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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 NTRS1984

Bending fatigue of electron-beam-welded foils. Application to a hydrodynamic air bearing in the Chrysler/DOE upgraded automotive gas tubine engine

A hydrodynamic air bearing with a compliment surface is used in the gas generator of an upgraded automotive gas turbine engine. In the prototype design, the compliant surface is a thin foil spot welded at one end to the bearing cartridge. During operation, the foil failed along the line of spot welds which acted as a series of stress concentrators. Because of its higher degree of geometric uniformity, electron beam welding of the foil was selected as an alternative to spot welding. Room temperature bending fatigue tests were conducted to determine the fatigue resistance of the electron beam welded foils. Equations were determined relating cycles to crack initiation and cycles to failure to nominal total strain range. A scaling procedure is presented for estimating the reduction in cyclic life when the foil is at its normal operating temperature of 260 C (500 F).

Saltsman, J. F.↗
NASA NTRS2015

Electron Beam Irradiated Intercalated CNT Yarns For Aerospace Applications

Multi-walled CNT yarns have been experimentally and commercially created to yield lightweight, high conductivity fibers with good tensile properties for application as electrical wiring and multifunctional tendons. Multifunctional tendons are needed as the cable structures in tensegrity robots for use in planetary exploration. These lightweight robust tendons can provide mechanical strength for movement of the robot in addition to power distribution and data transmission. In aerospace vehicles, such as Orion, electrical wiring and harnessing mass can approach half of the avionics mass. Use of CNT yarns as electrical power and data cables could reduce mass of the wiring by thirty to seventy percent. These fibers have been intercalated with mixed halogens to increase their specific electrical conductivity to that near copper. This conductivity, combined with the superior strength and fatigue resistance makes it an attractive alternative to copper for wiring and multifunctional tendon applications. Electron beam irradiation has been shown to increase mechanical strength in pristine CNT fibers through increased cross-linking. Both pristine and intercalated CNT yarns have been irradiated using a 5-megavolt electron beam for various durations and the conductivities and tensile properties will be discussed. Structural information obtained using a field emission scanning electron microscope, energy dispersive X-ray spectroscopy (EDS), and Raman spectroscopy will correlate microstructural details with bulk properties.

electrical wiring↗
NASA NTRS1972

Metastable atom probe for measuring electron beam density profiles

Metastable atom probe was developed for measuring current density in electron beam as function of two arbitrary coordinates, with spatial resolution better than 0.5 mm. Probe shows effects of space charge, magnetic fields, and other factors which influence electron current density, but operates with such low beam densities that introduced perturbation is very small.

Lockhart, J. M.↗
NASA NTRS1988

Magnetic fields in the vicinity of pulsed electron beams in space

The electric component of the fields generated by a pulsed electron beam in a magnetized plasma was derived by Harker and Banks (1987). The beam was modeled as an infinite train of square-wave pulses and the radiation was obtained by adding coherently the radiation from each individual electron in the idealized helical trajectory assumed by the beam. Here the analysis is completed by presenting the magnetic components.

Neubert, T.↗
NASA NTRS1965

Tantalum cathode improves electron-beam evaporation of tantalum

Tantalum cathode is used in assembly for electron beam evaporation of tantalum onto a substrate. The cathode and anode are made of pure tantalum rather than tungsten to prevent contamination of the tantalum film deposited on the substrate.

Source record↗
NASA NTRS1993

Ion acceleration and abundance enhancements by electron beam instabilities in impulsive solar flares

We show that a nonrelativistic electron beam in a hydrogen-helium solar flare plasma will excite H(+) electromagnetic ion cyclotron, shear Alfven, and R-X waves, in addition to waves resulting from the two-stream instability. The H(+) electromagnetic ion cyclotron and shear Alfven waves are able to selectively accelerate ambient He-3 and Fe, respectively, to MeV energies through first harmonic gyroresonance, and thereby account for the large (He-3)/(He-4) and Fe/C ratios seen in the energetic particles from impulsive solar flares. In this model, separate heating and acceleration mechanisms for either He-3 or Fe are not required, and Fe acceleration is quite efficient since it does not need to occur by second harmonic gyroresonance. The combination of the other two unstable modes is able to accelerate ions to hundreds of MeV if the particles become trapped in an electrostatic potential well of a two-stream wave.

