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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 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Properties and Acceleration Mechanisms of Electrons Up To 200 keV Associated With a Flux Rope Pair and Reconnection X-Lines Around It in Earth's Plasma Sheet

The properties and acceleration mechanisms of electrons (<200 keV) associated with a pair of tailward traveling flux ropes and accompanied reconnection X-lines in Earth's plasma sheet are investigated with MMS measurements. Energetic electrons are enhanced on both boundaries and core of the flux ropes. The power-law spectra of energetic electrons near the X-lines and in flux ropes are harder than those on flux rope boundaries. Theoretical calculations show that the highest energy of adiabatic electrons is a few keV around the X-lines, tens of keV immediately downstream of the X-lines, hundreds of keV on the flux rope boundaries, and a few MeV in the flux rope cores. The X-lines cause strong energy dissipation, which may generate the energetic electron beams around them. The enhanced electron parallel temperature can be caused by the curvature-driven Fermi acceleration and the parallel electric potential. Betatron acceleration due to the magnetic field compression is strong on flux rope boundaries, which enhances energetic electrons in the perpendicular direction. Electrons can be trapped between the flux rope pair due to mirror force and parallel electric potential. Electrostatic structures in the flux rope cores correspond to potential drops up to half of the electron temperature. The energetic electrons and the electron distribution functions in the flux rope cores are suggested to be transported from other dawn-dusk directions, which is a 3-dimensional effect. The acceleration and deceleration of the Betatron and Fermi processes appear alternately indicating that the magnetic field and plasma are turbulent around the flux ropes.

58 GEOSCIENCES↗
NASA NTRS1977

A rocket-borne airglow photometer

The design of a rocket-borne photometer to measure the airglow emission of ionized molecular nitrogen in the 391.4 nm band is presented. This airglow is a well known and often observed phenomenon of auroras, where the principal source of ionization is energetic electrons. It is believed that at some midlatitude locations energetic electrons are also a source of nighttime ionization in the E region of the ionosphere. If this is so, then significant levels of 391.4 nm airglow should be present. The intensity of this airglow will be measured in a rocket payload which also contains instrumentation to measured in a rocket payload which also contains instrumentation to measure energetic electron differential flux and the ambient electron density. An intercomparison of the 3 experiments in a nightime launch will allow a test of the importance of energetic electrons as a nighttime source of ionization in the upper E region.

Paarmann, L. D.↗
DOE OSTI2026

Energetic Nonthermal Electrons within the Above-the-looptop Regions in Solar Flares: Acceleration, Feedback, and Quasiperiodic Pulsations

Solar flares are among the most dramatic events in the solar system, releasing substantial magnetic energy and accelerating a large number of electrons to high energies. Notably, in certain events, the above-the-looptop region may contain a significant population of nonthermal electrons, both in number and energy. For the first time, we adopt a novel numerical method that combines magnetohydrodynamics with energetic particles incorporating feedback from nonthermal electrons to investigate electron acceleration and transport in solar flares. We find that a large fraction of energetic electrons are accelerated via the current sheet and termination shock regions. Most energetic electrons are concentrated in the above-the-looptop region, carrying a sizable amount of the released energy. We observe that greater feedback of nonthermal electrons leads to steeper energy spectra. The energy density of the nonthermal electrons oscillates due to the periodic impact of magnetic islands into the above-the-looptop region, which may help explain the observed quasiperiodic pulsations. Our simulations provide new insights into the origin of nonthermal electrons and associated emissions in the above-the-looptop region.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1990

Gyroharmonic maser instability for weakly relativistic electrons with a loss-cone distribution

The weakly relativisitic dielectric tensor for a system of electrons comprised of cold and energetic populations, embedded in a neutralizing background, is reformulated in terms of an infinite series representation in powers of lamba = alpha ck(perpendicular)/omega (c), where alpha-squared is a parameter proportional to the average thermal energy of the energetic electrons, k(perpendicular) is the perpendicular component of the wave vector k, and omega (c) is the electron gyrofrequency. The energetic electrons are assumed to have a loss-cone feature in the perpendicular momentum space. The present formalism can be used in the problem of cyclotron maser as well as more general gyroharmonic maser (i.e., multiharmonics) emissions resulting from weakly relativistic loss-cone electrons. This is because, unlike the previous theories in which certain approximations such as the single-harmonic approximations are made, the present formalism retains contributions from the entire harmonics.

