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At least 955 records · Page 53
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Microwave power transmission system studies. Volume 2: Introduction, organization, environmental and spaceborne systems analyses

Introduction, organization, analyses, conclusions, and recommendations for each of the spaceborne subsystems are presented. Environmental effects - propagation analyses are presented with appendices covering radio wave diffraction by random ionospheric irregularities, self-focusing plasma instabilities and ohmic heating of the D-region. Analyses of dc to rf conversion subsystems and system considerations for both the amplitron and the klystron are included with appendices for the klystron covering cavity circuit calculations, output power of the solenoid-focused klystron, thermal control system, and confined flow focusing of a relativistic beam. The photovoltaic power source characteristics are discussed as they apply to interfacing with the power distribution flow paths, magnetic field interaction, dc to rf converter protection, power distribution including estimates for the power budget, weights, and costs. Analyses for the transmitting antenna consider the aperture illumination and size, with associated efficiencies and ground power distributions. Analyses of subarray types and dimensions, attitude error, flatness, phase error, subarray layout, frequency tolerance, attenuation, waveguide dimensional tolerances, mechanical including thermal considerations are included. Implications associated with transportation, assembly and packaging, attitude control and alignment are discussed. The phase front control subsystem, including both ground based pilot signal driven adaptive and ground command approaches with their associated phase errors, are analyzed.

Maynard, O. E.↗
NASA NTRS1981

Mechanisms for intense relativistic electron precipitation

An analysis of data gathered over a period of 14 months by the S3-3 satellite has revealed the detection of 313 relativistic electron precipitation events with isotropic flux over the upward-looking hemisphere, of which the majority occur at night in a narrow latitudinal zone which is embedded within a broader region of intense energetic ion precipitation. Three classes of precipitation are found to be associated with strong, diffusion resonant scattering due to known magnetospheric plasma waves. It is also found that intense electron energy deposition is a major source of middle-atmospheric, odd-hydrogen and odd-nitrogen molecules at sub-auroral latitudes, leading to an observable catalytic destruction of mesospheric ozone.

Thorne, R. M.↗
NASA NTRS2019

Deciphering the nature of the pulsar wind nebula CTB 87 with XMM-Newton

CTB 87 (G74.9+1.2) is an evolved supernova remnant (SNR) which hosts a peculiar pulsar wind nebula (PWN). The X-ray peak is offset from that observed in radio and lies towards the edge of the radio nebula. The putative pulsar, CXOU J201609.2+371110, was first resolved with Chandra and is surrounded by a compact and a more extended X-ray nebula. Here, we use a deep XMM–Newton observation to examine the morphology and evolutionary stage of the PWN and to search for thermal emission expected from a supernova shell or reverse shock interaction with supernova ejecta. We do not find evidence of thermal X-ray emission from the SNR and place an upper limit on the electron density of 0.05 per cu.cm for a plasma temperature kT ∼ 0.8 keV. The morphology and spectral properties are consistent with a ∼20-kyr-old relic PWN expanding into a stellar wind-blown bubble. We also present the first X-ray spectral index map from the PWN and show that we can reproduce its morphology by means of 2D axisymmetric relativistic hydrodynamical simulations.

B Guest↗
DOE OSTI2024

Laser-driven ion and electron acceleration from near-critical density gas targets: Towards high-repetition rate operation in the 1 PW, sub-100 fs laser interaction regime

Ion acceleration from gaseous targets driven by relativistic-intensity lasers was demonstrated as early as the late 1990s, yet most of the experiments conducted to date have involved picosecond-duration, Nd:glass lasers operating at low repetition rate. Here, we present measurements on the interaction of ultraintense ( ≈ 10 20 W cm − 2 , 1 PW ) , ultrashort ( ≈ 70 fs ) Ti:Sa laser pulses with near-critical ( ≈ 10 20 cm − 3 ) helium gas jets, a debris-free targetry with the potential for future compatibility with high ( ≈ 1 Hz ) repetition rate operation. We provide evidence of α particles being forward accelerated up to ≈ 2.7 − MeV energy with a total flux of ≈ 10 11 sr − 1 as integrated over > 0.1 − MeV energies and detected within a 0.5 − mrad solid angle. We also report on on-axis emission of relativistic electrons with an exponentially decaying spectrum characterized by a ≈ 10 − MeV slope, i.e., five times larger than the standard ponderomotive scaling. The total charge of these electrons with energy above 2 MeV is estimated to be of ≈ 1 nC , corresponding to ≈ 0.1 % of the laser drive energy. In addition, we observe the formation of a plasma channel, extending longitudinally across the gas density maximum and expanding radially with time. These results are well captured by large-scale particle-in-cell simulations, which reveal that the detected fast ions most likely originate from reflection off the rapidly expanding channel walls. The latter process is predicted to yield ion energies in the MeV range, which compare well with the measurements. Finally, direct laser acceleration is shown to be the dominant mechanism behind the observed electron energization. Published by the American Physical Society 2024

