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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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2002

Synchrotron and Synchrotron Self-Compton Spectral Signatures and Blazar Emission Models

We find that energy losses due to synchrotron self-Compton (BBC) emission in Blazar jets can produce distinctive signatures in the time-averaged synchrotron and SSC spectra of these objects. For a fairly broad range of particle injection distributions, SSC-loss-dominated synchrotron emission exhibits a spectral dependence Fv approximately v (exp -3/2). The presence or absence of this dependence in the optical and ultraviolet spectra of flat-spectrum radio quasars such as PC 279 and in the soft X-ray spectra of high-frequency BL Lac objects such as Mark 501 gives a robust measure of the importance of SSC losses. Furthermore, for partially cooled particle distributions, spectral breaks of varying sizes can appear in the synchrotron and SSC spectra and will be related to the spectral indices of the emission below the break. These spectral signatures place constraints on the size scale and the nonthermal particle content of the emitting plasma, as well as the observer orientation relative to the jet axis.

Chiang, James↗
DOE OSTI2022

A laser powder bed fusion system for operando synchrotron x-ray imaging and correlative diagnostic experiments at the Stanford Synchrotron Radiation Lightsource

Laser powder bed fusion (LPBF) is a highly dynamic multi-physics process used for the additive manufacturing (AM) of metal components. Improving process understanding and validating predictive computational models require high-fidelity diagnostics capable of capturing data in challenging environments. Synchrotron x-ray techniques play a vital role in the validation process as they are the only in situ diagnostic capable of imaging sub-surface melt pool dynamics and microstructure evolution during LPBF-AM. In this article, a laboratory scale system designed to mimic LPBF process conditions while operating at a synchrotron facility is described. The system is implemented with process accurate atmospheric conditions, including an air knife for active vapor plume removal. Significantly, the chamber also incorporates a diagnostic sensor suite that monitors emitted optical, acoustic, and electronic signals during laser processing with coincident x-ray imaging. The addition of the sensor suite enables validation of these industrially compatible single point sensors by detecting pore formation and spatter events and directly correlating the events with changes in the detected signal. Experiments in the Ti–6Al–4V alloy performed at the Stanford Synchrotron Radiation Lightsource using the system are detailed with sufficient sampling rates to probe melt pool dynamics. X-ray imaging captures melt pool dynamics at frame rates of 20 kHz with a 2 µm pixel resolution, and the coincident diagnostic sensor data are recorded at 470 kHz. Furthermore, this work shows that the current system enables the in situ detection of defects during the LPBF process and permits direct correlation of diagnostic signatures at the exact time of defect formation.

36 MATERIALS SCIENCE↗
DOE OSTI2022

GeoSoilEnviroCARS (Sector 13) at the Advanced Photon Source: a comprehensive synchrotron radiation facility for Earth science research at ambient and extreme conditions

GeoSoilEnviroCARS (GSECARS) is a comprehensive analytical laboratory for Earth and environmental science research using X-ray beams from the Advanced Photon Source, Argonne National Laboratory. State-of-the-art instruments are available for (1) high-pressure/high- or low-temperature diffraction, total scattering, and spectroscopy (Brillouin, Raman, and VIS-IR) using the laser heated diamond anvil cell (DAC); (2) high-pressure/high-temperature diffraction, scattering, and imaging as well as acoustic emission (AE) and ultrasonics using the large-volume press (LVP); (3) powder, single crystal, and surface/interface diffraction; (4) X-ray absorption fine structure spectroscopy; (5) X-ray fluorescence microprobe analysis; and (6) microtomography. As shown here, experiments are facilitated by senior level staff who collaborate on all aspects of the analytical work including experiment design, sample preparation, data collection, data interpretation, and publication preparation. Both technical and scientific synergies occur as a result of the intimate association of the various techniques and scientists experienced in the applications of synchrotron radiation to Earth, environmental, and planetary science problems. The facility includes state-of-the-art instrumentation designed and built in-house, including custom X-ray optics, online and offline laser-based systems, specialized sample environments and positioning systems, as well as pixel-array and multi-crystal energy dispersive X-ray detectors, which are available to be shared among the experimental stations.

