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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS2019

Contribution of ULF Wave Activity to the Global Recovery of the Outer Radiation Belt During the Passage of a High‐Speed Solar Wind Stream Observed in September 2014

Energy coupling between the solar wind and the Earth's magnetosphere can affect the electron population in the outer radiation belt. However, the precise role of different internal and external mechanisms that leads to changes of the relativistic electron population is not entirely known. This paper describes how ultralow frequency (ULF) wave activity during the passage of Alfvenic solar wind streams contributes to the global recovery of the relativistic electron population in the outer radiation belt. To investigate the contribution of the ULF waves, we searched the Van Allen Probes data for a period in which we can clearly distinguish the enhancement of electron fluxes from the background. We found that the global recovery that started on 22 September 2014, which coincides with the corotating interaction region preceding a high‐speed stream and the occurrence of persistent substorm activity, provides an excellent scenario to explore the contribution of ULF waves. To support our analyses, we employed ground‐ and space‐based observational data and global magnetohydrodynamic simulations and calculated the ULF wave radial diffusion coefficients employing an empirical model. Observations show a gradual increase of electron fluxes in the outer radiation belt and a concomitant enhancement of ULF activity that spreads from higher to lower L‐shells. Magnetohydrodynamic simulation results agree with observed ULF wave activity in the magnetotail, which leads to both fast and Alfven modes in the magnetospheric nightside sector. The observations agree with the empirical model and are confirmed by phase space density calculations for this global recovery period.

Silva, L. A. Da↗
NASA NTRS1996

3C 279 Multiwavelength Monitoring: The Ground-Based Campaign - 2

The optically violently variable quasar 3C 279 was monitored simultaneously from radio to gamma-ray frequencies in 1992 December - 1993 January. We report a detailed study of the ground-based results from radio to optical wavelengths. These data show that 3C 279 has a typical blazar spectrum, slightly rising at radio frequency and then progressively steeper above a first turnover frequency between 37 and 90 GHz. In the millimeter wavelength region, a simple power law is not an adequate description of the spectrum. We suggest that the millimeter "shoulder" corresponds to an additional emission component, self-absorbed between 150 and 375 GHz, possibly associated with the detachment of a new Very Long Base Interferometry (VLBI) knot and with the start of radio flare. A flux increase of 20% over 20 days was observed at 37 and 90 GHz, while contemporaneously the R-band flux doubled in about two weeks. The lack of strong variability in contemporaneous X-ray light curves (possible X-ray variations are less than 30%) implies no direct (i.e., zero lag) correlation between the optical and X-ray fluxes. If X-rays are produced by inverse-Compton scattering of relativistic electrons on some seed photons, the above results exclude that the observed optical photons are the seeds and/or that the relativistic electrons radiating via synchrotron in the optical band are responsible for the scattering to X-ray energies. We suggest that the X-rays are instead produced through the inverse-Compton process by electrons of lower energy, which radiate via synchrotron in the radio to millimeter wave bands and which scatter either on the synchrotron photons themselves or on external photons.

Grandi, P.↗
NASA NTRS1988

Low-energy Galactic centre gamma-rays from low-mass X-ray binaries

Nonthermal processes in low-mass X-ray binaries concentrated in the Galactic bulge are proposed as the direct source of the three continuum components of the emission from the Galactic center region (GCR) and also, possibly, as the indirect source of the 511-keV electron-positron annihilation line. It is suggested that the softer power-law component of the GCR continuum arises from synchrotron emission of relativistic electrons in the strongly nonuniform magnetic field of the neutron star and, more tentatively, that the MeV bump is the result of interaction of harder gamma rays with power-law photons. The hardest power law may be due to Compton scattering of relativistic electrons or photons.

