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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Ionizing gas breakdown waves in strong electric fields.

A previous analysis by Albright and Tidman (1972) of the structure of an ionizing potential wave driven through a dense gas by a strong electric field is extended to include atomic structure details of the background atoms and radiative effects, especially, photoionization. It is found that photoionization plays an important role in avalanche propagation. Velocities, electron densities, and temperatures are presented as a function of electric field for both negative and positive breakdown waves in nitrogen.

Klingbeil, R.↗
NASA NTRS1972

Pyrometer for measurement of surface temperature distribution on a rotating turbine blade.

A conceptual optical method and some test results are presented for measuring the surface temperature distribution on one of the rotating turbine blades with a surface resolution of 0.05 cm spot diameter at a tip speed of 400 m/sec. The blade is scanned line-by-line by a fixed optical system. During each line-scan, the detector analog output signal is converted to 200 consecutive digital values that are temporarily stored in a high-speed buffer memory and then transferred at a slower rate to a computer for processing. The signal-to-noise ratio of the silicon avalanche detector is large enough to obtain an accuracy of 1% at 1050 K blade temperature. By averaging 25 scans of the same line the same accuracy can be obtained at 900 K.

Buchele, D. R.↗
NASA NTRS1972

Single photon detection and timing - Experiments and techniques.

Single photon detection and timing means essentially the detection and timing of a single photoelectron released by light from a photosensitive surface of a photomultiplier, channel multiplier, avalanche multiplier photodiode, or other photodevice. Necessary photodevice gain and detection circuits, mechanisms and statistics of photodevice gain, photodevice and background noise and their reduction, and practical photodevice techniques and photon detection performance tests are discussed. Fast timing with single photons, and single photon detection with moderate timing requirements are considered.

Poultney, S. K.↗
NASA NTRS1972

Astronaut observations from lunar orbit and their geologic significance.

To supplement orbital photography and other remotely sensed data, visual observations were made of 15 lunar surface targets during Apollo mission 15. Among the significant results are (1) characterization of the floor material of Tsiolkovsky as no darker than the average (Eratosthenian) mare material, and interpretration of the lineated unit on the crater rim as a rock avalanche; (2) identification of layers on the wall of the crater Picard, which is probably volcanic in origin, (3) explanation of the ray-excluded zone of the crater Proclus as the result of structurally controlled ray shadowing; (4) observation of cinder cones in the Littrow area with dark haloes that probably are composed of pyroclastic deposits; and (5) recognition that the termini of numerous sinuous rilles in Oceanus Procellarum are flooded with younger mare materials that may have covered older terminal deposits.

El-Baz, F.↗
NASA NTRS1972

Mineralogy and origin of Fra Mauro fines and breccias.

Textural features, glassy spherule and glassy aggregate contents, and size-frequency distributions of lithic components of the regolith fines indicate that the Fra Mauro regolith of the smooth terrain is a highly reworked accumulation of debris derived primarily by impact comminution of annealed breccias. Analyses of the glassy spherules suggest that mare-derived debris must amount to less than 5% of the regolith, but exotic materials having the composition of the Fra Mauro breccias (highland-like) cannot be recognized. Breccia samples from the Fra Mauro site include (1) regolith breccias derived by lithification of local regolith material, (2) texturally and compositionally unique white rock breccias that may have been derived from ancient ejecta buried beneath the Fra Mauro formation, and (3) annealed breccias that are excavated samples of the Fra Mauro formation. The latter were deposited as heated impact ejecta, probably by avalanches produced by the Imbrian event and were annealed in situ in a thermal regime perhaps equivalent to that responsible for the pyroxene-hornfels facies of metamorphism in terrestrial rocks.

Quaide, W.↗
NASA NTRS1974

Laser-induced electric breakdown in solids

A review is given of recent experimental results on laser-induced electric breakdown in transparent optical solid materials. A fundamental breakdown threshold exists characteristic for each material. The threshold is determined by the same physical process as dc breakdown, namely, avalanche ionization. The dependence of the threshold on laser pulse duration and frequency is consistent with this process. The implication of this breakdown mechanism for laser bulk and surface damage to optical components is discussed. It also determines physical properties of self-focused filaments.

