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At least 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Fast Scanning Diamond Detector for Electron Beam Profile Monitoring

The first prototype of a fast scanning diamond beam profile detector (DBPD) suitable for invasive high power CW electron beam core profile measurements in transmittance mode was developed. It consists of a multi-strip solid state diamond detector to scan with high speed (up to 1 m/s) and precision (about 5 μm) through the core of an electron beam. The diamond sensor was made from a thin polycrystalline diamond (PCD) plate with highly B-doped diamond conductive strips both grown by CVD. Transient currents from the multi-strip detector were measured with fast digitizing electrometers. Successful operation of the DBPD was demonstrated for pulsed (5 Hz) and CW (78 kHz) CeC beams, including the detector’s ability to withstand a 20 sec insertion into the CW CeC beam core. The X-Y beam spatial profile was measured in one scan. Thermal modelling demonstrated a manageable thermal impact even from a relatively long insertion of the diamond sensor into the CW CeC core and very short (0.2 s) insertion into the CW LEReC beam core. Electrical impedance modelling of the detector and vacuum chamber assembly demonstrated minimal impact on beam line impedance with diamond sensor insertion.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1975

Results of convective heating tests of a longitudinal gap on the Rockwell flat plate model (15-0, insert 7) in the NASA/Ames Research Center

Results are presented which were obtained from tests in a hypersonic wind tunnel to determine aerodynamic heating rates in a gap running parallel or slightly askew to the flow direction. The model used was a flat plate instrumented in thin-skin sections with chromelconstantan thermocouples. Heating rate profiles lengthwise along and down into the gap were obtained, and additional data were obtained from a total temperature probe and rake fabricated during the test to investigate an apparent aerodynamic cooling trend in the gap. Model variables were width, depth, length, and orientation of the gap relative to the flow direction. The tests were conducted at Mach 5.1 and Reynolds numbers per foot of 500,000, 1,000,000, and 2,000,000.

Quan, M.↗
NASA NTRS1976

Electron-beam welder alinement

Parts are easily and quickly positioned in welding vacuum chamber with use of inexpensive thin metal-foil plate.

Whiffen, E. L.↗
NASA NTRS1980

Jig for assembling large composite panels

Layup of composite panels as large as 15 by 60 ft is greatly facilitated by simple mechanism. Jig consists of flat, detachable table, and curved laminating-plate joined by rack and pinion to insure accurate registration. Vacuum holds thin plastic film to laminating-plate. Preimpregnated composite sheet is applied to plate, which is then lowered face down onto table. Release of vacuum leaves layer and film and table. Film is peeled off, and steps are repeated for next layer of laminate.

Watts, J. T.↗
NASA NTRS1984

Ti/Pd/Cu Contacts for Semiconductor Devices

Copper systems equivalent in performance to silver or gold systems. Titanium layer and palladium layer deposited on semiconductor device by electron beam evaporation. Desired pattern etched using photoresist. Thin layer of copper plated on contact pattern from cyanide solution. Copper layer then built up to 4 to 8 microns by electroplatng from acid solution.

Campbell, R. B.↗
NASA NTRS1977

Metallurgical characterization of the fracture of several high strength aluminum alloys

The fracture behavior for structural aluminum alloys (2024, 6061, 7075, and 7178) was examined in selected heat treatments. The investigation included tensile, shear, and precracked notch-bend specimens fractured at ambient temperature under monotonic loading. Specimens were obtained from thin sheets and thick plates and were tested in longitudinal and transverse orientations at different strain rates. Microstructures of alloys were examined using the optical microscope and the scanning electron microscope with associated energy dispersive X ray chemical analysis. Several different types of second phase particles, some not reported by other investigators, were identified in the alloys. Fracture morphology was related to microstructural variables, test variables, and type of commercial product. Specimen orientation examined in the present investigation had little effect on fracture morphology. Test strain rate changes resulted in some change in shear fracture morphology, but not in fracture morphology of tensile specimens.

Bhandarkar, M. D.↗
NASA NTRS1986

Ion-Plated Soft Metallic Films Reduce Friction and Wear

Ion plating is ion-assisted or glow-discharge surface-deposition technique. In this process, ions or energetic atoms transfer energy, momentum, and charge to substrate and deposited surface film. Process controlled to modify physical characteristics of surface, subsurface chemical conditions, and surface and subsurface microstructures as well. Ion plating with such soft, thin metallic films as gold, silver, or lead has great potential for producing self-contained lubricating surfaces. Such films reduce friction, wear, and corrosion on sliding or rotating mechanical surfaces used in wide range of environments.

