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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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRS2012

A New Electron Source for Laboratory Simulation of the Space Environment

We have developed a new collimated electron source called the Photoelectron Beam Generator (PEBG) for laboratory and spaceflight applications. This technology is needed to replace traditional cathodes because of serious fundamental weaknesses with the present state of the art. Filament cathodes suffer from numerous practical problems, even if expertly designed, including the dependence of electron emission on filament temperature, short lifetimes (approx 100 hours), and relatively high power (approx 10s of W). Other types of cathodes have solved some of these problems, but they are plagued with other difficult problems, such as the Spindt cathode's extreme sensitivity to molecular oxygen. None to date have been able to meet the demand of long lifetime, robust packaging, and precision energy and flux control. This new cathode design avoids many common pitfalls of traditional cathodes. Specifically, there are no fragile parts, no sensitivity to oxygen, no intrinsic emission dependencies on device temperature, and no vacuum requirements for protecting the source from contamination or damage. Recent advances in high-brightness Light Emitting Diodes (LEDs) have provided the key enabling technology for this new electron source. The LEDs are used to photoeject electrons off a target material of a low work-function, and these photoelectrons are subsequently focused into a laminar beam using electrostatic lenses. The PEBG works by illuminating a target material and steering photoelectrons into a laminar beam using electrostatic lenses

Krause, Linda Habash↗
NASA NTRS1965

Radiation from electrons in magnetoplasma.

Magnetoplasma electron emission in whistler mode frequency band and extraordinary mode frequency band around plasma frequency where refractive indices are greater than one

MAGNETOPLASMA↗
NASA NTRS1977

Synchrotron emissivity near the electron cyclotron and upper hybrid frequencies

The spontaneous synchrotron emissivity from a high density, weakly relativistic plasma in thermal equilibrium is discussed. Thermal effects on the dielectric polarization of the plasma are included in the analysis, and the result is compared with computations of the emissivity based upon the cold plasma approximation. A numerical analysis is performed for frequencies in the vicinity of both the electron cyclotron frequency and the upper hybrid resonance. Significant modifications to the synchrotron emissivity in the cold plasma approximation are found in both of these frequency regimes.

Freund, H. P.↗
NASA NTRS1982

The importance of plasma effects on electron-cyclotron maser-emission from flaring loops

Electron cyclotron maser instability has been suggested as the cause of the observed short (10-20 msec), intense (an approximate brightness temperature of 10 to the 15th K) and up to 100% polarized microwave solar emission. It is shown that plasma effects and thermal cyclotron damping, ignored in previous theories, play an important role in controlling the frequency range of the emission. The radio emission is suppressed for ratios of the plasma frequency to the cyclotron frequency smaller than 0.4. An examination of the cyclotron damping, reveals that the maser action is suppressed unless a large fraction (i.e., over 10%) of the accelerated electrons participates in the emission process.

Sharma, R. R.↗
NASA NTRS1977

Active experiments in modifying spacecraft potential: Results from ATS-5 and ATS-6

Instruments on ATS-5 and ATS-6 were operated to study the phenomena of spacecraft charging. The ion engine neutralizers were operated in attempts to modify the spacecraft potentials. The neutralizer on ATS-5 is a hot filament emitting electrons, while the neutralizer on ATS-6 is a low energy plasma bridge. The diagnostics used were particle detectors, counting electrons and protons as a function of energy. Operations were conducted in daylight and eclipse. This report describes the processing data from these and other operations. Only preliminary analysis of some of this data has been carried out, with the following results: (1) electron emission does not perturb the status of a low potential satellite by more than 50 volts, (2) emission of a low energy plasma does not change low potentials by more than a few volts, (3) when ATS-6 enters eclipse in the presence of a high energy plasma, the neutralizer suppresses any rise in (within a few volts resolution), (4) when the electron emitter on ATS-5 is operated, it serves to discharge negative potentials from thousands to hundreds of volts.

Olsen, R.↗
NASA NTRS2002

Power-Efficient, High-Current-Density, Long-Life Thermionic Cathode Developed for Microwave Amplifier Applications

A power-efficient, miniature, easily manufactured, reservoir-type barium-dispenser thermionic cathode has been developed that offers the significant advantages of simultaneous high electron-emission current density (>2 A/sq cm) and very long life (>100,000 hr of continuous operation) when compared with the commonly used impregnated-type barium-dispenser cathodes. Important applications of this cathode are a wide variety of microwave and millimeter-wave vacuum electronic devices, where high output power and reliability (long life) are essential. We also expect it to enable the practical development of higher purveyance electron guns for lower voltage and more reliable device operation. The low cathode heater power and reduced size and mass are expected to be particularly beneficial in traveling-wave-tube amplifiers (TWTA's) for space communications, where future NASA mission requirements include smaller onboard spacecraft systems, higher data transmission rates (high frequency and output power) and greater electrical efficiency.

