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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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All sourcesNASA NTRSDOE OSTI
NASA NTRS2005

Instrumentation and Measurements for Electron Emission from Charged Insulators

The electron was first discovered in 1898 by Sir John Joseph Thomson and has since been the subject of detailed study by nearly every scientific discipline. At nearly the same time Heinrich Rudolf Hertz conducted a series of experiments using cathode tubes, high potentials and ultraviolet light. When applying a large potential to a cathode he found that an arching event across the metal plates would occur. In addition, when shining an ultraviolet light on the metal he found that less potential was required to induce the spark. This result, taken together with other electrical phenomena brought about by the shining of light upon metal and was eventually termed the photoelectric effect. The work of Thomson and Hertz represent the beginning of electron emission studies and a body of ideas that pervade nearly all aspects of physics. In particular these ideas tell us a great deal about the nature of physical interactions within solids. In this thesis we will focus on the emission of electrons induced by an incident electron source over a range of energies, in which one can observe changes in emitted electron flux and energy distribution. In particular, when energetic particles impinge on a solid they can impart their energy, exciting electrons within the material. If this energy is sufficient to overcome surface energy barriers such as the work function, electron affinity or surface charge potential, electrons can escape from the material. The extent of electron emission from the material can be quantified as the ratio of incident particle flux to emitted particle flux, and is termed the electron yield.

Sim, Alec M.↗
NASA NTRS2023

The 17 April 2021 Widespread Solar Energetic Particle Event

A complex and long-lasting solar eruption on 17 April 2021 produced a widespread solar energetic particle (SEP) event that was observed by five longitudinally well-separated observers in the inner heliosphere that covered distances to the Sun from 0.42 to 1 au: BepiColombo, Parker Solar Probe, Solar Orbiter, STEREO A, and near-Earth spacecraft. The event was the second widespread SEP event detected in solar cycle 25, and it produced relativistic electrons and protons. It was associated with a long-lasting solar hard X-ray flare that showed multiple hard X-ray peaks over a duration of one hour. The event was further accompanied by a medium-fast coronal mass ejection (CME) with a speed of 880 km s -1 that drove a shock, an extreme ultraviolet wave, and long-lasting and complex radio burst activity that showed four distinct type III burst groups over a period of 40 min. We aim to understand the reason for the wide spread of elevated SEP intensities in the inner heliosphere as well as identify the underlying source regions of the observed energetic electrons and protons. We applied a comprehensive multi-spacecraft analysis of remote-sensing observations and in situ measurements of the energetic particles and interplanetary context to attribute the SEP observations at the different locations to the various potential source regions at the Sun. We used an ENLIL simulation to characterize the complex interplanetary state and its role in the energetic particle transport. The magnetic connection between each spacecraft and the Sun was determined using ballistic backmapping in combination with potential field source surface extrapolations in the lower corona. Using also a reconstruction of the coronal shock front, we then determined the times when the shock establishes magnetic connections with the different observers. Radio observations were used to characterize the directivity of the four main injection episodes, which were then employed in a 2D SEP transport simulation to test the importance of these different injection episodes. A comprehensive timing analysis of the inferred solar injection times of the SEPs observed at each spacecraft suggests different source processes being important for the electron and proton events. Comparison among the characteristics and timing of the potential particle sources, such as the CME-driven shock or the flare, suggests a stronger shock contribution for the proton event and a more likely flare-related source for the electron event. In contrast to earlier studies on widespread SEP events, we find that in this event an important ingredient for the wide SEP spread was the wide longitudinal range of about 110 o covered by distinct SEP injections, which is also supported by our SEP transport modeling.

sun↗
NASA NTRS2008

Virtual Energetic Particle Observatory (VEPO)