Spalvins, T.↗
NASA NTRS1985

Control of an orbiting flexible square platform in the presence of solar radiation

An analysis is made of the dynamics of a thin, homogeneous, flexible square plate exposed to solar radiation disturbance. It is shown that only the first three flexible modes of the plate generate a first order net moment about the center of mass and that the solar radiation pressure does not influence the flexible modes of the plate for small-amplitude vibrations. In the absence of control, for a symmetrical homogeneous square platform, the solar radiation induces a steady angular drift about one of the body principal axes. For extremely flexible platforms, nominally oriented in the local horizontal plane, appreciable rigid modal amplitudes can be induced due to solar radiation, even in the presence of both active and passive control. Optimal control law and feedback gain values are obtained using linear quadratic Gaussian methods.

Bainum, P. M.↗
NASA NTRS1989

Spectrometer system for diffuse extreme ultraviolet radiation

A unique grazing incidence spectrometer system has been designed to study diffuse line emission between 80 and 650 A with 10-30 A resolution. The minimum detectable emission line strength during a 5-min observation ranges from 100-2000 ph/sq cm sec str. The instrument uses mechanically ruled reflection gratings placed in front of a linear array of mirrors. These mirrors focus the spectral image on microchannel plate detectors located behind thin filters. The field of view is 40 min of arc by 15 deg, and there is no spatial imaging. This instrument has been fabricated, calibrated, and successfully flown on a sounding rocket to observe the astronomical background radiation.

Labov, Simon E.↗
NASA NTRS1991

A numerical study of the flow establishment time in hypersonic shock tunnels

This paper presents a numerical study of unsteady hypersonic viscous flows in 2D hypersonic shock tunnels. The numerical experiments on the combined nozzle/model flows, utilizing the configurations mounted in the test section of a 14.7-long shock tunnel, which has a design Mach number of Me = 6 and a stagnation temperature of T(0) = 3063 R, have been performed by solving the 2D Navier-Stokes equations with an ADI-type TVD scheme. The flow establishment times around aerodynamic models, such as a flat plate, a biconvex airfoil, thin and thick double wedges, and a circular cylinder, are calculated and compared. The analysis shows that, for the most severely separated case of a circular cylinder, the flow becomes stabilized within about 8 msec including the starting process, and its nondimensional flow establishment time is 46. The flow establishment time increases with increasing length of the separated region and decreases with increasing freestream velocity.

Lee, Jang-Yeon↗
NASA NTRS1992

LEO effects on candidate solar cell cover materials

The Long Duration Exposure Facility (LDEF) test samples discussed within are part of the Solar Array Materials Passive (SAMPLE) LDEF experiment, which included contributions from NASA and Jet Propulsion Lab (JPL). Only the JPL portion is described in this paper. The JPL test plate contains 30 individual thin silicon solar cell/cover samples. It was the intent of the experiment to evaluate the stability and protective capability of various cover materials such as conventional fused silica and potential alternative materials such as Teflon, silicone RTV's, glass resins, polyimides, and a copolymer encapsulate. Examination of the recovered experiment shows extensive physical changes have occurred. Approximately 150 micrometeoroid/debris impact were noted, some directly on the solar cells. Of particular interest are the results of ultraviolet and atomic oxygen interactions with the various cover materials. Initial results show that the fused silica cover is the most stable and protective, with performance of other materials varying widely. Electrical measurements of the cell/cover samples are presented as part of the evaluation of cover materials to protect cells in low earth orbit environments.

Stella, Paul M.↗
NASA NTRS1992

Application of elastic and elastic-plastic fracture mechanics methods to surface flaws

Fuel tanks that are a part of the External Tank assembly for the Space Shuttle are made of relatively thin 2219-T87 aluminum plate. These tanks contain about 917 m of fusion weld seam, all of which is nondestructively inspected for flaws and all those found are repaired. The tanks are subsequently proof-tested to a pressure that is sufficiently severe to cause weld metal yielding in a few local regions of the weld seam. The work undertaken in the present project was to develop a capability to predict flaw growth from undetected surface flaws that are assumed to be located in the highly stressed regions. The technical challenge was to develop R-curve prediction capability for surface cracks in specimens that contain the flaws of unusual sizes and shapes deemed to be of interest. The test techniques developed and the elastic-plastic analysis concepts adopted are presented. The flaws of interest were quite small surface cracks that were narrow-deep ellipses that served to exacerbate the technical difficulties involved.