Kluzniak, W.↗
NASA NTRS1976

Gamma-ray and microwave evidence for two phases of acceleration in solar flares

Relativistic electrons in large solar flares produce gamma-ray continuum by bremsstrahlung and microwave emission by gyrosynchrotron radiation. Using observations of the August 4, 1972, flare, a detailed evaluation is made of the electron spectrum and the physical properties (density, magnetic field, size, and temperature) of the common emitting region of these radiations. Information is also obtained on energetic protons in this flare by using gamma-ray lines. From the electron spectrum, the proton-to-electron ratio, and the time dependences of the microwave emission, the 2.2-MeV line, and the gamma-ray continuum, it is concluded that relativistic electrons and energetic nuclei are accelerated in large solar flares by a mechanism which is different from the mechanism which accelerates electrons with energies not exceeding about 100 keV in flares.

Bai, T.↗
DOE OSTI2024

Sunbeam: Near-sun statites as beam platforms for beam-driven rockets

Here, we outline a method of beamed power for propulsion that utilizes relativistic electron beams. The physics of charged particle beam propagation in the space plasma environment is discussed and the long-range (> 100 AU) advantage of relativistic electron beams is emphasized. A preliminary statite-based beam emitter for powering probes to 0.1c is proposed and the challenges in beamed-power uses are explored.

33 ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2020

Resonant four-photon scattering of collinear laser pulses in plasma

Exact four-photon resonance of collinear planar laser pulses is known to be prohibited by the classical dispersion law of electromagnetic waves in plasma. We show here that the renormalization produced by an arbitrarily small relativistic electron nonlinearity removes this prohibition. The laser frequency shifts in collinear resonant four-photon scattering increase with laser intensities. For laser pulses of frequencies much greater than the electron plasma frequency, the shifts can also be much greater than the plasma frequency and even nearly double the input laser frequency at still small relativistic electron nonlinearities. Furthermore, this may enable broad range tunable lasers of very high frequencies and powers. Since the four-photon scattering does not rely on the Langmuir wave, which is very sensitive to plasma homogeneity, such lasers would also be able to operate at much larger plasma inhomogeneities than lasers based on stimulated Raman scattering in plasma.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1984

A detailed X-ray and radio comparison of Kepler's supernova remnant

High-resolution radio images of Kepler's SNR (SNR (SN 1604) at 6 and 21 cm have been obtained using the VLA. The orientation of linear polarization in the SNR implies a substantial nonrandom radial component for the magnetic field of the remnant. Based on a new X-ray picture of the SNR, obtained using the Einstein Observatory, a detailed comparison of the X-ray and radio morphology is carried out. There is a good correlation between rotation measure, obtained from the radio maps, and emission measure, an X-ray-derived quantity in the SNR shell. From the mean electron density value infered from an analysis of X-ray fluxes, a mean radial magnetic field of 14 micro G and a total magnetic field of 70 microG are estimated. The energy density of relativistic electrons in Kepler's SNR in the shell comparable to the energy density in the magnetic field; the relativistic electron-pressure is 2 percent of the thermal gas pressure. The strong correlation between radio emissivity and X-ray emissivity found over the SNR in somewhat large scale can be ascribed to acceleration of thermal electrons at the shock wave and insignificant diffusion of resultant relativistic electrons.

Matsui, Y.↗
NASA NTRS1976

Gamma-ray and microwave evidence for two phases of acceleration in solar flares

Relativistic electrons in large solar flares produce gamma ray continuum by bremsstrahlung and microwave emission by gyrosynchrotron radiation. Using observations of the 1972, August 4 flare, the electron spectrum and the physical properties of the common emitting region of these radiations were evaluated. Information was also obtained on energetic protons in this flare by using gamma ray lines. From the electron spectrum, the proton-to-electron ratio, and the time dependences of the microwave emission, the 2.2 MeV line and the gamma ray continuum, it was concluded that in large solar flares relativistic electrons and energetic nuclei are accelerated by a mechanism which is different from the mechanism which accelerates approximately less than 100 keV electrons in flares.

