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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Energetic ion and electron beams at the plasma-sheet boundary in the distant tail

Several energetic particle bursts observed by ISEE 3 in the distant tail are analyzed. The energetic particle data are supplemented by the electron plasma and magnetic field measurements. These bursts are characterized by large velocity-dispersion effects, with energetic electrons observed first, followed by ions with continuously lower velocities. Both ions and electrons stream in the tailward direction. Protons and alpha particles of the same energy per nucleon are observed at the same time. The dispersion effects are observed in reverse order when the spacecraft leaves from the boundary layer into the lobe. No obvious signature indicating the passage of a plasmoid has been observed in the particle or magnetic field data during or immediately following these bursts. It is concluded that these beams at the plasma-sheet boundary originate at a steady source, presumably close to a neutral line, and not at a time varying source. The velocity filter effect in a dawn-dusk electric field arranges particles with progressively lower velocity further inside the wedge-shaped region of reconnected field lines. The plasma electron distribution exhibits a tailward directed heat flux within this layer.

Scholer, M.↗
NASA NTRS2003

The Effect of Rotating a Faraday Disc Perpendicular to an Applied Magnetic Field Theory and Experiment

A magnetohydrodynamic model that examines the effect of rotating an electrically conducting cylinder with a uniform external magnetic field applied orthogonal to its axis is presented. Noting a simple geometry, it can be classified as a fundamental dynamo problem. For the case of an infinitely long cylinder, an analytical solution is obtained and analyzed in detail. A semi-analytical model was developed that considers a finite cylinder. Experimental data from a spinning brass wheel in the presence of Earth's magnetic field were compared to the proposed theory and found to fit well.

Mazuruk, Konstantin↗
NASA NTRS1979

Countercurrent distribution of biological cells

A neutral polymer phase system consisting of 7.5 percent dextran 40/4.5 percent PEG 6, 0.11 M Na phosphate, 5 percent fetal bovine serum (FBS), pH 7.5, was developed which has a high phase droplet electrophoretic mobility and retains cell viability over many hours. In this and related systems, the drop mobility was a linear function of drop size, at least in the range 4-30 micron diameter. Applications of and electric field of 4.5 v/cm to a system containing 10 percent v/v bottom phase cleared the system more than two orders of magnitude faster than in the absence of the field. At higher bottom phase concentrations a secondary phenomenon intervened in the field driven separations which resulted in an increase in turbidity after clearing had commenced. The increase was associated with a dilution of the phase system in the chamber. The effect depended on the presence of the electric field. It may be due to electroosmotic flow of buffer through the Amicon membranes into the sample chamber and flow of phase system out into the rinse stream. Strategies to eliminate this problem are proposed.

Brooks, D. E.↗
NASA NTRS2006

Design and Modelling of a Microfluidic Electro-Lysis Device with Controlling Plates

Many Lab-on-Chip applications require sample pre-treatment systems. Using electric fields to perform cell-lysis in bio-MEMS systems has provided a powerful tool which can be integrated into Lab-on-a-Chip platforms. The major design considerations for electro-lysis devices include optimal geometry and placement of micro-electrodes, cell concentration, flow rates, optimal electric field (e.g. pulsed DC vs. AC), etc. To avoid electrolysis of the flowing solution at the exposed electrode surfaces, magnitudes and the applied voltages and duration of the DC pulse, or the AC frequency of the AC, have to be optimized for a given configuration. Using simulation tools for calculation of electric fields has proved very useful, for exploring alternative configurations and operating conditions for achieving electro cell-lysis. To alleviate the problem associated with low electric fields within the microfluidics channel and the high voltage demand on the contact electrode strips, two "control plates" are added to the microfluidics configuration. The principle of placing the two controlling plate-electrodes is based on the electric fields generated by a combined insulator/dielectric (gladwater) media. Surface charges are established at the insulator/dielectric interface. This paper discusses the effects of this interface charge on the modification of the electric field of the flowing liquid/cell solution.

Jenkins, A.↗
NASA NTRS1988

The effect of mid-latitude electron precipitation on the geoelectric field

A simple model is outlined to describe electron precipitation from the population of charged particles trapped in the earth's magnetic field; almost all of the precipitation is shown to occur in the region of the South Atlantic Anomaly. When the effect of a dawn-to-dusk electric field across the magnetosphere is included in the model, a diurnal modulation of the precipitated electron flux is predicted. Experimental evidence which supports the diurnal modulation model is described.

