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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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Source variations of interplanetary Jovian electrons - Voyagers 1 and 2 results

The large intensity of interplanetary Jovian electrons at 1 AU and near the Jovian magnetosphere have been attributed to the large scale solar wind structure. The only variations that can be definitely attributed to the source (i.e. the magnetosphere) are the 10 hour variations observed within about 1 AU of Jupiter. During the pre-Jupiter-encounter period, the Voyagers 1 and 2 spacecraft are separated by about 1 corotation day, facilitating the separation of variations due to corotating streams, which occur 1 day apart on the two spacecraft

Conlon, T. F.↗
NASA NTRS2011

High Energy Cosmic Electrons: Messengers from Nearby Cosmic Ray Sources or Dark Matter?

This slide presentation reviews the recent discoveries by the Large Area Telescope (LAT) and the Gamma-ray Burst Monitor (GBM) on board the Fermi Gamma-Ray Telescope in reference to high energy cosmic electrons, and whether their source is cosmic rays or dark matter. Specific interest is devoted to Cosmic Ray electrons anisotropy,

Moiseev, Alexander↗
NASA NTRS1987

A possible energy source to power stable auroral red arcs - Precipitating electrons

Results of coincident measurements by ground-based photometers and the low-altitude plasma instrument on board the Dynamics Explorer 2 satellite are presented that demonstrate the association of precipitating low-energy electrons with stable auroral red (SAR) arcs. A search of available data has yielded 23 instances of DE 2 overflights during the presence of SAR arcs being monitored by the photometers. For each case, downward fluxes of electrons are found to be enhanced along field lines penetrating the arcs in relation to regions both north and south of the features. Modeling of the atmospheric response to these influxes indicates that these electrons can represent a major source of the energy required to establish temperature profiles within the ionospheric electron gas that are sufficient to produce the recorded 6300-A emission rates. The sensitivity of these results to uncertainties of the assumed spacecraft potential and thermospheric composition has been investigated and found to be important, but does not alter the conclusion that precipitating electrons are a fundamental link in the production of SAR arcs.

Slater, D. W.↗
NASA NTRS2004

The Wind and Temperature Spectrometer (WTS) in the Atmospheric Neutral Density Experiment (ANDE) Satellite

Miniaturization efforts in new spectrometers for ionosphere/thermosphere investigations of the ion-drifts and neutral winds and corresponding temperatures make possible very light (about 250 g) packages consuming less than 0.4 W. Previously described, our approach measures the angular and energy distributions of neutral atoms and molecules (or ions) in two perpendicular planes; using those distributions to determine the full wind vector, the temperature and the relative densities of O and N2, as required for the ANDE mission. The measurements require two separate electron impact ion sources each with its own electron beam cathode. We have developed a low-temperature thermionic emission cathode that delivers 1 mA electron current at 80 mW power, making it possible to operate neutral wind-temperature experiments for the first time with powers less than 0.5 W. Advances in the ion optics of the energy-angle spectrometer enhance the energy resolution-aperture product more than a factor of 3 to enable energy resolutions of a few percent with large apertures. With these technology improvements it is now possible to obtain the full neutral wind vector, temperature and O/N2, density ratio once per second in a 250g/0.4W package with sensitivity up to about 500 km altitude in the thermosphere. We will describe the WTS as deployed in ANDE and show simulated data with the non-linear least squares analysis to illustrate expected performance of the WTS in the estimated errors in the three components of the wind, the temperature, and the relative densities.

Herrero, F. A.↗
NASA NTRS1987

Solar cycle changes in the ionization sources of the nightside Venus ionosphere

Using new and previous experimental evidence, it is argued that the height-integrated flux of O(+) ions transported from the dayside Venus ionosphere into the nightside ionosphere is strongly reduced (shut off) at solar cycle minimum (SCmin) and that the electron impact source becomes the predominant nightside ionization source during this phase of the solar cycle. The height-integrated transterminator O(+) flux, which is probably the dominant nightside ionization source at solar cycle maximum (SCmax), is shut off at SCmin by compression of the dayside ionopause to low altitude. It is suggested that the ionopause is depressed because the dayside ionospheric kinetic pressure field is reduced by a factor of approximately 3 from its SCmas value and that the typical SCmin solar wind dynamic pressure, which is not less than the typical SCmax value, cannot be balanced by the ionospheric pressure field at altitudes above approximately 250 km.

