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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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NASA NTRS1984

Experimental observations of nonlinearly enhanced 2omega-UH electromagnetic radiation excited by steady-state colliding electron beams

Counterstreaming large-diameter electron beams in a steady-state laboratory experiment are observed to generate transverse radiation at twice the upper-hybrid frequency (2omega-UH) with a quadrupole radiation pattern. The electromagnetic wave power density is nonlinearly enhanced over the power density obtained from a single beam-plasma system. Electromagnetic power density scales exponentially with beam energy and increases with ion mass. Weak turbulence theory can predict similar (but weaker) beam energy scaling but not the high power density, or the predominance of the 2omega-UH radiation peak over the omega-UH peak. Significant noise near the upper-hybrid and ion plasma frequencies is also measured, with normalized electrostatic wave energy density W(ES)/n(e)T(e) approximately 0.01.

Intrator, T.↗

NASA NTRS1994

Formation of Na-containing molecular ions at Io

Fast sodium atoms, which appear to be associated with the motion of the magnetic 'field lines' downstream from Io (Schneider et al. 1991), are thought to be produced by dissociation of NaX(+) in Io's plasma torus. It was suggested that these molecular ions are formed near Io's exobase by electron-impact ionization and picked up be the corotating filed lines (Wilson and Schneider 1994). Because electron cooling processes dominate electron-impact ionization in Io's corona, two reactions are suggested here as sources of NaX(+) and, hence, as the ultimate sources of the observed fast Na. First, the charge-exchange cross sections for forming NaX(+) are shown to be large for plasma torus ions (O(+), S(+), O(2+), S(3+)) colliding with NaX molecules in Io's corona. Sputtering from the surface (Chrisey et al. 1988) and rapid transport to the exobase is a potential source of NaX, where X is O,S, Na, or a molecular species such as NaS or O2. Second ions of the more abundant molecules (e.g., SO(+), SO2(+), O2(+), and S2(+)) can react efficiently with atomic Na in Io's corona to form NaX(+). Here cross sections are estimated for these two processes, as well as for charge exchange in O(+) and S(+) on Na collisions.

Johnson, R. E.↗

NASA NTRS1979

Calculation of resonant effects in electron-impact excitation of positive ions Application to oxygen VII

The general reaction theory of Feshbach is applied to the calculation of resonant effects in near-threshold electron-positive-ion excitation. The theory divides configuration space into open- and closed-channel parts, resonance effects being described by the closed-channel part. The open-channel part is handled in a distorted-wave approximation to the set of open-channel coupled equations. Various methods are suggested for handling the closed-channel part. However, an 'attached-excited-target approximation' is used explicitly, which is further approximated by a set of uncoupled closed-channel equations. As an example, the 1 1S-2 1P excitation cross section of O VII below the 3 3S threshold is calculated. Various distorted-wave approximations are investigated and results from most of them are quite similar. Resonant effects arising from the attachment of the colliding electron with the 3 3S state are found to be small, but other close-lying n = 3 states have not yet been included.

Pindzola, M. S.↗

NASA NTRS2016

MMS Observations of Large Guide Field Symmetric Reconnection Between Colliding Reconnection Jets at the Center of a Magnetic Flux Rope at the Magnetopause

We report evidence for reconnection between colliding reconnection jets in a compressed current sheet at the center of a magnetic flux rope at Earth's magnetopause. The reconnection involved nearly symmetric Inflow boundary conditions with a strong guide field of two. The thin (2.5 ion-skin depth (d(sub i) width) current sheet (at approximately 12 d(sub i) downstream of the X line) was well resolved by MMS, which revealed large asymmetries in plasma and field structures in the exhaust. Ion perpendicular heating, electron parallel heating, and density compression occurred on one side of the exhaust, while ion parallel heating and density depression were shifted to the other side. The normal electric field and double out-of-plane (bifurcated) currents spanned almost the entire exhaust. These observations are in good agreement with a kinetic simulation for similar boundary conditions, demonstrating in new detail that the structure of large guide field symmetric reconnection is distinctly different from antiparallel reconnection.

Oieroset, M.↗

NASA NTRS2018

Observations of Mercury's Exosphere: Composition and Structure: Chapter - 14

Mercury is surrounded by a tenuous exosphere in which particles travel on ballistic trajectories under the influence of a combination of gravity and solar radiation pressure. The densities are so small that the surface forms the exobase and particles in the exosphere are more likely to collide with it rather than with each other. For a planet with a more substantial collision-dominated atmosphere, a population of particles that enters from below the exobase supplies the exosphere. In contrast Mercury's exosphere is supplied both by incoming sources including the solar wind (hydrogen and helium), micrometeoroids (dust), meteoroids and cornets, and by particles released from the surface through a variety of processes that include sputtering by solar wind ions, desorption by solar photons and electrons, impacts by micrometeoroids, and thermal desorption of surface materials. These source processes are balanced by loss processes, which include impact with and sticking to the surface, Jeans (or thermal) escape, ionization followed by transport along magnetic field lines, and acceleration by solar radiation pressure to escape velocity. Ground-based attempts to detect an atmosphere around Mercury before Mariner 10 first visited the planet in 1974 were unsuccessful and led only to increasingly tight upper limits, culminating in a limiting value for surface atmospheric pressure of 0.015 Pascal (Pa) determined by Fink et al. (1974).

Solar↗