Bloembergen, N.↗
NASA NTRS1975

A study of the interaction of neutral and charged particles

Preliminary experimental data on the number of charged neutral nuclear-active particles were obtained at 200 BeV. The ratio of the number of charged particles to the number of neutral particles was 2.1 + or - 0.3. Nuclear cascade curves in iron and distributions over the portions of energy transferred to neutral pions in lead were obtained for avalanches generated by charged and neutral particles. The characteristics of interactions of the charged neutral particles at the existing experimental errors showed no difference.

Kim, V. M.↗
NASA NTRS1975

Effect of electron divergence in air gaps on the measurement of the energy of cascades in emulsion chambers

The effect of an increase in electron density in the vicinity of the cascade axis caused by an avalanche passing through the gap between lead filters of the emulsion chamber was investigated experimentally. Optical densities were measured in three X-ray films spaced at 400, 800 and 1200 micrometer from the filter surface having a thickness of 6 cascade units. The optical densities of blackening spots caused by electron photon cascades of 1 to 2, 2 to 7 and greater than 7 BeV energies were measured. The results prove the presence of a gap between the filter and the nuclear emulsion which results in the underestimation of energy by several tenths of a percent.

Apanasenko, A. V.↗
NASA NTRS1974

Nonlinear analysis of a family of LC tuned inverters

A family of four dc-to-square-wave LC tuned inverters are analyzed using singular point. Limit cycles and waveshape characteristics are given for three modes of oscillation: quasi-harmonic, relaxation, and discontinuous. An inverter in which the avalanche breakdown of the transistor emitter-to-base junction occurs is discussed and the starting characteristics of this family of inverters are presented. The LC tuned inverters are shown to belong to a family of inverters with a common equivalent circuit consisting of only three 'series' elements: a five-segment piecewise-linear current-controlled resistor, linear inductor, and linear capacitor.

Lee, F. C. Y.↗
NASA NTRS1974

Petrography of Apollo 17 soils

An analysis of soils collected on the valley floor at Taurus-Littrow (dark mantle) reveals that these soils are formed by comminution of mare basalt flows and a clastic deposit consisting of black and orange glass spheres. There is no evidence for the pyroclastic origin of the dark mantle. It is found that the North Massif soils contain a large amount of mare-derived fragments being transported horizontally from the basaltic valley floor. A light mantle deposit of uniform composition including comminuted noritic and anorthositic breccia is observed. It is suggested that the light mantle is an avalanche deposit from regolith developed high on the South Massif.

Heiken, G.↗
NASA NTRS1976

Calculations of the Electron Energy Distribution Function in a Uranium Plasma by Analytic and Monte Carlo Techniques

Electron energy distribution functions were calculated in a U235 plasma at 1 atmosphere for various plasma temperatures and neutron fluxes. The distributions are assumed to be a summation of a high energy tail and a Maxwellian distribution. The sources of energetic electrons considered are the fission-fragment induced ionization of uranium and the electron induced ionization of uranium. The calculation of the high energy tail is reduced to an electron slowing down calculation, from the most energetic source to the energy where the electron is assumed to be incorporated into the Maxwellian distribution. The pertinent collisional processes are electron-electron scattering and electron induced ionization and excitation of uranium. Two distinct methods were employed in the calculation of the distributions. One method is based upon the assumption of continuous slowing and yields a distribution inversely proportional to the stopping power. An iteration scheme is utilized to include the secondary electron avalanche. In the other method, a governing equation is derived without assuming continuous electron slowing. This equation is solved by a Monte Carlo technique.

Bathke, C. G.↗
NASA NTRS1976

High-resolution surface temperature measurements on rotating turbine blades with an infrared pyrometer

A high-resolution pyrometer was developed and tested on a modified turbine engine. The pyrometer was used to obtain temperature profiles of the viewed surface of turbine blades in the engine at tip speeds up to 366 meters per second. The combination of coherent fiber optics, a silicon avalanche detector, and high-speed electronics enabled surface resolution of a spot diameter of 0.05 centimeter. The data, in the form of temperature profiles, was obtained in near real time as a hard copy output from a computer display terminal. Temperatures measured with the pyrometer and with thermocouples agreed within 2 percent at temperatures between 977 to 1144 K.