Sheldon, W. R.↗
NASA NTRS1988

MOSFET Electric-Charge Sensor

Charged-particle probe compact and consumes little power. Proposed modification enables metal oxide/semiconductor field-effect transistor (MOSFET) to act as detector of static electric charges or energetic charged particles. Thickened gate insulation acts as control structure. During measurements metal gate allowed to "float" to potential of charge accumulated in insulation. Stack of modified MOSFET'S constitutes detector of energetic charged particles. Each gate "floats" to potential induced by charged-particle beam penetrating its layer.

Robinson, Paul A., Jr.↗
NASA NTRS1983

Warm fog dispersal

The charged particle generator was further tested after some design modification. The generator performance was measured with additional instrumentation and found to confirm previous measurements. Plans for a field testing were than developed. The overall status of the program and the field test plans were presented to a group of atmospheric scientists and electrostatic experts at the NASA/MSFC sponsored USRA Workshop on Electrostatic Fog Dispersal at NCAR, Boulder, Colorado discussed in previous sections. The recommendations from this workshop are being evaluated as to whether NASA should proceed with the field test or whether further theoretical research on the phenomenon of electrostatic fog dispersal and additional development of the charged particle generator should be carried out. Information obtained from the USRA Workshop clearly identified three physical mechanisms that could possibly influence the fog dispersal process, which heretofore have not been considered, and which may provide additional insight to the direction of further fog dispersal work. These mechanisms are: the effect of corona discharge on the electric field strength at the surface, the influx of fog into the cleared volume by turbulent diffusion, and the increase in supersaturation as liquid water is removed, activating haze particles, and thus generating more fog. Plans are being formulated to investigate these mechanisms.

Frost, W.↗
NASA NTRS2000

Electrical Charging Hazards Originating from the Surface (ECHOS): Understanding the Martian Electro-Meteorological Environment

In 1999, the NASA/Human Exploration and Development of Space (HEDS) enterprise selected a number of payloads to fly to the Martian surface in an 03 opportunity (prior to the MPL loss). Part of a proposed experiment, ECHOS, was selected to specifically understand the electrical charging hazards from tribocharged dust in the ambient atmosphere, in dust devils, and in larger storms. It is expected that Martian dust storms become tribocharged much like terrestrial dust devils which can possess almost a million elementary charges per cubic centimeter. The ECHOS package features a set of instruments for measuring electric effects: a radio to detect AC electric fields radiating from discharges in the storm,a DC electric field system for sensing electrostatic fields from concentrations of charged dust grains, and a lander electrometer chain for determining the induced potential on its body and MAV (Mars Ascent Vehicle) during the passages of a charged dust storm. Given that electricity is a systemic process originating from wind-blown dust, we also proposed to correlate the electrical measurements with fundamental fluid/meteorological observations, including wind velocity and vorticity, temperature, and pressure. Triboelectricity will also affect local chemistry, and chemical-sensing devices were also considered a feature of the package. The primary HEDS objectives of the ECHOS sensing suite is to discover and monitor the natural electrical hazards associated with dust devils and storms, and determine their enviro-effectiveness on human systems. However, ECHOS also has a strong footprint in the overarching science objectives of the Mars Surveyor Program.

Farrell, W. M.↗
NASA NTRS1986

Measurements of the dynamics of the high-latitude thermosphere

The study of the dynamics and thermodynamics of the earth's upper atmosphere has made significant progress over the past few years owing to the availability of new global-scale data sets from the Dynamics Explorer satellites. The thermospheric wind and temperature fields at high altitude have been observed to depend strongly on forcing processes of magnetospheric origin. A key momentum source is due to the drag effect of ions convecting in response to electric fields mapped down on the ionosphere from magnetospheric boundary regions. Likewise, an important heat source derives from Joule or frictional dissipation due to ion/neutral difference velocities governed by magnetospheric forcing. In this paper the progress made over the last 2-3 years initiated by the new satellite measurements is discussed, and published data on ion and neutral motions are reviewed in the context of the energy and momentum coupling between the magnetosphere and the ionosphere/neutral upper atmosphere.

Killeen, T. L.↗
NASA NTRS2005

Diamond-Coated Carbon Nanotubes for Efficient Field Emission

Field-emission cathodes containing arrays of carbon nanotubes coated with diamond or diamondlike carbon (DLC) are undergoing development. Multiwalled carbon nanotubes have been shown to perform well as electron field emitters. The idea underlying the present development is that by coating carbon nanotubes with wideband- gap materials like diamond or DLC, one could reduce effective work functions, thereby reducing threshold electric-field levels for field emission of electrons and, hence, improving cathode performance. To demonstrate feasibility, experimental cathodes were fabricated by (1) covering metal bases with carbon nanotubes bound to the bases by an electrically conductive binder and (2) coating the nanotubes, variously, with diamond or DLC by plasma-assisted chemical vapor deposition. In tests, the threshold electric-field levels for emission of electrons were reduced by as much as 40 percent, relative to those of uncoated- nanotube cathodes. Coating with diamond or DLC could also make field emission-cathodes operate more stably by helping to prevent evaporation of carbon from nanotubes in the event of overheating of the cathodes. Cathodes of this type are expected to be useful principally as electron sources for cathode-ray tubes and flat-panel displays.