Bai, T.↗
DOE OSTI2020

Time-resolved measurement of electron beam neutralization

An intense relativistic electron beam (IREB) incident on a target generates positive ions by stimulated and thermal desorption of adsorbed gas, and subsequent electron impact ionization. These ions are accelerated upstream by the beam space-charge potential, thereby partially neutralizing the beam. If there is enough neutralization, the repulsive space-charge force can be overcome by the magnetic-pinch force due to the beam current. This so-called ion focusing is responsible for time dependent defocusing of the radiographic source spot. Since a single monolayer of adsorbed gas has a surface density of about 10 15 /cm 2 and is formed in about one second in a one micro-Torr vacuum, there is always enough adsorbed gas to make this a concern in our accelerators. Therefore, time-resolved measurements of the degree of neutralization are valuable for better understanding of this process with an eye to mitigation for improvement of our radiography. Moreover, these measurements would aid quantification of uncertainties due to these effects when using invasive beam diagnostics, such as OTR imaging targets.

43 PARTICLE ACCELERATORS↗
DOE OSTI2020

Fast electron transport dynamics and energy deposition in magnetized, imploded cylindrical plasma

Inertial confinement fusion approaches involve the creation of high-energy-density states through compression. High gain scenarios may be enabled by the beneficial heating from fast electrons produced with an intense laser and by energy containment with a high-strength magnetic field. Here, we report experimental measurements from a configuration integrating a magnetized, imploded cylindrical plasma and intense laser-driven electrons as well as multi-stage simulations that show fast electrons transport pathways at different times during the implosion and quantify their energy deposition contribution. The experiment consisted of a CH foam cylinder, inside an external coaxial magnetic field of 5 T, that was imploded using 36 OMEGA laser beams. Two-dimensional (2D) hydrodynamic modelling predicts the CH density reaches 9.0 g cm − 3 , the temperature reaches 920 eV and the external B-field is amplified at maximum compression to 580 T. At pre-determined times during the compression, the intense OMEGA EP laser irradiated one end of the cylinder to accelerate relativistic electrons into the dense imploded plasma providing additional heating. The relativistic electron beam generation was simulated using a 2D particle-in-cell (PIC) code. Finally, three-dimensional hybrid-PIC simulations calculated the electron propagation and energy deposition inside the target and revealed the roles the compressed and self-generated B-fields play in transport. During a time window before the maximum compression time, the self-generated B-field on the compression front confines the injected electrons inside the target, increasing the temperature through Joule heating. For a stronger B-field seed of 20 T, the electrons are predicted to be guided into the compressed target and provide additional collisional heating. This article is part of a discussion meeting issue ‘Prospects for high gain inertial fusion energy (part 2)’.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1977

Radio and X-ray variability of the nucleus of Centaurus A (NGC 5128)

Centaurus A was observed at radio frequencies of 10.7, 31.4, 85.2, and 89 GHz and at X-ray energies greater than 20 keV. The source exhibits significant variability in all the observed radio frequencies. The observed radio and X-ray intensities show some concurrent variations but do not track one another throughout the observations. A model of the source in which X-rays are produced by inverse Compton scattering of blackbody photons by relativistic electrons is proposed to explain these observations. The observed variations in the electromagnetic spectrum are consistent with adiabatic expansion of a trapped plasma in conjunction with turbulent accelerations of the relativistic electrons.

Beall, J. H.↗
NASA NTRS2018

Ultralow Frequency Waves as an Intermediary for Solar Wind Energy Input Into the Radiation Belts

Enhancements of electron fluxes in the outer radiation belt have been closely linked to increases in solar wind speed and density as well as to prolonged intervals of southward interplanetary magnetic field. Periodic oscillations in the Earth's magnetic field with frequencies in the range of a few millihertz (ultralow frequency or ultralow frequency waves) may be an intermediary through which these solar wind drivers influence radiation belt dynamics due to their potential for resonant interactions with energetic electrons causing the radial migration of resonant electrons. Using data from more than 180 ground magnetometers contributing to the worldwide SuperMAG collaboration, we explore possible relationships between relativistic electron flux variations and the spatial and temporal profiles of ultralow frequency wave power contained in the Pc5 frequency band (2–7 mHz). During 19 geomagnetic storms marked by relativistic (1.5 MeV < E < 6 MeV) electron flux enhancements and 19 storms that led to prolonged electron flux depletions, Pc5 wave power is found penetrating to L shells as low as 2–3. The enhancement of Pc5 wave power starts almost simultaneously with the storm onset. The depth of wave activity penetration was found associated with the strength of geomagnetic activity (Spearman's ρ = 0.54), which is also related to the location of electron flux maximum observed in the recovery phase. Pc5 wave activity persists longer (for up to ≈62 hr) for those storms that produced relativistic electrons. We also investigate the combination of interplanetary conditions necessary to differentiate the response of relativistic electron fluxes to geomagnetic storms. A coupling function that captures the increased reconnection rate at the dayside magnetopause affecting magnetospheric processes which may produce Pc5 wave power offers an additional key to further understanding the outer belt dynamics.

