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At least 1,135 records · Page 63
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Simulation of electrostatic turbulence in the plasma sheet boundary layer with electron currents and bean-shaped ion beams

Plasma data from ISEE-1 show the presence of electron currents as well as energetic ion beams in the plasma sheet boundary layer. Broadband electrostatic noise and low-frequency electromagnetic bursts are detected in the plasma sheet boundary layer, especially in the presence of strong ion flows, currents, and steep spacial gradients in the fluxes of few-keV electrons and ions. Particle simulations have been performed to investigate electrostatic turbulence driven by a cold electron beam and/or ion beams with a bean-shaped velocity distribution. The simulation results show that the counterstreaming ion beams as well as the counterstreaming of the cold electron beam and the ion beam excite ion acoustic waves with a given Doppler-shifted real frequency. However, the effect of the bean-shaped ion velocity distributions reduces the growth rates of ion acoustic instability. The simulation results also show that the slowing down of the ion bean is larger at the larger perpendicular velocity. The wave spectra of the electric fields at some points of the simulations show turbulence generated by growing waves.

Nishikawa, K.-I.↗
NASA NTRS1972

Outer magnetosphere near midnight at quiet and disturbed times.

Ogo 5 magnetic-field and energetic-electron (E greater than 50 keV) data are used to study both the quiet-time, steady-state configuration of the outer magnetosphere or near tail region near midnight and the disturbed time changes of this configuration. The nighttime cusp is found to be a distinct feature within the plasma sheet at quiet times but indistinguishable from the plasma sheet at disturbed times. The sequence of thinning and expansion of the plasma sheet in this region in association with the substorms is studied. The response of the plasma sheet in the near tail at about 10 earth radii is found to be similar to that in the more distant tail at more than 20 earth radii. Finally, the nature of field-aligned currents flowing on the plasma-sheet boundary is investigated. Assuming infinite current sheets, the sheet current density at Ogo 5 is found to be approximately .01 A/m.

Aubry, M. P.↗
DOE OSTI2021

Microfabricated ion trap chip with an integrated microwave antenna

An ion trap chip, which may be used for quantum information processing and the like, includes an integrated microwave antenna. The antenna is formed as a radiator connected by one of its ends to the center trace of a microwave transmission line and connected by its other end to a current return path through a ground trace of the microwave transmission line. The radiator includes several parallel, coplanar radiator traces connected in series. The radiator traces are connected such that they all carry electric current in the same direction, so that collectively, they simulate a single, unidirectionally flowing sheet of current. In embodiments, induced currents in underlying metallization planes are suppressed by parallel slots that extend in a direction perpendicular to the radiator traces.

