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At least 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Noncollinear spin order, field-induced transitions, and short-range correlations in Cu 4 ⁢SO 4 ⁢(OH) 6

We report a comprehensive study of spin-$\frac{1}{2}$ quantum magnet brochantite, Cu 4 ⁢SO 4 ⁢(OH) 6 , combining high-field thermodynamic measurements, polarized neutron diffraction, inelastic neutron scattering, and nuclear magnetic resonance spectroscopy. Using bulk magnetization and specific heat measurements we construct the magnetic 𝐻−𝑇 phase diagram for magnetic fields applied along main crystallographic directions up to 24.1 T. Polarized neutron diffraction reveals a noncollinear magnetic ground state confined to the 𝑎⁢𝑏 plane. A field-induced transition is observed for magnetic fields in the 𝑎⁢𝑏 plane whose critical field and character evolve continuously with field direction in the 𝑎⁢𝑏 plane. While the transition for 𝐻 ∥ 𝑏 might be a spin-flop-like transition, the one for 𝐻 ∥ 𝑎 resembles the short-range correlated state above 𝑇 N , suggesting a magnetic configuration related to the quasi-two-dimensional correlations in the 𝑏⁢𝑐 planes. The experimental results demonstrate that the ground-state and field-induced phases cannot be explained by a simple XXZ model with a single dominant exchange interaction and that weaker interchain and anisotropic interactions have to be taken into account. Our work establishes brochantite as a low-symmetry Cu-based quantum magnet with noncollinear order and complex field-induced behavior.

Prokhnenko, Oleksandr [Helmholtz-Zentrum Berlin (H↗
NASA NTRS2011

Two Azimuthally Separated Regions of Cusp Ion Injection Observed via Energetic Neutral Atoms

The low-energy neutral atom (LENA) imager on the IMAGE spacecraft can detect energetic neutral atoms produced by ion injection into the cusp through a charge exchange with the Earth's hydrogen exosphere. We examined the occurrence of the LENA cusp signal during positive IMF B(sub z) in terms of the arrival direction and the IMF clock angle theta(sub CA). Results of statistical analyses show that the occurrence frequency is high on the postnoon side when theta(sub CA) is between approximately 20 degrees and approximately 50 degrees. This is ascribed to ion injection caused by cusp reconnection typical of positive IMF B(sub z). Our results also show that there is another situation of high occurrence frequency, which can be identified with theta(sub CA) of approximately 30 degrees to approximately 80 degrees. When theta(sub CA) is relatively large (60 degrees - 80 degrees), occurrence frequencies are high at relatively low latitudes over a wide extent spanning both prenoon and postnoon sectors. This feature suggests that the ion injection is caused by reconnection at the dayside magnetopause. Its postnoon side boundary shifts toward the prenoon as theta(sub CA) decreases. When theta(sub CA) is less than approximately 50 degrees, the high occurrence frequency exists well inside the prenoon sector, which is azimuthally separated from the postnoon region ascribed to cusp reconnection. The prenoon region, which is thought due to ion injection caused by dayside reconnection, may explain the recent report that proton aurora brightening occurs in the unanticipated prenoon sector of the northern high-latitude ionosphere for IMF B(sub y) greater than 0 and B(sub z) greater than 0.

Abe, M.↗
NASA NTRS1978

Rapid laser induced energy transfer in atomic systems

Analytical and experimental studies of the rapid transfer of stored populations from metastable states to selected target states of a different species are reported. Both laser-induced or laser-switched collision and laser-induced two-photon spontaneous emission are described. It is shown that the laser-induced collision method is particularly useful in the visible and UV spectral regions. It has applications in photochemistry, gas-phase kinetics, and in high-power, high-energy gas-phase lasers. The anti-Stokes source is useful in the VUV and soft X-ray spectral regions.

Harris, S. E.↗
DOE OSTI2025

Competition between mass-symmetric and asymmetric fission modes in 258 Md produced in the 4 He+ 254 Es reaction

Earlier studies of spontaneous fission of heavy actinides found that the fission-fragment mass distribution suddenly changes from predominantly asymmetric to symmetric, when the mass number of the fissioning nucleus becomes larger than A c = 257. We have measured for the first time fission-fragment mass and totalkinetic-energy (TKE) distributions of the excited compound nucleus 258 Md∗ (Z = 101), populated in the reaction 4 He + 254 Es, using the rare radioactive target isotope 254 Es with a short half-life, T1/2 = 275.7 d. The fission of 258 Md∗ can be interpreted as involving three fission modes: one mass-asymmetric and two mass-symmetric fission modes, the latter two are manifested by different TKE values. In this assumption, symmetric and asymmetric fission modes have nearly similar yields at the excitation energy of 15.0 MeV. The spectrum of 18.0 MeV can be explained as due to the increase of asymmetric fission mode.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS1995

Kinetic Energy Distribution of H(2p) Atoms from Dissociative Excitation of H2

The kinetic energy distribution of H(2p) atoms resulting from electron impact dissociation of H2 has been measured for the first time with uv spectroscopy. A high resolution uv spectrometer was used for the measurement of the H Lyman-alpha emission line profiles at 20 and 100 eV electron impact energies. Analysis of the deconvolved 100 eV line profile reveals the existence of a narrow line peak and a broad pedestal base. Slow H(2p) atoms with peak energy near 80 meV produce the peak profile, which is nearly independent of impact energy. The wings of H Lyman-alpha arise from dissociative excitation of a series of doubly excited Q(sub 1) and Q(sub 2) states, which define the core orbitals. The fast atom energy distribution peaks at 4 eV.