Georgiou, M.↗
DOE OSTI2024

Generation of attosecond gigawatt soft x-ray pulses through coherent Thomson backscattering

Collision between relativistic electron sheets and counterpropagating laser pulses is recognized as a promising way to produce intense attosecond x rays through coherent Thomson backscattering (TBS). In a double-layer scheme, the electrons in an ultrathin solid foil are first pushed out by an intense laser driver and then interact with the laser reflected off a second foil to form a high-density relativistic electron sheet with vanishing transverse momentum. However, the repulsion between these concentrated electrons can increase the thickness of the layer, reducing both its density and subsequently the coherent TBS. Here, we present a systematic study on the evolution of the flying electron layer and find that its resulting thickness is determined by the interplay between the intrinsic space-charge expansion and the velocity compression induced by the drive laser. How the laser driver, the target areal density, the reflector, and the collision laser intensity affect the properties of the produced x rays is explored. Multidimensional particle-in-cell simulations indicate that employing this scheme in the nonlinear regime has the potential to stably produce soft x rays with several gigawatt peak power in hundreds of terawatt ultrafast laser facilities. The pulse duration can be tuned to tens of attoseconds. Here, this compact and intense attosecond x-ray source may have broad applications in attosecond science.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1978

Radio and X-ray variability of the nucleus of Centaurus A /NGC 5128/

Centaurus A (NGC 5128) has been observed at radio frequencies of 10.7, 31.4, 85.2, and 89 GHz and at X-ray energies greater than 20 keV. These observations, together with results reported by other workers, are interpreted in terms of models of the nucleus of this radio galaxy. The radio observations cover the period from 1973 through early 1977. The X-ray observations cover two 10-day intervals, one in July and August (1975) and the other in July and August 1976. The source exhibits significant variability in all the observed radio frequencies. The observed radio and X-ray intensities show some concurrent variations but do not track one another throughout the observations. A model of the source in which X-rays are produced by inverse Compton scattering of blackbody photons by relativistic electrons is proposed to explain these observations. The observed variations in the electromagnetic spectrum are shown to be consistent with adiabatic expansion of a trapped plasma in conjunction with turbulent accelerations of the relativistic electrons. Upper limits obtained with the model indicate that there may be sufficient energy available in the nucleus to form radio lobes with the same total energy as those already present.

Beall, J. H.↗
NASA NTRS2012

The Radiation Belt Storm Probes Mission: Advancing Our Understanding of the Earth's Radiation Belts

We describe NASA's Radiation Belt Storm Probe (RBSP) mission, whose primary science objective is to understand, ideally to the point of predictability, the dynamics of relativistic electrons and penetrating ions in the Earth's radiation belts resulting from variable solar activity. The overarching scientific questions addressed include: 1. the physical processes that produce radiation belt enhancement events, 2. the dominant mechanisms for relativistic electron loss, and 3. how the ring current and other geomagnetic processes affect radiation belt behavior. The RBSP mission comprises two spacecraft which will be launched during Fall 2012 into low inclination lapping equatorial orbits. The orbit periods are about 9 hours, with perigee altitudes and apogee radial distances of 600 km and 5.8 RE respectively. During the two-year primary mission, the spacecraft orbits precess once around the Earth and lap each other twice in each local time quadrant. The spacecraft are each equipped with identical comprehensive instrumentation packages to measure, electrons, ions and wave electric and magnetic fields. We provide an overview of the RBSP mission, onboard instrumentation and science prospects and invite scientific collaboration.

