Charge of ions emitting spectral lines
Ion charge determination from emitting spectral lines using beam foil light source technique
Bashkin, S.↗
SEARCH · Engineering Papers
Results for “beam techniques”
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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Charge identification for spectral lines in nitrogen
Ion charge identification for spectral lines in nitrogen by beam foil light source technique
Bashkin, S.↗
Sky-wave backscatter - A means for observing our environment at great distances.
During the last five years, much progress has been made in the understanding of sky-wave backscatter. An explanation of the various interacting phenomena is presented, as is a review of the current state of knowledge reflecting recent advances in observational methods and analytic techniques. New narrow-beam antennas, coupled with signal modulations that permit fine resolution in time delay, are beginning to yield information concerning the character of the scatterers, which now can be separately discerned. These narrow beams also permit study of polarization fading from small regions, and this shows promise as a means for learning the distant sea state. Doppler shifts of a fraction of a hertz on signals of tens of megahertz are separable, permitting isolation of sea returns from ground returns by virtue of the Doppler effect resulting from sea-wave speed; this also suggests a potential sea-monitoring principle. Despite these advances, there is little practical application of sky-wave backscatter as a means of environmental monitoring. This lack is attributed to the large remaining gaps in our understanding of the echoes and our inability to interpret the forms of data that can be acquired with equipment of reasonable cost.
Croft, T. A.↗
The initiation of boiling during pressure transients
The initiation of boiling of water on metal surfaces during pressure transients has been investigated. The data were obtained by a new technique in which light beam fluctuations and a pressure signal were simultaneously recorded on a dual beam oscilloscope. The results obtained agreed with those obtained using high speed photography. It was found that, for water temperatures between 90-150 C, the wall superheat required to initiate boiling during a rapid pressure transient was significantly higher than required when the pressure was slowly reduced. This result is explained by assuming that a finite time is necessary for vapor to fill the cavity at which the bubble originates. Experimental measurements of this time are in reasonably good agreement with calculations based on the proposed theory. The theory includes a new procedure for estimating the coefficient of vaporization.
Weisman, J.↗
A numerical-perturbation method for the nonlinear analysis of structural vibrations
A numerical-perturbation method is proposed for the determination of the nonlinear forced response of structural elements. Purely analytical techniques are capable of determining the response of structural elements having simple geometries and simple variations in thickness and properties, but they are not applicable to elements with complicated structure and boundaries. Numerical techniques are effective in determining the linear response of complicated structures, but they are not optimal for determining the nonlinear response of even simple elements when modal interactions take place due to the complicated nature of the response. Therefore, the optimum is a combined numerical and perturbation technique. The present technique is applied to beams with varying cross sections.
Nayfeh, A. H.↗
Research in large adaptive antenna arrays
The feasibility of microwave holographic imaging of targets near the earth using a large random conformal array on the earth's surface and illumination by a CW source on a geostationary satellite is investigated. A geometrical formulation for the illuminator-target-array relationship is applied to the calculation of signal levels resulting from L-band illumination supplied by a satellite similar to ATS-6. The relations between direct and reflected signals are analyzed and the composite resultant signal seen at each antenna element is described. Processing techniques for developing directional beam formation as well as SNR enhancement are developed. The angular resolution and focusing characteristics of a large array covering an approximately circular area on the ground are determined. The necessary relations are developed between the achievable SNR and the size and number of elements in the array. Numerical results are presented for possible air traffic surveillance system. Finally, a simple phase correlation experiment is defined that can establish how large an array may be constructed.
Berkowitz, R. S.↗
Development and fabrication of a solar cell junction processing system
Experiments were completed which indicate that single-pulse, liquid-phase epitaxial regrowth is the optimum technique for pulsed electron beam annealing of ion implantation damage in silicon wafers. An electron beam which covers the entire area of the wafer was chosen for the solar cell processor. Beam control experiments to improve beam propagation and to test the concept of partial space charge and current neutralization were initiated. The electrical parameters of the pulsed electron beam subsystem were chosen on the basis of computer calculations and past experience in pulsed electron accelerator design and operation. The pulser, designated SPI-PULSE 7000, is designed to anneal 10 cm diameter silicon wafers at a rate of 30 per minute. The preliminary design of the major elements of the SPI-PULSE 7000 was completed, and the detailed design of many of the components begun. These elements include a capacitive energy store and charging system, an electron accelerator, a beam control system, a wafer handling system and pressure and vacuum assemblies.
Halvason, W.↗
The 30/20 Gigahertz transponder study
Design features and performance parameters are described for three types of wideband multiple channel satellite transponders for use in a 30/20 GHz communications satellite, which provides high data rate trunking service to ten ground station terminals. The three types of transponder are frequency division multiplex (FDM), time division multiplex (TDM), and a hybrid transponder using a combination of FDM and TDM techniques. The wideband multiple beam trunking concept, the traffic distribution between the trunking terminals, and system design constraints are discussed. The receiver front end design, the frequency conversion scheme, and the local oscillator design are described including the thermal interface between the transponders and the satellite. The three designs are compared with regard to performance, weight, power, cost and initial technology. Simplified block diagrams of the baseline transponder designs are included.