Nordquist, Christopher↗
NASA NTRS2008

Electromagnetically Clean Solar Arrays

The term 'electromagnetically clean solar array' ('EMCSA') refers to a panel that contains a planar array of solar photovoltaic cells and that, in comparison with a functionally equivalent solar-array panel of a type heretofore used on spacecraft, (1) exhibits less electromagnetic interferences to and from other nearby electrical and electronic equipment and (2) can be manufactured at lower cost. The reduction of electromagnetic interferences is effected through a combination of (1) electrically conductive, electrically grounded shielding and (2) reduction of areas of current loops (in order to reduce magnetic moments). The reduction of cost is effected by designing the array to be fabricated as a more nearly unitary structure, using fewer components and fewer process steps. Although EMCSAs were conceived primarily for use on spacecraft they are also potentially advantageous for terrestrial applications in which there are requirements to limit electromagnetic interference. In a conventional solar panel of the type meant to be supplanted by an EMCSA panel, the wiring is normally located on the back side, separated from the cells, thereby giving rise to current loops having significant areas and, consequently, significant magnetic moments. Current-loop geometries are chosen in an effort to balance opposing magnetic moments to limit far-0field magnetic interactions, but the relatively large distances separating current loops makes full cancellation of magnetic fields problematic. The panel is assembled from bare photovoltaic cells by means of multiple sensitive process steps that contribute significantly to cost, especially if electomagnetic cleanliness is desired. The steps include applying a cover glass and electrical-interconnect-cell (CIC) sub-assemble, connecting the CIC subassemblies into strings of series-connected cells, laying down and adhesively bonding the strings onto a panel structure that has been made in a separate multi-step process, and mounting the wiring on the back of the panel. Each step increases the potential for occurrence of latent defects, loss of process control, and attrition of components. An EMCSA panel includes an integral cover made from a transparent material. The silicone cover supplants the individual cover glasses on the cells and serves as an additional unitary structural support that offers the advantage, relative to glass, of the robust, forgiving nature of the silcone material. The cover contains pockets that hold the solar cells in place during the lamination process. The cover is coated with indium tin oxide to make its surface electrically conductive, so that it serves as a contiguous, electrically grounded shield over the entire panel surface. The cells are mounted in proximity to metallic printed wiring. The painted-wiring layer comprises metal-film traces on a sheet of Kapton (or equivalent) polyimide. The traces include contact pads on one side of the sheet for interconnecting the cells. Return leads are on the opposite side of the sheet, positioned to form the return currents substantially as mirror images of, and in proximity to, the cell sheet currents, thereby minimizing magnetic moments. The printed-wiring arrangement mimics the back-wiring arrangement of conventional solar arrays, but the current-loop areas and the resulting magnetic moments are much smaller because the return-current paths are much closer to the solar-cell sheet currents. The contact pads are prepared with solder fo electrical and mechanical bonding to the cells. The pocketed cover/shield, the solar cells, the printed-wiring layer, an electrical bonding agent, a mechanical-bonding agent, a composite structural front-side face sheet, an aluminum honeycomb core, and a composite back-side face sheet are all assembled, then contact pads are soldered to the cells and the agents are cured in a single lamination process.

Stem, Theodore G.↗
DOE OSTI2026

Casimir interactions between two parallel graphene sheets carrying steady-state drift currents

Here, we investigate the fluctuation-induced Casimir interactions between two parallel graphene sheets carrying steady-state drift currents. The graphene properties are modeled based on the shifted Fermi disk model to capture the nonequilibrium optical response of the system. We find that the drift current introduces a repulsive correction to the perpendicular to the layers Casimir interaction, thereby reducing the overall attractive force. Although the correction is repulsive, it does not overcome the underlying attraction between the layers. It also generates a lateral force that opposes the carrier flow direction. Both contributions are studied in terms of distance and drift velocity functionalities showing pathways for Casimir force control.

Ke, Modi [University of South Florida, Tampa, FL (↗
DOE OSTI2020

Measuring multiple cosmogenic nuclides in glacial cobbles sheds light on Greenland Ice Sheet processes

The behavior of the Greenland Ice Sheet during the Pleistocene remains uncertain due to the paucity of evidence predating the Last Glacial Maximum. In this study, we employ a novel approach, cosmogenic nuclide analysis of individual subglacially-derived cobbles, which allows us to make inferences about ice sheet processes and subglacial erosion. From three locations in western Greenland, we collected 86 cobbles from the current ice sheet margin and nine cobbles exposed on the modern proglacial land surface. We measured the concentration of in situ 10 Be in all cobbles (n = 95) and 26 Al and 14 C in a subset (n = 14). Cobbles deposited during Holocene retreat have 10 Be exposure ages generally consistent with the timing of ice retreat determined by other methods. Conversely, most of the 86 subglacial cobbles contain very low concentrations of 10 Be (median 1.0×10 3 atoms g –1 ), although several have ~10 4 and one has ~10 5 atoms g –1 . The low concentrations of 10 Be in most subglacial cobbles imply that their source areas under the Greenland Ice Sheet are deeply eroded, preserving minimal evidence of surface or near-surface exposure. The presence of measurable 14 C in ten of the cobbles requires that they experienced cosmogenic nuclide production within the past ~30 ka; however, 14 C/ 10 Be ratios of ~6 suggest that nuclide production occurred during shielding by overlying material. Only two of the 86 subglacial cobbles definitively have cosmogenic nuclide concentrations consistent with prior surface exposure. Overall, isotopic analysis of subglacial cobbles indicates that much of western Greenland's subglacial landscape is characterized by deep erosion and minimal subaerial exposure.