Sibeck, David↗
DOE OSTI2026

Near-infrared noise in intense electron bunches

This article investigates electron bunch density fluctuations in the 1 −10 μ⁢m wavelength range, focusing on their impact on coherent electron cooling (CEC) in hadron storage rings. In this study, we compare the shot-noise model with experimental observations using bandwidth-filtered near-infrared optical transition radiation (OTR) photodiode signals, where the transverse bunch size is much larger than the OTR wavelength of interest. The relativistic electron bunch (𝛾 ≈ 50) parameters are close to those proposed for the coherent electron cooler in the electron-ion collider (EIC) project. Preliminary feasibility experiments were conducted, and the noise factors are presented, supported by particle tracking. No major density fluctuations or effective cooling rate decrease were revealed for EIC CEC design parameters. Additionally, longitudinal-space-charge-induced microbunching for the chicane-compressed bunch was observed with coherent OTR enhancements up to 100 times, providing further calibration of the measurement method.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1994

Relativistic induced Compton scattering in synchrotron self-absorbed sources

We present a model of the radio emission from synchrotron self-absorbed sources, including the effects of induced Compton scattering by the relativistic electrons in the source. Order of magnitude estimates show that stimulated scattering becomes the dominant absorption process when (kT(sub B)/m(sub e) c(exp 2))Tau(sub T) greater than or approximately 1.0. Numerical simulations demonstrate that relativistic induced Compton scattering limits the brightness temperature of a self-absorbed synchroton sources to T(sub B) less than or approximately 2 x 10(exp 11) nu(exp -1/p + 3) (sub zero, 9) gamma(exp p + 2/p + 5) (sub min) K, where gamma(sub min) is the low-energy cutoff to the relativistic electron distribution with a power-law index of p. It can also significantly flatten the radio spectrum. The radio spectrum of the core of 3C 279 is well matched by a model in which stimulated scattering is important, and the additional constraint T(sub B) less than 2 x 10(exp 11)K may be important to the interpretation of the broadband spectra in variable extragalactic compact radio sources. Stimulated scattering reduces the amplitude of the radio frequency variability relative to the X-ray variability, an effect which can be detected by multiwavelength variability studies. Data for a sample of resolved compact radio cores indicate that it is inconsistent to neglect induced Compton scattering when inferring the physical parameters of the sources. The necessary generalizations to the standard synchrotron self-Compton theory are p resented.

Sincell, Mark W.↗
NASA NTRS1994

Comptonization of diffuse ambient radiation by a relativistic jet: The source of gamma rays from blazars?

Recent Energy Gamma Ray Experiment Telescope (EGRET) observations of blazars have revealed strong, variable gamma-ray fluxes with no signatures of gamma-ray absorption by pair production. This radiation probably originates from the inner parts of relativistic jets which are aimed nearly toward us. On sub-parsec scales, the jet will be pervaded by radiation from the broad-line region, as well as by photons from the central continuum source (some of which will be scattered by thermal plasma). In a frame moving with the relativistic outflow, the energy of this ambient radiation would be enhanced. This radiation would be Comptonized by both cold and relativistic electrons in the jet, yielding (in the observer's frame) a collimated beam of X-rays and gamma rays. On the assumption that this process dominates self-Comptonization of synchrotron radiation, we develop a self-consistent model for variable gamma-ray emission, involving a single population of relativistic electrons accelerated by a disturbance in the jet. The spectral break between the X-ray and gamma-ray band, observed in 3C 279 and deduced for other blazars, results from inefficient radiative cooling of lower energy electrons. The existence of such a break strongly favors a model involving Comptonization of an external radiation field over a synchrotron self-Compton model. We derive constraints on such model parameters as the location and speed of the source, its dimensions and internal physical parameters, the maximum photon energies produced in the source, and the density and distribution of ambient radiation. Finally, we discuss how observations might discriminate between our model and alternative ones invoking Comptonization of ambient radiation.

Sikora, Marek↗