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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

The production of ion conics by oblique double layers

Magnetized test ions are subjected to acceleration through a numerically simulated oblique double layer in order to determine whether they emerge with velocity vectors aligned with or oblique to the ambient magnetic field. A criterion for oblique alignment, depending on the double-layer parameters and on the external magnetization, is obtained. When it is applied to observed and theoretical auroral double layers, this criterion predicts that accelerated heavy ions will be substantially less magnetic field aligned than will accelerated hydrogen ions, thus suggesting auroral double layers as a source of high-energy ion conics. Test particle simulations are also used to investigate the perpendicular heating of ions at low altitudes by the electric fields associated with moving auroral arcs. The rapid motion of small-scale structures in the arcs is suggested as a source of low-energy conical ion distributions, and the slow drifts of the entire arc forms are inferred to heat ionospheric ions.

Borovsky, J. E.↗
NASA NTRS1984

Electron precipitation zones around major ground-based VLF signal sources

The spatial distribution of electron precipitation induced by VLF signals from ground-based transmitters is determined by using a test particle computer model of the gyroresonant wave-particle interaction (Inan et al., 1982). The results are presented as contours of energy flux on a map of the region around each transmitter. It is shown that the size of the precipitation zones is a strong function of the geographic location of the transmitter, as well as its radiated power and operating frequency. In general, the precipitation zones are much wider in longitude than in latitude and are oriented along lines of constant geomagnetic latitude. Assuming backscatter and/or wave echoing, precipitation zones around the points that are magnetically conjugate to the sources are also estimated. The results presented can be used to interpret satellite- or ground-based measurements of the precipitation induced by ground-based VLF transmitters.

Inan, U. S.↗
NASA NTRS1984

Predictions of lithium interactions with earth's bow shock in the presence of wave activity

The results of a test-particle simulation studying the movement of a lithium tracer ion injected upstream of the bow shock are reported. Wave activity consists of parallel and antiparallel propagating Alfven waves characterized by a frequency power spectrum within a frequency or range of amplitudes defined separately in the upstream and downstream regions. The results show that even a moderate level of wave activity can substantially change the results obtained in the absence of waves. Among the effects observed are: (1) increased ion transmission; (2) both the average energy gain and spread about the average are increased for transmitted and reflected particles; (3) the average final pitch angle for transmitted particles tends to 90 deg, and the spread of reflected particles is reduced; and (4) the spatial dispersion of the ions on the bow shock after a single encounter is increased.

Decker, R. B.↗
NASA NTRS1985

Effects of coating rectangular microscopic electrophoresis chamber with methylcellulose

One of the biggest problems in obtaining high accuracy in microscopic electrophoresis is the parabolic flow of liquid in the chamber due to electroosmotic backflow during application of the electric field. In chambers with glass walls the source of polarization leading to electroosmosis is the negative charge of the silicare and other ions that form the wall structure. It was found by Hjerten, who used a rotating 3.0 mm capillary tube for free zone electrophoresis, that precisely neutralizing this charge was extremely difficult, but if a neutral polymer matrix (formaldehyde fixed methylcellulose) was formed over the glass (quartz) wall the double layer was displaced and the viscosity at the shear plane increased so that electroosmotic flow could be eliminated. Experiments were designed to determine the reliability with which methylcellulose coating of the Zeiss Cytopherometer chamber reduced electroosmotic backflow and the effect of coating on the accuracy of cell electrophoretic mobility (EPN) determinations. Fixed rat erythrocytes (RBC) were used as test particles.

Plank, L. D.↗
NASA NTRS1985

Electrophoretic mobility of cells in a vertical Ficoll gradiant

The upward migration of living cells and test particles under the influence of a constant electric field in a low conductivity Ficoll gradient occurs at nearly constant velocity. Viscosity and neutral polymer concentration affect migration rate. Decreasing viscosity speeds up the particle migration, decreasing neutral polymer (Ficoll) concentration, slows particle migration, since electrophoretic mobility increases approximately linearly with neutral polymer concentration. Neutral polymers interact with the cell surface to effectively raise its zeta potential. An analytic function was developed from the known dependence of these physical variables on migration distance; the analysis expresses migration velocity as an explicit function of position in the density gradient. It predicts an almost linear increase in velocity of about 12 to 16% over the working region of the gradient. It was numerically integrated and correctly predicts cell migration distance vs time curves without the use of any fitted parameters. The resulting migration curves follow the expected slowly varying exponential form that closely resembles a straight line. The ability to determine standard electrophoretic mobilities from such curves depends on knowledge of the effect of Ficoll on the zeta potential of the cell type that is separated.

