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At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

High-Entropy Alloys for Accelerator Beam Window Applications

Development of novel high-entropy alloys (HEAs) is currently underway for potential use as beam windows in future multi-megawatt target systems at Fermilab. HEAs encompass a new class of materials with a vast design space allowing for material properties to be tailored for particular applications and to potentially offer improved resistance to beam-induced radiation damage and thermal shock effects. The alloy systems being studied consist of several compositions of AlCoCrMnTiV with 4 6 component elements. These alloys are all predicted by CALPHAD simulation to have a single-phase BCC crystal structure and low density, with some compositions displaying ordered, nanoscale precipitates. This presentation will briefly discuss alloy design and synthesis before giving a detailed description of the characterization studies of these HEAs in both the pristine state and post-irradiation by low-energy heavy ions to high damage levels. Electron microscopy techniques to quantify elemental homogeneity and composition, determine grain size, shape, and orientation, and quantify lattice parameters, defect structures and precipitate phases are all being used to study alloy microstructures. Mechanical properties of the alloys at the microscale will be reported. The evolution of these properties as a function of radiation damage will also be described. Bulk thermal characteristics of these HEAs have been tested to measure specific heat capacity and coefficient of thermal expansion as a function of temperature. To determine bulk tensile properties a miniature tensile testing apparatus is under development; it s commissioning will be covered briefly. The talk will conclude with our plans for alloy down-selection.

Burleigh, A. [Fermilab]↗
NASA NTRS1974

Optical polarimeters in space

A review is presented of the instrumentation used for the measurement of optical polarization from aircraft, balloon, rocket, satellite, and spacecraft platforms. The four parameters which can be measured at a given wavelength, time, and direction in an incoherent beam of radiation include intensity, linear polarization, its position angle, and circular polarization. An instrument that by design is made sensitive to any of the three polarization parameters is considered a polarimeter. Attention is given to passive polarimeters operating in the range from 0.1 to 1000 micrometers. All known optical space polarimeters are listed in a table. Questions of instrument operation in space are discussed along with details of polarization analysis, aspects of accuracy and calibration, and the scientific studies conducted with the polarimeters.

Coffeen, D. L.↗
NASA NTRS1975

Radiated microwave power transmission system efficiency measurements

The measured and calculated results from determining the operating efficiencies of a laboratory version of a system for transporting electric power from one point to another via a wireless free space radiated microwave beam are reported. The system's overall end-to-end efficiency as well as intermediated conversion efficiencies were measured. The maximum achieved end-to-end dc-to-ac system efficiency was 54.18% with a probable error of + or - 0.94%. The dc-to-RF conversion efficiency was measured to be 68.87% + or - 1.0% and the RF-to-dc conversion efficiency was 78.67 + or - 1.1%. Under these conditions a dc power of 495.62 + or - 3.57 W was received with a free space transmitter antenna receiver antenna separation of 170.2 cm (67 in).

Dickinson, R. M.↗
NASA NTRS1976

The period-pulse-width distribution of pulsars and their division into three classes

The period-pulse-width (P-W) distribution of sample of 41 pulsars has been reanalyzed under two versions of a model where radiation is beamed from magnetic polar caps which are isotropically oriented with respect to the rotation axis of the neutron stars (IOPC models). It is found that neither IOPC model can explain the P-W distribution of the entire sample. Pulsars with simple unimodal (U) or complicated multimodal (M) pulse shapes show significantly different P-W distributions. Class M pulsars have a narrower P-W distribution than do class U pulsars and, taken separately, are compatible with either IOPC model. Class U pulsars divide into two subgroups, those with relatively narrower pulses (UN) and those with relatively wider pulses (UW), each of which is compatible with either IOPC model. One interpretation of these results is that the pulsars in classes UN, M, and UW have different intrinsic beam sizes, roughly in the ratios 1:2:4, respectively. The possible origins of the three classes are discussed in terms of the force-balance magnetosphere model (Roberts et al., 1972, 1973), where the differences may be attributed to different-mass neutron stars and the structure of the polar caps. An alternative interpretation is that the angle between the rotation and emission axes is not isotropically distributed, but can take only certain preferred values.

Roberts, D. H.↗
NASA NTRS1978

An emission mechanism for the Io-independent Jovian decameter radiation

A theory of the Io-independent decameter radiation is developed. The radiation results from excitation of the electromagnetic loss-cone instability by keV electrons, stably trapped near L = 6. The radiation is excited in Band 3 of the extraordinary mode. When the effects of refraction are estimated, it is shown that above 10 MHz radiation is beamed into the equatorial plane in a wide, but thin, conical sheet (Psi approximately equals 80 degrees). When the instability analysis is coupled with one of the octupole models of the Jovian magnetic field, the maximum convective growth of the instability occurs in the directions of the non-Io A, B, and C sources. The shape of the peak radio flux frequency spectrum is found to be a consequence of the loss cone shape of the electron distribution function.

Goldstein, M. L.↗
NASA NTRS1979

An emission mechanism for the Io-independent Jovian decameter radiation

A theory of the Io-independent decameter radiation is developed. The radiation results from excitation of the electromagnetic loss-cone instability by keV electrons, stably trapped near L = 6. The radiation is excited in band III of the extraordinary mode. When the effects of refraction are estimated, it is shown that above 10 MHz radiation is beamed into the equatorial plane in a wide, but thin, conical sheet. When the instability analysis is coupled with one of the octopole models of the Jovian magnetic field, the maximum convective growth of the instability occurs in the directions of the non-Io A, B, and C sources. The shape of the peak radio flux frequency spectrum is found to be a consequence of the loss-cone shape of the electron distribution function.