Mccabe, Donald E.↗
NASA NTRS1948

Photographic Study of Combustion in a Rocket Engine I : Variation in Combustion of Liquid Oxygen and Gasoline with Seven Methods of Propellant Injection

Motion pictures at camera speeds up to 3000 frames per second were taken of the combustion of liquid oxygen and gasoline in a 100-pound-thrust rocket engine. The engine consisted of thin contour and injection plates clamped between two clear plastic sheets forming a two-dimensional engine with a view of the entire combustion chamber and nozzle. A photographic investigation was made of the effect of seven methods of propellant injection on the uniformity of combustion. From the photographs, it was found that the flame front extended almost to the faces of the injectors with most of the injection methods, all the injection systems resulted in a considerable nonuniformity of combustion, and luminosity rapidly decreased in the divergent part of the nozzle. Pressure vibration records indicated combustion vibrations that approximately corresponded to the resonant frequencies of the length and the thickness of the chamber. The combustion temperature divided by the molecular weight of the combustion gases as determined from the combustion photographs was about 50 to 70 percent of the theoretical value.

Bellman, Donald R↗
NASA NTRS1998

The Fundamental Gain Limitation of High-Rate Gaseous Detectors and Optimum Designs for High-Rate Applications

We have performed a systematic study of the breakdown mechanism of high-rate detectors: MSGC, MGC, MICROMEGAS and GEM, recently chosen or considered as candidates for high-luminosity applications, together with newly elaborated designs such as high-rate wire chambers, thin gap parallel-plate chamber and super-high-rate RPC's. It was found for all these that the maximum breakdown-limited dramatically with incident flux and further decreases in the presence of alpha particles which are typical of the backgrounds in high-energy experiments. It was determined that the key parameter that limits a detector's performance is the effective current density in the avalanche, and that above a certain value breakdowns occur. At these limits the subsequent breakdowns take place by a mechanism which does not seem to have been previously reported in the literature. We present the results of this study together with a qualitative theory of this new type of breakdown and suggestions for optimizing high-rate detectors which we have verified experimentally.

Fonte, Paulo↗
NASA NTRS2000

Internally Cooled Monolithic Silicon Nitride Aerospace Components

A set of rapid prototyping (RP) processes have been combined with gelcasting to make ceramic aerospace components that contain internal cooling geometry. A mold and core combination is made using a MM6Pro (Sanders Prototyping, Inc.) and SLA-250/40 (3Dsystems, Inc.). The MM6Pro produces cores from ProtoBuild (trademarked) wax that are dissolved in room temperature ethanol following gelcasting. The SLA-250/40 yields epoxy/acrylate reusable molds. Parts produced by this method include two types of specimens containing a high density of thin long cooling channels, thin-walled cylinders and plates, as well as a model hollow airfoil shape that can be used for burner rig evaluation of coatings. Both uncoated and mullite-coated hollow airfoils has been tested in a Mach 0.3 burner rig with cooling air demonstrating internal cooling and confirming the effectiveness of mullite coatings.

Best, Jonathan E.↗
NASA NTRS2001

Passive Gas-Gap Heat Switches for Use in Adiabatic Demagnetization Refrigerators

We have designed, built, and tested a gas gap heat switch that works passively, without the need for a separate, thermally activated getter. This switch uses He-3 condensed as a thin film on alternating plates of copper. The switch is thermally conductive at temperatures above about 0.2 K, and is insulating if either end of the switch is below about 0.15 K. The "on" conductance (7 mW/K at 0.25K) is limited by the surface area and gap between the copper leaves, the saturated vapor pressure of the He-3, and the Kapitza boundary resistance between the He-3 and the copper. The "off" conductance is determined by the helium containment shell which physically supports the two conductive ends. We have also designed and are building passive gas gap heat switches which will passively turn off near 1 K and 4 K. For these switches we rely on the rapidly changing vapor pressure of He-4 above neon or copper substrates, respectively, when the coverage is less than one monolayer. The different binding energies of the He-4 to the neon or copper give rise to the different temperatures where the switches transition between the on and off states.

Shirron, P. J.↗
NASA NTRS1988

Light Reflector

Ultra Sales, Inc.'s fluorescent lighting fixture gets a boost in reflectivity through installation of Lightdriver, a thin tough thermoplastic film plated with aluminum, capable of reflecting 95 percent of visible light striking it. Lightdriver increases brightness without adding bulbs, and allows energy savings by removing some bulbs because the mirrorlike surface cuts light loss generally occasioned by conventional low reflectivity white painted surface above the bulbs in many fluorescent fixtures. Forty-five percent reduction in lighting electricity is attainable.

Source record↗