Plank, L. D.↗
NASA NTRS1985

Density gradient electrophoresis of cultured human embryonic kidney cells

Ground based confirmation of the electrophoretic heterogeneity of human embryonic kidney cell cultures, the general characterization of their electrophoretic migration, and observations on the general properties of cultures derived from electrophoretic subpopulations were studied. Cell migration in a density gradient electrophoresis column and cell electrophoretic mobility was determined. The mobility and heterogeneity of cultured human embryonic kidney cells with those of fixed rat erythrocytes as model test particle was compared. Electrophoretically separated cell subpopulations with respect to size, viability, and culture characteristics were examined.

Plank, L. D.↗
NASA NTRS1985

Energetic ion acceleration at collisionless shocks

An example is presented from a test particle simulation designed to study ion acceleration at oblique turbulent shocks. For conditions appropriate at interplanetary shocks near 1 AU, it is found that a shock with theta sub B n = 60 deg is capable of producing an energy spectrum extending from 10 keV to approx. 1 MeV in approx 1 hour. In this case total energy gains result primarily from several separate episodes of shock drift acceleration, each of which occurs when particles are scattered back to the shock by magnetic fluctuations in the shock vicinity.

Decker, R. B.↗
NASA NTRS1985

Onion-shell model for cosmic ray electrons and radio synchrotron emission in supernova remnants

The spectrum of cosmic ray electrons, accelerated in the shock front of a supernova remnant (SNR), is calculated in the test-particle approximation using an onion-shell model. Particle diffusion within the evolving remnant is explicity taken into account. The particle spectrum becomes steeper with increasing radius as well as SNR age. Simple models of the magnetic field distribution allow a prediction of the intensity and spectrum of radio synchrotron emission and their radial variation. The agreement with existing observations is satisfactory in several SNR's but fails in other cases. Radiative cooling may be an important effect, especially in SNR's exploding in a dense interstellar medium.

Beck, R.↗
NASA NTRS1985

Shock drift acceleration in the presence of waves

Attention is given to the initial results of a model designed to study the modification of the scatter-free, shock drift acceleration of energetic test particles by wave activity in the vicinity of a quasi-perpendicular, fast-mode MHD shock. It is emphasized that the concept of magnetic moment conservation is a valid approximation only in the perpendicular and nearly perpendicular regimes, when the angle theta-Bn between the shock normal and the upstream magnetic field vector is in the range from 70 deg to 90 deg. The present investigation is concerned with one step in a program which is being developed to combine the shock drift and diffusive processes at a shock of arbitrary theta-Bn.

Decker, R. B.↗
NASA NTRS1984

Dust in magnetised plasmas - Basic theory and some applications

In this paper the theory of charged test particle motion in magnetic fields is reviewed. This theory is then extended to charged dust particles, for which gravity and charge fluctuations play an important role. It is shown that systematic drifts perpendicular to the magnetic field and stochastic transport effects may then have to be considered none of which occur in the case of atomic particles (with the exception of charge exchange reactions). Some applications of charged dust particle transport theory to planetary rings are then briefly discussed.

Northrop, T. G.↗
NASA NTRS1986

Calibration of the ISEE plasma composition experiment

The Plasma Composition experiment on the ISEE-1 satellite was designed to measure ions from 1 to 16 amu, at energies from near zero to 16 keV. The two nearly identical flight instruments were calibrated by means of preflight laboratory tests and in-flight data comparisons. This document presents most of the details of those efforts, with special emphasis on the low energy (0 to 100 eV) portion of the instrument response. The analysis of the instrument includes a ray-tracing calculation, which follows an ensemble of test particles through the detector.

Baugher, C. R.↗
NASA NTRS1985

A tandem mirror plasma source for a hybrid plume plasma propulsion concept

This paper describes a tandem mirror magnetic plasma confinement device to be considered as a hot plasma source for the hybrid plume rocket concept. The hot plasma from this device is injected into an exhaust duct, which will interact with an annular layer of hypersonic neutral gas. Such a device can be used to study the dynamics of the hybrid plume and to experimentally verify the numerical predictions obtained with computer codes. The basic system design is also geared toward being lightweight and compact, as well as having high power density (i.e., several kW/sq cm) at the exhaust. This feature is aimed toward the feasibility of 'space testing'. The plasma is heated by microwaves. A 50 percent heating efficiency can be obtained by using two half-circle antennas. The preliminary Monte Carlo modeling of test particles result reported here indicates that interaction does take place in the exhaust duct. Neutrals gain energy from the ion, which confirms the hybrid plume concept.