Knudsen, William C.↗
NASA NTRS1983

Voyager observations of Saturnian ion and electron phase space densities

Voyager 1 and 2 low-energy charged particle (LECP) observations of 30-keV to 2-MeV electron and ion energy spectra and angular distributions have been used to calculate phase space densities at constant first and second adiabatic invariants in the Saturnian magnetosphere. The results are generally consistent with inward radial diffusion from an external source. The data obtained also indicate a source of ions located within the orbital distance of Enceladus capable of producing 10- to 40-MeV/Gauss ions as well as a source of electrons at about 3.5 Saturn radii which produces particles at 100 to 200 MeV/Gauss. Higher magnetic moment (200-400 MeV/Gauss) ions extend from the sunward boundary between a plasma mantle and the region of durable trapping at the Saturn radius; the behavior of the phase space density suggests inward diffusion of these particles from a source at the boundary. The identification of sources of low (10 to 200 MeV/Gauss) magnetic moment particles deep in the Saturnian magnetosphere is a new result of this work. Several analyses of the observed phase space densities in terms of time-independent radial diffusion are presented.

Armstrong, T. P.↗
NASA NTRS1983

Electron velocity distributions near the earth's bow shock

New information is presented on the general characteristics of electron distribution functions upstream, within, and downstream of the earth's bow shock, thereby providing new insights into the instabilities in collisionless shocks. The results presented are from a survey of electron velocity distributions measured near the earth's bow shock between October 1977 and December 1978 using the Los Alamos/Garching plasma instrumentation aboard ISEE 2. A wide variety of distribution shapes is found within the different plasma regions in close proximity to the bow shock. It is found that these shapes can be classified into general types that are characteristic of three different plasma regions, namely the upstream region or electron foreshock, the shock proper where most of the heating occurs, and the downstream region or the magnetosheath. Evidence is provided that field-aligned, rather than cross-field, instabilities are the major source of electron dissipation in the earth's bow shock.

Feldman, W. C.↗
NASA NTRS1992

Hollow Cathode With Multiple Radial Orifices

Improved hollow cathode serving as source of electrons has multiple radial orifices instead of single axial orifice. Distributes ion current more smoothly, over larger area. Prototype of high-current cathodes for ion engines in spacecraft. On Earth, cathodes used in large-diameter ion sources for industrial processing of materials. Radial orientation of orifices in new design causes current to be dispersed radially in vicinity of cathode. Advantageous where desireable to produce plasma more nearly uniform over wider region around cathode.

Brophy, John R.↗
NASA NTRS1976

Electron transport and the magnetic field in the Crab Nebula

Observational data obtained at radio, optical, and X-ray frequencies on the size of the emission region in the Crab Nebula are used to examine various energy-transport models. It is shown that the data cannot be fitted by diffusion models, even when the energy-injection region is extended. A more favorable comparison is made with an extended source model in which bulk motion is the transport mechanism. Assuming a point source of electrons and a uniform nebular magnetic field, a perpendicular magnetic-field component of less than 0.0008 gauss is determined. Combining this with the lower limit obtained from gamma-ray observations, a perpendicular field component of between 0.0005 and 0.0008 gauss is obtained. A break in the size dependence is predicted at about 12 microns and 45 keV. Above 45 keV, the size should decrease as the inverse square root of proton energy.

Wolff, R. S.↗
NASA NTRS2011

Operational Parameters, Considerations, and Design Decisions for Resource-Constrained Ion Trap Mass Spectrometers

Mass spectrometers are increasingly finding applications in new and unique areas, often in situations where key operational resources (i.e. power, weight and size) are limited. One such example is the Mars Organic Molecule Analyzer (MOMA). This instrument is a joint venture between NASA and the European Space Agency (ESA) to develop an ion trap mass spectrometer for chemical analysis on Mars. The constraints on such an instrument are significant as are the performance requirements. While the ideal operating parameters for an ion trap are generally well characterized, methods to maintain analytical performance with limited power and system weight need to be investigated and tested. Methods Experiments have been performed on two custom ion trap mass spectrometers developed as prototypes for the MOMA instrument. This hardware consists of quadrupole ion trap electrodes that are 70% the size of common commercial instrumentation. The trapping RF voltage is created with a custom tank circuit that can be tuned over a range of RF frequencies and is driven using laboratory supplies and amplifiers. The entire instrument is controlled with custom Lab VIEW software that allows a high degree of flexibility in the definition of the scan function defining the ion trap experiment. Ions are typically generated via an internal electron ionization source, however, a laser desorption source is also in development for analysis of larger intact molecules. Preliminary Data The main goals in this work have been to reduce the power required to generate the radio frequency trapping field used in an ion trap mass spectrometer. Generally minimizing the power will also reduce the volume and mass of the electronics to support the instrument. In order to achieve optimum performance, commercial instruments typically utilize RF frequencies in the 1 MHz range. Without much concern for power usage, they simply generate the voltage required to access the mass range of interest. In order to reduce the required RF voltage (and power), operation of the ion trap at lower RF frequencies has been investigated. Surprisingly, the performance of the instrument has only been slightly degraded at RF frequencies all the way down to 500 kHz. Mass resolution is relatively stable to this point and depending on the resonant ejection point used, the peak intensity is also quite stable. To date only masses up to m/z 200 have been fully investigated, however, additional studies are planned to verify the performance with higher mass ions. The lower frequency and voltage should reduce the pseudo potential well depth, eventually affecting the trapping efficiency of the instrument -- effect that could manifest itself in significantly limiting the mass range of trapped ions. Other methods to reduce the RF power while maintaining analytical performance are also under investigation. This includes ion ejection at lower q(sub z) values to access a given mass with a lower RF voltage. The loss of mass resolution at lower q(sub eject) points has been measured and current work is underway to leverage scan speed and the use of non-linear resonances in order to counter this trend. The overall trap performance under this range of operating conditions will be presented with a goal of identifying what trade-offs are acceptable.