The Virtual Energetic Particle Observatory (VEPO) focuses on improved discovery, access, and usability of heliospheric energetic particle and ancillary data products from selected spacecraft and sub-orbital instruments of the heliophysics data environment. The energy range of interest extends over the full range of particle acceleration from keV energies of suprathermal seed particles to GeV energies of galactic cosmic ray particles. Present spatial coverage is for operational and legacy spacecraft operating from the inner to the outer heliosphere, e.g. from measurements by the two Helios spacecraft to 0.3 AU to the inner heliosheath region now being traversed by the two Voyager spacecraft. This coverage will eventually be extended inward to ten solar radii by the planned NASA solar probe mission and at the same time beyond the heliopause into the outer heliosheath by continued Voyager operations. The geospace fleet of spacecraft providing near-Earth interplanetary measurements, selected magnetospheric spacecraft providing direct measurements of penetrating interplanetary energetic particles, and interplanetary cruise measurements from planetary spacecraft missions further extend VEPO resources to the domain of geospace and planetary interactions. Ground-based (e.g., neutron monitor) and high-altitude suborbital measurements can expand coverage to the highest energies of galactic cosmic rays affected by heliospheric interaction and of solar energetic particles. Science applications include investigation of solar flare and coronal mass ejection events. acceleration and transport of interplanetary particles within the inner heliosphere, cosmic ray interactions with planetary surfaces and atmospheres, sources of suprathermal and anomalous cosmic ray ions in the outer heliosphere, and solar cycle modulation of galactic cosmic rays. Robotic and human exploration, and eventual habitation, of planetary and space environments beyond the Earth require knowledge of radiation hazards informed by VEPO data resources. The VEPO project has completed the first year of work to define science requirements, to document and register selected data products in SPASE format while evolving SPASE for increased applicability to VEPO data, and to support enhanced discovery and access for these products through the evolving data query and middleware system of the Virtual Heliospheric Observatory (VHO). The VEPO team operates as a heliophysics focus group for energetic particle data resources in partnership with VHO and also leverages existing data services of NASA's Space Physics Data Facility. We invite comments from the U.S. and international data provider and user communities on review of the current VEPO/VHO user interface, on directions for future evolution of VEPO and supporting data systems including VHO and SPDF, and on relations to other elements of the heliophysics virtual observatory environment.

Cooper, John F.↗
NASA NTRS1985

The structure of ion plated films in relation to coating properties

Ion plating is an ion assisted or glow discharge deposition technique, where ions or energetic atoms transfer energy, momentum and charge to the substrate and the growing film in a manner which can be controlled to favorably modify surface, subsurface chemistry, and microstructure. The glow discharge energizing effects from the initial nucleation stages to the final film growth are discussed. As a result, adherence, coherence, internal stresses, density and morphology of the coatings are significantly improved, over the conventional (nonion-assisted) techniques which in turn favorably affect the surface initiated failures caused by friction, wear, erosion, corrosion and fatigue. Ion plated films because of their graded coating/substrate interface, fine, uniform, densely packed film structure also induce a surface strengthening effect which improved the mechanical properties such as yield, tensile strength and fatigue life. Since a uniform, continuous film can be obtained at lower nominal film thickness, this effect is of great importance in solid film lubrication and in corrosion protection.

Spalvins, T.↗
NASA NTRS1994

Simulation studies for surfaces and materials strength

Computer simulation studies were conducted to investigate materials properties. All the calculations were carried out using atomic level simulation techniques which are based on semiempirical or model functions. During this project, functions with varying degrees of complexity were derived and employed in simulations. Investigations include covalently bonded materials as well as systems involving metal atoms. For small clusters calculated results provided information on various energy- and structure-related properties along with vibrational characteristics. Also, energy barriers for configurational transitions were calculated for selected cases. Simulation calculations for surfaces produced new results in areas related to surface energies, reconstructions and relaxations, surface defects, surface stresses as well as adsorption and nucleation processes. Simulations were also performed on bulk materials. Calculated results provided an atomic level understanding on energetics and structures of point defects, crystal stability, elastic properties, and materials strength for various systems. Calculations involving polymeric materials include studies of polar polymer melts and polymer/solid interfaces. Simulations employing specially developed codes provided significant information about energetics and conformational characteristics of different polymeric chains.

Halicioglu, Timur↗
NASA NTRS2002

Controlling Electron Backstreaming Phenomena Through the Use of a Transverse Magnetic Field