Yang, T. F.↗
NASA NTRS1986

Jovian VLF chorus and Io torus aurora

A test particle model of the cyclotron resonance interaction of waves and trapped radiation belt particles is used to estimate the energetic electron fluxes precipitated by Jovian VLF chorus waves observed on the Voyager 1 and 2 spacecraft near the Io torus. The precipitation fluxes induced by 1-s-long chorus wave packets at L = 7.6 and 8.6 are estimated to be bursts of 5s duration with a peak of 0.3-3 and 0.7-7 ergs/sq cm s that consist of electrons of 5-100 keV energy and that arrives at the ionosphere 15 s after the generation of the chorus wave at the equatorial plane. The effects in the Jovian ionosphere of the chorus-induced precipitation are estimated using existing ionospheric models. A possible experiment for measuring Jovian chorus-induced aurora is proposed and discussed.

Inan, U. S.↗
NASA NTRS1986

Production of flickering aurora and field-aligned electron flux by electromagnetic ion cyclotron waves

Recent observations have suggested that flickering aurora is produced by a modulation of the field-aligned component of the electron flux within an auroral arc. It is proposed that a portion of the field-aligned electrons are of ionospheric origin and that these electrons are accelerated and their flux modulated by electromagnetic ion cyclotron waves that occur below the main acceleration region on auroral arc field lines. A model of the electromagnetic ion cyclotron wave shows that the parallel phase velocity of the wave increase as the wave propagates toward the ionosphere. A test particle calculation shows that ionospheric electrons trapped or reflected by the wave are accelerated to energies of several keV and that their flux is modulated at the wave frequency. The relative amplitudes of the model wave electric fields are consistent with the observations of small-scale low-frequency ionospheric and magnetospheric electric fields near auroral arcs of approximately 10 mV/m and 100 mV/m, respectively. The large-amplitude ion cyclotron waves also produce a ponderomotive force and a self-consistent ambipolar electric field. Energy considerations show that the downward energy flux in the electromagnetic ion cyclotron wave can be several percent of the total downward auroral electron energy flux.

Temerin, M.↗
NASA NTRS1987

Electron acceleration in stochastic double layers

Transversely localized double layers evolve randomly in turbulent regions of strongly magnetized plasma carrying current along the magnetic field. Results from numerical simulations and spacecraft observations in the auroral plasma indicate that the parallel electric field in such regions is microscopically intermittent or stochastic. The implications of stochastic double layer fields on electron acceleration will be discussed in terms of a statistical process involving ensemble averages over test particle motion. A Fokker-Planck equation can be derived for the electron phase space density, which depends on the mean and rms amplitudes of the double layers, the mean double layer density, and the initial electron velocity distribution. It is shown that the resulting electron acceleration is very sensitive to the ratio of the initial electron energy to the rms double layer amplitude. When this ratio is large, the acceleration process differs little from that expected in a dc electric field. When it is small, stochastic heating competes with directed acceleration. Evidence for both cases can be found in the auroral ionosphere in association with so-called inverted-V precipitation and collimated edge precipitation.

Lotko, William↗
NASA NTRS1986

The acceleration of ions and electrons by electromagnetic ion cyclotron waves

Test particle calculations of the interaction of electrons and ions with electromagnetic ion cyclotron waves are examined. It is observed that field-aligned electrons can be accelerated parallel to the magnetic fields by the cyclotron waves and that the ions can be accelerated perpendicular to the magnetic field. The data reveal that the ions can be accelerated more effectively when the wave frequency is half (.5) the ion gyrofrequency.

Temerin, M.↗
NASA NTRS1986

Ion heating by waves with frequencies below the ion gyrofrequency

Ion heating by broadband and coherent waves with relatively small amplitude and frequencies below the ion gyrofrequency is examined. The theoretical results, verified by test particle calculations, show that such waves can heat ions to high energies, and in particular produce the ion conic distributions observed in the earth's magnetosphere. The model utilized differs from other approaches in that neither quasi-linear theory nor stochastic acceleration in a large amplitude wave are used to heat ions. This heating mechanism may be significant in other geophysical and astrophysical environments.

Temerin, M.↗
NASA NTRS1986

Origin of large magnetic fluctuations in the magnetosheath of Venus

The origin of large-amplitude hydromagnetic waves in the Venus magnetosheath downstream of the quasi-parallel bow shock is investigated by means of numerical simulations. It is shown that the most likely source of these waves is the bow shock itself, rather than an instability involving the solar wind and oxygen ions of planetary origin. Pickup of O(+) ions by these waves is also examined and shown to be in agreement with previous test particle calculations. The effect of mass loading on the structure of the shock is also discussed.

Winske, D.↗