Search NASA⌕ Search

SEARCH · Search NASA

Results for “Double Beam”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS2006

Domed, 40-cm-Diameter Ion Optics for an Ion Thruster

Improved accelerator and screen grids for an ion accelerator have been designed and tested in a continuing effort to increase the sustainable power and thrust at the high end of the accelerator throttling range. The accelerator and screen grids are undergoing development for intended use as NASA s Evolutionary Xenon Thruster (NEXT) a spacecraft thruster that would have an input-power throttling range of 1.2 to 6.9 kW. The improved accelerator and screen grids could also be incorporated into ion accelerators used in such industrial processes as ion implantation and ion milling. NEXT is a successor to the NASA Solar Electric Propulsion Technology Application Readiness (NSTAR) thruster - a state-of-the-art ion thruster characterized by, among other things, a beam-extraction diameter of 28 cm, a span-to-gap ratio (defined as this diameter divided by the distance between the grids) of about 430, and a rated peak input power of 2.3 kW. To enable the NEXT thruster to operate at the required higher peak power, the beam-extraction diameter was increased to 40 cm almost doubling the beam-extraction area over that of NSTAR (see figure). The span-to-gap ratio was increased to 600 to enable throttling to the low end of the required input-power range. The geometry of the apertures in the grids was selected on the basis of experience in the use of grids of similar geometry in the NSTAR thruster. Characteristics of the aperture geometry include a high open-area fraction in the screen grid to reduce discharge losses and a low open-area fraction in the accelerator grid to reduce losses of electrically neutral gas atoms or molecules. The NEXT accelerator grid was made thicker than that of the NSTAR to make more material available for erosion, thereby increasing the service life and, hence, the total impulse. The NEXT grids are made of molybdenum, which was chosen because its combination of high strength and low thermal expansion helps to minimize thermally and inertially induced deflections of the grids. A secondary reason for choosing molybdenum is the availability of a large database for this material. To keep development costs low, the NEXT grids have been fabricated by the same techniques used to fabricate the NSTAR grids. In tests, the NEXT ion optics have been found to outperform the NSTAR ion optics, as expected.

Soulas, George C.↗
NASA NTRS1976

Electrostatic shocks as nonlinear ion acoustic waves

A cold fluid approach is presented which yields exact double-layer solutions that can be used to model electrostatic S-type shocks. Solutions derived from the two-temperature electron model are presented in order to show the range of amplitudes and scale lengths possible for this plasma model and to examine how shock properties depend on orientation of the shock. The dependence of various double-layer quantities on plasma composition is then considered for the cold electron beam model. Double-layer solutions pertinent to describing electrostatic shocks are pointed out.

Witt, E.↗
NASA NTRS1992

Acoustic double layers in multispecies plasma

The formation of acoustic double layers in the presence of two ion species is examined via a particle simulation in a 1D bounded system. The effect of having two ion components, an H(+) and an O(+) beam, on double-layer evolution from ion acoustic turbulence driven by an electron drift relative to the H(+) beam of about 0.5 u sub e, where u sub e is the electron thermal speed, is examined. It is found that acoustic double layers form in either ion species on a time scale of about 100 omega sub ps exp -1, where omega sub ps is the ion plasma frequency for species 's' and s = H or O, and for drifts relative to the electrons lower than that required for double layer formation in simulations of single ion component plasma.

Gray, Perry C.↗
NASA NTRS1992

Double-slot antennas on extended hemispherical dielectric lenses

An investigation of the coupling efficiencies to a gaussian-beam of a double-slot antenna on a hyperhemispherical lens is presented. It is shown that both lenses couple equally well to an appropriate gaussian beam (about 80 percent). The radiation patterns of both lenses with a double-slot antenna are computed using the ray-tracing method. The experimental radiation patterns are presented and show close agreement to the theoretically computed patterns.