DEEP-SPACE mission propulsion requirements can be satisfied by the use of high specific impulse systems such as ion thrusters. For such missions. however. the ion thruster will be required to provide thrust for long periods of time. To meet the long operation time and high-propellant throughput requirements, thruster lifetime must be increased. In general, potential ion thruster failure mechanisms associated with long-duration thrusting can be grouped into four areas: (1) ion optics failure; (2) discharge cathode failure; (3) neutralizer failure; and (4) electron backstreaming caused by accelerator grid aperture enlargement brought on by accelerator grid erosion. The work presented here focuses on electron backstreaming. which occurs when the potential at the center of an accelerator grid aperture is insufficient to prevent the backflow of electrons into the ion thruster. The likelihood of this occurring depends on ion source operation time. plasma density, and grid voltages, as accelerator grid apertures enlarge as a result of erosion. Electrons that enter the gap between the high-voltage screen and accelerator grids are accelerated to the energies approximately equal to the beam voltage. This energetic electron beam (typically higher than 1 kV) can damage not only the ion source discharge cathode assembly. but also any of the discharge surfaces upstream of the ion acceleration optics that the electrons happen to impact. Indeed. past backstreaming studies have shown that near the backstreaming limit, which corresponds to the absolute value of the accelerator grid voltage below which electrons can backflow into the thruster, there is a rather sharp rise in temperature at structures such as the cathode keeper electrode. In this respect operation at accelerator grid voltages near the backstreaming limit is avoided. Generally speaking, electron backstreaming is prevented by operating the accelerator grid at a sufficiently negative voltage to ensure a sufficiently negative aperture center potential. This approach can provide the necessary margin assuming an expected aperture enlargement. Operation at very negative accelerator grid voltages, however, enhances ion charge-exchange and direct impingement erosion of the accelerator grid. The focus of the work presented here is the mitigation of electron backstreaming by the use of a magnetic field. The presence of a magnetic field oriented perpendicular to the thruster axis can significantly decrease the magnitude of the backflowing electron current by significantly reducing the electron diffusion coefficient. Negative ion sources utilize this principle to reduce the fraction of electrons in the negative ion beam. The focus of these efforts has been on the attenuation of electron current diffusing from the discharge plasma into the negative ion extraction optics by placing the transverse magnetic field upstream of the extraction electrodes. In contrast. in the case of positive ion sources such as ion thrusters, the approach taken in the work presented here is to apply the transverse field downstream of the ion extraction system so as to prevent electrons from flowing back into the source. It was found in the work presented here that the magnetic field also reduces the absolute value of the electron backstreaming limit voltage. In this respect. the applied transverse magnetic field provides two mechanisms for electron backstreaming mitigation: (1) electron current attenuation and (2) backstreaming limit voltage shift. Such a shift to less negative voltages can lead to reduced accelerator grid erosion rates.

Foster, John E.↗
NASA NTRS2013

Solar Flares

Because the Earth resides in the atmosphere of our nearest stellar neighbor, events occurring on the Sun's surface directly affect us by interfering with satellite operations and communications, astronaut safety, and, in extreme circumstances, power grid stability. Solar flares, the most energetic events in our solar system, are a substantial source of hazardous space weather affecting our increasingly technology-dependent society. While flares have been observed using ground-based telescopes for over 150 years, modern space-bourne observatories have provided nearly continuous multi-wavelength flare coverage that cannot be obtained from the ground. We can now probe the origins and evolution of flares by tracking particle acceleration, changes in ionized plasma, and the reorganization of magnetic fields. I will walk through our current understanding of why flares occur and how they affect the Earth and also show several examples of these fantastic explosions.

Savage, Sabrina↗
NASA NTRS2004

H2O2 Synthesis Induced by Irradiation of H2O with Energetic H(+) and Ar(+) Ions at Various Temperatures

The detection of H2O2 on Jupiter's icy satellite Europa by the Galileo NIMS instrument presented a strong evidence for the importance of radiation effects on icy surfaces. A few experiments have investigated whether solar flux of protons incident on Europa ice could cause a significant if any H2O2 production. These published results differ as to whether H2O2 can be formed by ions impacting water at temperatures near 80 K, which are appropriate to Europa. This discrepancy may be a result of the use of different incident ion energies, different vacuum conditions, or different ways of processing the data. The latter possibility comes about from the difficulty of identifying the 3.5 m peroxide OH band on the long wavelength wing of the much stronger water 3.1 m band. The problem is aggravated by using straight line baselines to represent the water OH band with a curvature, in the region of the peroxide band, that increases with temperature. To overcome this problem, we use polynomial baselines that provide good fits to the water band and its derivative.

Baragiola, R. A.↗
NASA NTRS2010

Radiolysis and Photolysis of Icy Satellite Surfaces: Experiments and Theory

The transport and exchange of material between bodies in the outer solar system is often facilitated by their exposure to ionizing radiation. With this in mind we review the effects of energetic ions, electrons and UV photons on materials present in the outer solar system. We consider radiolysis, photolysis, and sputtering of low temperature solids. Radiolysis and photolysis are the chemistry that follows the bond breaking and ionization produced by incident radiation, producing, e.g., O2 and H2 from irradiated H2O ice. Sputtering is the ejection of molecules by incident radiation. Both processes are particularly effective on ices in the outer solar system. Materials reviewed include H2O ice, sulfur-containing compounds (such as S02 and S8), carbon~contajning compounds (such as CH4), nitrogen-containing compounds (such as NH3 and N2), and mixtures of those compounds. We also review the effects of ionizing radiation on a mixture of N2 and CH4 gases, as appropriate to Titan's upper atmosphere, where radiolysis and photolysis produce complex organic compounds (tholins).