Uguccini, O. W.↗
NASA NTRS1976

Dielectric breakdown induced by picosecond laser pulses

The damage thresholds of transparent optical materials were investigated. Single picosecond pulses at 1.06 microns, 0.53 microns and 0.35 microns were obtained from a mode locked Nd-YAG oscillator-amplifier-frequency multiplier system. The pulses were Gaussian in space and time and permitted the determination of breakdown thresholds with a reproducibility of 15%. It was shown that the breakdown thresholds are characteristic of the bulk material, which included nine alkali halides, five different laser host materials, KDP, quartz, sapphire and calcium fluoride. The extension of the damage data to the ultraviolet is significant, because some indication was obtained that two- and three-photon absorption processes begin to play a role in determining the threshold. Throughout the visible region of the spectrum the threshold is still an increasing function of frequency, indicating that avalanche ionization is the dominant factor in determining the breakdown threshold. This was confirmed by a detailed study of the damage morphology with a high resolution microscope just above the threshold. The influence of self focusing is discussed, and evidence for beam distortion below the power threshold for complete self focusing is presented, confirming the theory of Marburger.

Smith, W. L.↗
NASA NTRS1976

Photomultiplier tube development for the 1.06 micrometer wavelength

High speed, electrostatic photomultipliers were developed for use in 400 megabit laser communication systems operating at the 1.06 micron wavelength. A high performance, electrostatic III-V photocathode PMT was shown in communication system tests to perform competitively with solid state and avalanche photodiodes. Signal-induced noise and III-V cathode stability were identified as remaining technical problems while cathode quantum efficiencies of or = 5% at 1.06 micron and 320 picosecond rise and fall time pulse performance were achieved.

Enck, R. S., Jr.↗
NASA NTRS1976

Sound-producing dune and beach sands

Acoustic and seismic outputs of booming sands and singing (squeaking) sands in response to shearing are investigated, with samples of silent sands studied for controls. A vertical-axis geophone buried at shallow depth and an air microphone were used in the studies. The frequency spectra of the acoustic and seismic responses, propagation delays, comparison of acoustic and seismic traces, grain size and grain surface texture, particle morphology, coherent behavior of grains in assemblages, and relation to prevalent local winds were studied. Mechanisms are still obscure and disputed; slumping and avalanches were induced artificially in some studies. Existence of booming dune phenomena on Mars or on the moon is conjectured.

Lindsay, J. F.↗
NASA NTRS1976

A mechanism for the production of pulsar radio radiation

Recent theoretical studies have suggested that avalanches of electron-positron pairs are produced by spark discharges near the magnetic poles of pulsars. This pair production mechanism may result in a double-peaked particle distribution function. We investigate collective effects caused by a high-energy electron-positron beam traversing a low-energy electron-positron plasma for an astrophysically interesting range of physical parameters. The principal result of this paper is to identify transverse unstable waves whose phase propagation may occur at any arbitrary angle (other than zero) with respect to the magnetic field but whose group velocity is along the magnetic field and approximately the speed of light. It is suggested that the observed radio pulses from pulsars may be caused by the focusing of these transverse waves along the open field lines extending from a pulsar's polar cap to the light cylinder.

Hardee, P. E.↗
NASA NTRS1977

High sensitivity 1.06 micron optical receiver for precision laser range finding

Aluminum gallium antimonide avalanche photodiodes with average gain of 10, internal quantum efficiency of greater than 60%, capacitance less than 0.2pf, and dark current of less than 1 micron were designed and fabricated for use in a low noise optical receiver suitable for 2 cm accuracy rangefinding. Topics covered include: (1) design of suitable photodetector structures; (2) epitaxial growth of AlGaSb devices; (3) fabrication of photodetectors; and (4) electro-optics characterization.

Scholl, F. W.↗
NASA NTRS1977

Picosecond laser-induced breakdown at 5321 and 5347 A - Observation of frequency-dependent behavior

A study is presented of picosecond laser-induced breakdown at 3547 and 5321 A of several materials. The thresholds obtained for breakdown at 5321 A are compared to previous results obtained at 1.064 microns using the same laser system. This comparison illustrates the transition of bulk laser-induced breakdown as it becomes increasingly frequency dependent. UV picosecond pulses are obtained by mixing 5321 A and 1.064 micron pulses in a KH2PO4 crystal. Upper and lower bounds on the 3547 A breakdown threshold are defined, although some effects of walk-off distortion and self-focusing are observed. The results are discussed with reference to models for the intrinsic processes involved in the breakdown, i.e., avalanche and multiphoton ionization.

Smith, W. L.↗