Yoon, Peter H.↗
DOE OSTI2020

Dynamical Modulation of Solar Flare Electron Acceleration due to Plasmoid-shock Interactions in the Looptop Region

A fast-mode shock can form in the front of reconnection outflows and has been suggested as a promising site for particle acceleration in solar flares. Recent developments in the study of magnetic reconnection have shown that numerous plasmoids can be produced in a large-scale current layer. Here we investigate the dynamical modulation of electron acceleration in the looptop region when plasmoids intermittently arrive at the shock by combining magnetohydrodynamics simulations with a particle kinetic model. As plasmoids interact with the shock, the looptop region exhibits various compressible structures that modulate the production of energetic electrons. The energetic electron population varies rapidly in both time and space. The number of 5–10 keV electrons correlates well with the compression area, while that of >50 keV electrons shows good correlation with the strong compression area but only moderate correlation with shock parameters. We further examine the impacts of the first plasmoid, which marks the transition from a quasi-steady shock front to a distorted and dynamical shock. The number of energetic electrons is reduced by ~20% at 15–25 keV and nearly 40% for 25–50 keV, while the number of 5–10 keV electrons increases. In addition, the electron energy spectrum above 10 keV evolves softer with time. We also find that double or even multiple distinct sources can develop in the looptop region when the plasmoids move across the shock. Our simulations have strong implications to the interpretation of nonthermal looptop sources, as well as the commonly observed fast temporal variations in flare emissions, including the quasi-periodic pulsations.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1980

The energy loss of relativistic electrons in energetic photon gases and its relation to the equilibrium spectrum of electrons

The energy loss of relativistic electrons is considered for astrophysical objects which contain energetic photon gases in the XUV-range. Such objects have been suggested as possible candidates for gamma-ray point sources through the mechanism of inverse Compton scattering. In certain cases where inverse Compton scattering is the dominant energy loss mechanism, an equilibrium spectrum results which can deviate from a strict power law. Such an effect can have consequences on the observed radiation spectrum from such objects.

Prince, T.↗
NASA NTRS1992

On the modulation of X ray fluxes in thunderstorms

The production of X-ray fluxes in thunderstorms has been attributed to bremsstrahlung. Assuming this, another question arises. How can a thunderstorm modulate the number density of electrons which are sufficiently energetic to produce X-rays? As a partial answer to this question, the effects of typical thunderstorm electric fields on a background population of energetic electrons, such as produced by cosmic ray secondaries and their decays or the decay of airborne radionuclides, are considered. The observed variation of X-ray flux is shown to be accounted for by a simple model involving typical electric field strengths. A necessary background electron number density is found from the model and is determined to be more than 2 orders of magnitude higher than that available from radon decay and a factor of 8 higher than that available from cosmic ray secondaries. The ionization enhancement due to energetic electrons and X-rays is discussed.

Mccarthy, Michael P.↗
NASA NTRS1978

The TELEC - A plasma type of direct energy converter

The Thermo-Electronic Laser Energy Converter (TELEC) is a high-power density plasma device designed to convert a 10.6-micron CO2 laser beam into electric power. Electromagnetic radiation is absorbed in plasma electrons, creating a high-electron temperature. Energetic electrons diffuse from the plasma and strike two electrodes having different areas. The larger electrode collects more electrons and there is a net transport of current. An electromagnetic field is generated in the external circuit. A computer program has been designed to analyze TELEC performance allowing parametric variation for optimization. Values are presented for TELEC performance as a function of cesium pressure and for current density and efficiency as a function of output voltage. Efficiency is shown to increase with pressure, reaching a maximum over 45%.

