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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Computation on collisionless steady-state plasma flow past a charged disk

A computer method is presented using the 'inside-out' approach, for predicting the structure of the disturbed zone near a moving body in space. The approach uses fewer simplifying assumptions than other available methods, and is applicable to large ranges of the values of body and plasma parameters. Two major advances concerning 3-dimensional bodies are that thermal motions of ions as well as of electrons are treated realistically by following their trajectories in the electric field, and the technique for achieving self-consistency is promising for very large bodies. Three sample solutions were obtained for a disk-shaped body, charged negatively to a potential 4kT/e. With ion Mach number 4, and equal ion and electron temperatures, the wakes of a relatively small body (radius 5 Debye lengths) and a relatively large body (radius 100 Debye lengths) both begin to fill up between 2 and 3 body radii downstream. For the large body there is in addition a potential well (about 6kT/e deep) behind the body. Increasing the ion Mach number to 8 for the large body causes the potential well to become wider and longer but not deeper. For the large body, the quasineutrality assumption is validated outside of a cone-shaped region in the very near wake. For the large as well as the small body, the disturbed zone behind the body extends transversely no more than 2 or 3 body radii, a result of significance for the design of spacecraft boom instrumentation.

Parker, L. W.↗
NASA NTRS1977

Technique for measuring the differential ion flux vector

A diagnostic technique is discussed which gives the angle of incidence of a plasma stream, the energy corresponding to the mean velocity of the ions, and the distribution of the ion thermal motion superimposed on the drift. The technique is shown to be operable for low-energy plasma streams (5-60 eV) and in the presence of multiple plasma streams differing in direction and/or energy. Resolution is better than 3.5 deg with approximately 1% energy spread in the streams. The instrument samples the plasma at a single region in space, independent of the number of plasma streams or their characteristics. The technique was developed to investigate plasma flow interactions in the laboratory. Its capabilities are demonstrated by some preliminary data taken for the case of a long cylindrical body immersed in a drifting, collisionless plasma.

Stone, N. H.↗
NASA NTRS1979

Magnetic diffusion and ionization fractions in dense molecular clouds - The role of charged grains

The physics of magnetic diffusion in dense molecular clouds is examined, with particular attention given to the role of charged grains in controlling the process. The ionization fraction of dense molecular clouds in the presence of grains is determined from considerations of charge exchange, dissociative recombination, radiative recombination and collisions between grains and charged species, and it is found that the inclusion of grains tends to lower the ionization fraction for a given cosmic-ray ionization rate and metal depletion. The kinematics of grain motion is discussed and it is shown that at temperatures less than 30 K, each grain alternates rapidly in charge between -1 and 0 and thus executes periodic motion in a self-gravitating cloud containing a magnetic field. The full kinematics of magnetic diffusion including the motions of ions and electrons are then examined, taking into account the additional viscous force from charged grains, and numerical calculations of the diffusion time scales of uniform, magnetically supported clouds or cloud cores are presented.

Elmegreen, B. G.↗
NASA NTRS1981

The CAMEO barium release - E/parallel/ fields over the polar cap

Four successive thermite barium releases at an altitude of 965 km over polar cap invariant latitudes 84 to 76 deg near magnetic midnight were conducted from the orbiting second stage of the vehicle that launched Nimbus 7; the releases were made as part of the CAMEO (Chemically Active Material Ejected in Orbit) program. This was the first opportunity to observe the behavior of conventional barium release when conducted at orbital velocity in the near-earth magnetic field. The principal unexpected characteristic in the release dynamics was the high, 1.4 to 2.6 km/s, initial Ba(+) expansion velocity relative to an expected velocity of 0.9 km/s. Attention is also given to neutral cloud expansion, initial ion cloud expansion, convective motion, and the characteristics of field-aligned motion. The possibility of measuring parallel electric fields over the polar cap by observing perturbations in the motion of the visible ions is assessed.

Heppner, J. P.↗
NASA NTRS1982

The polar ionosphere

Self-consistent concepts which in many cases demonstrate the required relationships between electric currents, conductivity and electric fields are emerging from International Magnetospheric Study period research on the polar ionosphere and its role in the coupling between the ionosphere and the magnetopause. Observed phenomena may now be explained in terms of realistic variations in the electric current, conductivity and electric field parameters, and the distribution and composition of plasma can be reconciled with large scale plasma motion and ion production regions. Gaps remain, however, in the current understanding of the polar ionosphere's electrodynamic and plasma properties.

