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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Ion accelerator systems for high power 30 cm thruster operation

Two and three-grid accelerator systems for high power ion thruster operation were investigated. Two-grid translation tests show that over compensation of the 30 cm thruster SHAG grid set spacing the 30 cm thruster radial plasma density variation and by incorporating grid compensation only sufficient to maintain grid hole axial alignment, it is shown that beam current gains as large as 50% can be realized. Three-grid translation tests performed with a simulated 30 cm thruster discharge chamber show that substantial beamlet steering can be reliably affected by decelerator grid translation only, at net-to-total voltage ratios as low as 0.05.

Aston, G.↗
NASA NTRS1974

Ion acceleration in a plasma focus

The electric and magnetic fields associated with anomalous diffusion to the axis of a linear plasma discharge are used to compute representative ion trajectories. Substantial axial acceleration of the ions is demonstrated.

Gary, S. P.↗
NASA NTRS1990

A quasi-linear theory to explain ion acceleration in the distant cometary environment

Spacecraft observations at comet Halley as well as computer simulations have shown that pitch angle scattering of newborn cometary ions proceeds at a relatively fast rate, leading to relatively isotropic shell-like velocity distribution functions. Energization processes whereby shell distributions become more Maxwellian and a few ions are accelerated to high energies appear to proceed more slowly. The research on the latter, slower process is described, in which the scattering is assumed to be due to the resonant, growing magnetic fluctuations driven by the non-Maxwellian nature of the ion distribution. An ion shell distribution which is isotropic in the wave frame begins the process and a Fokker-Plank derived from quasilinear plasma theory is used to describe the broadening and energization of the cometary ion distribution.

Sinha, Raji↗
NASA NTRS1992

Ion acceleration at collisionless shock interactions

When two collisionless shocks collide, a population of high energy ions is produced. Using hybrid numerical simulations, it is shown that when the two shocks are quasi-perpendicular, ions with energies up to 15 E sub 0 (where E sub 0 is the initial kinetic energy of upstream ions in the shock frame) are produced by direct electric field acceleration. In the quasi-parallel regime, energies as high as 80 E sub 0 can be obtained. These ions are accelerated by both scattering off the approaching shocks and subsequently in the intense turbulence left behind by the shock collision.

Cargill, Peter J.↗
NASA NTRS1983

Energetic ion acceleration and transport in the upstream region of Jupiter - Voyager 1 and 2

Long-lived upstream energetic ion events at Jupiter appear to be very similar in nearly all respects to upstream ion events at earth. A notable difference between the two planetary systems is the enhanced heavy ion compositional signature reported for the Jovian events. This compositional feature has suggested that ions escaping from the Jovian magnetosphere play an important role in forming upstream ion populations at Jupiter. In contrast, models of energetic upstream ions at earth emphasize in situ acceleration of reflected solar wind ions within the upstream region itself. Using Voyager 1 and 2 energetic ion measurements near the magnetopause, in the magnetosheath, and immediately upstream of the bow shock, the compositional patterns are examined together with typical energy spectra in each of these regions. Characteristic spectral changes are found late in ion events observed upstream of the bow shock at the same time that heavy ion fluxes are enhanced and energetic electrons are present. A model involving upstream Fermi acceleration early in events and emphasizing energetic particle escape in the prenoon part of the Jovian magnetospehre late in events is presented to explain many of the features in the upstream region of Jupiter.

Baker, D. N.↗
NASA NTRS1986

On ion acceleration in interplanetary quasi-perpendicular shock waves

The kinematic and pitch angle scattering constraints for multiple shock encounters to occur are investigated. The results suggest that (1) large particle anisotropies and a large number of shock encounters are not mutually exclusive and (2) solar wind ions are not directly injected into the nearly perpendicular interplanetary shock acceleration process. Also, the average number of shock encounters required to accelerate an ion between two energies is calculated. The results are consistent with the shock geometry dependence observed in interplanetary shock spike and corotating interaction region associated energetic ion events.

Pesses, M. E.↗
NASA NTRS1982

Energetic-ion acceleration and transport in the upstream region of Jupiter: Voyager 1 and 2

Long-lived upstream energetic ion events at Jupiter appear to be very similar in nearly all respects to upstream ion events at Earth. A notable difference between the two planetary systems is the enhanced heavy ion compositional signature reported for the Jovian events. This compositional feature has suggested that ions escaping from the Jovian magnetosphere play an important role in forming upstream ion populations at Jupiter. In contrast, models of energetic upstream ions at Earth emphasize in situ acceleration of reflected solar wind ions within the upstream region itself. Using Voyager 1 and 2 energetic ( approximately 30 keV) ion measurements near the magnetopause, in the magnetosheath, and immediately upstream of the bow shock, the compositional patterns are examined together with typical energy spectra in each of these regions. A model involving upstream Fermi acceleration early in events and emphasizing energetic particle escape in the prenoon part of the Jovian magnetosphere late in events is presented to explain many of the features in the upstream region of Jupiter.