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1988

Fluctuation analysis of relativistic nucleus-nucleus collisions in emulsion chambers

An analytical technique was developed for identifying enhanced fluctuations in the angular distributions of secondary particles produced from relativistic nucleus-nucleus collisions. The method is applied under the assumption that the masses of the produced particles are small compared to their linear momenta. The importance of particles rests in the fact that enhanced fluctuations in the rapidity distributions is considered to be an experimental signal for the creation of the quark-gluon-plasma (QGP), a state of nuclear matter predicted from the quantum chromodynamics theory (QCD). In the approach, Monte Carlo simulations are employed that make use of a portable random member generator that allow the calculations to be performed on a desk-top computer. The method is illustrated with data taken from high altitude emulsion exposures and is immediately applicable to similar data from accelerator-based emulsion exposures.

Mcguire, Stephen C.↗
DOE OSTI2022

Relativistic Alfvén Waves Entering Charge-starvation in the Magnetospheres of Neutron Stars

Instabilities in a neutron star can generate Alfvén waves in its magnetosphere. Propagation along the curved magnetic field lines strongly shears the wave, boosting its electric current j A . We derive an analytic expression for the evolution of the wavevector k and the growth of j A . In the strongly sheared regime, j A may exceed the maximum current j0 that can be supported by the background e ± plasma. We investigate these charge-starved waves, first using a simplified two-fluid analytic model, then with first-principles kinetic simulations. We find that the Alfvén wave is able to propagate successfully even when κ ≡ j A /j 0 $\ll$ 1. It sustains j A by compressing and advecting the plasma along the magnetic field lines with an increasing Lorentz factor, γ ≳ κ 1/2 . The simulations show how plasma instabilities lead to gradual dissipation of the wave energy. Our results suggest that an extremely high charge-starvation parameter κ ≳ 10 4 may be required in order for this mechanism to power the observed fast radio bursts (FRBs) from SGR 1935+2154. However, cosmological FRBs with much higher luminosities are unlikely to be a result of charge-starvation.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2008

Chandra X-ray Spectroscopy of the Focused Wind In the Cygnus X-1 System I. The Non-Dip Spectrum in the Low/Hard State

We present analyses of a 50 ks observation of the supergiant X-ray binary system CygnusX-1/HDE226868 taken with the Chandra High Energy Transmission Grating Spectrometer (HETGS). CygX-1 was in its spectrally hard state and the observation was performed during superior conjunction of the black hole, allowing for the spectroscopic analysis of the accreted stellar wind along the line of sight. A significant part of the observation covers X-ray dips as commonly observed for CygX-1 at this orbital phase, however, here we only analyze the high count rate non-dip spectrum. The full 0.5-10 keV continuum can be described by a single model consisting of a disk, a narrow and a relativistically broadened Fe K line, and a power law component, which is consistent with simultaneous RXTE broad band data. We detect absorption edges from overabundant neutral O, Ne and Fe, and absorption line series from highly ionized ions and infer column densities and Doppler shifts. With emission lines of He-like Mg XI, we detect two plasma components with velocities and densities consistent with the base of the spherical wind and a focused wind. A simple simulation of the photoionization zone suggests that large parts of the spherical wind outside of the focused stream are completely ionized, which is consistent with the low velocities (<200 km/s) observed in the absorption lines, as the position of absorbers in a spherical wind at low projected velocity is well constrained. Our observations provide input for models that couple the wind activity of HDE 226868 to the properties of the accretion flow onto the black hole.

Hanke, Manfred↗
DOE OSTI2021

Using extended MHD to explore lasers as a trigger for x-pinches

X-pinches have been shown to be a source of extremely intense x-ray emissions useful for diagnosing plasma dynamics and imaging biological objects. The most striking feature of an x-pinch is the hotspot, the point source from where all the x rays come from. Unfortunately, the exact timing and location of the hotspot are still unpredictable. Since an x-pinch hotspot forms from instabilities (like an m = 0 mode), we will computationally explore whether we can use a high-power laser to control the timing and location of these instabilities. Our goal is to reduce the temporal and spatial jitter associated with the x-ray burst. Using an extended MHD (XMHD) code, we explore the non-relativistic instability generation using a current profile of a 250 kA linear transformer driver system and laser characteristics of SLAC's Matter in Extreme Conditions laboratory. Our results include both laser-penetration results using a boundary-defined electromagnetic (EM) wave and instability results from a power-deposition method.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1985