Filipovic, Daniel F.↗
NASA NTRS1998

Reciprocal Space Mapping of Macromolecular Crystals in the Laboratory

The technique of reciprocal space mapping applied to the physical measurement of macromolecular crystals will be described. This technique uses a triple axis diffractometer setup whereby the monochromator is the first crystal, the sample is the second and the third crystal (of the same material as the monochromator) analyzes the diffracted beam. The geometry is such that it is possible to separate mosaic volume effects from lattice strain effects. The deconvolution of the instrument parameters will also be addressed. Results from measurements at Brookhaven National Synchrotron Radiation Source carried out on microgravity and ground-grown crystals will be presented. The required beam characteristics for reciprocal space mapping are also ideal for topographic studies and the first topographs ever recorded from microgravity protein crystal samples will be shown. We are now working on a system which will enable reciprocal space mapping, mosaicity and topography studies to be carried out in the home laboratory. This system uses a rotating anode X-ray source to provide an intense beam then a Bartels double crystal, four reflection monochromator to provide the spectral and geometric beam conditioning necessary such that the instrument characteristics do not mask the measurement. This is coupled to a high precision diffractometer and sensitive detector. Commissioning data and first results from the system will be presented.

Snell, Edward H.↗
NASA NTRS1975

Performance mapping of a 30 cm engineering model thruster

A 30 cm thruster representative of the engineering model design has been tested over a wide range of operating parameters to document performance characteristics such as electrical and propellant efficiencies, double ion and beam divergence thrust loss, component equilibrium temperatures, operational stability, etc. Data obtained show that optimum power throttling, in terms of maximum thruster efficiency, is not highly sensitive to parameter selection. Consequently, considerations of stability, discharge chamber erosion, thrust losses, etc. can be made the determining factors for parameter selection in power throttling operations. Options in parameter selection based on these considerations are discussed.

Poeschel, R. L.↗
NASA NTRS1980

Cycle II.5 aircraft aero-optical turbulent boundary-layer/shear-layer measurements

The aero-optical effects associated with propagating a laser beam through aircraft turbulent boundary layers and shear layers were examined. Observed laser optical performance levels were compared with those inferred from aerodynamic measurements of unsteady densities and correlation lengths within these random flows. Optical instrumentation included a fast shearing interferometer (FSI). A 9 cm diameter collimated helium neon laser beam made a double pass through the aircraft random flow via an airfoil mirror located one meter from the fuselage. Typical aircraft turbulent boundary layer thickness measured 0.3 meters. Averaging many FSI generated modulation transfer functions (MTFs) and Fourier transforming, this average yields the expected far field intensity degradation associated with an aircraft mounted laser system. Aerodynamic instrumentation included fine wire probes to measure unsteady temperature and mass flux. A laser doppler velocimeter measured unsteady velocity within the flows. An analysis of these data yielded point measurements of unsteady density and correlation length.

Gilbert, K.↗
NASA NTRS1985

Space Station structures

A brief overview of some structural results that came from space station skunk works is presented. Detailed drawings of the pressurized modules, and primary truss structures such as deployable single fold beams, erectable beams and deployable double folds are given. Typical truss attachment devices and deployable backup procedures are also given.

Schneider, W.↗
NASA NTRS1990

Damage induced constitutive response of a thermoplastic related to composites and adhesive bonding

The volume-averaged constitutive behavior of a polymer sustaining void growth under dilational deformation is addressed. Polyvinylacetate is deformed between two aluminum beams in a double cantilever geometry and the deformations, recorded with the aid of optical interferometry, are used to deduce the stress-strain behavior of the material as it passes from small strain behavior, through the voiding process, to near-failure under exclusion of rate-sensitivity considerations.

