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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 919 records · Page 51
All sourcesNASA NTRSDOE OSTI
NASA NTRS2004

High Power Light Gas Helicon Plasma Source For VASMIR

The VASIMR space propulsion development effort relies on a high power (greater than 10kW) helicon source to produce a dense flowing plasma (H, D and He) target for ion cyclotron resonance (ICR) acceleration of the ions. Subsequent expansion in an expanding magnetic field (magnetic nozzle) converts ion lunetic energy to directed momentum. This plasma source must have critical features to enable an effective propulsion device. First, it must ionize most of the input neutral flux of gas, thus producing a plasma stream with a high degree of ionization for application of ICR power. This avoids propellant waste and potential power losses due to charge exchange. Next, the plasma stream must flow into a region of high magnetic field (approximately 0.5 T) for efficient ICR acceleration. Third, the ratio of input power to plasma flux must be low, providing an energy per ion-electron pair approaching 100 eV. Lastly, the source must be robust and capable of very long life-times (years). In our helicon experiment (VX-10) we have measured a ratio of input gas to plasma flux near 100%. The plasma flows from the helicon region (B approximately 0.1 T) into a region with a peak magnetic field of 0.8 T. The energy input per ion-electron pair has been measured at 300 plus or minus 100 eV. Recent results at Oak Ridge National Laboratory (ORNL) show an enhanced efficiency mode of operation with a high power density, over 5 kW in a 5 cm diameter tube. Our helicon is presently 9 cm in diameter and operates up to 3.5 kW of input power. An upgrade to a power level of 10 kW is underway. Much of our recent work has been with a Boswell double-saddle antenna design. We are also converting the antenna design to a helical type. With these modifications, we anticipate an improvement in the ionization efficiency. This paper presents the results from scaling the helicon in the VX-10 device from 3.5 to 10 kW. We also compare the operation with a double-saddle to a helical antenna design. Finally, we discuss modeling of these configurations using ORNL's EMIR code.

Squire, J. P.↗
DOE OSTI2022

Sensitivity of the GAPS experiment to low-energy cosmic-ray antiprotons

The General Antiparticle Spectrometer (GAPS) is an upcoming balloon mission to measure low-energy cosmic-ray antinuclei during at least three ~35-day Antarctic flights. With its large geometric acceptance and novel exotic atom-based particle identification, GAPS will detect ~500 cosmic antiprotons per flight and produce a precision cosmic antiproton spectrum in the kinetic energy range of ~0.07–0.21 GeV/n at the top of the atmosphere. With these high statistics extending to lower energies than any previous experiment, and with complementary sources of experimental uncertainty compared to traditional magnetic spectrometers, the GAPS antiproton measurement will be sensitive to dark matter, primordial black holes, and cosmic ray propagation. The antiproton measurement will also validate the GAPS antinucleus identification technique for the antideuteron and antihelium rare-event searches. Finally, this analysis demonstrates the GAPS sensitivity to cosmic-ray antiprotons using a full instrument simulation and event reconstruction, and including solar and atmospheric effects.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2020

First Global Images of Ion Energization in the Terrestrial Foreshock by the Interstellar Boundary Explorer

The Interstellar Boundary Explorer (IBEX) mission provides global energetic neutral atom (ENA) observations from the heliosphere and the Earth's magnetosphere, including spatial, temporal, and energy information. IBEX views the magnetosphere from the sides and almost always perpendicular to noon-midnight plane. We report the first ENA images of the energization process in the Earth's ion foreshock and magnetosheath regions. We show ENA flux and spectral images of the dayside magnetosphere with significant energization of ENA plasma sources (above ~2.7 keV) in the region magnetically connected to the Earth's bow shock (BS) in its quasi-parallel configuration of the interplanetary magnetic field (IMF). We also show that the ion energization increases gradually with decreasing IMF-BS angle, suggesting more efficient suprathermal ion acceleration deeper in the quasi-parallel foreshock.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Hints of primordial magnetic fields at recombination and implications for the Hubble tension