Source record↗
On-board processing for future satellite communications systems: Satellite-Routed FDMA
A frequency division multiple access (FDMA) 30/20 GHz satellite communications architecture without on-board baseband processing is investigated. Conceptual system designs are suggested for domestic traffic models totaling 4 Gb/s of customer premises service (CPS) traffic and 6 Gb/s of trunking traffic. Emphasis is given to the CPS portion of the system which includes thousands of earth terminals with digital traffic ranging from a single 64 kb/s voice channel to hundreds of channels of voice, data, and video with an aggregate data rate of 33 Mb/s. A unique regional design concept that effectively smooths the non-uniform traffic distribution and greatly simplifies the satellite design is employed. The satellite antenna system forms thirty-two 0.33 deg beam on both the uplinks and the downlinks in one design. In another design matched to a traffic model with more dispersed users, there are twenty-four 0.33 deg beams and twenty-one 0.7 deg beams. Detailed system design techniques show that a single satellite producing approximately 5 kW of dc power is capable of handling at least 75% of the postulated traffic. A detailed cost model of the ground segment and estimated system costs based on current information from manufacturers are presented.
Berk, G.↗
The control and estimation of large space structures
A shape control or estimation problem for a large space structure can be modeled by a partial differential equation which represents changes in shape with respect to space and time, together with spatially discrete forcing functions or observations which represent the placement of actuators or sensors at discrete points along the structure. The use of Green's functions to convert boundary value problems into integral equations provides a convenient treatment of this mixture of continuous and discrete mathematics. Control and estimation algorithms are developed for the one-dimensional static beam to illustrate this technique.
Weeks, C.↗
Minority carrier diffusion length measurements - A review and comparison of techniques
A review of the major techniques for measuring minority carrier diffusion lengths in solar cells is given. Limits of applicability are indicated for each method, as relevant to indirect bandgap materials such as silicon, and direct bandgap materials like gallium arsenide. A discussion and bibliography is presented for the following techniques: uniform generation, electron beam induced current, Schottky barrier (and other steady-state) photocurrent, surface photovoltage, transient decay, and luminescence.
Khan, A. A.↗
New absolute spectroscopic measurement of the solar equatorial rotation rate
An atomic-beam resonance-scattering technique applied to the 7699 A solar potassium absorption line is used to make an absolute spectroscopic determination of the solar equatorial rotation rate. This is believed to be a new method which has not previously been used for studying solar rotation. The measurements were made during 1979-82, initially with a permanent apparatus at Oberlin College and more recently with a portable apparatus installed at the Snow Telescope on Mt. Wilson. After carefully allowing for possible systematic errors, it is concluded that the solar sidereal equatorial rotation rate is 13.8 + or - 0.3 deg/day and that it has not varied significantly over the period of these observations.
Snider, J. L.↗
Magnetospheric and interplanetary physics 1979-1982
Major trends in the study of magnetospheric and interplanetary physics during the 1979-1982 period are surveyed. Topics discussed include the exploration of the Saturnian and Jovian magnetospheres by Voyagers 1 and 2, the behavior of different ions in the earth magnetosphere, auroral kilometric radiation, computer modeling of global magnetospheric MHD flow, the magnetic substorm, the quiet state, the earth's bow shock, the heliospheric current sheet, and new techniques such as electron beam experiments, 'active' injection experiments, auroral radars, and observations of the earth's distant magnetic tail. The future of this area of research is seen in the combination of data from different spacecraft and ground observations in a single correlated data set, and in the consolidation of past gains by analysis of the large data backlog, while a small number of new missions goes forward.
Stern, D. P.↗
Electron-beam induced current characterization of back-surface field solar cells using a chopped scanning electron microscope beam
A chopped electron beam induced current (EBIC) technique for the chacterization of back-surface field (BSF) solar cells is presented. It is shown that the effective recombination velocity of the low-high junction forming the back-surface field of BSF cells, in addition to the diffusion length and the surface recombination velocity of the surface perpendicular to both the p-n and low-high junctions, can be determined from the data provided by a single EBIC scan. The method for doing so is described and illustrated. Certain experimental considerations taken to enhance the quality of the EBIC data are also discussed.
Luke, K. L.↗
Recombination-active defects in silicon ribbon and polycrystalline solar cells
This paper reports results from a study of recombination-active structural defects in silicon ribbon and polycrystalline solar cells using the electron beam induced current (EBIC) technique in a scanning electron microscope. It is demonstrated that low temperature EBIC measurements can reveal a range of defects that are not observable at room temperature, including slip dislocations in silicon dendritic web ribbons as well as decorated twin boundaries and dislocation complexes in cast polycrystalline silicon solar cell materials.
Cheng, L. J.↗
Defect characterization of silicon dendritic web ribbons
Progress made in the study of defect characterization of silicon dendritic web ribbon is presented. Chemical etching is used combined with optical microscopy, as well as the electron beam induced current (EBIC) technique. Thermal annealing effect on carrier lifetime is examined.
Cheng, L. J.↗
The use of multiple EBIC curves and low voltage electron microscopy in the measurement of small diffusion lengths
Accurate evaluations of diffusion lengths for heavily to moderately doped III-V semiconductors and/or radiation damaged solar cells have been made possible by using experimental and numerical techniques. The techniques employed were electron beam induced current and low voltage electron microscopy.
Leon, R. P.↗
Three dimensional flow simulation with application to aeroelastic analysis
The three-dimensional flowfield about realistic launch vehicle configurations is simulated using the Reynolds-averaged Navier-Stokes equations. Turbulent mixing is accounted for by means of the two-layer Baldwin and Lomax (1978) algebraic eddy viscosity model. The Beam and Warming (1976) implicit approximate factorization algorithm is used for the solution of the finite difference equations. Applications include the study of the flowfield about a hemisphere-cylinder configuration both in the subsonic and supersonic flight regimes, and about two hammerhead payload configurations at transonic speeds. A method is also described which permits incorporating this flow solver into a complete algorithm to perform time-domain aeroelastic stability analyses. The vehicle is modeled as a free-free beam and modal superposition techniques are used for the structural-dynamic formulation. Aeroelastic analyses were performed for the hammerhead configurations.
Azevedo, Joao Luiz F.↗