Dimitrijevic, Stevan↗
NASA NTRS1991

A preliminary characterization of applied-field MPD thruster plumes

Electric probes, quantitative imaging, and emission spectroscopy were used to study the plume characteristics of applied field magnetohydrodynamic thrusters. The measurements showed that the applied magnetic field plays the dominant role in establishing the plume structure, followed in importance by the cathode geometry and propellant. The anode radius had no measurable impact on the plume characteristics. For all cases studied the plume was highly ionized, though spectral lines of neutral species were always present. Centerline electron densities and temperatures ranged from 2 times 10 (exp 18) to 8 times 10 (exp 18) m(exp -3) and from 7500 to 20,000 K, respectively. The plume was strongly confined by the magnetic field, with radial density gradients increasing monotonically with applied field strength. Plasma potential measurements show a strong effect of the magnetic field on the electrical conductivity and indicate the presence of radial current conduction in the plume.

Myers, Roger M.↗
NASA NTRS1991

A preliminary characterization of applied-field MPD thruster plumes

Electric probes, quantitative imaging, and emission spectroscopy were used to study the plume characteristics of applied-field MPD thrusters. The measurements showed that the applied magnetic field plays the dominant role in establishing the plume structure, followed in importance by the cathode geometry and propellant. The anode radius had no measurable impact on the plume characteristics. For all cases studied the plume was highly ionized, though spectral lines of neutral species were always present. Centerline electron densities and temperatures ranged from 2 x 10 to the 18th to 8 x 10 to the 18th cu m and from 7500 to 20,000 K, respectively. The plume was strongly confined by the magnetic field, with radial density gradients increasing monotonically with applied field strength. Plasma potential measurements show a strong effect of the magnetic field on the electrical conductivity and indicate the presence of radial current conduction in the plume.

Myers, Roger M.↗
NASA NTRS1994

Inertial currents in isotropic plasma

The magnetospheric convection electric field contributes to Birkeland currents. The effects of the field are to polarize the plasma by displacing the bounce paths of the ions from those of electrons, to redistribute the pressure so that it is not constant along magnetic field lines, and to enhance the pressure gradient by the gradient of the bulk speed. Changes in the polarization charge during the convection of the plasma are neutralized by electrons in the form of field-aligned currents that close through the ionosphere. The pressure drives field-aligned currents through its gradient in the same manner as in quasi-static plasmas, but with modifications that are important if the bulk speed is of the order of the ion thermal speed; the variations in the pressure along field lines are maintained by a weak parallel potential drop. These effects are described in terms of the field-aligned currents in steady state, isotropic, MHD plasma. Solutions are developed by taking the MHD limit ot two-fluid solutions and illustrated in the special case of Maxwellian plasma for which the temperature is constant along magnetic field lines. The expression for the Birkeland current density is a generalization of Vasyliunas' expression for the field-aligned current density in quasi-static plasma and provides a unifying expression when both pressure gradients and ion inertia operate simultaneously as sources of field-aligned currents. It contains a full account of different aspects of the ion flow (parallel and perpendicular velocity and vorticity) that contribute to the currents. Contributions of ion inertia to field-aligned currents will occur in regions of strong velocity shear, electric field reversal, or large gradients in the parallel velocity or number density, and may be important in the low-latitude boundary layer, plasma sheet boundary layer, and the inner edge region of the plasma sheet.