36 MATERIALS SCIENCE↗
DOE OSTI2021

In situ synchrotron diffraction of pressure-induced phase transition in DyPO 4 under variable hydrostaticity

In situ synchrotron x-ray diffraction was conducted on polycrystalline DyPO 4 to elucidate the details of the pressure-induced transition from the xenotime polymorph to the monazite polymorph. We used three different pressure-transmitting media (neon, a 16:3:1 methanol-ethanol-water mixture, and potassium chloride) to investigate the effect of hydrostaticity on the phase behavior. Specifically, our data clearly show a hydrostatic onset pressure of the xenotime-monazite transition of 9.1 GPa, considerably lower than the 15.3 GPa previously determined by Raman spectroscopy. Based on (quasi)hydrostatic data taken in a neon environment, third-order Birch-Murnaghan equation-of-state fits give a xenotime bulk modulus of 144 GPa and a monazite bulk modulus of 180 GPa (both with pressure derivatives of 4.0). Structural data and axial compressibilities show that DyPO 4 is sensitive to shear and has an anisotropic response to pressure. More highly deviatoric conditions cause the onset of the transition to shift to pressures at least as low as 7.0 GPa. We attribute early transition to shear-induced distortion of the PO4 tetrahedra. Finally, our characterization of the high-pressure behavior of DyPO 4 under variable hydrostaticity is critical for advancing rare earth orthophosphate fiber coating applications in ceramic matrix composites and may inform future tailoring of phase composition for controlled shear and pressure applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Synchrotron self-Compton radiation from magnetically dominated turbulent plasmas in relativistic jets

ABSTRACT Relativistic jets launched by rotating black holes are powerful emitters of non-thermal radiation. Extraction of the rotational energy via electromagnetic stresses produces magnetically dominated jets, which may become turbulent. Studies of magnetically dominated plasma turbulence from first principles show that most of the accelerated particles have small pitch angles, i.e. the particle velocity is nearly aligned with the local magnetic field. We examine synchrotron self-Compton radiation from anisotropic particles in the fast cooling regime. The small pitch angles reduce the synchrotron cooling rate and promote the role of inverse Compton (IC) cooling, which can occur in two different regimes. In the Thomson regime, both synchrotron and IC components have soft spectra, νFν ∝ ν1/2. In the Klein–Nishina regime, synchrotron radiation has a hard spectrum, typically νFν ∝ ν, over a broad range of frequencies. Our results have implications for the modelling of BL Lacertae objects (BL Lacs) and gamma-ray bursts (GRBs). BL Lacs produce soft synchrotron and IC spectra, as expected when Klein–Nishina effects are minor. The observed synchrotron and IC luminosities are typically comparable, which indicates a moderate anisotropy with pitch angles θ ≳ 0.1. Rare orphan gamma-ray flares may be produced when θ ≪ 0.1. The hard spectra of GRBs may be consistent with synchrotron radiation when the emitting particles are IC cooling in the Klein–Nishina regime, as expected for pitch angles θ ∼ 0.1. Blazar and GRB spectra can be explained by turbulent jets with a similar electron plasma magnetization parameter, σe ∼ 104, which for electron–proton plasmas corresponds to an overall magnetization σ = (me/mp)σe ∼ 10.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2010

Steady X-Ray Synchrotron Emission in the Northeastern Limb of SN 1006

We investigate time variations and detailed spatial structures of X-ray synchrotron emission in the northeastern limb of SN 1006, using two Chandra observations taken in 2000 and 2008. We extract spectra from a number of small ([approx]10'') regions. After taking account of proper motion and isolating the synchrotron from the thermal emission, we study time variations in the synchrotron emission in the small regions. We find that there are no regions showing strong flux variations. Our analysis shows an apparent flux decline in the overall synchrotron flux of [approx]4% at high energies, but we suspect that this is mostly a calibration effect, and that flux is actually constant to [approx]1%. This is much less than the variation found in other remnants where it was used to infer magnetic-field strengths up to 1 mG. We attribute the lack of variability to the smoothness of the synchrotron morphology, in contrast to the small-scale knots found to be variable in other remnants. The smoothness is to be expected for a Type Ia remnant encountering uniform material. Finally, we find a spatial correlation between the flux and the cutoff frequency in synchrotron emission. The simplest interpretation is that the cutoff frequency depends on the magnetic-field strength. This would require that the maximum energy of accelerated electrons is not limited by synchrotron losses, but by some other effect. Alternatively, the rate of particle injection and acceleration may vary due to some effect not yet accounted for, such as a dependence on shock obliquity.

Katsuda, Satoru↗
NASA NTRS2015

Synchrotron Self-Compton Emission from the Crab and Other Pulsars

Results of a simulation of synchrotron-self Compton (SSC) emission from a rotation-powered pulsar are presented. The radiating particles are assumed to be both accelerated primary electrons and a spectrum of electron-positron pairs produced in cascades near the polar cap. They follow trajectories in a slot gap using 3D force-free magnetic field geometry, gaining pitch angles through resonant cyclotron absorption of radio photons, radiating and scattering synchrotron emission at high altitudes out to and beyond the light cylinder. Full angular dependence of the synchrotron photon density is simulated in the scattering and all processes are treated in the inertial observer frame. Spectra for the Crab and Vela pulsars as well as two energetic millisecond pulsars, B1821-24 and B1937+21 are simulated using this model. The simulation of the Crab pulsar radiation can reproduce both the flux level and the shape of the observed optical to hard X-ray emission assuming a pair multiplicity of M+ = 3x10(exp 5), as well as the very-high- energy emission above 50 GeV detected by MAGIC and VERITAS, with both the synchrotron and SSC components reflecting the shape of the pair spectrum. Simulations of Vela, B1821-24 and B1937+21, for M+ up to 10(exp 5), do not produce pair SSC emission that is detectable by current telescopes, indicating that only Crab-like pulsars produce significant SSC components. The pair synchrotron emission matches the observed X-ray spectrum of the millisecond pulsars and the predicted peak of this emission at 1-10 MeV would be detectable with planned Compton telescopes.

