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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1971

Spectroscopic investigation of electric field fluctuations in a steady plasma

The electric fluctuations caused by plasma oscillations of a steady plasma were investigated. In order to observe this phenomenon electric field fluctuations are created in a helium plasma by an electron beam. Spectroscopic analysis reveals satellite lines disposed symmetrically in pairs about a forbidden atomic line and separated from it by the frequency of the electric field oscillations.

Druetta, M. P.↗
NASA NTRS1973

Observation of the J = 2 to J = 1 transition of interstellar CO at 1.3 millimeters

The NRAO 36-foot antenna at Kitt Peak with a novel type of millimeter-wave superheterodyne receiver was used in observations of 1.3-mm line interstellar radiation due to J ? 2-1 transitions of C(12)0(16) and C(13)0(16). The liquid-helium-cooled hot-electron bolometer mixer of the superheterodyne receiver was used as the detecting element. The Orion Nebula CO system was found to be thermalized, showing a peak excitation temperature of about 76 K.

Phillips, T. G.↗
NASA NTRS2023

Energetic Ion Variations During Substorm Intervals Using the Van Allen Probes Data

The study investigates ion flux variations for the substorms in the inner magnetosphere. The effect of substorm-induced magnetic field dipolarization on the O + and H + ion flux is analysed for 22 events from the year 2018 using the Helium, Oxygen, Proton, and Electron (HOPE) Mass Spectrometer data on board the Van Allen Probes (VAP/RBSP) satellite. The clear dipolarization signatures are observed using the Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) suite from the VAP. These observations provide evidence of the ion flux enhancement at 1–50 keV energy after the substorm onset, in particular, the energy range of 20–50 shows dominance. The typical characteristics of magnetic field dipolarization and its time scales are investigated. It is found that the O + ion flux enhances greater in magnitude than H + ion flux at energies 20–50 keV after the substorm onset. In addition to it, the correlation of these enhanced oxygen fluxes with the related interplanetary magnetic field (IMF) B z , solar wind velocity (V sw ), and the auroral electrojet (AE) index are found good. The new results reports that the ion flux variation ratio shows the MLT dependence for different energy ranges and found that the peak of the O + / H + ion flux ratio centred near midnight for the energy range of 8–20 keV, whereas the O + / H + ion flux ratio of the energy 20–50 keV is high within the post-midnight. The possible mechanisms for the enhanced ion flux are discussed.

Trunali Shah↗
NASA NTRS1971

Physical electronics and surface physics

Diffraction of helium atoms from tungsten (112) crystal surface and measurement of time of flight distribution of deuterium molecules desorbed from nickel surfaces

Source record↗
NASA NTRS1972

Ionization of multielectron atoms by fast charged particles.

Using plane waves to describe the incident and scattered particles, and screened hydrogenic and Coulomb functions to describe the atomic electrons before and after ejections, we have calculated the differential and total ionization cross sections of 11 atoms and one ion by electron impact, and ionization of helium by proton impact. The effective charges of the screened hydrogenic functions are fixed by the Hartree-Fock calculations. Calculations have been carried out for the atomic s, p, and d electrons. For low atomic numbers, we find reasonable agreement with the experimental data. For intermediate atomic numbers, we expect our results to overestimate the actual cross sections, since our choice of a unit charge for the Coulomb function of the ejected electrons will overestimate the atomic dipole potential strength, and in turn the high-energy cross sections. The advantage of the method presented here is that the ionization amplitude is given in analytic form. This may allow further analysis on this amplitude, and facilitates extension of the numerical integration for the cross section to high impact energies.

Omidvar, K.↗
NASA NTRS1973

The scattering of low energy positrons by helium

Kohn's variational method is used to calculate the positron-helium scattering length and low energy S-wave phase shifts for a quite realistic Hylleraas type of helium function containing an electron-electron correlation term. The zero energy wavefunction is used to calculate the value of the annihilation rate parameter Z sub eff. All the results are significantly different from those for Drachman's helium model B, but are in better agreement with the available experimental data.

