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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 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Electrostatic wave generation above and below the plasma frequency by electron beams

The unmagnetized electrostatic dispersion equation is solved numerically to study the growth of electrostatic waves near the plasma frequency resulting from a unstable electron beam. An attempt is made to find the dispersion relations, frequencies of maximum growth, and the resonant or nonresonant character of the waves for particular beam parameters. It is found that the unstable waves do not have the Langmuir dispersion relation except in the limit of a very dilute beam with growth on the connected mode of O'Neil and Malmberg. The properties of the unstable mode depend strongly on beam parameters such as beam density, speed, and temperature.

Cairns, Iver H.↗
NASA NTRS2016

Electron-Beam Deposition of Superconducting Molybdenum Thin Films for the Development of Mo/Au TES X-Ray Microcalorimeter

We are exploring the properties of electron-beam evaporated molybdenum thin films on silicon nitride coated silicon wafers at substrate temperatures between room temperature and 650 C. The temperature dependence of film stress, transition temperature, and electrical properties are presented. X-ray diffraction measurements are performed to gain information on molybdenum crystallite size and growth. Results show the dominant influence of the crystallite size on the intrinsic properties of our films. Wafer-scale uniformity, wafer yield, and optimal thermal bias regime for TES fabrication are discussed.

Microcalorimeter↗
NASA NTRS1973

Electron-beam studies of Schottky-barrier detector surfaces

Review of the surface anomalies occurring in Schottky-barrier particle detectors identifiable by means of an electron beam technique employed by Czaja (1965) for analyzing defects in diode structures. The technique is shown to make possible the detection and identification of the following anomalies: (1) chemical contamination of the detector surface; (2) mechanical damage of the wafer substrates; (3) damage introduced in semiconductor surface preparation; (4) radiation damage; and (5) defective surface metallization.

Peckerar, M. C.↗
NASA NTRS1985

Electron beam charging of Space Shuttle thermal protection system tiles

Six space shuttle reusable surface insulation tiles were tested in the NASA Lewis Research Center's electron bombardment test facility. The 30-cm-square specimens were assembled by using the same materials and techniques used to apply the tiles to the space shuttle and were composed to 15-cm- and 20-cm-square tiles and pieces on 0.6-cm-thick aluminum substrates. There were two specimens of each of three thicknesses. One specimen of each thickness had gaps of less than 0.1 cm between tiles, and the other had gaps of approximately 0.15 cm. The specimens were exposed to monoenergetic electron beams (2 to 25 keV) with nominal fluxes of 0.1 and 1 nA/sq. cm. Tests were conducted with both grounded and floating substrates. The data presented include charging rates, equilibrium potentials, and substrate currents. There is evidence that discharging occurred.

Staskus, J. V.↗
NASA NTRS1986

Waves generated during electron beam emissions from the Space Shuttle

Observations from the SEPAC (Space Experiments with Particle Accelerators) experiment on Spacelab 1 Shuttle mission of waves generated during electron beam emissions are presented. The dependence of the wave intensity on the beam parameters and the Shuttle attitude is outlined, and the shape of the wave spectra are discussed. It is found that the noise in the 0.75- to 10 kHz band has a spectral shape that can be characterized by an f exp -n law, and that the VLF signal level depends on the beam angle to the magnetic field, the strongest emissions being observed for parallel beams. These features are found to be consistent with a drift wave instability.

Neubert, T.↗
NASA NTRS1990

Preventing Contamination In Electron-Beam Welds

Simple expedient eliminates time-consuming, expensive manual hand grinding. Use of groove and backup tube greatly reduces postweld cleanup in some electron-beam welding operations. Tube-backup method developed for titanium parts, configurations of which prevents use of solid-block backup. In new welding configuration, tube inserted in groove to prevent contact between alumina beads and molten weld root. When welding complete and beads and tube removed, only minor spatter remains and is ground away easily.