Energetic solar electrons in the interplanetary medium

Results are given of ISEE-3 measurements of energetic solar electrons extending down to 2 keV energy. Such measurements have provided a new perspective on energetic solar electrons in the interplanetary medium. Impulsive solar electron events are observed, on the average, several times a day near solar maximum, with about 40 percent detected only below about 15 keV. The electron energy spectra have a nearly power-law shape extending smoothly down to 2 keV, indicating that the origin of these events is high in the corona. In large solar flares which accelerate electrons and ions to relativistic energies, the electron spectrum appears to be modified by a second acceleration which results in a double power-law shape above about 10 keV with a break near 100 keV and flattening from about 10-100 keV. Solar type-III radio bursts are produced by the escaping 2-100 keV electrons through a beam-plasma instability.

Lin, R. P.↗
DOE OSTI2023

Three-dimensional Dynamics of Strongly Twisted Magnetar Magnetospheres: Kinking Flux Tubes and Global Eruptions

Abstract The origins of the various outbursts of hard X-rays from magnetars (highly magnetized neutron stars) are still unknown. We identify instabilities in relativistic magnetospheres that can explain a range of X-ray flare luminosities. Crustal surface motions can twist the magnetar magnetosphere by shifting the frozen-in footpoints of magnetic field lines in current-carrying flux bundles. Axisymmetric (2D) magnetospheres exhibit strong eruptive dynamics, i.e., catastrophic lateral instabilities triggered by a critical footpoint displacement of ψ crit ≳ π . In contrast, our new three-dimensional (3D) twist models with finite surface extension capture important non-axisymmetric dynamics of twisted force-free flux bundles in dipolar magnetospheres. Besides the well-established global eruption resulting (as in 2D) from lateral instabilities, such 3D structures can develop helical, kink-like dynamics, and dissipate energy locally (confined eruptions). Up to 25% of the induced twist energy is dissipated and available to power X-ray flares in powerful global eruptions, with most of our models showing an energy release in the range of the most common X-ray outbursts, ≲10 43 erg. Such events occur when significant energy builds up while deeply buried in the dipole magnetosphere. Less energetic outbursts likely precede powerful flares, due to intermittent instabilities and confined eruptions of a continuously twisting flux tube. Upon reaching a critical state, global eruptions produce the necessary Poynting-flux-dominated outflows required by models prescribing the fast radio burst production in the magnetar wind—for example, via relativistic magnetic reconnection or shocks.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

The Energetics of the Central Engine in the Powerful Quasar 3C 298

The compact steep-spectrum radio source 3C 298 (redshift of 1.44) has the largest 178 MHz luminosity in the Third Cambridge Revised Catalogue (3CR); its radio lobes are among the most luminous in the universe. The plasma state of the radio lobes is modeled with the aid of interferometric radio observations (in particular, the new Low Frequency Array observation and archival MERLIN data) and archival single-station data. It is estimated that the long-term time-averaged jet power required to fill these lobes with leptonic plasma is $\overline{Q}\,\approx 1.28\pm 0.51\times {10}^{47}\,\mathrm{erg}\,{{\rm{s}}}^{-1}$, rivaling the largest time-averaged jet powers from any quasar. Supporting this notion of extraordinary jet power is a 0.5–10 keV luminosity of ≈ 5.2 × 10 46 erg s –1 , comparable to luminous blazars, yet there is no other indication of strong relativistic beaming. We combine two new high signal-to-noise ratio optical spectroscopic observations from the Hobby-Eberly Telescope with archival Hubble Space Telescope, Two Micron All Sky Survey, and Galaxy Evolutionary Explorer data to compute a bolometric luminosity from the accretion flow of L bol ≈ 1.55 ± 0.15 × 10 47 erg s –1 . The ratio, $\overline{Q}/{L}_{\mathrm{bol}}\approx 1$, is the approximate upper limit for quasars. Characteristic of a large $\overline{Q}/{L}_{\mathrm{bol}}$, we find an extreme-ultraviolet (EUV) spectrum that is very steep (the "EUV deficit" of powerful radio quasars relative to radio-quiet quasars), and this weak ionizing continuum is likely a contributing factor to the relatively small equivalent widths of the broad emission lines in this quasar.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1995