58 GEOSCIENCES↗
NASA NTRS2020

Measuring Multiple Cosmogenic Nuclides in Glacial Cobbles Sheds Light on Greenland Ice Sheet Processes

The extent and erosivity of the Greenland Ice Sheet during the Pleistocene remain uncertain due to the paucity of evidence predating the Last Glacial Maximum. Here, we employ a novel approach, cosmogenic nuclide analysis of individual subglacial cobbles, which allows us to infer the behavior of the ice sheet over time and space. From three locations in western Greenland, we collected 86 cobbles from the current ice sheet margin and nine cobbles exposed on the modern proglacial land surface. We measured the concentration of in situ 10Be in all cobbles (n= 95) and 26Al and 14C in a subset (n= 14). Cobbles deposited during Holocene retreat have 10Be exposure ages generally consistent with the timing of ice retreat determined by other means. Conversely, most of the 86 subglacial cobbles contain very low concentrations of 10Be (median 1.0 x 10^3 atoms g-1), although several have ~10^4 and one has ~10^5 atoms g-1. The low concentrations of 10Be in most subglacial cobbles imply that their source areas under the Greenland Ice Sheet are deeply eroded, preserving minimal evidence of surface or near-surface exposure. The presence of measurable 14C in ten of the cobbles requires that they experienced cosmogenic nuclide production within the past ~30 ka; however, 14C/10Be ratios of ~6 suggest that production occurred beneath thin overlying rock, sediment, and/or ice, where the muon component of 14C production dominates. Only two of the 86 subglacial cobbles definitively have cosmogenic nuclide concentrations consistent with prior surface exposure during times of reduced ice extent. Overall, isotopic analysis of subglacial cobbles indicates that western Greenland's subglacial landscape is characterized by deep erosion and minimal subaerial exposure.

Pliocene↗
NASA NTRS2020

Measuring multiple cosmogenic nuclides in glacial cobbles sheds light on Greenland Ice Sheet processes

The behavior of the Greenland Ice Sheet during the Pleistocene remains uncertain due to the paucity of evidence predating the Last Glacial Maximum. Here, we employ a novel approach, cosmogenic nuclide analysis of individual subglacially-derived cobbles, which allows us to make inferences about ice sheet processes and subglacial erosion. From three locations in western Greenland, we collected 86 cobbles from the current ice sheet margin and nine cobbles exposed on the modern proglacial land surface. We measured the concentration of in situ 10Be in all cobbles (n =95) and 26Al and 14C in a subset (n =14). Cobbles deposited during Holocene retreat have 10Be exposure ages generally consistent with the timing of ice retreat determined by other methods. Conversely, most of the 86 subglacial cobbles contain very low concentrations of 10Be (median 1.0×10^3atoms/g), although several have ∼104and one has ∼10^5atoms/g. The low concentrations of 10Be in most subglacial cobbles imply that their source areas under the Greenland Ice Sheet are deeply eroded, preserving minimal evidence of surface or near-surface exposure. The presence of measurable 14C in ten of the cobbles requires that they experienced cosmogenic nuclide production within the past ∼30 ka; however, 14C/10Be ratios of ∼6 suggest that nuclide production occurred during shielding by overlying material. Only two of the 86 subglacial cobbles definitively have cosmogenic nuclide concentrations consistent with prior surface exposure. Overall, isotopic analysis of subglacial cobbles indicates that much of western Greenland’s subglacial landscape is characterized by deep erosion and minimal subaerial exposure.