Primordial Magnetic Fields (PMFs), long studied as relics of the early Universe, accelerate recombination and have been proposed as a way to relieve the Hubble tension. However, previous studies relied on simplified toy models. Here, in this study, we use recent evaluations of recombination with PMFs, incorporating full magnetohydrodynamic (MHD) simulations and detailed Lyman-alpha radiative transfer, to test PMF-enhanced recombination (bΛCDM) against observational data from the cosmic microwave background (CMB), baryon acoustic oscillations (BAO), and Type Ia supernovae (SN). Focusing on non-helical PMFs with a Batchelor spectrum, we find a preference for presentday total field strengths of approximately 5-10 pico-Gauss. Depending on the dataset combination, this preference ranges from mild (∼ 1.8σ with Planck + DESI) to moderate (∼ 3σ with Planck + DESI + SH0ES-calibrated SN) significance. The bΛCDM has Planck + DESI χ 2 values equal to or better than ΛCDM while predicting a higher Hubble constant. Future high-resolution CMB temperature and polarization measurements will be crucial for confirming or further constraining PMFs at recombination. Field strengths of 5-10 pico-Gauss align closely with those required for cluster magnetic fields to originate entirely from primordial sources, without the need for additional dynamo amplification.

Jedamzik, Karsten [Centre National de la Recherche↗
DOE OSTI2020

Spin current generation and detection in uniaxial antiferromagnetic insulators

Spin current represents a flow of spin angular momentum and does not require movement of charges. Magnetic insulators can therefore work as a source as well as a medium of spin currents, which has been established in ferrimagnetic insulators. Here, we report recent progress in the generation and electrical detection of spin currents in uniaxial antiferromagnetic insulators carried by antiferromagnetic magnons, both thermally and resonantly excited, respectively, via the spin Seebeck effect and antiferromagnetic spin pumping by subterahertz microwaves. These findings open up many exciting possibilities of potential antiferromagnetic applications.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

MPEX High Heat Flux Plasma Dump Design, Manufacture, and Articles Test

Here, the Material Plasma Exposure eXperiment (MPEX) device is a steady-state linear plasma device currently in the final design phase at the Oak Ridge National Laboratory. This device will reach ion fluences up to 10 31 m -2 and will be used to expose neutron-irradiated materials to divertor-relevant plasmas and to study the effects of plasma-material interactions. These studies will elucidate the complex effects of plasmas with divertor candidate materials capable of withstanding high heat flux and high fluences for next-generation fusion devices. Bidirectional plasma will be generated using a high-power (200 kW) helicon source. Plasma will be confined by superconducting magnets. The last plasma-facing component on the upstream side of the MPEX device is the dump, which has been designed to intercept plasma and energetic particles. The dump will have a total heat load of 9.2 kW. A copper alloy (Glidcop AL-15) was selected for use in the water-cooled flange design because of its high thermal conductivity, its retaining strength at elevated temperatures, and its ability to be used in the high-temperature braze joints used in this application. Titanium-zirconium-molybdenum (TZM) tiles are brazed to the Glidcop AL-15 flange using high-temperature braze alloy. External water-cooling channels are used on the dump flange to prevent water leakage inside the vacuum space. This article discusses the details of the high heat flux dump design, including the computational fluid dynamics (CFD) and structural analyses performed to validate the design to meet the operational requirements of the MPEX device.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Contributing to Sunny open source code

The Sunny package is an existing open source software to support the simulation of magnetic spin systems. It is available online under the MIT license here: https://github.com/SunnySuite/Sunny.jl The package aims to include the following features: - Analysis for symmetry-allowed interactions - Monte Carlo algorithms for simulating equilibrium configurations. - Schemes for integrating spin dynamics. - Inference of model Hamiltonians - Support for generalized SU(N) spins - Tools for interpreting experimental data, such as diffraction data, magnetization curves, and heat capacity data

Barros, Kipton↗
DOE OSTI2021

Modeling Induction Stirring and Particle Tracking in Molten Uranium

Two independent numerical models have been developed to simulate the behavior of carbon impurities in molten uranium metal. Informed by experimental parameters, one model was created using the commercial software Star-CCM+ and compared with another developed using open-source codes, including OpenFOAM, Finite Element Method Magnetics (FEMM) and a First Passage Kinetic Monte Carlo (FPKMC) approach. The target experimental system features a 404g uranium metal charge containing an average carbon concentration of 139 ppm which was melted in a vacuum induction furnace at 1400° C then resolidified. The microstructures of the uranium and its impurities before and after melting have been characterized and reported separately. Prior to simulating the uranium-carbon system described, the numerical models were validated using a previously published nonradioactive experimental system to ensure agreement with expected output values. Focus has been placed on modeling velocity fields under induction stirring and impurity particle trajectories.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Surface Electronic Structure of Cr Doped Bi 2 Se 3 Single Crystals

Here, by using angle-resolved photoemission spectroscopy, we showed that Bi 2-x Cr x Se 3 single crystals have a distinctly well-defined band structure with a large bulk band gap and undistorted topological surface states. These spectral features are unlike their thin film forms in which a large nonmagnetic gap with a distorted band structure was reported. We further provide laser-based high resolution photoemission data which reveal a Dirac point gap even in the pristine sample. The gap becomes more pronounced with Cr doping into the bulk of Bi 2 Se 3 . These observations show that the Dirac point can be modified by the magnetic impurities as well as the light source.