Ajello, Joseph M.↗
NASA NTRS2006

Comparison of Atomic Oxygen Erosion Yields of Materials at Various Energy and Impact Angles

The atomic oxygen erosion yields of various materials, measured in volume of material oxidized per incident atomic oxygen atom, are compared to the commonly accepted standard of Kapton H (DuPont) polyimide. The ratios of the erosion yield of Kapton H to the erosion yield of various materials are not consistent at different atomic oxygen energies. Although it is most convenient to use isotropic thermal energy RF plasma ashers to assess atomic oxygen durability, the results can be misleading because the relative erosion rates at thermal energies are not necessarily the same as low Earth orbital (LEO) energies of approx.4.5 eV. An experimental investigation of the relative atomic oxygen erosion yields of a wide variety of polymers and carbon was conducted using isotropic thermal energy (approx.0.1 eV) and hyperthermal energy (approx.70 eV) atomic oxygen using an RF plasma asher and an end Hall ion source. For hyperthermal energies, the atomic oxygen erosion yields relative to normal incident Kapton H were compared for sweeping atomic oxygen arrival with that of normal incidence arrival. The results of isotropic thermal energy, normal incident, and sweeping incident atomic oxygen are also compared with measured or projected LEO values.

Banks, Bruce A.↗
DOE OSTI2025

Characterization of detachment inferred from the Balmer line ratios in JET-ILW low-confinement mode plasmas

Spectroscopic measurements of the hydrogenic Balmer-α and Balmer-γ line emission in JET-ILW low-confinement mode (L-mode) deuterium plasmas are used to assess the onset of volume recombination in the low-field side (LFS) divertor. The evolution of the EDGE2D-EIRENE predicted Balmer-γ to Balmer-α emission ratio from low-recycling to detached conditions is in qualitative agreement with the measured ratio. In low-recycling conditions the EDGE2D-EIRENE predicted line-emission is within 30% of measured emission, in high-recycling within 20%t, and in detached conditions lower by a factor of 2.5.

Divertor visible spectroscopy↗
DOE OSTI2026

Experimental observation and integrated modelling of proton-beryllium fusion in He and D plasmas at JET

Validated integrated modelling of JET ITER-like wall experiments in which fusion performance is driven by reactions between fast ions and intrinsically present metal wall impurities is presented. A steady-state L-mode plasma with dominant proton-beryllium fusion and neutron yields of up to ≈ 6·10 13 s -1 is developed in He and D, via radiofrequency heating of a H minority. The fusion drive is unambiguously confirmed by the neutral particle analyser, fast ion loss detector, and γ-ray diagnostics. Experiments are analysed via an integrated modelling framework, developed to model the two-stage proton beryllium-fusion chain and produce high-fidelity fusion product source terms. The modelling chain comprises TRANSP and JETTO for plasma core modelling, LOCUST for full orbit product tracking and collisional slowing-down, DRESS to resolve two- and three-body fusion kinematics, and MCNP for neutron transport calculations. Modelling shows that the primary 9 Be(p,n) 9 B reaction is the dominant neutron emitter at naturally present concentrations of beryllium in these experiments. The yield contribution of secondary reactions between fusion products and beryllium, 9 Be(d,n) 10 B and 9 Be(α,n) 12 C, is found to be negligible. The proton-deuteron knock-on effect in D plasmas is modelled, which is calculated to contribute ≈ 25% to the total neutron yield. For both He and D discharges the total computed neutron rates match fission chamber (FC) measurements within the combined experimental and computational uncertainty, with an average discrepancy of ≈ ± 20%. Realistic proton-beryllium neutron sources are propagated through JET’s MCNP neutron transport model which shows that 235 U FCs’ response is sensitive to p–Be source changes, with up to ≈ 10% variation compared to a D–D neutron source. We show that the high-energy tail of the fast proton minority can be studied with multi-foil neutron activation. The framework is also applied to the study of interactions between fast protons and boron impurities, of relevance to ITER. We calculate that in JET conditions a significant alpha source with DT-like energies could be generated through 11 B(p, α)2α fusion, and detected via γ-emission in secondary interactions between fast alphas and boron. The work represents an important step towards validating predictive integrated modelling capabilities for non-standard fusion reactions.