cosmogenic nuclides↗
NASA NTRS1990

Extreme energetic particle decreases near geostationary orbit - A manifestation of current diversion within the inner plasma sheet

A qualitative model of magnetic field reconfiguration as might result from neutral line formation in the central plasma sheet late in a substorm growth phase is considered. It is suggested that magnetic reconnection probably begins before the substorm expansion phase and that cross-tail current is enhanced across the plasma sheet both earthward and tailward of a limited region near the neutral line. Such an enhanced cross-tail current earthward of the original X line region may contribute to thinning the plasma sheet substantially, and this would in turn affect the drift currents in that location, thus enhancing the current even closer toward the earth. In this way a redistribution and progressive diversion of normal cross-tail current throughout much of the inner portion of the plasma sheet could occur. The resulting intensified current, localized at the inner edge of the plasma sheet, would lead to a very thin plasma confinement region. This would explain the very taillike field and extreme particle dropouts often seen late in substorm growth phases.

Baker, D. N.↗
DOE OSTI2023

Microstructure development in a cold worked SRF Nb sheet undergoing 700°C-900°C/3h heat treatments.

Bulk Nb for TESLA shaped SRF cavities is a mature technology, with high gradient (>35 MV/m) and high Q cavities (>1010, ~2K) routinely fabricated. Significant advances are in order to push Q?s to 1011 (~2K), and involve modifications to the sub-surface Nb layers by impurity doping (N, O). In order to achieve the lowest surface resistance any trapped flux needs to be expelled for cavities to reach high Q?s. There is clear evidence that cavities fabricated from polycrystalline sheets meeting current specifications require higher temperatures beyond 800oC leads to better flux expulsion, and hence improves Q. Recently, cavities fabricated with a non-traditional Nb sheet with initial cold work due to cold rolling expelled flux better after 800°C/3h heat treatment than cavities fabricated using fine-grain polycrystalline Nb sheets. Here, we analyze the microstructure development in Nb from the vendor supplied cold work non-annealed sheet that was fabricated into an SRF cavity as a function of heat treatment building upon the methodology development to analyze microstructure being developed by the FSU-MSU-UT-Austin- JLAB collaboration. The results indicate correlation between full recrystallization and better flux expulsion.

Balachandran, S.↗
NASA NTRS1974

Field-aligned currents and the auroral electrojet

A Nike Tomahawk with fields and particles payload was launched on Nov. 18, 1970, over a strong westward electrojet current and auroral forms moving rapidly to the east. Electron fluxes moving up and down the magnetic field lines were measured. Upward-moving electrons below 1-keV energy were dominant and were equivalent to a net downward electric current that fluctuated between .2 and .6 microamp/sq m during the flight above 130 km. As the rocket traversed this broad region of downward electric current over and to the north of the auroral forms, the horizontal electric field slowly rotated from east to west. The magnetic measurements indicate that the westward electrojet was a horizontal sheet of current several hundred kilometers in north-south extent.

Cahill, L. J.↗
NASA NTRS1988

Field-aligned current signatures in the near-tail region. I - ISEE observations in the plasma sheet boundary layer

Field-aligned currents in the near-tail region are examined using ISEE magnetometer data. Two substorms (the 1054 UT and the 1436 UT substorms on March 22, 1979) were examined, demonstrating the consistency of the current polarity and intensity with observations at lower altitudes, which suggests that field-aligned currents in the plasma sheet boundary layer are parts of the large-scale current system, the region-1 system. An examination of the steplike changes of the magnetic field direction, which correspond to the spacecraft crossing of a net field-aligned current, showed that the field-aligned currents in the plasma sheet boundary layer have the same polarity as the region-1 system.

Ohtani, S.↗
NASA NTRS1972

State-of-technology for joining TD-NiCr sheet.

