used for flow control in systems with gamma nuclear reactors and reprocessing plants in and monitoring atmosphere around these facilities, this in order to protect staff. In the Laboratory Detection and Measures (LDM) Division for Study and Development of Nuclear Instrumentation (DSDNI) of CRNB, we designed, developed and characterized a versatile gamma ionization chamber (VGIC) to study experimentally its characteristics according to the geometry of the electrodes, the volume and pressure of the filler gas for the design of a gamma sealed chamber. The tests were conducted under the IEC (International Electro-technical Commission). In this paper, we present the results obtained in the various nuclear tests for characterization and calibration that we have made on the ionization chamber gamma VGIC prototype developed at our Department. To do this, three irradiators were operated at the Laboratory Calibration (SSDL) of the Department of Medical Physics Nuclear Research Center of Algiers (CRNA). Irradiator intensive gamma ({sup 60}Co: 1.25 MeV), one medium intensity gamma ({sup 137}Cs: 0.662 MeV) and 3rd low intensity ({sup 60}Co). Saturation curves and linearity were identified and the operating range and the sensitivity of the chamber have been deducted. The (I,V) characteristics of the chamber filled, with argon gas at 3 bar (0.3 M pa) pressure, for gamma ray irradiator sources were studied. To do so, the chamber was irradiated with gamma rays using different numbers of gamma sources (i.e. Up to 5). The plateau region is reached above 200 V and the detector operating voltage is found to be 600 V. It is observed that in the plateau region the slope is constant with an increase in the exposure rate. The (1/I, 1/V) and (I, l/V{sup 2}) characteristic curves reveal the presence of the initial and volume recombination losses. The volume recombination losses are found to be smaller than the initial recombination losses. Finally, in order to strengthen our results, we performed in the same conditions, a comparative characterization with another ionization gamma chamber type reference LND 504 (USA). (authors)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2020

Raman spectroscopy coupled with ambient ionization mass spectrometry: A forensic laboratory investigation into rapid and simple dual instrumental analysis techniques

We present a laboratory experiment, developed around a pair of instrumental analysis techniques, Raman spectroscopy and ambient ionization mass spectrometry (MS), conducted by senior chemistry undergraduate students for bulk analysis of over-the-counter drugs using benchtop versions of the two instruments, as well as trace analysis of illicit drugs utilizing the corresponding portable instruments. The identification and confirmation of seized drugs is a routine operation in forensic laboratories that can be simplified using these two instrumental techniques in tandem. Bulk samples are readily analyzed using conventional Raman spectroscopy followed by paper cone spray ionization (PCSI) MS, while trace analysis is allowed by a simple single-substrate dual-analyzer method using surface enhanced Raman spectroscopy (SERS) from paper followed by paper spray ionization (PSI) MS. The introduction of these novel strategies to the students exposed them to potential career paths in forensic science by means of a hands-on experience that provided fundamental knowledge about this set of analytical methods, including intercomparisons of their performance, as well as practical issues like costs, regulations and databases. The use of portable instrumentation represents an additional learning experience for the students, considering that it is cutting-edge technology that is just now being transferred from academic to industrial labs and that it allows a valuable discussion of the advantages and disadvantages of bringing the laboratory to the field.

47 OTHER INSTRUMENTATION↗
DOE OSTI2021

Enhanced ionization of counter-rotating electrons via doorway states in ultrashort circularly polarized laser pulses

We have performed single-active-electron numerical calculations of neon- and argonlike atoms interacting with short, intense, circularly polarized laser pulses at wavelengths between 10 nm and 1000 nm. Our results reveal a surprisingly large change by a factor of about 100 in the ionization ratio of electrons in initial states counter-rotating with respect to the field over corotating electrons in the previously unexplored intermediate few-photon ionization regime. The physical mechanism behind this observation is related to resonant enhanced ionization via states close in energy to the initial states. These doorway states are accessible exclusively from the initial state for counter-rotating electrons within the respective wavelength regime. Furthermore, the results may open a new route for controlling the generation of spin-polarized electrons by ultrashort laser pulses.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2021

Mass Spectrometry Imaging of Bio‐oligomer Polydispersity in Plant Tissues by Laser Desorption Ionization from Silicon Nanopost Arrays

Abstract Mass spectrometry imaging (MSI) enables simultaneous spatial mapping for diverse molecules in biological tissues. Matrix‐assisted laser desorption ionization (MALDI) mass spectrometry (MS) has been a mainstream MSI method for a wide range of biomolecules. However, MALDI‐MSI of biological homopolymers used for energy storage and molecular feedstock is limited by, e.g., preferential ionization for certain molecular classes. Matrix‐free nanophotonic ionization from silicon nanopost arrays (NAPAs) is an emerging laser desorption ionization (LDI) platform with ultra‐trace sensitivity and molecular imaging capabilities. Here, we show complementary analysis and MSI of polyhydroxybutyric acid (PHB), polyglutamic acid (PGA), and polysaccharide oligomers in soybean root nodule sections by NAPA‐LDI and MALDI. For PHB, number and weight average molar mass, polydispersity, and oligomer size distributions across the tissue section and in regions of interest were characterized by NAPA‐LDI‐MSI.