Wintucky, Edwin G.↗
NASA NTRS1994

Analytical Instrument

BEEM (Ballistic Electron Emission Microscopy) was invented at Jet Propulsion Laboratory's Center for Microelectronics Technology. It is a significant research instrument for microelectronics research because it is able to image underlying layers or interfaces of surface structures. A tiny current is injected into a metal layer and the electrons travel ballistically through the metal allowing the researcher to study the operation and performance of a structure. Other advantages include nondestructive imaging of barrier heights and electronic characterization of devices, as well as the potential to observe processes like molecular beam epitaxy (crystal growth) in situ.

Source record↗
NASA NTRS1982

Electric thruster research

It has been customary to assume that ions flow nearly equally in all directions from the ion production region within an electron-bombardment discharge chamber. In general, the electron current through a magnetic field can alter the electron density, and hence the ion density, in such a way that ions tend to be directed away from the region bounded by the magnetic field. When this mechanism is understood, it becomes evident that many past discharge chamber designs have operated with a preferentially directed flow of ions. Thermal losses were calculated for an oxide-free hollow cathode. At low electron emissions, the total of the radiation and conduction losses agreed with the total discharge power. At higher emissions, though, the plasma collisions external to the cathode constituted an increasingly greater fraction of the discharge power. Experimental performance of a Hall-current thruster was adversely affected by nonuniformities in the magnetic field, produced by the cathode heating current. The technology of closed-drift thrusters was reviewed. The experimental electron diffusion in the acceleration channel was found to be within about a factor of 3 of the Bohm value for the better thruster designs at most operating conditions. Thruster efficiencies of about 0.5 appear practical for the 1000 to 2000 s range of specific impulse. Lifetime information is limited, but values of several thousands of hours should be possible with anode layer thrusters operated or = to 2000 s.

Kaufman, H. R.↗
NASA NTRS1990

A summary of the CHARGE-2 electron beam rocket experiment

The major purpose of the CHARGE-2 experiment was to study the interaction of a vehicle at high potential (up to 1 kV) with the ionosphere. The payload consisted of two parts that were separated during the flight. The high potential was obtained by electron emission from the mother vehicle, and by voltage-biasing of the daughter vehicle. Measurements of transient vehicle potential were obtained with a sample internal of 100 ns. The mother current collection exhibited magnetic limitations above 240 km. Below 240 km the mother collected a current far in excess of the magnetically limited models. This demonstrates the ability of an electron beam to interact with the neutral atmosphere at altitudes below 240 km.

Myers, Neil B.↗
NASA NTRS1989

Effects of a hot intergalactic medium

One effect a hot intergalactic medium (IGM) would have would be to produce an isotropic X-ray background through thermal bremsstrahlung. Such a background was modeled including both relativistic electron-ion and electron-electron emission; the observed X-ray measurements could be fit with a current temperature of 10.2 keV and Omega (IGM) of 0.27, assuming that the IGM was instantaneously heated at a redshift of 5 and cools by relativistic adiabatic expansion and Compton cooling. Such a hot IGM would also distort the cosmic microwave background spectrum by inverse Compton scattering off relativistic electrons. This distortion was modeled using the relativistic treatment. When including the recent data of Matsumoto et al., an undistorted radiation temperature of 2.86 K and an Omega (IGM) of 0.41 was found.

Taylor, Gregory B.↗
NASA NTRS1994

High-Performance X-ray Detection in a New Analytical Electron Microscope

X-ray detection by energy-dispersive spectrometry in the analytical electron microscope (AEM) is often limited by low collected X-ray intensity (P), modest peak-to-background (P/B) ratios, and limitations on total counting time (tau) due to specimen drift and contamination. A new AFM has been designed with maximization of P. P/B, and tau as the primary considerations. Maximization of P has been accomplished by employing a field-emission electron gun, X-ray detectors with high collection angles, high-speed beam blanking to allow only one photon into the detector at a time, and simultaneous collection from two detectors. P/B has been maximized by reducing extraneous background signals generated at the specimen holder, the polepieces and the detector collimator. The maximum practical tau has been increased by reducing specimen contamination and employing electronic drift correction. Performance improvments have been measured using the NIST standard Cr thin film. The 0-3 steradian solid angle of X-ray collection is the highest value available. The beam blanking scheme for X-ray detection provides 3-4 times greater throughput of X-rays at high count rates into a recorded spectrum than normal systems employing pulse-pileup rejection circuits. Simultaneous X-ray collection from two detectors allows the highest X-ray intensity yet recorded to be collected from the NIST Cr thin film. The measured P/B of 6300 is the highest level recorded for an AEM. In addition to collected X-ray intensity (cps/nA) and P/B measured on the standard Cr film, the product of these can be used as a figure-of-merit to evaluate instruments. Estimated minimum mass fraction (MMF) for Cr measured on the standard NIST Cr thin film is also proposed as a figure-of-merit for comparing X-ray detection in AEMs. Determinations here of the MMF of Cr detectable show at least a threefold improvement over previous instruments.