Danell, Ryan M.↗
NASA NTRS1978

Interplanetary electrons - What is the strength of the Jupiter source

On the basis of conservative assumptions, a phenomenological approach is used to address the source strength of Jupiter for interplanetary electrons. It is estimated that Jupiter emits approximately 10 to the 24th - 10 to the 26th electrons per sec with energies in excess of 6 MeV, which sources may be compared with the population of approximately 3 x 10 to the 28th electrons of the same energy in the Jovian outer magnetosphere. It is concluded that Jupiter accelerates particles at a rate exceeding that of ordinary trapped particle dynamic processes.

Fillius, W.↗
NASA NTRS1977

A rocket-borne airglow photometer

The design of a rocket-borne photometer to measure the airglow emission of ionized molecular nitrogen in the 391.4 nm band is presented. This airglow is a well known and often observed phenomenon of auroras, where the principal source of ionization is energetic electrons. It is believed that at some midlatitude locations energetic electrons are also a source of nighttime ionization in the E region of the ionosphere. If this is so, then significant levels of 391.4 nm airglow should be present. The intensity of this airglow will be measured in a rocket payload which also contains instrumentation to measured in a rocket payload which also contains instrumentation to measure energetic electron differential flux and the ambient electron density. An intercomparison of the 3 experiments in a nightime launch will allow a test of the importance of energetic electrons as a nighttime source of ionization in the upper E region.

Paarmann, L. D.↗
NASA NTRS2005

Ferroelectric Devices Emit Charged Particles and Radiation

Devices called solid-state ferroelectric- based sources (SSFBSs) are under development as sources of electrons, ions, ultraviolet light, and x-rays for diverse applications in characterization and processing of materials. Whereas heretofore it has been necessary to use a different device to generate each of the aforementioned species of charged particles or radiation, a single SSFBS can be configured and operated to selectively generate any of the species as needed using a single source. Relative to comparable prior sources based, variously, on field emission, thermionic emission, and gaseous discharge plasmas, SSFBSs demand less power, and are compact and lightweight. An SSFBS exploits the unique physical characteristics of a ferroelectric material in the presence of a high-frequency pulsed electric field. The basic building block of an SSFBS is a ferroelectric cathode -- a ferroelectric wafer with a solid electrode covering its rear face and a grid electrode on its front face (see figure). The application of a voltage pulse -- typically having amplitude of several kilovolts and duration of several nanoseconds -- causes dense surface plasma to form near the grid wires on the front surface.

Bar-Cohen, Yoseph↗
NASA NTRS1971

A survey of Kaufman thruster cathodes

A survey is presented of the various cathodes which were developed and used in the Kaufman ion thruster. The electron bombardment type ion source is briefly described. The general design, operating characteristics, and power requirements are shown for each type of cathode from the refractory metals used in 1960 to the plasma discharge hollow cathodes of today. A detailed discussion of the hollow cathode is given, including starting and cyclic operating characteristics as well as more fundamental design parameters. Tests to date show that the plasma hollow cathode is an efficient electron source with demonstrated durability over 10,000 hours.

Weigand, A. J.↗
NASA NTRS1971

A survey of Kaufman thruster cathodes.

A survey is presented of various cathodes which have been developed and used in the Kaufman ion thruster. The electron-bombardment type ion source used in the thruster is briefly described. The general design, operating characteristics, and power requirements are shown for each type of cathode from the refractory metals used in 1960 to the plasma discharge hollow cathodes of today. A detailed discussion of the hollow cathode is given describing starting and cyclic operating characteristics as well as more fundamental design parameters. Tests to date show that the plasma hollow cathode is an efficient electron source with demonstrated durability over 10,000 hours and should offer further performance and life improvements.

