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Results for “ATOMIC IONS”

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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Broadening of the Interplanetary Helium Cone Structure Due to Elastic Collisions of LISM Helium Atoms with Solar Wind Ions

Neutral interstellar particles penetrating into the heliosphere, besides being subject there to specific loss processes, suffer elastic collisions with KeV-solar wind ions. The momentum transfer to the neutrals connected with these collisions leads to a loss of angular momentum with respect to the Sun and to a fractional compensation of the effective solar gravity. The dynamical particle trajectories hence are changed into non-Keplerians leading to density and temperature distributions differing from those calculated in the past. This is found from a solution of the Boltzmann equation that linearizes the effect of this additional force. It is shown that the HeI-584A resonance glow of the heliospheric helium cone lead to substantially lower interstellar helium temperatures if re-interpreted on the basis of this revised theory. These temperatures now seem to be in accordance with the derived temperatures for interstellar hydrogen.

Fahr, H. J.↗
DOE OSTI2025

Deep potential molecular dynamics simulations of ion-enhanced etching of silicon by atomic chlorine

The continued development of plasma-assisted processing techniques requires a fundamental understanding of plasma-surface interactions. Molecular dynamics (MD) simulations have been employed to complement experimental studies and better understand the properties of such systems. Recently, machine learning (ML) methods have enabled the development of ab initio-based interatomic potentials, which can be generalized to complex combinations of multiple atom types. In this work, we use ML potentials developed using the Deep Potential Molecular Dynamics (DeepMD) framework to provide a model of ion-enhanced etching of Si by Cl atoms. We demonstrate the importance of proper selection of the training data set to the accuracy of the DeepMD model and compare our results to MD results using empirical potentials, as well as to experimental measurements. Exposure of undoped Si at 300 K to thermal Cl atoms yields a steady-state Cl coverage of 1.25 monolayers, which is slightly lower than the value obtained in previous experimental studies. Predictions of Si etch yields by simultaneous Cl atom and Ar + ion impacts as a function of ion energy, neutral to ion flux ratio, and angle of incidence of the ions are in reasonably good agreement with classical MD results and experimental measurements. Finally, etch yields and SiCl x mixed layer thicknesses during simultaneous bombardment of the Si(100) surface by Cl atoms and Cl + ions are in good agreement with experimental data. In conclusion, the present work is a necessary condition for the extension of the DeepMD procedure to more complex systems of interest in plasma-surface interactions.

Artificial neural networks↗
NASA NTRS2002

Laboratory Measurements of Charge Transfer on Atomic Hydrogen at Thermal Energies

We describe our ongoing program to measure velocity dependent charge transfer (CT) cross sections for selected ions on atomic hydrogen using the ion-aloin merged-beams apparatus at Oak Ridge Natioiial Laboralory. Our focus is on those ions for which CT plays an important role in determining the ionization structure, line emis sion, and thermal structure of observed cosmic photoionized plasmas.

Havener, C. C.↗
NASA NTRS1985

Empirical model of the composition of the Venus ionosphere Repeatable characteristics and key features not modeled

In-situ measurements of positive ion composition of the ionosphere of Venus are combined in an empirical model which is a key element for the Venus International Reference Atmosphere (VIRA) model. The ion data are obtained from the Pioneer Venus Orbiter Ion Mass Spectrometer (OIMS) which obtained daily measurements beginning in December 1978 and extending to July 1980 when the uncontrolled rise of satellite periapsis height precluded further measurements in the main body of the ionosphere. For this period, measurements of 12 ion species are sorted into altitude and local time bins with altitude extending from 150 to 1000 km. The model results exhibit the appreciable nightside ionosphere found at Venus, the dominance of atomic oxygen ions in the dayside upper ionosphere and the increase in prominence of atomic oxygen and deuterium ions on the nightside. Short term variations, such as the abrupt changes observed in the ionopause, cannot be represented in the model.