Cassidy, T.↗
NASA NTRS1981

Two-dimensional electron beam charging model for polymer films

A two-dimensional model is developed to describe the charging of strips of thin polymer films above a grounded substrate exposed to a uniform mono-energetic electron beam. The study is motivated by the observed anomalous behavior of geosynchronous satellites, which has been attributed to differential charging of the satellite surfaces exposed to magnetospheric electrons. Surface and bulk electric fields are calcuated at steady state in order to identify regions of high electrical stress, with emphasis on behavior near the material's edge. The model is used to study the effects of some of the experimental parameters, notably beam energy, beam angle of incidence, beam current density, material thickness and material width. Also examined are the consequences of a central gap in the material and a discontinuity in the material thickness.

Reeves, R. D.↗
NASA NTRS1987

Si(111) cleavage and the (2 x 1) reconstruction process

Using a computer simulation technique with a semiempirical potential, a Si crystal was cleaved along the (111) plane. The pi-bonded chain structural features of the Si(111) cleavage surface are observed and found to be a consequence of the dynamics of this cleavage process and seem not to be influenced by the final energetics.

Pearson, E. M.↗
NASA NTRS1996

Turbulent Compressible Convection with Rotation: Flow Structure and Evolution - Part 1

The effects of Coriolis forces on compressible convection are studied using three-dimensional numerical simulations carried out within a local modified f-plane model. The physics is simplified by considering a perfect gas occupying a rectilinear domain placed tangentially to a rotating sphere at various latitudes, through which a destabilizing heat flux is driven. The resulting convection is considered for a range of Rayleigh, Taylor, and Prandtl (and thus Rossby) numbers, evaluating conditions where the influence of rotation is both weak and strong. Given the computational demands of these high-resolution simulations, the parameter space is explored sparsely to ascertain the differences between laminar and turbulent rotating convection. The first paper in this series examines the effects of rotation on the flow structure within the convection, its evolution, and some consequences for mixing. Subsequent papers consider the large-scale mean shear flows that are generated by the convection, and the effects of rotation on the convective energetics and transport properties. It is found here that the structure of rotating turbulent convection is similar to earlier nonrotating studies, with a laminar, cellular surface network disguising a fully turbulent interior punctuated by vertically coherent structures. However, the temporal signature of the surface flows is modified by inertial motions to yield new cellular evolution patterns and an overall increase in the mobility of the network. The turbulent convection contains vortex tubes of many scales, including large-scale coherent structures spanning the full vertical extent of the domain involving multiple density scale heights. Remarkably, such structures align with the rotation vector via the influence of Coriolis forces on turbulent motions, in contrast with the zonal tilting of streamlines found in laminar flows. Such novel turbulent mechanisms alter the correlations which drive mean shearing flows and affect the convective transport properties. In contrast to this large-scale anisotropy, small-scale vortex tubes at greater depths are randomly orientated by the rotational mixing of momentum, leading to an increased degree of isotropy on the medium to small scales of motion there. Rotation also influences the thermodynamic mixing properties of the convection. In particular, interaction of the larger coherent vortices causes a loss of correlation between the vertical velocity and the temperature leaving a mean stratification which is not isentropic.

Brummell, Nicholas H.↗
NASA NTRS2008

Impact of Universal Plasma and Energetic Particle Processes on Icy Bodies of the Kuiper Belt and the Oort Cloud

Modeling of space plasma and energetic particle interactions with icy bodies of the outer solar system is simplified when there is commonality of the underlying source, acceleration, and transport processes in spatially distinct regions from the supersonic heliosphere through the heliosheath into the local interstellar medium (LISM). Current trends in the Voyager heliosheath measurements suggest strong commonality to processes in the LISM. The Fisk-Gloeckler "universal" spectrum at suprathermal energies apparently plays a strong role in coupling the plasma and high energy particle regimes in the spatial and energetic transitions from the outer heliosphere to the LISM. Dominant processes in consecutive energy regimes project to varying effects versus irradiation depth on exposed upper surfaces of airless small icy bodies and to upper atmospheres of larger bodies such as Titan and Pluto. Relative absence of the universal suprathermal spectrum in the mid-heliospheric region of the classical Kuiper Belt may profoundly affect surface color diversity of icy bodies in this region.

