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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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Plasma waves and transversely accelerated ions in the terrestrial ionosphere

Developments in measuring the physical mechanisms responsible for strongly driven transverse ion acceleration in the ionosphere are reviewed. Lower-hybrid waves and ion Bernstein waves can be associated very closely with transversely accelerated ions in the auroral ionosphere. In a recent development, very intense and localized lower-hybrid waves have been observed to produce transversely accelerated ions with characteristic energies of 10 eV. The case for current-driven electrostatic oxygen cyclotron waves producing transversely accelerated ions is less compelling.

Kintner, Paul M.↗
NASA NTRS1986

Ion acceleration in expanding ionospheric plasmas

Plasma expansion along the ambient magnetic field in regions of density gradients provides a mechanism for accelerating ions. A brief review of the basic phenomenon of plasma expansion is given. Estimates of the energies of the accelerated ions in an expanding ionospheric plasma along geomagnetic flux tubes are obtained by solving the time-dependent hydrodynamic equations. It is found that, over certain altitude ranges, each ion species can be the most energetic; the maximum energies of the different ions are found to be limited to less than about 10 eV for H(+), 5 eV for He(+), and less than about 1.5 eV for O(+).

Singh, Nagendra↗
NASA NTRS1996

Micromachined Ion Accelerators

Proposed ion accelerators made by micromachining techniques. Advantages include small size and weight, modularity, and compatibility with integrated circuits. Used as sources of ion beams for industrial processes. Ion accelerator of this type combined with integrated electronic control and power circuitry, plus similarly miniaturized valves and other mechanisms for regulating flow of gas used to generate ions - all micromachined on single chip. Provides flexibility for tailoring characteristics of ion sources for specific applications; for example, construct array of many such devices to obtain large ion source or position multiple devices to obtain desired ion-beam pattern in processing chamber.

Brophy, John↗
NASA NTRS1992

Sounding rocket measurements of suprathermal ion acceleration

Transverse ion acceleration has been observed at rocket altitudes between 500 and 1000 km due to (1) the injection of 100-200 eV argon plasma; (2) auroral electron precipitation; and (3) the injection of electromagnetic waves. Field-aligned currents necessary to neutralize the plasma injection payloads and naturally occurring in the aurora could be responsible for the ions observed in (1) and (2) above. Associated with the aurora, both bulk heating and tail heating are observed, sometimes simultaneously. In this case, either different masses are accelerated or different mechanisms are responsible. The bulk heating is closely correlated with the aurora structure while tail heating is not so well correlated. Recent high-time-resolution rocket ion data have revealed that the transverse acceleration process is of very short duration (about 100 ms) and occurs in a very limited volume (a few hundred kilometers along B and on the order of the ion gyrodiameter across B). Such impulse acceleration events are correlated with waves near the lower hybrid resonance.

Arnoldy, Roger L.↗
NASA NTRS1981

Transversely accelerated ions in auroral arcs

Ionospheric ions apparently accelerated transversely to the geomagnetic field in the topside ionosphere are regularly detected by the soft particle spectrometers on the ISIS satellites. Such gyro-accelerated ions are observed in association with precipitating auroral electrons. A detailed study of their relationship with such electrons and with field-aligned currents, together with simultaneous measurements of the local plasma composition and density, reveals the specific conditions present in the topside ionosphere during the generation of such transversely accelerated ions (TAI). A proposed mechanism for generation of TAI involving acceleration by electrostatic ion cyclotron waves is consistent with the present observations.

Klumpar, D. M.↗
NASA NTRS1992

Characterization of ion accelerating systems on NASA LeRC's ion thrusters

An investigation is conducted regarding ion-accelerating systems for two NASA thrusters to study the limits of ion-extraction capability or perveance. A total of nine two-grid ion-accelerating systems are tested with the 30- and 50-cm-diam ring-cusp inert-gas ion thrusters emphasizing the extension of ion-extraction. The vacuum-tank testing is described using xenon, krypton, and argon propellants, and thruster performance is computed with attention given to theoretical design considerations. Reductions in perveance are noted with decreasing accelerator-hole-to-screen-hole diameter ratios. Perveance values vary indirectly with the ratio of discharge voltage to total accelerating voltage, and screen/accelerator electrode hole-pair alignment is also found to contribute to perveance values.

Rawlin, Vincent K.↗
NASA NTRS1986

Observations of plasma waves within regions of perpendicular ion acceleration

The acceleration of ionospheric ions transverse to the geomagnetic field by factors of 1000 is believed to be caused by plasma waves. The authors made simultaneous measurements of electric fields and energetic ions within regions of perpendicular ion acceleration from the sounding rocket MARIE. Perpendicular ion acceleration was correlated with plasma waves near and above the lower hybrid frequency. Ions were detected up to energies of 300 eV and the broadband lower hybrid waves reached an amplitude of 10-30 mV/m (RMS) over the frequency band 4-16 kHz. Although electric field amplitudes near the O(+) cyclotron frequency reached a maximum value of 10 mV/m (RMS), there was no spectral evidence of electrostatic ion cyclotron waves associated with ion acceleration. There was spectral evidence of H(+) Bernstein modes near the lower hybrid frequency.