Britt, E. J.↗
NASA NTRSDate not supplied

Electron Bombardment on Dione: Surface Compositional Effects and Temperature Anomalies

Saturn’s icy moons are composed primarily of water ice with minor other “contaminants,” such as CO2 ice, and a dark component thought to be organics, hematite and/or metallic Fe. The space weathering process of electron bombardment is expected to be particularly important on the surfaces of Saturn’s inner moons (Mimas, Tethys, Dione, and Rhea), as they orbit within Saturn’s inner magnetosphere. Terrains exhibiting thermal anomalies (i.e., colder temperatures in the day and warmer temperatures at night than surrounding areas) correspond to regions of high energy electron bombardment. Energetic electrons impact the surfaces, sintering ice grains together, and this process becomes more effective for increasing particle energies. Solar UV radiation, cosmic rays, dust in-fall, and cold plasma particles trapped in Saturn’s magnetic field also play an important role in altering the nature and the structure of the native surface ices by the implantation of contaminants, ionization, sputtering, and dissociation of water ice molecules. Additionally, CO2 could be sourced from irradiation of dark organic material. Many of these surface alterations are observable in Cassini’s Visible and Infrared Mapping Spectrometer (VIMS) spectra. We used similar methodologies as have been employed in previous works to derive surface temperatures from Cassini’s Composite Infrared Spectrometer (CIRS), which helped to isolate areas where space weathering due to electron bombardment is more predominant. The subtle changes in VIMS spectra were investigated using machine learning techniques. We present here our results for Dione.

C L Young↗
NASA NTRS1984

The High Latitude D Region During Electron Precipitation Events

The fluxes of energetic electrons entering the high-latitude atmosphere during auroral radio absorption events and their effect on the electron density in the auroral D region are discussed. An attempt was made to calculate the radio absorption during precipitation events from the fluxes of energetic electrons measured at geosynchronous orbit, and then to consider the use of absorption measurements to indicate the magnetospheric particle fluxes, the production rates, and electron densities in the D region.

Hargreaves, J. K.↗
NASA NTRS1980

Impulsive phase of solar flares

The present understanding of the impulsive phase of a solar flare, characterized by short-duration bursts of impulsive hard X-ray, EUV, optical and radio emission indicating the release of energetic electrons is reviewed. Observations of the spectral distribution of impulsive hard X-ray bursts and of Type III and radio continuum bursts are presented and interpreted in terms of energetic electron distributions, and impulsive EUV, XUV, soft X-ray and optical observations, which provide a lower limit to total energy release during the impulsive phase, are discussed. The role of energetic electrons in exciting the hard X-ray, EUV and microwave emissions is considered, and thin-target, thick-target, partial-precipitation and thermal models of impulsive phase electron acceleration are evaluated in light of the observations. It is noted that available data do not allow discrimination between a thermal or a nonthermal electron distribution, on which depends the proportion of flare energy supplied by the energetic electrons, and that data favors models which permit at least partial electron precipitation. Future observational and theoretical work is indicated.

Kane, S. R.↗
NASA NTRS1978

Reverse Current in Solar Flares

An idealized steady state model of a stream of energetic electrons neutralized by a reverse current in the pre-flare solar plasma was developed. These calculations indicate that, in some cases, a significant fraction of the beam energy may be dissipated by the reverse current. Joule heating by the reverse current is a more effective mechanism for heating the plasma than collisional losses from the energetic electrons because the Ohmic losses are caused by thermal electrons in the reverse current which have much shorter mean free paths than the energetic electrons. The heating due to reverse currents is calculated for two injected energetic electron fluxes. For the smaller injected flux, the temperature of the coronal plasma is raised by about a factor of two. The larger flux causes the reverse current drift velocity to exceed the critical velocity for the onset of ion cyclotron turbulence, producing anomalous resistivity and an order of magnitude increase in the temperature. The heating is so rapid that the lack of ionization equilibrium may produce a soft X-ray and EUV pulse from the corona.

Knight, J. W., III↗
NASA NTRS1982

Electromagnetic cyclotron-loss-cone instability associated with weakly relativistic electrons

The amplification of fast extraordinary mode waves at frequencies very close to the electron cyclotron frequency, due to the presence of a population of energetic electrons with a loss-cone type distribution, is studied. Low-energy background electrons are included in the analysis. Two types of loss-cone distribution functions are considered, and it is found that the maximum growth rates for both distribution functions are of the same order of magnitude. When the thermal effects of the energetic electrons are included in the dispersion equation, the real frequencies of the waves are lower than those obtained by using the cold plasma approximation. This effect tends to enhance the growth rate. An idealized case including a parallel electric field such that the distribution function of the trapped energetic electrons is modified is also considered. It is assumed that the parallel electric field can remove the low-energy background electrons away from the source region of radiation. Both these effects increase the growth rate.