Parvin, M.↗
NASA NTRS2011

Multi-Wavelength, Multi-Beam, and Polarization-Sensitive Laser Transmitter for Surface Mapping

A multi-beam, multi-color, polarized laser transmitter has been developed for mapping applications. It uses commercial off-the-shelf components for a lowcost approach for a ruggedized laser suitable for field deployment. The laser transmitter design is capable of delivering dual wavelengths, multiple beams on each wavelength with equal (or variable) intensities per beam, and a welldefined state of polarization. This laser transmitter has been flown on several airborne campaigns for the Slope Imaging Multi-Polarization Photon Counting Lidar (SIMPL) instrument, and at the time of this reporting is at a technology readiness level of between 5 and 6. The laser is a 1,064-nm microchip high-repetition-rate laser emitting energy of about 8 microjoules per pulse. The beam was frequency-doubled to 532 nm using a KTP (KTiOPO4) nonlinear crystal [other nonlinear crystals such as LBO (LiB3O5) or periodically poled lithium niobiate can be used as well, depending on the conversion efficiency requirements], and the conversion efficiency was approximately 30 percent. The KTP was under temperature control using a thermoelectric cooler and a feedback monitoring thermistor. The dual-wavelength beams were then spectrally separated and each color went through its own optical path, which consisted of a beam-shaping lens, quarterwave plate (QWP), and a birefringent crystal (in this case, a calcite crystal, but others such as vanadate can be used). The QWP and calcite crystal set was used to convert the laser beams from a linearly polarized state to circularly polarized light, which when injected into a calcite crystal, will spatially separate the circularly polarized light into the two linear polarized components. The spatial separation of the two linearly polarized components is determined by the length of the crystal. A second set of QWP and calcite then further separated the two beams into four. Additional sets of QWP and calcite can be used to further split the beams into multiple orders of two. The spatially separated beams had alternating linearly polarization states; a half-wave plate (HWP) array was then made to rotate the alternating states of A multi-beam, multi-color, polarized laser transmitter has been developed for mapping applications. It uses commercial off-the-shelf components for a lowcost approach for a ruggedized laser suitable for field deployment. The laser transmitter design is capable of delivering dual wavelengths, multiple beams on each wavelength with equal (or variable) intensities per beam, and a welldefined state of polarization. This laser transmitter has been flown on several airborne campaigns for the Slope Imaging Multi-Polarization Photon Counting Lidar (SIMPL) instrument, and at the time of this reporting is at a technology readiness level of between 5 and 6. The laser is a 1,064-nm microchip high-repetition-rate laser emitting energy of about 8 microjoules per pulse. The beam was frequency-doubled to 532 nm using a KTP (KTiOPO4) nonlinear crystal [other nonlinear crystals such as LBO (LiB3O5) or periodically poled lithium niobiate can be used as well, depending on the conversion efficiency requirements], and the conversion efficiency was approximately 30 percent. The KTP was under temperature control using a thermoelectric cooler and a feedback monitoring thermistor. The dual-wavelength beams were then spectrally separated and each color went through its own optical path, which consisted of a beam-shaping lens, quarterwave plate (QWP), and a birefringent crystal (in this case, a calcite crystal, but others such as vanadate can be used). The QWP and calcite crystal set was used to convert the laser beams from a linearly polarized state to circularly polarized light, which when injected into a calcite crystal, will spatially separate the circularly polarized light into the two linear polarized components. The spatial separation of the two linearly polarized components is determined by the length of the crystal. A cond set of QWP and calcite then further separated the two beams into four. Additional sets of QWP and calcite can be used to further split the beams into multiple orders of two. The spatially separated beams had alternating linearly polarization states; a half-wave plate (HWP) array was then made to rotate the alternating states of

Yu, Anthony W.↗
NASA NTRS1972

Ion thruster performance calibration.

The calibration of a typical 20-cm diameter ion thrustor was examined to determine performance penalties that must be assessed in projecting measured performance into a space environment. Four specific areas were investigated. These include (1) double ion content of the beam, (2) back ingestion from the vacuum facility, (3) beam spreading, and (4) propellant flow rate measurements. The double ion content was measured and found to be as high as 5.5% at an arc voltage of 35 volts. Back ingestion was observed to become significant above tank pressures of 6 microtorr. Beam spreading reduced effective thrust on the order of 2.5%.