Cooper, John F.↗
NASA NTRS2011

Using Supra-Arcade Downflows as Probes of Electron Acceleration During Solar Flares

Extracting information from coronal features above flares has become more reliable with the availability of increasingly higher spatial and temporal-resolution data in recent decades. We are now able to sufficiently probe the region high above long-duration flaring active regions where reconnection is expected to be continually occurring. Flows in the supra-arcade region, first observed with Yohkoh/SXT, have been theorized to be associated with newly-reconnected outflowing loops. High resolution data appears to confirm these assertions. Assuming that these flows are indeed reconnection outflows, then the detection of those directed toward the solar surface (i.e. downflowing) should be associated with particle acceleration between the current sheet and the loop footpoints rooted in the chromosphere. RHESSI observations of highly energetic particles with respect to downflow detections could potentially constrain electron acceleration models. I will discuss measurements of these supra-arcade downflows (SADs) in relation to reconnection model parameters and present preliminary findings comparing the downflow timings with high-energy RHESSI lightcurves.

Savage, Sabrina L.↗
NASA NTRS2010

An Assessment of the Surface Longwave Direct Radiative Effect of Airborne Saharan Dust During the NAMMA Field Campaign

In September 2006, NASA Goddard s mobile ground-based laboratories were deployed to Sal Island in Cape Verde (16.73degN, 22.93degW) to support the NASA African Monsoon Multidisciplinary Analysis (NAMMA) field study. The Atmospheric Emitted Radiance Interferometer (AERI), a key instrument for spectrally characterizing the thermal IR, was used to retrieve the dust IR aerosol optical depths (AOTs) in order to examine the diurnal variability of airborne dust with emphasis on three separate dust events. AERI retrievals of dust AOT are compared with those from the coincident/collocated multifilter rotating shadow-band radiometer (MFRSR), micropulse lidar (MPL), and NASA Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) sensors. The retrieved AOTs are then inputted into the Fu-Liou 1D radiative transfer model to evaluate local instantaneous direct longwave radiative effects (DRE(sub LW)) of dust at the surface in cloud-free atmospheres and its sensitivity to dust microphysical parameters. The top-of-atmosphere DRE(sub LW) and longwave heating rate profiles are also evaluated. Instantaneous surface DRE(sub LW) ranges from 2 to 10 W/sq m and exhibits a strong linear dependence with dust AOT yielding a DRE(sub LW) of 16 W/sq m per unit dust AOT. The DRE(sub LW) is estimated to be approx.42% of the diurnally averaged direct shortwave radiative effect at the surface but of opposite sign, partly compensating for the shortwave losses. Certainly nonnegligible, the authors conclude that DRE(sub LW) can significantly impact the atmospheric energetics, representing an important component in the study of regional climate variation.

Hansell, R. A.↗
NASA NTRS2012

Using Supra-Arcade Downflows as Probes of Particle Acceleration in Solar Flares

Extracting information from coronal features above flares has become more reliable with the availability of increasingly higher spatial- and temporal-resolution data in recent decades. We are now able to sufficiently probe the region high above long-duration flaring active regions where reconnection is expected to be continually occurring. Flows in the supra-arcade region, first observed with Yohkoh/SXT, have been theorized to be associated with newly-reconnected outflowing loops. High resolution data appears to confirm these assertions. Assuming that these flows are indeed reconnection outflows, then the detection of those directed toward the solar surface (i.e. downflowing) should be associated with particle acceleration between the current sheet and the loop footpoints rooted in the chromosphere. RHESSI observations of highly energetic particles with respect to downflow detections could potentially constrain electron acceleration models. We provide measurements of these supra-arcade downflows (SADs) in relation to reconnection model parameters and present preliminary findings comparing the downflow timings with high-energy RHESSI lightcurves.

Savage, Sabrina↗
NASA NTRSDate not supplied

NASA Radiation Operations Sources, Models, and Standards

Space radiation is one of the major challenges of spaceflight. Astronauts spending time in low Earth orbit, the lunar surface, deep space, and elsewhere will all be exposed to multiple space radiation sources. These sources include trapped radiation in Earth’s upper atmosphere, solar energetic particles, and the omnipresent galactic cosmic radiation, as well as non-ionizing radiation from inside and outside a vehicle or habitat. The Space Radiation Analysis Group (SRAG) at Johnson Space Center is responsible for ensuring astronauts are protected from short- and long-term risks of radiation exposure. This talk details the radiation operational standards employed by NASA.

space radiation↗