Heinemann, M.↗
NASA NTRS1993

Inertial Currents in Isotropic Plasma

The magnetospheric convection electric field contributes to Birkeland currents. The effects of the field are to polarize the plasma by displacing the bounce paths of the ions from those of electrons, to redistribute the pressure so that it is not constant along magnetic field lines, and to enhance the pressure gradient by the gradient of the bulk speed. Changes in the polarization charge during the convection of the plasma are neutralized by electrons in the form of field-aligned currents that close through the ionosphere. The pressure drives field-aligned currents through its gradient in the same manner as in quasi-static plasma, but with modifications that are important if the bulk speed is of the order of the ion thermal speed; the variations in the pressure along field lines are maintained by a weak parallel potential drop. These effects are described in terms of the field-aligned currents in steady state, isotropic, MED plasma. Solutions are developed by taking the MHD limit of two-fluid solutions and illustrated in the special case of Maxwellian plasma for which the temperature is constant along magnetic field lines. The expression for the Birkeland current density is a generalization of Vasyliunas' expression for the field-aligned current density in quasi-static plasma and provides a unifying expression when both pressure gradients and ion inertia operate simultaneously as sources of field-aligned currents. It contains a full account of different aspects of the ion flow (parallel and perpendicular velocity and vorticity) that contribute to the currents. Contributions of ion inertia to field-aligned currents will occur in regions of strong velocity shear, electric field reversal, or large gradients in the parallel velocity or number density, and may be important in the low-latitude boundary layer, plasma sheet boundary layer, and the inner edge region of the plasma sheet.

Heinemann, M.↗
NASA NTRS1994

Inertial currents in isotropic plasma

The magnetospheric convection electric field contributes to Birkeland currents. The effects of the field are to polarize the plasma by displacing the bounce paths of the ions from those of electrons, to redistribute the pressure so that it is not constant along magnetic field lines, and to enhance the pressure gradient by the gradient of the bulk speed. Changes in the polarization charge during the convection of the plasma are neutralized by electrons in the form of field-aligned currents that close through the ionosphere. The pressure drives field-aligned currents through its gradient in the same manner as in quasi-static plasma, but with modifications that are important if the bulk speed is of the order of the ion thermal speed; the variations in the pressure along field lines are maintained by a weak parallel potential drop. These effects are described in terms of the field-aligned currents in steady state, isotropic, magnetohyrodynamic (MHD) plasma. Solutions are developed by taking the MHD limit of two-fluid solutions and illustrated in the special case of Maxwellian plasma for which the temperature is constant along magnetic field lines. The expression for the Birkeland current density is a generalization of Vasyliunas' expression for the field-aligned current density in quasi-static plasma and provides a unifying expression when both pressure gradients and ion inertia operate simultaneously as sources of field-aligned currents. It contains a full account of different aspects of the ion flow (parallel and perpendicular velocity and vorticity) that contribute to the currents. Contributions of ion inertia to field-aligned currents will occur in regions of strong velocity shear, electric field reversal, or large gradients in the parallel velocity or number density, and may be important in the low-latitude boundary layer, plasma sheet boundary layer, and the inner edge region of the plasma sheet.

Heinemann, M.↗
NASA NTRS1986

Electron acceleration via kinetic Alfven waves

Kinetic effects on obliquely propagating shear Alfven waves are reviewed. The wave becomes dispersive and carries a significant parallel electric field. The polarization and dispersion of these waves are discussed, showing that electrons can be effectively accelerated along field lines by these waves. Nonlinear effects such as solitary waves, nonlinear damping due to current-driven instabilities, and anomalous resistivity are treated. Observations of electric and magnetic field perturbations on auroral field lines which seem to be related to these waves are studied. Evidence for the existence of these kinetic Alfven waves is not firm.

Goertz, C. K.↗
NASA NTRS1976

On the magnetic mirroring as the basic cause of parallel electric fields

Among the different proposed mechanisms for generating parallel electric fields, magnetic mirroring of charged particles seems to be the most plausible. In the present paper, it is suggested that magnetic mirroring is the basic cause of parallel electric fields in the magnetosphere and that the magnetic mirroring effect may be able to form the basis of an auroral theory that can remove a major portion of the ambiguity of observations. In the model proposed, the parallel electric field is due to a magnetic confinement of a negatively charged hot collision-free plasma. A transfer of electron gyroenergy into wave energy tends to weaken this confinement; if this energy transfer becomes too strong, the parallel potential gradient will break down. Hence, from this model, in contrast to certain other models of parallel electric fields, only a small fraction of the total auroral particle energy may be expected to be transformed into electromagnetic wave energy during the acceleration process.

Lennartsson, W.↗
NASA NTRS2015

Evidence of Processing Non-Idealities in 4H-SiC Integrated Circuits Fabricated With Two Levels of Metal Interconnect

The fabrication and prolonged 500 C electrical testing of 4H-SiC junction field effect transistor (JFET) integrated circuits (ICs) with two levels of metal interconnect is reported in another submission to this conference proceedings. While some circuits functioned more than 3000 hours at 500 C, the majority of packaged ICs from this wafer electrically failed after less than 200 hours of operation in the same test conditions. This work examines the root physical degradation and failure mechanisms believed responsible for observed large discrepancies in 500 C operating time. Evidence is presented for four distinct issues that significantly impacted 500 C IC operational yield and lifetime for this wafer.

JFET↗