Self-Compton↗
NASA NTRS1979

Compton and synchrotron processes in spherically-symmetric non-thermal sources

A framework is developed for the accurate calculation of Compton and synchrotron processes in a special class of spherically-symmetric sources. The models considered take a distribution in magnetic field values and high-energy electron density that varies smoothly from central values to values at the outer boundary of the source. Further, the assumption is made that the magnetic field has local disorder (isotropy) and the high-energy electron distribution has local isotropy. Then, in terms of parameters of the source, the synchrotron brightness distribution, total synchrotron flux, Compton-synchrotron flux, and synchrotron self-absorption turnover are all computed accurately. Results are given with a view toward application to the analysis of compact non-thermal sources.

Gould, R. J.↗
NASA NTRS1990

Synchrotron radiation - Applications in the earth sciences

Synchrotron-radiation sources and their characteristics are overviewed along with recent synchrotron-based research on earth materials and future earth-science applications utilizing the next generation of synchrotron-radiation sources presently under construction. Focus is placed on X-ray scattering studies of earth materials (crystalline and noncrystalline) under ambient conditions, diffraction studies of earth materials at high pressures and/or temperatures, spectroscopic studies, primarily X-ray absorption spectroscopy, and spatially resolved X-ray fluorescence studies of compositional variations in earth materials. It is noted that other synchrotron-based methods, such as X-ray tomography and topography may become important in characterizing earth materials, while soft X-ray/vacuum ultraviolet radiation from synchrotron sources can be applied to problems involving the structural environments of low-atomic-number elements and the characterization of surface reactions of minerals with liquids and gases.

Bassett, W. A.↗
DOE OSTI2024

A Self Consistent 2D Simulation of Coherent Synchrotron Radiation Effects on Beam Dynamics

An increasing interest in high quality and high current electron beams necessitates a thorough understanding and prediction of coherent synchrotron radiation effects. The self-interaction of charged particles in a beam undergoing synchrotron motion is a physically significant process that is all too often computationally intensive with very little analytical results to rely on for the general case. The coherent spectrum of this interaction is of utmost importance to the design of free electron lasers (FELs) and an accurate assessment is imperative for their design. This work presents a novel implementation to the numerical simulation of charged particle beams. The simulation is a self-consistent approach including the self-fields generated by the beam of which coherent synchrotron radiation effects are of primary interest. A particle-in-cell model is used where a planar beam sampled by point particles is deposited on an encompassing grid at each timestep. The electromagnetic fields are calculated on the grid using the retarded potentials according to causality. The electromagnetic forces from the fields are interpolated on each particle which in turn advance in time. The simulation is benchmarked against well-established results for coherent synchrotron radiation effects. In addition, studies are provided that show the convergence of simulation results for increasing resolution. A study into the transverse beam size effects on beam dynamics is performed as well as a proof of concept where the simulation is used by a genetic algorithm to optimize the design parameters of a beam lattice. The results of these studies in tandem verify the efficacy of the simulation for its practical use in accelerator design or the study of synchrotron radiation effects

Duffin, Dallan [Old Dominion Univ., Norfolk, VA (U↗
DOE OSTI2024

Electron tail suppression and effective collisionality due to synchrotron emission and absorption in mildly relativistic plasmas

Synchrotron radiation losses are a significant cause of concern for high-temperature aneutronic fusion reactions such as proton–Boron 11. The fact that radiation losses occur primarily in the high-energy tail, where the radiation itself has a substantial impact on the electron distribution, necessitates a self-consistent approach to modeling the diffusion and drag induced by synchrotron absorption and emission. Furthermore, an accurate model must account for the fact that the radiation emission spectrum is momentum-dependent, and the plasma opacity is frequency-dependent. Here, we present a simple Fokker–Planck operator, built on a newly solved-for blackbody synchrotron diffusion operator, which captures all relevant features of the synchrotron radiation. Focusing on magnetic mirror fusion plasmas, we show that significant suppression of the electron distribution occurs for relativistic values of the perpendicular electron momentum, which therefore emit much less radiation than predicted under the assumption of a Maxwell–Jüttner distribution.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