Goodin, Wesley D.↗
NASA NTRS1994

Analog Phase Holograms by Electron Beam Lithography

Phase holograms have been created on the surface of a thin film of poly-methyl methacrylate (PMMA, Plexiglas) by direct-write electron beam (E-Beam) lithography. The process involves delivering a patterned exposure dose followed by partial development with a strong developer. The patterned dose derives from arbitrary computer-calculated holograms, which must be corrected for the sensitivity characteristic of the PMMA and for the effective point-spread function of the E-Beam.

phase↗
NASA NTRS1985

Objectives and design of the Echo 6 electron beam experiment - Large ionospheric perturbations and energetic particle patterns

The data from the March 30, 1983 launching of Echo 6 are presented. Echo 6 contained duplex accelerators and a system of four throw away detectors to detect and analyze conjugate electron echoes. The model used to calculate the proper trajectory of the rocket and the reason for not detecting echoes are discussed. The components of the plasma diagnostic package which was used to study the electron beam interactions with the ionospheric plasma, and the functions of the two controllable electron guns and the two sets of orthogonal electric probes are described. The signal-mode potentials between each probe and the plasma diagnostic payload are investigated. The signals produced by the gun pulses are analyzed and the interpretation of the electric field probe response is examined.

Winckler, J. R.↗
NASA NTRS1989

Generation mechanism of whistler waves produced by electron beam injection in space

Electromagnetic particle simulations are used to determine the generation mechanism of the whistler waves observed in connection with the artificial injection of electron beams in the ionosphere. The production of the waves is shown to be closely connected with the beam-plasma interaction, which leads to the formation of a current structure which acts like an antenna and emits the whistler waves in a coherent manner. This process, in contrast to a mechanism involving amplification of radiation by a whistler mode plasma instability within the beam, allows the whistlers to be generated even though the beam width is less than one wavelength.

Pritchett, P. L.↗
NASA NTRS2008

Electron Beam Freeform Fabrication: A Fabrication Process that Revolutionizes Aircraft Structural Designs and Spacecraft Supportability

The technological inception and challenges, as well as current applications of the electron beam freeform fabrication (EBF3) process are outlined. The process was motivated by the need for a new metals technology that would be cost-effective, enable the production of new alloys and that would could be used for efficient, lightweight structures. EBF3 is a rapid metal fabrication, layer-additive process that uses no molds or tools and which yields properties equivalent to wrought. The benefits of EBF3 include it near-net shape which minimizes scrap and reduces part count; efficiency in design which allows for lighter weight and enhanced performance; and, its "green" manufacturing process which yields minimal waste products. EBF3 also has a high tensile strength, while a structural test comparison found that EBF3 panels performed 5% lower than machined panels. Technical challenges in the EBF3 process include a need for process control monitoring and an improvement in localized heat response. Currently, the EBF3 process can be used to add details onto forgings and to construct and form complex shapes. However, it has potential uses in a variety of industries including aerospace, automotive, sporting goods and medical implant devices. The novel structural design capabilities of EBF3 have the ability to yield curved stiffeners which may be optimized for performance, low weight, low noise and damage tolerance applications. EBF3 has also demonstrated its usefulness in 0-gravity environments for supportability in space applications.

Taminger, Karen M.↗
NASA NTRS1981

Two-dimensional electron beam charging model for polymer films

A two-dimensional model is developed to describe the charging of strips of thin polymer films above a grounded substrate exposed to a uniform mono-energetic electron beam. The study is motivated by the observed anomalous behavior of geosynchronous satellites, which has been attributed to differential charging of the satellite surfaces exposed to magnetospheric electrons. Surface and bulk electric fields are calcuated at steady state in order to identify regions of high electrical stress, with emphasis on behavior near the material's edge. The model is used to study the effects of some of the experimental parameters, notably beam energy, beam angle of incidence, beam current density, material thickness and material width. Also examined are the consequences of a central gap in the material and a discontinuity in the material thickness.

Reeves, R. D.↗
NASA NTRS1979

Test results for electron beam charging of flexible insulators and composites

Flexible solar-array substrates, graphite-fiber/epoxy - aluminum honeycomb panels, and thin dielectric films were exposed to monoenergetic electron beams ranging in energy from 2 to 20 keV in the Lewis Research Center's geomagnetic-substorm-environment simulation facility to determine surface potentials, dc currents, and surface discharges. The four solar-array substrate samples consisted of Kapton sheet reinforced with fabrics of woven glass or carbon fibers. They represented different construction techniques that might be used to reduce the charge accumulation on the array back surface. Five honeycomb-panel samples were tested, two of which were representative of Voyager antenna materials and had either conductive or nonconductive painted surfaces. A third sample was of Navstar solar-array substrate material. The other two samples were of materials proposed for use on Intelsat V. All the honeycomb-panel samples had graphite-fiber/epoxy composite face sheets. The thin dielectric films were 2.54-micrometer-thick Mylar and 7.62-micrometer-thick Kapton.