At the current state-of-technology there are many joining processes that can be used to make sound welds in TD-NiCr sheet. Some of these that are described in this report are electron beam welding (EBW), gas-tungsten arc welding (GTAW), diffusion welding (DFW), resistance spot welding (RSW), resistance seam welding (RSEW), and brazing. Roll welding (RW) and explosion welding (EXW) have not been developed to the point where they can be used to make sound welds in TD-NiCr. Joining work that has previously been done on TD-NiCr by various organizations, both privately supported and under Air Force and NASA contracts, is described in this summary. Current work is also described that is being done at General Dynamics/Convair (under NASA contract) and at NASA/Lewis to develop and evaluate DFW, RSW, RSEW, and brazing. Preliminary comparisons of joining processes are made for typical applications. A brief description of the manufacture of TD-NiCr sheet by a recently standardized process (under NASA contract) also is given.

Holko, K. H.↗
NASA NTRS1972

State-of-technology for joining TD-NiCr sheet

At the current state-of-technology there are many joining processes that can be used to make sound welds in TD-NiCr sheet. Some of these that are described in this report are electron beam welding, gas-tungsten arc welding, diffusion welding, resistance spot welding, resistance seam welding, and brazing. The strengths of the welds made by the various processes show considerable variation, especially at elevated temperatures. Most of the fusion welding processes tend to give weak welds at elevated temperatures (with the exception of fusion-type resistance spotwelds). However, solid-state welds have been made with parent metal properties. The process used for a specific application will be dictated by the specific joint requirements. In highly stressed joints at elevated temperatures, one of the solid-state processes, such as DFW, RSW (solid-state or fusion), and RSEW, offer the most promise.

Holko, K. H.↗
NASA NTRS1985

ISEE-1 and 2 observations of field-aligned currents in the distant midnight magnetosphere

Magnetic field measurements obtained in the nightside magnetosphere by the co-orbiting ISEE-1 and 2 spacecraft have been examined for signatures of field-aligned currents (FAC). Such currents are found on the boundary of the plasma sheet both when the plasma sheet is expanding and when it is thinning. Evidence is often found for the existence of waves on the plasma sheet boundary, leading to multiple crossings of the FAC sheet. At times the boundary layer FAC sheet orientation is nearly parallel to the X-Z GSM plane, suggesting 'protrusions' of plasma sheet into the lobes. The boundary layer current polarity is, as expected, into the ionosphere in the midnight to dawn local time sector, and outward near dusk. Current sheet thicknesses and velocities are essentially independent of plasma sheet expansion or thinning, having typical values of 1500 km and 20-40 km/s respectively. Characteristic boundary layer current densities are about 10 nanoamps per square meter.

Elphic, R. C.↗
DOE OSTI2025

Bacterial-Retted Hemp Fiber/PLA Composites

The push for sustainability in all facets of manufacturing has led to an increased interest in biomass as an alternative to non-renewable materials. Hemp bast fiber mats were produced from a bacterial retting process, named BFM, as the fiber reinforcement. The objective of this study was to evaluate the feasibility of laminating BFM with polylactic acid (PLA) for a composite panel product. Since both BFM and PLA are biodegradable, the resulting BFM-PLA composites will be 100% biodegradable. PLA pallets were processed into thin polymer sheets which served as the matrix. The BFM and PLA plates were laminated in five layers and compression-molded into composite panels. Experiments were conducted on the three BFM-to-PLA ratios (35/65, 45/55, and 50/50). Mechanical properties (tensile and bending properties) and physical properties (thickness swell and water absorption) were tested and compared to the currently commercial sheet molding compound (SMC) from fiber glass. The thermal behavior of the BFM/PLA composites was characterized using dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC). The developed BFM/PLA composite product is a sustainable alternative to existing synthetical fiber-reinforced polymer (FRP) that is biodegradable in landfill at the end of life.

Smith, Lee M. (ORCID:0000000264390357)↗