Taylor, H. A., Jr.↗
DOE OSTI2025

Half-life determination of heavy ions in a storage ring considering feeding and depleting background processes

Heavy-ion storage rings have relatively large momentum acceptance which allows for multiple ion species to circulate at the same time. This needs to be considered in radioactive decay measurements of highly charged ions, where atomic charge exchange reactions can significantly alter the intensities of parent and daughter ions. In this study, we investigate this effect using the decay curves of ion numbers in the recent 205 Tl 81+ bound-state beta decay experiment conducted using the Experimental Storage Ring at GSI Darmstadt. To understand the intricate dynamics of ion numbers, we present a set of differential equations that account for various atomic and nuclear reaction processes—bound state beta decay, atomic electron recombination and capture, and electron ionization. By incorporating appropriate boundary conditions, we develop a set of differential equations that accurately simulate the decay curves of various simultaneously stored ions in the storage ring: 205 Tl 81+ , 205 Pb 81+ , 205 Pb 82+ , 200 Hg 79+ , and 200 Hg 80+ . Through a quantitative comparison between simulations and experimental data, we provide insights into the detailed reaction mechanisms governing stored heavy ions within the storage ring. Our approach effectively models charge-changing processes, reduces the complexity of the experimental setup, and provides a simpler method for measuring the decay half-lives of highly charged ions in storage rings.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Cluster Expansion Analysis of Atomic Order in Li-Ion Battery Cathode Material LiCo y Ni 1-y O 2

A modified cluster-expansion treatment was developed recently to analyze atomic order in LiCo y Ni 1-y O 2 , a model cathode material for Li-ion batteries. In this treatment, referred to as a “spin-atom” cluster expansion, the occupant of a lattice site is identified by its spin state as well as its atomic species. Further, Effective Cluster Interaction (ECI) coefficients are derived from a large training data set (i.e., the set of atomic arrangements for which DFT calculations are performed) which is filtered by an anomaly detection algorithm to eliminate poorly converged DFT calculations. The cluster expansion incorporates Li-Ni (LN) exchange as well as intralayer Co-Ni (CN) exchange. Monte Carlo simulations based on the cluster expansion were applied to the Ni-rich part of the phase diagram. The simulations predict a miscibility gap between y = 0.05 and y = 0.65.

25 ENERGY STORAGE↗
NASA NTRS1980

Heavy ions in Jupiter's environment

The extended atmosphere of the Jupiter system consists of atoms and ions of heavy elements. This material originates on the satellite Io. Energy is lost from the thermal plasma in collisionally excited optical and ultraviolet emission. The juxtaposition of Earth and spacecraft measurements provide insight concerning the underlying processes of particle transport and energy supply.

Brown, R. A.↗
DOE OSTI2024

Laterally Modulating Carrier Concentration by Ion Irradiation in CdO Thin Films for Mid‐IR Plasmonics

This report demonstrates tunable carrier densities in CdO thin films through local ion irradiation, providing lateral control of mid‐IR optical properties. Ion‐solid interactions produce donor‐like defects that boost electron concentrations from the practical minimum of 2.5 × 10 19 cm −3 to a maximum of 2.5 × 10 20 cm −3 by metered ion exposure. This range is achieved using He, N, Ar, or Au ions at 1–2.8 MeV; when normalized by displacements per atom, all ion species produce comparable results. Since CdO is well‐described by the Drude model, irradiation‐tuned carrier densities directly alter the infrared dielectric function, and in turn, mid‐infrared optical properties. Further, it is demonstrated that by combining irradiation with traditional lithography, CdO films expose to ions in the presence of 3‐µm thick, patterned photoresist exhibit lateral carrier density profiles with ≈400‐nm resolution. Scanning near‐field optical microscopy reveals sharp optical interfaces with almost no companion contrast in surface morphology, microstructure, or crystallinity. Finally, CdO lateral homostructures supporting surface plasmon polaritons (SPPs) are demonstrated whose dispersion relation can be tuned through periodic patterning in a monolithic platform by simple nanofabrication. Numerical simulations show these polaritons result from strong coupling between excitations at CdO plasma frequencies and SPPs supported by the platinum substrate.