Wong, H. K.↗
NASA NTRS1978

Whistler mode noise in Jupiter's inner magnetosphere

A study is made of the amplitude and spectral extent of whistler mode noise in the inner magnetosphere of Jupiter. It is found that the 'hat-shaped' pitch angle distributions of energetic electrons (21 and 31 MeV at L=3) are consistent with those predicted in the presence of a band-limited spectrum of whistler mode noise. The equatorial maximum linear growth rate of parallel propagating whistlers are consistent with those necessary to limit the energetic electron intensities by the whistler mode instability. It is noted that the wave phase speeds before wave reflection can occur at high latitudes and that wave growth is limited to a disk-like region centered around the magnetic equator. The frequency extent of the whistler mode noise spectrum may be estimated by the range of frequencies maximally unstable to equatorial linear growth. A value is found for the spectral density of the broadband whistler mode noise necessary to balance radial diffusion of energetic electrons above the critical range, and an expression is derived for the energetic electron system response to fluctuations about the limiting flux value.

Sentman, D. D.↗
NASA NTRS1976

Reduction and analysis of ATS-6 data

The reduction of data obtained by the experiment on ATS-6 is presented and a scientific analysis of the data is included. During the period covered significant progress was made in both reduction and analysis of ATS-6 data. The relationship between the direction of the interplanetary magnetic field and the fluxes of energetic electrons at the synchronous altitude was clarified, and a simple model of the energetic electron environment as observed by ATS-6 was developed and a simple empirical relationship was extended, which predicts the maximum energetic electron flux to be expected at the synchronous orbit.

Paulikas, G. A.↗
NASA NTRS1977

The effects of the geosynchronous energetic particle radiation environment on spacecraft charging phenomena

The energetic electron environment at the geosynchronous orbit is responsible for a variety of adverse charging effects on spacecraft components. The most serious of these is the degradation and failure of a complementary-metal-oxide-semiconductor (CMOS) electronic components as a result of internal charge-buildup induced by the energetic electrons. Efforts to accurately determine the expected lifetime of these components in this orbit are hampered by the lack of detailed knowledge of the electron spectrum and intensity, particularly of the more penetrating energies greater than 1.5 MeV. This problem is illustrated through the calculation of the dose received by a CMOS device from the energetic electrons and associated bremsstrahlung as a function of aluminum shielding thickness using the NASA AE-6 and the Aerospace measured electron environments. Two computational codes which were found to be in good agreement were used to perform the calculations. For a given shielding thickness the dose received with the two radiation environments differ by as much as a factor of seven with a corresponding variation in lifetime of the CMOS.

Reagan, J. B.↗
NASA NTRS1988

Double-probe potential measurements near the Spacelab 2 electron beam

As part of the Spacelab 2 mission the plasma diagnostics package (PDP) was released from the shuttle as a free-flying satellite. The PDP carried a quasi-static electric field instrument which made differential voltage measurements between two floating probes. At various times during the free flight, an electron beam was ejected from the shuttle. Large differential voltages between the double probes were recorded in association with the electron beam. However, analysis indicates that these large signals are probably not caused by ambient electric fields. Instead, they can be explained by considering three effects: shadowing of the probes from streaming electrons by the PDP chassis, crossing of the PDP wake by the probes, and spatial gradients in the fluxes of energetic electrons reaching the probes. Plasma measurements on the PDP show that energetic electrons exist in a region 20 m wide and up to at least 170 m downstream from the electron beam. At 80 or more meters downstream from the beam, the double probe measurements show that the energetic electron flux is opposite to the injection direction, as would be expected for a secondary returning electron beam produced by scattering of the primary electron beam.

Steinberg, J. T.↗
NASA NTRS1978

Spontaneous synchrotron emission from a plasma with an energetic runaway electron tail

The emissivity of spontaneous synchrotron radiation is computed for a plasma consisting of a background thermal plasma in addition to an energetic runaway electron component. The analysis is performed for both the ordinary and extraordinary modes, for frequencies in the vicinity of the electron plasma frequency and the higher harmonics of the electron gyrofrequency, and for the case when the electron plasma frequency is approximately the same as or smaller than the cyclotron frequency. The relativistic gyroresonance with the runaway electrons is found to result in a level of spontaneous emission which, for frequencies in the neighborhood of the electron plasma frequency, is significantly enhanced over the thermal radiation.

Freund, H. P.↗