Staskus, J. V.↗
NASA NTRS1993

Electron beam flourescence measurements in low density free jets of heated nitrogen

Rotational temperatures have been measured in heated free jet expansions of low density nitrogen using the electron beam flourescence technique. Spectroscopic measurements of the (0,0) band of the first negative system of nitrogen revealed the rotational nonequilibrium behavior in the flow field upstream of and through the Mach disk, as well as the flow field farther downstream. These results are compared to free jet expansion data and computations regarding Mach disk location and terminal rotational temperature. Comparisons indicate a rotational relaxation-collision number of about 3. Both measurements and calculations show that these flow fields are generated from stagnation conditions of 240 to 475 Torr-mm and 700 to 1325 K. Results are also presented for shock thickness based on rotational temperature.

Gochberg, L. A.↗
NASA NTRS2002

Fabrication of Tunnel Junctions For Direct Detector Arrays With Single-Electron Transistor Readout Using Electron-Beam Lithography

This paper will describe the fabrication of small aluminum tunnel junctions for applications in astronomy. Antenna-coupled superconducting tunnel junctions with integrated single-electron transistor readout have the potential for photon-counting sensitivity at sub-millimeter wavelengths. The junctions for the detector and single-electron transistor can be made with electron-beam lithography and a standard self-aligned double-angle deposition process. However, high yield and uniformity of the junctions is required for large-format detector arrays. This paper will describe how measurement and modification of the sensitivity ratio in the resist bilayer was used to greatly improve the reliability of forming devices with uniform, sub-micron size, low-leakage junctions.

Stevenson, T. R.↗
NASA NTRS1980

Measurement of minority-carrier drift mobility in solar cells using a modulated electron beam

A determination of diffusivity on solar cells is here reported which utilizes a one dimensional treatment of diffusion under sinusoidal excitation. An intensity-modulated beam of a scanning electron microscope was used as a source of excitation. The beam was injected into the rear of the cell, and the modulated component of the induced terminal current was recovered phase sensitively. A Faraday cup to measure the modulated component of beam current was mounted next to the sample, and connected to the same electronics. A step up transformer and preamplifier were mounted on the sample holder. Beam currents on the order of 400-pA were used in order to minimize effects of high injection. The beam voltage was 34-kV, and the cell bias was kept at 0-V.

Othmer, S.↗
NASA NTRS1990

Effects of neutral gas releases on electron beam injection from electrically tethered spacecraft

The presence of high neutral densities at low altitudes and/or during thruster firings is known to modify the spacecraft potential during active electron beam injection. Two-dimensional (three velocity) particle simulations are used to investigate the ionization processes including the neutral density required, the modification of the spacecraft potential, beam profile and spatial distribution of the return current into the spacecraft. Three processes are identified: (1) beam-induced ionization, (2) vehicle-induced ionization, and (3) beam plasma discharge. Only in the first two cases does the beam propagate away with little distortion.

Winglee, R. M.↗
NASA NTRS1999

A Laboratory Study of the Charging/Discharging Mechanisms of a Dust Particle Exposed to an Electron Beam

The interaction of micron sized particles or "dust particles" with different space and planetary environments has become an important area of research. One particular area of interest is how dust particles interact with plasmas. Studies have shown that charged dust particles immersed in plasmas can alter plasma characteristics, while ions and electrons in plasmas can affect a particle's potential and thereby, its interaction with other particles. The basis for understanding these phenomena is the charging mechanisms of the dust particle, specifically, how the particle's charge and characteristics are affected when exposed to ions and electrons. At NASA Marshall Space Flight Center, a laboratory experiment has been developed to study the interaction of dust particles with electrons. Using a unique laboratory technique known as electrodynamic suspension, a single charged particle is suspended in a modified quadrupole trap. Once suspended, the particle is then exposed to an electron beam to study the charging/discharging mechanisms due to collisions of energetic electrons. The change in the particle's charge, approximations of the charging/discharging currents, and the charging/discharging yield are calculated.

Venturini, C. C.↗