Pawlik, E. V.↗
NASA NTRS1984

Measurements of the optical emission produced during the laboratory beam plasma discharge

Optical observations of a beam-plasma discharge (BPD) in the laboratory showed that the discharge remained confined to a diameter little more than double that of the beam for injection parallel to the magnetic field and approximately equal to that of the beam for injection at large pitch angles. The diameter was independent of beam current but varied linearly with beam velocity and inversely with magnetic field strength. The ionization rate inferred from the total emission of 3914 A, integrated over the radial extent of the beam, was proportional to the excess beam current above that requied for BPD ignition. The proportionality constant ( 12 + or - 2) x 10 to the 14th ions/cm s A was valid over a wide range of pressure and of magnetic field strength. Power loss to ionization in a 20 m path was estimated at up to 4 percent of the beam power. Evidence is presented for effective confinement of suprathermal electrons (parallel to B) by some unidentified process other than electrostatic confinement.

Hallinan, T. J.↗
NASA NTRS1984

Electrostatic hydrogen-cyclotron wave emission below the hydrogen-cyclotron frequency in the auroral acceleration region

A mechanism is suggested for the excitation of electrostatic ion-cyclotron waves at frequencies below the ion-cyclotron frequency in the midst of the auroral acceleration region, which is assumed to consist of downward moving double layers. The mechanism involves upward flowing ions interacting with a downward flowing background plasma. The upward flowing ions are the ion beams accelerated by the double layer. The downward motion of the background plasma corresponds to a plasma expansion into the density cavity that develops in connection with double layer formation in the acceleration region. The ion-cyclotron waves excited by the counterstreaming flows are doppler shifted to frequencies below the harmonics of the ion cyclotron frequency. It is suggested that such wave emissions could account for some very narrow-banded waves at frequencies below the hydrogen cyclotron frequency that were observed by the S3-3 satellite.

Singh, N.↗
NASA NTRS1987

Double Layers in Astrophysics

Topics addressed include: laboratory double layers; ion-acoustic double layers; pumping potential wells; ion phase-space vortices; weak double layers; electric fields and double layers in plasmas; auroral double layers; double layer formation in a plasma; beamed emission from gamma-ray burst source; double layers and extragalactic jets; and electric potential between plasma sheet clouds.

Williams, Alton C.↗
NASA NTRS1987

Double layers and plasma-wave resistivity in extragalactic jets: Cavity formation and radio-wave emission

For estimated values of the currents carried by extragalactic jets, current-driven electrostatic-wave- and electromagnetic-wave-produced resistivities do not occur. Strong plasma double layers, however, may exist within self-maintained density cavities, the relativistic double-layer-emitted electron, and ion beams driving plasma-wave resistivities in the low- and high-potential plasma adjacent to the double layers. The double-layer-emitted electron beams may also emit polarized radio waves via a collective bremsstrahlung process mediated by electrostatic two-stream instabilities.

Borovsky, Joseph E.↗
NASA NTRS1987

Double layers and plasma-wave resistivity in extragalactic jets - Cavity formation and radio-wave emission

Current driven electrostatic-wave- and electromagnetic-wave-produced resistivities do not occur in extragalactic jets for estimated values of the carried currents. Strong plasma double layers, however, may exist within self-maintained density cavities. The relativistic double-layer-emitted electron and ion beams drive plasma-wave resistivities in the low- and high-potential plasma adjacent to the double layers. The double-layer-emitted electron beams may also emit polarized radio waves via a collective bremsstrahlung process mediated by electrostatic two-stream instabilities.

Borovsky, Joseph E.↗
NASA NTRS1980

Over-under double-pass interferometer

An over-under double-pass interferometer in which the beamsplitter area and thickness can be reduced to conform only with optical flatness considerations is achieved by offsetting the optical center line of one cat's-eye retroreflector relative to the optical center line of the other in order that one split beam be folded into a plane distinct from the other folded split beam. The beamsplitter is made transparent in one area for a first folded beam to be passed to a mirror for doubling back and is made totally reflective in another area for the second folded beam to be reflected to a mirror for doubling back. The two beams thus doubled back are combined in the central, beam-splitting area of the beamsplitter and passed to a detector. This makes the beamsplitter insensitive to minimum-thickness requirements and selection of material.

Schindler, Rudolf A.↗