JET↗
NASA NTRS1987

Potential energy surfaces for atomic oxygen reactions: Formation of singlet and triplet biradicals as primary reaction products with unsaturated organic molecules

The experimental study of the interaction of atomic oxygen with organic polymer films under LEO conditions has been hampered by the inability to conduct detailed experiments in situ. As a result, studies of the mechanism of oxygen atom reactions have relied on laboratory O-atom sources that do not fully reproduce the orbital environment. For example, it is well established that only ground electronic state O atoms are present at LEO, yet most ground-based sources are known to produce singlet O atoms and molecules and ions in addition to O(3P). Engineers should not rely on such facilities unless it can be demonstrated either that these different O species are inert or that they react in the same fashion as ground state atoms. Ab initio quantum chemical calculations have been aimed at elucidating the biradical intermediates formed during the electrophilic addition of ground and excited-state O atoms to carbon-carbon double bonds in small olefins and aromatic molecules. These biradicals are critical intermediates in any possible insertion, addition and elimination reaction mechanisms. Through these calculations, we will be able to comment on the relative importance of these pathways for O(3P) and O(1D) reactions. The reactions of O atoms with ethylene and benzene are used to illustrate the important features of the mechanisms of atomic oxygen reaction with unsaturated organic compounds and polymeric materials.

Jaffe, Richard L.↗
NASA NTRSDate not supplied

Characterization of Novel Spacecraft Materials Under High Energy Electron and Atomic Oxygen Exposure

The harsh space environment imposes stringent requirements upon spacecraft materials, especially those located on exterior surfaces of space objects in low Earth orbit (LEO). As humankind moves from space exploration to space commercialization, these polymers may have to last for 15–20 years without considerable degradation of their material properties. Hence, we must understand the effects of the space environment on materials currently in use as well as on untested materials. In the presented study authors exposed several space-relevant polymers to the simulated space weather comprised by electrons and atomic oxygen irradiation. First, materials were thoroughly characterized in their pristine state to create a baseline for the ground- and space-based experiments. Next, alteration of optical, surface, and charge transport properties of the same materials were studied under space-simulated environment.

Elena A. Plis↗
DOE OSTI2026

Axisymmetric Eigenmodes Excited by Alpha Particle Energy Gradients in JET D-T Plasmas

Axisymmetric Alfvén eigenmodes have been observed at the plasma edge in deuterium-tritium (D-T) tokamak plasmas externally heated only by neutral beam injection in JET. The modes were detected only in D-T plasmas, not in pure D plasmas, indicating excitation by fusion-born 𝛼 particles. The presence of the axisymmetric mode suggests that the modes were driven by positive energy gradients in the 𝛼 particle distribution rather than radial gradients. The modes are driven by counter-current passing 𝛼 particles with large orbit widths, allowing core-born 𝛼 particles to interact with modes at the plasma edge. This reveals an excitation mechanism arising from positive energy gradients produced by the minimum energy required to confine particles at the edge, relevant to all burning plasmas.

Oliver, H. J. C. [United Kingdom Atomic Energy Aut↗
DOE OSTI2022

Investigation of Remanufacturing Methods Utilizing Mechanically-Generated and Gas-Atomized Feedstock Production for Directed Energy Deposition Processing Through Specific Energy Consumption Modeling

The goal of this work was to assess the energy consumption of a novel remanufacturing method that utilizes mechanically-generated feedstock for directed energy deposition. Gas-atomization is the state-of-the-art production process for directed energy deposition feedstock, and for this work was incorporated into a remanufacturing process path to provide a comparison method. Specific energy consumption models of remanufacturing utilizing both of these proposed process paths were developed and applied to a case study to investigate energy saving opportunities for future manufacturing paradigms. The energy modelling was done in three stages. First, the mechanically-generated feedstock production energy consumption model was generated from experimental observation. Second, the gas-atomized feedstock production energy consumption model was generated from a combination of experimental observation, reported estimates from the manufacturer, and data found in the literature. Lastly, the energy consumption model of directed energy deposition was derived from experimental observation and compares favorably with reported estimates in the literature. With the models, the specific energy consumption in the two process paths were compared and their application was demonstrated by estimating the energy consumption to remanufacture a bracket. The two feedstock production methods had similar specific energy consumptions. The specific energy consumption of the directed energy deposition process was the greatest component in the respective remanufacturing paths by an order of magnitude; increasing deposition rate is the most important factor for lowering the overall specific energy consumption. The analyzed remanufacturing technologies were estimated to consume less energy than replacement when repairing up to approximately 15% of the original part’s mass.

42 ENGINEERING↗
NASA NTRS1993

Measurements of Excitation Functions and Line Polarizations for Electron Impact Excitation of the n = 2, 3 States of Atomic Hydrogen in the Energy Range 11 - 2000 eV

The electron-atomic hydrogen scattering system is an important testing ground for theoretical models and has received a great deal of attention from experimentalists and theoreticians alike over the years. A complete description of the excitation process requires a knowledge of many different parameters, and experimental measurements of these parameters have been performed in various laboratories around the world. As far as total cross section data are concerned it has been noted that the discrepancy between the data of Long et al. and Williams for n = 2 excitations needs to be resolved in the interests of any further refinement of theory. We report new measurements of total cross sections and atomic line polarizations for both n=2 and n=3 excitations at energies from threshold to 2000 eV...

James, G. K.↗