Humberston, J. W.↗
NASA NTRS1973

Measurements of recombination of electrons with H3(plus) and H5(plus) ions

The electron-ion recombination coefficients for H3(+) and H5(+) ions were determined by means of a microwave afterglow/mass spectrometer apparatus. Measurements of electron density decays in helium-hydrogen mixtures are correlated with the decay of mass-identified ion currents to the wall of the microwave cavity. At low partial pressures of hydrogen in the mixture, the ion H3(+) dominates the ion composition and the ion wall current tracks the electron density decay curves. From recombination controlled electron density decay curves, the values alpha (H3(+)) = (2.9 + or - 0.3), (2.3 + or - 0.3), and (2.0 + or - 0.2) x 0.0000001 cu cm per sec, are obtained at 205, 300 and 450 K, respectively. At higher partial pressures of hydrogen and low temperatures, where (H5(+)) is the dominant ion, the value alpha (H5(+)) = (3.6 + or - 1.0) x 0.0000001 cu cm per sec is obtained at 205 K. The implications of these results concerning ionization levels in the atmospheres of the outer planets and in the interstellar medium are discussed.

Leu, M. T.↗
DOE OSTI2023

Spin dynamics in quantum dots on liquid helium

Liquid He-4 is free from magnetic defects, making it an ideal substrate for electrons with long-lived spin states. Such states can serve as qubit states. Here, in this study, we consider the spin states of electrons electrostatically localized in quantum dots on a helium surface. Efficient gate operations in this system require spin-orbit coupling. It can be created by a nonuniform magnetic field from a current-carrying wire, can be turned on and off, and allows one to obtain large electrodipole moment and comparatively fast coupling of spins in neighboring dots. Of central importance is to understand spin decay due to the spin-orbit coupling. We establish the leading mechanism of such decay and show that the decay is sufficiently slow to enable high-fidelity single- and two-qubit gate operations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1991

Energy deposition by X-ray photoelectrons into interstellar molecular clouds

The deposition of energy by 100-10,000 eV electrons into molecular hydrogen and helium gas of cosmic abundances and fractional ionization ranging from 10 to the -12th to 0.1 is considered. In order to account for energy deposition by both discrete and continuous degradation processes, the loss spectrum, a form of the Spencer-Fano degradation spectrum particularly suited to describing electron energy deposition in a partially ionized gas is considered. The calculated excitation and ionization yields drop as the fractional ionization increases. The dependences of these yields on fractional ionization are fitted to a form suitable for swift numerical computation.

Voit, G. M.↗
DOE OSTI2024

Spatially resolved measurements of electron density of a magnetically confined split-ring resonator source

Laser-collisional induced fluorescence is used to study the plasma generated by a split-ring resonator discharge under an external cusp shaped magnetic field created by permanent magnets. The electron density and electron temperature are measured for a helium plasma at different pressures, powers, and magnet field strengths. It is found that the magnetic fields produce higher electron temperatures with peak temperatures of ∼3 eV, while the no magnet case has peak temperatures of ∼0.8 eV. Conversely, the peak electron density is obtained in the no magnet case at a value of ∼1.9 × 1011 cm−3. This indicates that the cusp-field did magnetize the electrons, but contrary to expectations, it resulted in a decrease in electron density. This is believed to be due to the magnetic field having negative effects on the resonance of the plasma source.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Generalized rate theory for void and bubble swelling and its application to δ -plutonium

A rate theory for void and bubble swelling is derived that allows both vacancies and self-interstitial atoms to be generated by thermal activation at all sinks. In addition, they can also be produced by displacement damage from external and internal radiation. This generalized rate theory (GRT) is applied to swelling of gallium-stabilized δ-plutonium in which α-decay causes the displacement damage. Since the helium atoms produced also become trapped in vacancies, a distinction is made between empty and occupied vacancies. The growth of helium bubbles observed by transmission electron microscopy in weapons-grade and in material enriched with Pu238 is analyzed, using different values for the formation energy of self-interstitial atoms (SIA) and two different sets of relaxation volumes for the vacancy and for the SIA. One set allows preferential capture of SIA at dislocations, while the other set gives equal preference to both vacancy and SIA. It is found that the helium bubble diameters observed are in better agreement with GRT predictions if no preferential capture occurs at dislocations. Therefore, helium bubbles in δ-plutonium will not evolve into voids. Furthermore, the helium density within the bubbles remains sufficiently high to cause thermal emission of SIA. Based on a helium density between two to three helium atoms per vacant site, the sum of formation and migration energies must be around 2.0 eV for SIA in δ-plutonium.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