Heelis, R. A.↗
NASA NTRS1987

Effect of object potentials on the wake of a flowing plasma

The structure of the electric potential and ion density of the ion front in the near wake created by the flow of synthetic plasma past a conducting plate was investigated experimentally and numerically, with particular attention given to the effect of plate potential on the structure of the ion front. Results were obtained for a molecular nitrogen plasma with ambient electron densities of about 100,000/cu cm, ion temperatures of about 0.025 eV, electron temperatures of about 0.3 eV, and plasma flow velocities of about 10,000 m/s. Two-dimensional simulations of the laboratory experiments were performed by using a multiple waterbag technique. The calculated and experimental results show that wake closure is well described by the acceleration of ions in the plasma steady-state electric field. However, the ion-front motion is strongly affected by the imposed potential of the object creating the wake.

Katz, I.↗
NASA NTRS1982

Ion frictional heating at high latitudes and its possible use for an in situ determination of neutral thermospheric winds and temperatures

The Atmosphere Explorer C data base of ion temperature and ion drift velocities has been used to study the long recognized principle that large scale convection electric fields are responsible for substantial enhancements in the ion temperature at high latitudes. As had been indicated by various authors previously, the present study shows that there is a clear relationship between large ion velocities and ion temperature enhancements. Furthermore, with the help of a more quantitative study, it is found that, since ion heating is sensitive to the relative motion between the ion and neutral gases, the ion temperature and drift measurements can be used to extract neutral wind and neutral temperature information along the satellite track. From a study of several examples, it is concluded that the present approach can be used with varying degrees of accuracy for the diagnostic of thermospheric dynamical properties above 300 km when those properties are not measured directly. When neutral dynamical properties are measured, the approach could be used for a detailed study of the ion energy balance at high latitudes.

Saint-Maurice, J.-P.↗
NASA NTRS1976

Beam efflux measurements

Measurements have been made of the high energy thrust ions, (Group I), high angle/high energy ions (Group II), and high angle/low energy ions (Group IV) of a mercury electron bombardment thruster in the angular divergence range from 0 deg to greater than 90 deg. The measurements have been made as a function of thrust ion current, propellant utilization efficiency, bombardment discharge voltage, screen and accelerator grid potential (accel-decel ratio) and neutralizer keeper potential. The shape of the Group IV (charge exchange) ion plume has remained essentially fixed within the range of variation of the engine operation parameters. The magnitude of the charge exchange ion flux scales with thrust ion current, for good propellant utilization conditions. For fixed thrust ion current, charge exchange ion flux increases for diminishing propellant utilization efficiency. Facility effects influence experimental accuracies within the range of propellant utilization efficiency used in the experiments. The flux of high angle/high energy Group II ions is significantly diminished by the use of minimum decel voltages on the accelerator grid. A computer model of charge exchange ion production and motion has been developed. The program allows computation of charge exchange ion volume production rate, total production rate, and charge exchange ion trajectories for "genuine" and "facilities effects" particles. In the computed flux deposition patterns, the Group I and Group IV ion plumes exhibit a counter motion.

Komatsu, G. K.↗
NASA NTRS1981

The Retarding Potential Analyzer for Dynamics Explorer-B

The Retarding Potential Analyzer for Dynamics Explorer B measures the bulk ion velocity in the direction of the spacecraft motion, the constituent ion concentrations and the ion temperature along the satellite path. These parameters are derived from a least squares fit to the ion number flux versus energy curve obtained by sweeping or stepping the voltage applied to the internal retarding grids of the RPA. In addition, the spectral characteristics of irregularities in the total ion concentration are determined by high time resolution measurements and by use of a comb filter. These data are obtained from a separate wide aperture-sensor.

Hanson, W. B.↗
NASA NTRS1987

Ion energetics in the inner coma of Comet Halley

The cometary plasma in the magnetic barrier just outside the diamagnetic cavity which surrounds the nucleus of Comet Halley is virtually stagnant. The outflowing neutral gas exerts an outward ion-neutral drag force on this plasma, which balances the inward magnetic pressure gradient force in the vicinity of the contact surface. The cometary ions are frictionally heated due to the relative motion of the ion and neutral gases. The ion flow velocity must have a few km/s nonradial component in order to explain the ion temperatures measured by the ion mass spectrometer on Giotto.

Cravens, T. E.↗