Baker, D. N.↗
NASA NTRS1999

What We Don't Understand About Ion Acceleration Flares

There are now strong associations between the (3)He-rich, Fe-rich ions in "impulsive" solar energetic particle (SEP) events and the similar abundances derived from gamma-ray lines from flares. Compact flares, where wave energy can predominate, are ideal sites for the study of wave-particle physics. Yet there are nagging questions about the magnetic geometry, the relation between ions that escape and those that interact, and the relative roles of cascading Alfven waves and the EMIC waves required to enhance He-3. There are also questions about the relative timing of ion and electron acceleration and of heating; these relate to the variation of ionization states before and during acceleration and during transport out of the corona. We can construct a model that addresses many of these issues, but problems do remain. Our greatest lack is realistic theoretical simulations of element abundances, spectra, and their variations. By contrast, we now have a much better idea of the acceleration at CME-driven shock waves in the rare but large "gradual" SEP events, largely because of their slow temporal evolution and great spatial extent.

Reames, Donald V.↗
NASA NTRS2007

Electrostatic Wave Generation and Transverse Ion Acceleration by Alfvenic Wave Components of BBELF Turbulence

We present results here from 2.5-D particle-in-cell simulations showing that the electrostatic (ES) components of broadband extremely low frequency (BBELF) waves could possibly be generated by cross-field plasma instabilities driven by the relative drifts between the heavy and light ion species in the electromagnetic (EM) Alfvenic component of the BBELF waves in a multi-ion plasma. The ES components consist of ion cyclotron as well as lower hybrid modes. We also demonstrate that the ES wave generation is directly involved in the transverse acceleration of ions (TAI) as commonly measured with the BBELF wave events. The heating is affected by ion cyclotron resonance in the cyclotron modes and Landau resonance in the lower hybrid waves. In the simulation we drive the plasma by the transverse electric field, E(sub y), of the EM waves; the frequency of E(sub y), omega(sub d), is varied from a frequency below the heavy ion cyclotron frequency, OMEGA(sub h), to below the light ion cyclotron frequency, OMEGA(sub i). We have also performed simulations for E(sub y) having a continuous spectrum given by a power law, namely, |Ey| approx. omega(sub d) (exp -alpha), where the exponent alpha = _, 1, and 2 in three different simulations. The driving electric field generates polarization and ExB drifts of the ions and electrons. When the interspecies relative drifts are sufficiently large, they drive electrostatic waves, which cause perpendicular heating of both light and heavy ions. The transverse ion heating found here is discussed in relation to observations from Cluster, FAST and Freja.

Singh, Nagendra↗
NASA NTRS1993

Ponderomotive effects on ion acceleration in the auroral zone

Low frequency, large amplitude Alfven waves occur in the auroral zone. Such waves have a ponderomotive effect on both ions and electrons. In the region between the large wave field and the ionosphere, the ponderomotive force accelerates electrons downward and ions upward, which produces an ambipolar electric field. The combined effect is to produce a differential acceleration between O(+) and H(+) with the O(+) accelerated more out of the ionosphere. The typical resulting energization for O(+) is tens of eV, which is sufficient for the ions to escape the ionosphere. We demonstrate this by means of analysis and test-particle calculation.

Li, Xinlin↗
NASA NTRS2017

MMS Observation of Inverse Energy Dispersion in Shock Drift Accelerated Ions

The four Magnetospheric Multiscale (MMS) spacecraft observed a ∼1 min burst of energetic ions (50–1000 keV) in the region upstream from the subsolar quasi-perpendicular bow shock on 6 December 2015. The composition, flux levels, and spectral indices of these energetic protons, helium, and oxygen ions greatly resemble those seen in the outer magnetosphere earlier while MMS crossed the magnetopause and differ significantly from those simultaneously observed far upstream by Advanced Composition Explorer (ACE). However, the event cannot be explained solely in terms of leakage from the magnetosphere. The strongly southward orientation of the interplanetary magnetic field (IMF) lines at the time of the event precludes any connection to the magnetosphere. This point is confirmed by the presence of energetic electrons, known to occur on magnetic field lines that graze the bow shock rather than connect to the magnetosphere. We suggest that the ions gradient drifted out of the nearby quasi-parallel foreshock and into the quasi-perpendicular bow shock. Each of the ion species exhibited an inverse energy dispersion. As predicted by models for shock drift acceleration, the energies of the ions increased as 𝜃(sub Bn), the angle between the IMF and the shock normal, increased. Finally, we note that a similar event was observed a few minutes later in the subsolar magnetosheath, indicating that such events can be swept downstream of the bow shock.

Lee, S. H.↗
NASA NTRS1989

Seed population for about 1 MeV per nucleon heavy ions accelerated by interplanetary shocks

Data obtained between 1977 and 1982 by the ISEE 1 and ISEE 3 satellites on the composition of heavy ions of about 1 MeV per nucleon, accelerated in interplanetary shock events which followed solar flare events, are examined. It was found that the average relative abundances for C, O, and Fe in the shock events were very close to those found for energetic ions in the solar flares, suggesting that, at these energies, the shock accelerated particles have the solar energetic particles as their seed population. This hypothesis is supported by the fact that the Fe/O ratio in the solar particle events is very strongly correlated with the Fe/O ratio in associated diffusive shock events.