ASCA and ROSAT observations of NRAO 140 and IX Persei

We report the results from observations of National Radio Astronomy Observatory (NRAO) 140 carried out in the X-ray band using ROSAT and Advanced Satellite for Cosmology and Astrophysics (ASCA) in 1992 and 1994. We find the source to be absorbed by an effective hydrogen column density of approximately 3 x 10(exp 21) atoms/sq cm during both epochs, consistent with the combined atomic and molecular column inferred from radio measurements along this line of sight through the Perseus cloud complex. We compare these results with previous X-ray absorption measurements and briefly comment upon the origin of the excess absorption which has been seen toward this source. We find the ASCA spectrum of NRAO 140 is well described by a power law of energy index alpha = 0.73 +/- 0.03 and also yields the tightest constraint to date on Fe K-shell emission, with 90% confidence upper limits of 38 and 31 eV for a narrow line at a rest frame energy of 6.4 and 6.7 keV respectively. This, along with a lack of hardening towards higher energies, suggests that either NRAO 140 is devoid of cold reprocessing material, the reprocessing material has a geometry in which the imprinted features are weak, and/or the X-ray emission is relativistically beamed towards us. We also report the detection of a serendipitous source in both the Advanced Satellite for Cosmology and Astrophysics Gas Imaging Spectrometer (ASCA GIS) and ROSAT fields of view. We identify this source as the binary star system IX Per and find its spectrum to be well fitted by a two-temperature Raymond-Smith plasma.

Turner, T. J.↗
NASA NTRS2009

The Invariant Twist of Magnetic Fields in the Relativistic Jets of Active Galactic Nuclei

The origin of cosmic magnetic (B) fields remains an open question. It is generally believed that very weak primordial B fields are amplified by dynamo processes, but it appears unlikely that the amplification proceeds fast enough to account for the fields presently observed in galaxies and galaxy clusters. In an alternative scenario, cosmic B fields are generated near the inner edges of accretion disks in Active Galactic Nuclei (AGNs) by azimuthal electric currents due to the difference between the plasma electron and ion velocities that arises when the electrons are retarded by interactions with photons. While dynamo processes show no preference for the polarity of the (presumably random) seed field that they amplify, this alternative mechanism uniquely relates the polarity of the poloidal B field to the angular velocity of the accretion disk, resulting in a unique direction for the toroidal B field induced by disk rotation. Observations of the toroidal fields of 29 AGN jets revealed by parsec-scale Faraday rotation measurements show a clear asymmetry that is consistent with this model, with the probability that this asymmetry came about by chance being less than 1 %. This lends support to the hypothesis that the Universe is seeded by B fields that are generated in AGN via this mechanism

Contopoulos, Ioannis↗
DOE OSTI2024

Covariant formulation of spinodal decomposition in rapidly expanding quark gluon plasma

Quantum chromodynamics (QCD) is expected to have a first order phase transition between the confined hadron gas and the deconfined quark gluon plasma at high baryon densities. This will result in phase boundary effects in the metastable and unstable regions. It is important to include these effects in phenomenological models of heavy ion collisions to identify experimental signatures of a phase transition. This requires building intuition on phase separation in rapidly expanding fluids. In this work we present the covariant equations of relativistic hydrodynamics with a phase boundary, provide prescriptions to extend the equation of state to metastable and unstable regions, and show the effects of spinodal separation in a Bjorken flow. Published by the American Physical Society 2024

Kapusta, Joseph I. (ORCID:0000000259429835)↗
NASA NTRS1992

X-ray flares from runaway pair production in active galactic nuclei

The hard X-ray spectrum of AGNs is nonthermal, probably arising from an electron-positron pair cascade, with some emission reflected off relatively cold matter. There has been interest in models on which protons are accelerated and create relativistic electrons on interaction with a local radiation field. It is shown here that a sufficient column density of protons can lead to runaway pair production: photons generated by the relativistic pairs are the targets for the protons to produce more pairs. This can produce X-ray fluxes with the characteristics observed in AGN. The model predicts the maximum ratio of luminosity to source size as well as their spectrum in the early phases. The same mechanism may also be able to create the knots of synchrotron-radiating pair plasma seen in sources such as 3C273.

Kirk, J. G.↗
DOE OSTI2026

Neutrinos as Dark Matter

Active neutrinos in standard cosmology were ruled out as a dark matter candidate in the 1980's. The reason is twofold: they are too light to account for the observed energy density of dark matter in the Universe, and their relativistic nature would spoil structure formation. In this note we suggest that an enhanced density of cold Standard Model active neutrinos today could behave effectively as dark matter, avoiding constraints from recombination and structure formation. Such an enhancement could be produced, for instance, by late-time decays of a light scalar field that is not in thermal equilibrium with the plasma. This mechanism is testable through the detection of the Cosmic Neutrino Background (C$\nu$B), which could have an average cosmological energy density a factor of $\sim 100-200$ times larger than expected in $\Lambda$CDM. The postulated light neutrinophilic scalar field may be observable, with Yukawa couplings in the range $y \sim 5 \times 10^{-16}-10^{-12}$. A scenario preferred by structure formation constraints is that the scalar is a Majoron, and the neutrinos have an inverted mass hierarchy.

Cline, James M. [McGill U.] (ORCID:000000017437419↗