Goldstein, M. L.↗
NASA NTRS1986

Random scattering approach to gravitational microlensing

Small random deflections of a narrow beam of radiation due to gravitational scattering by stars randomly distributed within the deflector plane are considered. Using a Fouriere transform method, the probability of scattering is obtained as a function of scattering angle for an arbitrary number of stars with an arbitrary distribution of masses. The probability density, expressed in proper units, depends on one parameter only: the effective number of stars. At small scattering angles the density is a Gaussian, and at large angles it falls off as the scattering angle to the minus fourth power. The probability distribution for scatterings is simply related to the angular distribution of the surface brightness of a macroimage, averaged over many microimages. The isophotes are ellipses, with the ratio of the major axis to the minor axis, determined by the dimensionless surface mass density and the shear of the lensing system. The number of stars that has to be included in the modeling of microlensing is proportional to the amplification due to the macrolens, and to the square of the dimensionless surface mass density.

Katz, N.↗
NASA NTRS1986

Simultaneous imaging and spectral observations in microwaves and hard X-rays of the impulsive phase of a solar limb flare

Observations of the impulsive phase of a solar flare at microwave wavelengths and in hard X-rays are used to deduce the strength of the magnetic field and the number of energetic electrons producing the burst. The microwave observations, using the VLA at 6 cm, had spatial resolution of 8 x 8 arcsec, close to the resolution of the Hard X-ray Imaging Spectrometer on SMM which also imaged this flare. The Hard X-ray Burst Spectrometer determined the spectrum of the burst in the range 25-512 keV, and several patrol telescopes recorded the microwave time profile at frequencies from 2.8 to 19.6 GHz. The combined data show that the derived number of microwave-emitting electrons is at least three orders of magnitude fewer than the number of thick target electrons producing the hard X-rays. It is proposed that the fast electrons are highly beamed and radiate gyrosynchrotron emission less efficiently than isotropically distributed electrons.

Schmahl, E. J.↗
NASA NTRS1988

Neptune radio emission - Predictions based on planetary scaling laws

In this paper a prediction is advanced concerning Neptune's low-frequency radio emission based on the radiometric Bode's law for radio planets in combination with the magnetostrophic scaling law for magnetized planets. The total emitted radio power is predicted to be about 1.6 x 10 to the 7th W, very nearly the same as that predicted and observed for Uranus. Possible emission spectral shapes, based on Saturn and earth-like models, are shown. Using these models, the radio emission frequency range is predicted to extend from approximately 100 to just over 1000 kHz, with a spectral peak between 350 and 500 kHz. If radiation is beamed approximately in the sunward direction, Neptune should be detectable by the planetary radio astronomy experiment onboard the Voyager spacecraft sometime between 45 and 90 days before closest approach. This detection is likely to represent the first direct evidence of a Neptune magnetic field. Possible implications for Neptune's magnetosphere with regard to the time of first detection are discussed.

Desch, Michael D.↗
NASA NTRS1988

Observations of electron beam structure in space experiments

Observations of a 100-mA, 1-keV electron beam were made with a low light level TV system and other instruments aboard the space shuttle STS 3 in March 1982. When fired at a moderate pitch angle with respect to the magnetic field, the beam electrons initially moved outward along a classical helical trajectory. Within a short distance, however, the beam electrons were deflected away from the helical trajectory into paths parallel to magnetic field lines threading the primary helix. This resulted in the formation of a thin-walled, cylindrical electron beam structure having a radius equal to the primary beam gyroradius. This structure, which is consistent with earlier laboratory vacuum chamber observations and recent two-dimensional computer electrostatic plasma simulations, has important implications for determining the extent to which pulsed electron beams can radiate electromagnetic energy in the ionosphere.

Banks, Peter M.↗
NASA NTRS1988

Planetary scaling laws and predictions for Neptune

This paper offers a prediction concerning Neptune's low-frequency radio emission based on the radiometric Bode's law in combination with a recent prediction for Neptune's global magnetic field strength. The latter is based on a dynamo scaling relation derived from the magnetospheric balance condition within planetary cores. The radio emission frequency range is predicted to extend from approximately 100 to 1000 kHz, with a spectral peak between 350 and 500 kHz. A crude estimate of the emission spectral shape, based on Saturn and earth-like models, is shown. If radiation is beamed approximately in the sunward direction, Neptune should be detectable by the Planetary Radio Astronomy experiment onboard the Voyager spacecraft sometime between 45 and 60 days before closest approach.

Desch, Michael D.↗
NASA NTRS1990

Method of radiographic inspection of wooden members

The invention is a method to be used for radiographic inspection of a wooden specimen for internal defects which includes the steps of introducing a radiopaque penetrant into any internal defects in the specimen through surface openings; passing a beam of radiation through a portion of the specimen to be inspected; and making a radiographic film image of the radiation passing through the specimen, with the radiopaque penetrant in the specimen absorbing the radiation passing through it, thereby enhancing the resulting image of the internal defects in the specimen.

Berry, Maggie L.↗