Tan, L. C.↗
NASA NTRS1980

Solar wind ions accelerated to 40 keV by shock wave disturbances

Observations in the solar wind with the LASL/MPI fast plasma experiment on ISEE 1 and 2 reveal the common presence of ions with energies extending from 100 eV up to at least 40 keV in a broad region, typically 10 million kilometers wide, following interplanetary shocks. Peak differential fluxes up to 5000/sq cm s sr keV at 28 keV are observed either at the shock or within the first 1.5 hours following shock passage. In the solar wind frame the distribution function of these ions is roughly isotropic, peaks near zero velocity, and above 5 keV can adequately be characterized as power law in energy with a spectral index of 2.7. The effective 'temperature' of these ions generally exceeds 100 million K. These suprathermal interplanetary ions are almost certainly solar wind ions which have been accelerated by some mechanism associated with the shock wave disturbance. Present evidence leads the authors to favor stochastic particle acceleration involving electrostatic and/or electromagnetic turbulence in the postshock flow.

Gosling, J. T.↗
NASA NTRS1989

Anisotropy of shock-accelerated ion distributions in interplanetary space

The discrepancy between theory and observation is discussed with regard to the ability of interplanetary shock waves to accelerate a small percentage of the thermal ion population. The major point of departure rests with the spatial dependence of the energetic particle intensity and anisotropy in the region upstream of interplanetary shocks. It is argued that the discrepancy is due to the presence of solar flare particles forming an additional seed population which alters the upstream boundary condition of the energetic population. The resulting anisotropy of the energetic particle distribution several scale lengths upstream of the shock is proportional to the ratio of the streaming of the shock-accelerated population to the density of the solar flare population. This theory is then compared with the results of observed upstream anisotropy and measured particle intensities and anisotropies.

Smith, Charles W.↗
NASA NTRS1987

The 'convection surge' mechanism of ion acceleration during substorms

To explain the presence of the so-called 'bounce-phase-bunched' ion distributions (eV range to about 20 keV) observed in the earth's geosynchronous magnetosphere in association with substorm expansion phases, Quinn and Southwood proposed the 'convection surge' mechanism of ion energization. This mechanism is associated with a sudden earthward displacement of curved field lines resulting from the short-lived application of an intense, east-west electric field. A quantitative computer model of the mechanism has been constructed here. It is found that the mechanism easily generates the bounce-phase-bunched ion distributions in question. Additionally, the mechanism can generate dramatically field-aligned distributions. It is proposed that a key general characteristic of geosynchronous ion pitch angle distributions, field-aligned low energies, and field-perpendicular high energies is a signature of this energization mechanism. The presence of field-aligned ions cannot be presumed to be a signature of recent ionospheric extraction.

Mauk, B. H.↗
NASA NTRS2003

Proton and heavy ion acceleration facilities for space radiation research

The particles and energies commonly used for medium energy nuclear physics and heavy charged particle radiobiology and radiotherapy at particle accelerators are in the charge and energy range of greatest interest for space radiation health. In this article we survey some of the particle accelerator facilities in the United States and around the world that are being used for space radiation health and related research, and illustrate some of their capabilities with discussions of selected accelerator experiments applicable to the human exploration of space.

NASA Discipline Radiation Health↗
NASA NTRS2023

Heavy Ion Acceleration in 3he-Rich Solar Energetic Particle Events: New Insights From Solar Orbiter

We present Solar Orbiter energetic particle observations of two 3 He-rich events with features more clearly observed than in prior studies. The event of 2022 November 9 observed from 0.59 au contained hundreds of ultra-heavy ions (UH, mass >78 amu) whereas previous observations at 1 au have shown only an occasional count or two. The event of 2023 April 8 observed from 0.29 au fortuitously had very low ambient activity, making it possible to observe spectra from the 3 He acceleration mechanism without contamination, revealing extremely low H and 4 He intensities arriving simultaneously with other ions observed in typical 3 He-rich events. Taken together with previous studies we believe these data show that 3 He-rich events have a single acceleration mechanism that is responsible for the unique abundance features of 3 He, heavy ions, and UH ions. Considering the acceleration model of Roth and Temerin (1997) that heats the ions over a broad range of gyrofrequencies away from those damped by H and 4 He, we calculate reasonable fits to the observed abundances O-Fe. A key result is that high values of, e.g., Fe/O typical of such events is not due to preferential Fe heating, but on the contrary is due mainly to the depletion of O which at elevated temperatures has a charge-to-mass ratio in the region of the waves damped by 4He. The model also naturally incorporates features of high ionization states and neutron-rich isotope enhancements that have been long-standing puzzles in observations of this type of flare.

Solar flares↗