cadmium oxide↗
NASA NTRS1986

Apparatus for producing diamond-like carbon flakes

A vacuum arc from a spot at the face of a graphite cathode to a graphite anode produces a beam of carbon ions and atoms. A carbon coating from this beam is deposited on an ion beam sputtered target to produce diamond-like carbon flakes. A graphite tube encloses the cathode, and electrical isolation is provided by an insulating sleeve. The tube forces the vacuum arc spot to be confined to the surface on the outermost end of the cathode. Without the tube the arc spot will wander to the side of the cathode. This spot movement results in low rates of carbon deposition, and the properties of the deposited flakes are more graphite-like than diamond-like.

Banks, Bruce A.↗
NASA NTRS1989

Radiation of hot atomic hydrogen

A nonlinear collisional-radiative model for the determination of nonequilibrium production of electrons, ions, excited atoms, and spectral and continuum line intensities in stationary partially-ionized atomic hydrogen is presented. Transport of radiation is included by coupling the rate equations for production of the electrons and excited atoms with the radiation escape factors which are not constant but depend on plasma conditions.

Kunc, J. A.↗
NASA NTRS1994

The chemistry of hydrocarbon ions in the Jovian ionosphere

We have modeled the chemistry of hydrocarbon ions in the jovian ionosphere. We find that a layer of hydrocarbon ions is formed in the altitude range 300-400 km above the ammonia cloud tops, due largely to direct ionization of hydrocarbons by photons in the wings of the H2 absorption lines in the 912- to 1100-A region that penetrate to below the methane homopause. We have explicitly included in the model 156 ion-neutral reactions involving hydrocaron ions with up to two carbon atoms. Larger hydrocarbon ions are included as two pseudoions, C3Hn(+) and C4Hn(+). The model shows that 15 reactions of H(+), CH3(+), CH5(+), C2H3(+), C2H5(+), and C2H6(+) with hydrocarbon neutrals are the major processes that are responsible for the production and growth of C1-, C2- and C3- or C4-ions in the hydrocarbon ion layer. The model also shows that ions initially produced in the hydrocarbon ion layer are converted into hydrocarbon ions with more than two carbon atoms with very little loss by recombination. It is likely that successive hydrocarbon ion-neutral reactions continue to produce even larger hydrocarbon ions, so the terminal ions probably have more than three or four carbon atoms. In the auroral regions, the chemistry of hydrocarbon ions may modify the densities of neutral hydrocarbons, especially C2H2 in the upper mesosphere, and may play a major role in the production of polar haze particles.

Kim, Y. H.↗
NASA NTRS1981

Heavy ions in Jupiter's environment

The extended atmosphere of the Jupiter system consists of heavy-element atoms and ions. This material originates on the satellite Io. Energy is lost from the thermal plasma in collisionally-excited optical and ultraviolet emission. The juxtaposition of earth and spacecraft measurements provide insight concerning the underlying processes of particle transport and energy supply.

Brown, R. A.↗
DOE OSTI2025

Correlated transmission electron microscopy and atom probe tomography characterization of ion irradiated Ni-based alloy Hastelloy N

Ion irradiation of Hastelloy N was conducted to better characterize the effects of irradiation on Hastelloy N using modern tools compared to studies done in the 1950s. The 2 MeV Ni + ion irradiation at 600 °C of Hastelloy N has been investigated using atom probe tomography, transmission electron microscopy and energy dispersive spectroscopy. Irradiation is found to promote formation of nanoscale M 2 C carbides over the thermodynamically favored M 6 C. Segregation of Si to dislocation loops and grain boundaries was also evident and may have assisted in formation of M 2 C. These microstructural changes result in a 20 % hardness increase caused by irradiation alone. These observations are useful in the design of new materials better suited for the harsh environment of a molten salt reactor.

Atom probe tomography↗