Samarah, Laith Z.↗
DOE OSTI2018

Integration of paper spray ionization high‐field asymmetric waveform ion mobility spectrometry for forensic applications

Rationale Paper spray ionization (PSI) is an attractive ambient ionization source for mass spectrometry (MS) since it allows the combination of surface sampling and ionization. The minimal sample preparation inherent in this approach greatly reduces the time needed for analysis. However, the ions generated from interfering compounds in the sample and the paper substrate may interfere with the analyte ions. Therefore, the integration of PSI with high‐field asymmetric ion mobility spectrometry (FAIMS) is of significant interest since it should reduce the background ions entering the mass analyzer without complicating the analysis or increasing analysis time. Here we demonstrate the integration of PSI with FAIMS/MS and its potential for analysis of samples of forensic interest. Methods In this work, the parameters that can influence the integration, including sampling and ionization by paper spray, the FAIMS separation of analytes from each other and background interferences, and the length of time that a usable signal can be observed for explosives on paper, were evaluated with the integrated system. Results In the negative ion analysis of 2,4,6‐trinitrotoluene (TNT), pentaerythritol tetranitrate (PETN), octahydro‐1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocine (HMX), and 1,3,5‐trinitroperhydro‐1,3,5‐triazine (RDX), amounts as low as 1 ng on paper were readily observed. The successful positive ion separation of a set of illicit drugs including heroin, methamphetamine, and cocaine was also achieved. In addition, the positive ion analysis of the chemical warfare agent simulants dimethyl methylphosphonate (DMMP) and diisopropyl methylphosphonate (DIMP) was evaluated. Conclusions The integration of PSI‐FAIMS/MS was demonstrated for the analyses of explosives in negative ion mode and for illicit drugs and CW simulants in positive mode. Paper background ions that could interfere with these analyses were separated by FAIMS. The compensation voltage of an ion obtained by FAIMS provided an additional identification parameter to be combined with the mass spectrum for each analyte.

Tsai, Chia‐Wei↗
DOE OSTI2025

Multireference Equation-of-Motion Driven Similarity Renormalization Group: Theoretical Foundations and Applications to Ionized States

We present a formulation and implementation of an equation-of-motion (EOM) extension of the multireference driven similarity renormalization group (MR-DSRG) formalism for ionization potentials (IP-EOM-DSRG). The IP-EOM-DSRG formalism results in a Hermitian generalized eigenvalue problem, delivering accurate ionization potentials for strongly correlated systems. The EOM step scales as O(N 5 ) with the basis set size N, allowing for efficient calculation of spectroscopic properties, such as transition energies and intensities. The IP-EOM-DSRG formalism is combined with three truncation schemes of the parent MR-DSRG theory: an iterative nonperturbative method with up to two-body excitations [MR-LDSRG(2)] and second- and third-order perturbative approximations [DSRG-MRPT2/3]. We benchmark these variants by computing (1) the vertical valence ionization potentials of a series of small molecules at both equilibrium and stretched geometries; (2) the spectroscopic constants of several low-lying electronic states of the OH, CN, N 2 + , and CO + radicals; and (3) the binding curves of low-lying electronic states of the CN radical. A comparison with experimental data and theoretical results shows that all three IP-EOM-DSRG methods accurately reproduce the vertical ionization potentials and spectroscopic constants of these systems. Notably, the DSRG-MRPT3 and MR-LDSRG(2) versions outperform several state-of-the-art multireference methods of comparable or higher cost.

Hamiltonians↗
DOE OSTI2020

Efficient Intermolecular Energy Exchange and Soft-ionization of Water at Nanoplatelet Interfaces

X-ray, energetic photon and electron irradiation can ionize and electronically excite target atoms and molecules. These excitations undergo complicated relaxation and energy transfer processes that ultimately determine the manifold of system responses to the deposited excess energy. In weakly bound gas- and solution-phase samples, intermolecular Coulomb decay (ICD) and electron-transfer mediated decay (ETMD) can occur with neighboring atoms or molecules leading to efficient transfer of the excess energy to the surroundings. In ionic solids such as metal-oxides, intra- and inter-atomic Auger decay produces localized final states that lead to lattice damage and typically removal of cations from the substrate. The relative importance of Auger stimulated damage (ASD) versus ICD and ETMD in micro-solvated nanoparticle interfaces is not known. Though ASD is generally expected, essentially no lattice damage and very efficient ICD and ETMD resulting from ionization and electronic excitation of micro-solvated boehmite (AlOOH) nanoplatelets has been observed. Efficient energy transfer and soft ionization of interfacial molecules is likely a general phenomenon at gas-oxyhydroxide nanoparticle interfaces where the density of states of the ionized chemisorbed species significantly overlap the core hole states of the solid.

Jones, Brant M.↗
DOE OSTI2023

World’s strongest laser enables pressure-driven ionization

The degree of ionization inside giant planets and stars determines their material properties. In burning stars, ionization is controlled by temperature, whereas pressure-driven ionization is dominant in cooler objects. Finally, experiments creating the extreme conditions needed for pressure-driven ionization in the laboratory shed light on this complex process.

47 OTHER INSTRUMENTATION↗