36 MATERIALS SCIENCE↗
NASA NTRS1966

Spool valve cycles at controlled frequency

Spool valve accurately controls the cycle of a pneumatically-actuated system over long periods. Regulation of pressure from the external source, positioning of the adjusting plugs, and magnet selection, together afford wide variation in cyclic timing and speed of closure in either direction.

Charlton, K. W.↗
NASA NTRS1972

Universal instability associated with the plasmapause and its role in geomagnetic micropulsations.

The observed close correlation between the plasmapause and micropulsations is explained on the basis of a universal instability model. Both theoretical and experimental studies of a nonhomogeneous magnetoplasma indicate that a steep plasma density gradient at the plasmapause is likely the origin of the universal instability in the magnetosphere. Drift waves excited at the plasmapause may be unstable in the direction of the electron drift and propagate eastward nearly perpendicularly to the magnetic field. The drift waves, however, tend to convert very quickly to ion sound or Alfven waves with a much larger phase velocity parallel to the magnetic field. This may be a possible source mechanism for rather regular geomagnetic micropulsations, and specific mechanisms are identified for the long- and short-period cases.

Kikuchi, H.↗
NASA NTRS1973

White dwarfs as infrared sources in the galactic centre.

It is shown that quantized magnetic bremsstrahlung radiation in intense magnetic fields from the surface layers of white dwarfs could serve as one of the possible explanations for the infrared emission from the center of the galaxy that has been detected by Hoffmann et al. (1971). It is assumed, in particular, that the infrared radiation is from clusters of white dwarfs.

Chow, T. L.↗
NASA NTRS1974

The repulsive 1 Sigma g/+/ He2 potential obtained from total cross sections

An improved apparatus for obtaining short-range molecular potentials is described. The setup is a refined version of that used by Jordan-Amdur and by Leonas. The ion source is provided with a mass analyzing magnet, the capacitance manometer in the scattering cell is calibrated with a McCleod gauge, and the detection unit substitutes a Channeltron multiplier for the thermopile. The measured ground-state He-He potential for radii between 0.49 and 1.56 A is approximately V(r) = 215 x exp(-3.95r) eV, which is 25% higher than the earlier experiments. The result is supported by molecular orbital and statistical model calculations.

Foreman, P. B.↗
NASA NTRS1977

Bright X-ray arcs and the emergence of solar magnetic flux

The Skylab S-056 and S-082A experiments and ground-based magnetograms have been used to study the role of bright X-ray arcs and the emergence of solar magnetic flux in the McMath region 12476. The S-056 X-ray images show a system of one or sometimes two bright arcs within a diffuse emitting region. The arcs seem to directly connect regions of opposite magnetic polarity in the photosphere. Magnetograms suggest the possible emergence of a magnetic flux. The width of the main arc is approximately 6 arcsec when most clearly defined, and the length is approximately 30-50 arcsec. Although the arc system is observed to vary in brightness over a period exceeding 24 hours, it remains fixed in orientation. The temperature of the main arc is approximately 3 x 10 to the 6th K. It is suggested that merging magnetic fields may provide the primary energy source, perhaps accompanied by resistive heating from a force-free current.

Chapman, G. A.↗
NASA NTRS1977

Electrostatically unstable heat flow during solar flares and its consequences

This paper examines some of the consequences of an electrostatically unstable return current associated with heat conduction during a solar flare. It is noted that an electrostatically unstable return current will lead to strong hydrodynamic effects and more rapid magnetic-field thermalization if reconnection is the source of primary energy release during a solar flare.

Spicer, D. S.↗
NASA NTRS1979

The search for the ultimate gimbal

The need for higher accuracy in pointing systems continues to grow. Fundamental limitations are inherent in the components used for gimbals. This paper discusses some developments which are expected to make it possible to achieve higher accuracy and stability. Ironless armature torque motors are described which exhibit zero hysteresis and no preferred position. Non-contacting signal and power transfer devices to eliminate friction and cable-wrap torques have also been developed. Magnetic bearings can eliminate the last remaining source of erratic frictional effects. Controllers using Kalman estimation techniques can accommodate constant residual effects.

Studer, P. A.↗