Miller, James A.↗
NASA NTRS1978

Analysis of bunching of an electron beam at optical wavelengths

This paper presents an analysis of the bunching of an electron beam at optical wavelengths by means of the inverse Cerenkov effect. A laser light beam is used to modulate the velocity of the electrons, and this velocity modulation becomes charge-density modulation after an appropriate drift distance. The effects of energy and angular spread of the electrons are included, as well as the impact of scatterings in the index-matching medium. Bunching can occur with reasonable parameter values and the drift distance is of the order of several centimeters.

Chen, C. K.↗
NASA NTRS1985

A simple model of electron beam initiated dielectric breakdown

A steady state model that describes the internal charge distribution of a planar dielectric sample exposed to a uniform electron beam was developed. The model includes the effects of charge deposition and ionization of the beam, separate trap-modulated mobilities for electrons and holes, electron-hole recombination, and pair production by drifting thermal electrons. If the incident beam current is greater than a certain critical value (which depends on sample thickness as well as other sample properties), the steady state solution is non-physical.

Beers, B. L.↗
NASA NTRS1981

Preliminary comparison of material charging properties using single-energy and multienergy electron beams

Results of tests designed to compare the charging properties of spacecraft material under a monoenergetic beam and under a continuously distributed beam are summarized. In the test setup the electron source was mounted in the top of a cylindrical vacuum chamber. A sheet of 5-mil-thick Kapton was placed on an insulated metal substrate at the bottom of the vacuum chamber. The dc current arriving on the substrate was measured and a field meter measured the potential of the test sample. A retarding potential analyzer measured the energy spectrum of the incident electron beam. With the monoenergetic beam, the sample charged to 12 kV and electrical discharges occurred. With the multi-energy spectra the samples charged to only 6 kV and 4 kV, and no discharger were observed. In these experiments, no effort was made to duplicate the spectra occurring in space. The tests were intended to simply to compare spacecraft material charging properties using monoenergetic and continuous multi-energy beams.

Adamo, R. C.↗
NASA NTRS1999

How an Electron Beam (Eventually) Penetrates Ceramic Cloth

In anticipation of the International Space Welding Experiment (ISWE) the effect of an electron beam was investigated on Nextel AF-62 ceramic cloth designed to withstand temperatures up to 1427 C. It was anticipated that the cloth would take a static charge that would repel the beam and remain undamaged. It was found that after some seconds the impinging beam penetrated penetrated the cloth. Further, the penetration time went up significantly both at longer and at closer standoff distances. A tentative explanation appears to fit the observed facts. The electrons in the beam generate positive ions by collisions with the contaminant gas molecules in the vacuum chamber. The positive ions transfer a small but significant fraction of the beam power to the cloth. Under the impingement of the positive ions the cloth heats up until sufficient outgassing occurs to initiate arcing. Once arcing occurs the full beam power impinges on the cloth and, almost instantaneously, burns a hole.

Nunes, A. C., Jr.↗
NASA NTRS1985

Examination of nonadiabatic effects during an electron beam experiment in the ionosphere

Prompt and delayed echo fluxes and superacceleration of electrons were observed during the sounding rocket flight Several Coordinated Experiments using an electron accelerator. Magnetospheric electric fields parallel to the magnetic field were investigated. The degree of nonadiabatic behavior of the injected electron beam and the return flux was examined. It is shown that the region of strong beam-plasma interaction is limited to 300 km in length along the magnetic field but that backscatter or energetic electrons could occur from much larger distances. By appraising the difference in transit times of 1.9 and 3.9 keV electrons it is established that a continuous backscatter model operating out to several thousand kilometres is not consistent with the observations.

Wilhelm, K.↗