Lyman, C. E.↗
NASA NTRS2011

Simulation and Characterization of a Miniaturized Scanning Electron Microscope

A miniaturized Scanning Electron Microscope (mSEM) for in-situ lunar investigations is being developed at NASA Marshall Space Flight Center with colleagues from the University of Alabama in Huntsville (UAH), Advanced Research Systems (ARS), the University of Tennessee in Knoxville (UTK) and Case Western Reserve University (CWRU). This effort focuses on the characterization of individual components of the mSEM and simulation of the complete system. SEMs can provide information on the size, shape, morphology and chemical composition of lunar regolith. Understanding these basic properties will allow us to better estimate the challenges associated with In-Situ Resource Utilization and to improve our basic science knowledge of the lunar surface (either precluding the need for sample return or allowing differentiation of unique samples to be returned to Earth.) The main components of the mSEM prototype includes: a cold field emission electron gun (CFEG), focusing lens, deflection/scanning system and backscatter electron detector. Of these, the electron gun development is of particular importance as it dictates much of the design of the remaining components. A CFEG was chosen for use with the lunar mSEM as its emission does not depend on heating of the tungsten emitter (lower power), it offers a long operation lifetime, is orders of magnitude brighter than tungsten hairpin guns, has a small source size and exhibits low beam energy spread.

Gaskin, Jessica A.↗
NASA NTRS1989

Inspection Tools

A "NASA Tech Briefs" article describing an inspection tool and technique known as Optically Stimulated Electron Emission (OSEE) led to the formation of Photo Acoustic Technology, Inc. (PAT). PAT produces sensors and scanning systems which assure surface cleanliness prior to bonding, coating, painting, etc. The company's OP1000 series realtime pre-processing detection capability assures 100 percent surface quality testing. The technique involves brief exposure of the inspection surface to ultraviolet radiation. The energy interacts with the surface layer, causing free electrons to be emitted from the surface to be picked up by the detector. When contamination is present, it interferes with the electron flow in proportion to the thickness of the contaminant layer enabling measurement by system signal output. OP1000 systems operate in conventional atmospheres on all types of material and detect both organic and inorganic contamination.

Source record↗
NASA NTRS1990

Surface studies on scandate cathodes and synthesized scandates

Auger, ESCA, electron emission, evaporation, and desorption measurements were made on three different types of scandate surfaces. They are: (1) an impregnated top layer scandate cathode, (2) an unimpregnated top layer scandate cathode with a deposited barium or barium oxide adsorbate surface layer, and (3) a synthesized scandate surface, which replicates a scandate cathode surface. The purpose of these experiments was to determine the role that Sc2O3 plays in making the scandate cathode a more copious electron emitter than the conventional impregnated-type cathode. The synthesized scandate surface experiments consisted of depositing multilayer scandium on a tungsten surface, oxidizing the scandium, and then depositing either Ba or BaO on the scandium oxide surface. The results of these measurements showed that the low work function portions of the thin-film scandate cathode are where the Sc2O3 is the substrate and BaO is the adsorbate.

Lesny, Gary↗
NASA NTRS1991

Ballistic-carrier spectroscopy of the CoSi2/Si interface

Ballistic-electron-emission microscopy and related ballistic-hole and carrier-scattering spectroscopies were used to investigate carrier transport in the epitaxial CoSi2/Si system. An unexpected degree of variation in interface transmission was observed despite the high crystal quality of the epitaxial silicide layer. Furthermore, clear evidence of the CoSi2 band structure was observed, which has a dramatic effect on interface transport. The major effect of the silicide band structure is to increase the interfacial barrier to electron transmission to a value in excess of the Schottky barrier height.

Kaiser, W. J.↗
NASA NTRS2008

Simulation of a Miniature, Low-Power Time-of-Flight Mass Spectrometer for In Situ Analysis of Planetary Atmospheres

We are implementing nano- and micro-technologies to develop a miniaturized electron impact ionization mass spectrometer for planetary science. Microfabrication technology is used to fabricate the ion and electron optics, and a carbon nanotube (CNT) cathode is used to generate the ionizing electron beam. Future NASA planetary science missions demand miniaturized, low power mass spectrometers that exhibit high resolution and sensitivity to search for evidence of past and present habitability on the surface and in the atmosphere of priority targets such as Mars, Titan, Enceladus, Venus, Europa, and short-period comets. Toward this objective, we are developing a miniature, high resolution reflectron time-of-flight mass spectrometer (Mini TOF-MS) that features a low-power CNT field emission electron impact ionization source and microfabricated ion optics and reflectron mass analyzer in a parallel-plate geometry that is scalable. Charged particle electrodynamic modeling (SIMION 8.0.4) is employed to guide the iterative design of electron and ion optic components and to characterize the overall performance of the Mini TOF-MS device via simulation. Miniature (less than 1000 cubic centimeters) TOF-MS designs (ion source, mass analyzer, detector only) demonstrate simulated mass resolutions greater than 600 at sensitivity levels on the order of 10(exp -3) cps/molecule N2/cc while consuming 1.3 W of power and are comparable to current spaceflight mass spectrometers. Higher performance designs have also been simulated and indicate mass resolutions approximately 1000, though at the expense of sensitivity and instrument volume.

King, Todd T.↗