Kintner, P. M.↗
NASA NTRS1992

Bursts of transverse ion acceleration at rocket altitudes

High-time-resolution ion mass spectrometer distribution function measurements and wave data from a sounding rocket flight over an aurora have revealed the fine structure of the transverse ion acceleration mechanism in the upper ionosphere. The transversely accelerated ion (TAI) events can occur in a volume with a cross-field dimension as small as several tens of meters and thus appear as 50-100 ms ion bursts due to the rocket payload motion. Bulk heating to a characteristic energy of several eV and tail heating in the direction perpendicular to B of a few percent of ambient ions to a characteristic energy the order of 10 eV occur for both hydrogen and oxygen ions. The TAI at 90 deg pitch angle occur in localized regions of intense lower hybrid waves and in regions of density depletion. On close examination of the correlation between the wave bursts and the TAI it is believed that the waves produce the ion acceleration. The TAI occur during periods of field-aligned auroral electron bursts. Finally, near 1000 km altitude they occur about once every second. If the event presented here is considered average, the flux of TAI oxygen ions above 7 eV could account for the ion conic fluxes measured by the ISIS spacecraft.

Arnoldy, R. L.↗
NASA NTRS2012

Temporal Variability of Ion Acceleration and Abundances in Solar Flares

solar flares accelerate both ions and electrons to high energies, and their x-ray and gamma-ray signatures not only probe the relationship between their respective acceleration, but also allow for the measurement of accelerated and ambient abundances. RHESSI observations have shown a striking close linear correlation of gamma-ray line fluence from accelerated ions > approx 20 MeV and bremsstrahlung emission from relativistic accelerated electrons >300 kev, when integrated over complete flares, suggesting a common acceleration mechanism. SMM/GRS observations, however, show a weaker correlation, and this discrepancy might be associated with previously observed electron-rich episodes within flares and/or temporal variability of gamma-ray line fluxes over the course of flares. We use the latest RHESSI gamma-ray analysis techniques to study the temporal behavior of the RHESSI flares, and determine what changes can be attributed to an evolving acceleration mechanism or to evolving abundances. We also discuss possible explanations for changing abundances.

Shih, Albert Y.↗
NASA NTRS2011

Temporal Variability of Ion Acceleration and Abundances in Solar Flares

Solar flares accelerate both ions and electrons to high energies, and their X-ray and gamma-ray signatures not only probe the relationship between their respective acceleration, but also allow for the measurement of accelerated and ambient abundances. RHESSI observations have shown a striking close linear correlation of gamma-ray line fluence from accelerated ions greater than approximately 20 MeV and bremsstrahlung emission from relativistic accelerated electrons greater than 300 keV, when integrated over complete flares, suggesting a common acceleration mechanism. SMM/GRS observations, however, show a weaker correlation, and this discrepancy might be associated with previously observed electron-rich episodes within flares and/or temporal variability of gamma-ray line fluxes over the course of flares. We use the latest RHESSI gamma-ray analysis techniques to study the temporal behavior of the RHESSI flares, and determine what changes can be attributed to an evolving acceleration mechanism or to evolving abundances. We also discuss possible explanations for changing abundances.

Shih, Albert↗
NASA NTRS1968

Composite ion accelerator grids.

Ion extraction system for low voltage mercury electron bombardment thrustors using glass coating fused to perforated metal grid

Banks, B.↗
NASA NTRS1986

Ion acceleration in laboratory plasmas

Recent experiments which investigate ion acceleration in 'collisionless' laboratory plasmas are described. The experiments fall into two classes - those involving stationary and those involving time dependent processes.Among the stationary structures which accelerate ions are sheaths, presheaths, double layers, multiple double layers and ambipolar potentials. RF is an example of time dependent processes. Both classes of experiments are considered. Experiments with 'collisionless' plasmas in multidipole triple plasma-type devices and novel phenomena associated with the use of Ion Cyclotron Resonance Heating in the inhomogeneous magnetic field of a tandem mirror 'fusion' plasma are described. New RF phenomenon include RF pitch angle scattering, RF electron pumping, and ICRF ponderomotive force.

Hershkowitz, Noah↗
NASA NTRS1983

Particle and wave observations of low-altitude ionospheric ion acceleration events

Two sounding rockets were launched into the expansive phases of two auroral substorms and passed through source regions of transversely accelerated ionospheric ions. Energetic ion and electron, wave, and ambient plasma observations were made. The events were observed in the 400-600 km range and resulted in the ion energization of hundreds of electron volts. In the acceleration region the ionospheric ion velocity distribution function in the direction perpendicular to the local magnetic field showed a non-Maxwellian, high-energy tail. Plasma density was lower than theoretical quiescent values. Strong thermal ion drift was observed only in the perpendicular direction. Large-amplitude, low-frequency fluctuations in plasma density were present along with a number of different wave modes. The characteristics of the ion energy spectra agreed with a model of ion cyclotron acceleration and energy loss due to ion-neutral collisions.

Yau, A. W.↗
NASA NTRS1996

Substorm associated ion acceleration in the dynamic magnetotail

Ion acceleration and flux increase associated with substorm energetic particle injections are investigated on the basis of geosynchronous observations and test proton orbits in the dynamic fields of a three dimensional magnetohydrodynamic simulation of neutral line formation and dipolarization in the magnetotail. The energetic particle flux changes obtained from the test particle orbits agree well with observations that demonstrate rapid ion flux increases at energies of above 20 keV. The injection region inferred from the test particles has a sharp earthward boundary and a sharp ragged tailward boundary. The earthward portion of the enhanced ion flux can be traced to the enhanced cross-tail electric field associated with the near-earth x-type neutral line. Due to the rapid earthward motion of accelerated ions away from the neutral line, this boundary is displaced earthward to where the energetic ions become more adiabatic in the stronger dipolar field.

Birn, J.↗