Weigand, A. J.↗
NASA NTRS2000

Behavior of the Aurora During 10-12 May, 1999 When The Solar Wind Nearly Disappeared

The aurora was still active with occasional pseudobreakup events when the solar wind density diminished to unusually small densities (0.2 cc -1) during May 10-12, 1999. The aurora was observed at high magnetic latitudes indicating that the electron precipitation source moved northward as the geomagnetic activity decreased. The events we have studied indicate that the solar wind density alone is not the primary parameter that controls the auroral activity. The weak auroral activity was observed with 150 nT magnetic bays and when the interplanetary magnetic field (IMF) Bz was small and positive resulting in small _ parameter. A new auroral feature was observed on May 11, 1999, between 0900-2000 UT. The electron precipitation was energetic, uniform, and covered the region commonly identified as the polar cap. This precipitation lasted for more than 10 hours and was stable over time scales of tens of minutes. On May 12, as the solar wind began to recover, a prolonged period of dayside activity occurred and was followed by a typical aurora at 0500 UT.

Parks, G.↗
NASA NTRS2003

X-Ray Testing Constellation-X Optics at MSFC's 100-m Facility

In addition to the 530-m-long X-Ray Calibration Facility (XRCF), NASA's Marshall Space Flight Center (MSFC) operates a 104-m-long (source-to-detector) X-ray-test facility. Originally developed and still occasionally used for stray-light testing of visible-fight optical systems, the so-called "Stray-Light Facility" now serves primarily as a convenient and inexpensive facility for performance evaluation and calibration of X-ray optics and detectors. The facility can accommodate X-ray optics up to about 1-m diameter and 12-m focal length. Currently available electron-impact sources at the facility span the approximate energy range 0.2 to 100 keV, thus supporting testing of soft- and hard-X-ray optics and detectors. Available MSFC detectors are a front-illuminated CCD (charge-coupled device) and a scanning CZT (cadmium--zinc--telluride) detector, with low-energy cut-offs of about 0.8 and 3 keV, respectively. In order to test developmental optics for the Constellation-X Project, led by NASA's Goddard Space Flight Center (GSFC), MSFC undertook several enhancements to the facility. Foremost among these was development and fabrication of a five-degree-of-freedom (5-DoF) optics mount and control system, which translates and tilts the user-provided mirror assembly suspended from its interface plate. Initial Constellation-X tests characterize the performance of the Optical Alignment Pathfinder Two (OAP2) for the large Spectroscopy X-ray Telescope (SXT) and of demonstration mirror assemblies for the Hard X-ray Telescope (HXT). With the Centroid Detector Assembly (CDA), used for precision alignment of the Chandra (nee AXAF) mirrors, the Constellation-X SXT Team optically aligned the individual mirrors of the OAPZ at GSFC. The team then developed set-up and alignment procedures, including transfer of the alignment from the optical alignment facility at GSFC to the X-ray test facility at MSFC, using a reference flat and fiducials. The OAPZ incorporates additional ancillary features --- fixed aperture mask and movable sub-aperture mask --- to facilitate X-ray characterization of the optics. Although the OAPZ was designed to- have low sensitivity to temperature offsets and gradients, analyses showed the necessity of active temperature control for the X-ray performance testing. Thus, the Smithsonian Astrophysical Observatory (SAO) implemented a thermal control and monitoring system, designed to hold the OAP2 close to its assembly.

O'Dell, Stephen↗
NASA NTRS2000

Behavior of the Aurora During the 10-12 May, 1999 When the Solar Wind Nearly Disappeared

We show that die aurora was still active with occasional pseudo breakup events when die solar wind density diminished to unusually small densities during May 10-12, 1999. The aurora was observed at high magnetic latitudes indicating that the electron precipitation source moved northward as die soar wind and geomagnetic activities decreased. These features are well known and seen at other times when the geomagnetic activities are weak. Intense auroral events accompanied other periods of low solar wind density (for example, February 10, 1997 and May 5,1998) indicating that the solar wind density alone is not die primary parameter that controls die auroral activity. However, a new auroral feature was observed on May, 11, 1999 during approx. 09-20 LIT hours. The electron precipitation was energetic, uniform and covered the polar latitudes commonly identified as die polar cap region. This precipitation lasted form ore that 10 hours and was stable over time scales of tens of minutes. On May 12, as the solar wind began to recover, a prolonged period of dayside activity occurred and was subsequently followed by a "typical" aurora at approx. 05 UT. All of the auroral activities occurred accompanying weak auroral electrojet activity (approx. 150 nT maximum).

Parks, G. K.↗