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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Study of micro-pinches in wire-array Z pinches

Bright and hot areas with a high plasma density and temperature are observed in all kinds of Z pinches. We studied bright radiating spots produced by micro-pinches in cylindrical and planar wire-arrays at the 1 MA Zebra pulsed power generator using an x-ray streak camera synchronized with laser diagnostics, x-ray time-gated pinhole camera, and spectroscopy. Hot spots with extremely dense and relatively hot plasma arise during the collapse of the micro-pinches. These hot spots radiate a continuum spectrum with energy >2.5 keV. Typical micro-pinches in Al wire arrays generate x-ray bursts with durations of 0.4–1 ns in the soft x-ray range and 0.1–0.4 ns in the keV range. UV two-frame shadowgraphy shows spatial correlation of hot spots with the collapse and explosion of micro-pinches. Micro-pinches typically occur at the necks of the Z pinch, but can demonstrate a variety of parameters and different dynamics. An analysis of x-ray streak images shows that micro-pinches can generate >20% of the x-ray energy in some types of wire-array Z pinches.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2010

Electron beam-based sources of ultrashort x-ray pulses.

A review of various methods for generation of ultrashort x-ray pulses using relativistic electron beam from conventional accelerators is presented. Both spontaneous and coherent emission of electrons is considered. The importance of the time-resolved studies of matter at picosecond (ps), femtosecond (fs), and atttosecond (as) time scales using x-rays has been widely recognized including by award of a Nobel Prize in 1999 [Zewa]. Extensive reviews of scientific drivers can be found in [BES1, BES2, BES3, Lawr, Whit]. Several laser-based techniques have been used to generate ultrashort x-ray pulses including laser-driven plasmas [Murn, Alte, Risc, Rose, Zamp], high-order harmonic generation [Schn, Rund, Wang, Arpi], and laser-driven anode sources [Ande]. In addition, ultrafast streak-camera detectors have been applied at synchrotron sources to achieve temporal resolution on the picosecond time scale [Wulf, Lind1]. In this paper, we focus on a different group of techniques that are based on the use of the relativistic electron beam produced in conventional accelerators. In the first part we review several techniques that utilize spontaneous emission of electrons and show how solitary sub-ps x-ray pulses can be obtained at existing storage ring based synchrotron light sources and linacs. In the second part we consider coherent emission of electrons in the free-electron lasers (FELs) and review several techniques for a generation of solitary sub-fs x-ray pulses. Remarkably, the x-ray pulses that can be obtained with the FELs are not only significantly shorter than the ones considered in Part 1, but also carry more photons per pulse by many orders of magnitude.

43 PARTICLE ACCELERATORS↗
NASA NTRS1990

Plasma density enhancements created by the ionization of the Earth's upper atmosphere by artificial electron beams

Analytical calculations and experimental observations relating to the interaction with the Earth's upper atmosphere of electron beams emitted from low altitude spacecraft are presented. The problem is described by two coupled nonlinear differential equations in the up-going (along a magnetic field line) and down-going differential energy flux. The equations are solved numerically, using the MSIS atmospheric model and the IRI ionospheric model. The results form the model compare well with recent observations from the CHARGE 2 sounding rocket experiment. Two aspects of the beam-neutral atmosphere interaction are discussed. First, the limits on the electron beam current that can be emitted from a spacecraft without substantial spacecraft charging are investigated. This is important because the charging of the spacecraft to positive potentials limits the current and the escape energy of the beam electrons and thereby limits the ionization of the neutral atmosphere. As an example, we find from CHARGE 2 observations and from the model calculations that below about 180 km, secondary electrons generated through the ionization of the neutral atmosphere by 1 to 10 keV electron beams from sounding rockets, completely balance the beam current, thereby allowing the emission of very high beam currents. Second, the amount of plasma production in the beam-streak is discussed. Results are shown for selected values of the beam energy, spacecraft velocity, and spacecraft altitude.

Neubert, Torsten↗
NASA NTRS1993

Test results from LAGEOS-2 optical characterization using pulsed lasers

The Laser Geodynamic Satellite-2 (LAGEOS-2) has undergone extensive optical testing at NASA Goddard Space Flight Center during 1989. The techniques included measuring the far field diffraction pattern using cw and pulsed lasers. In the pulsed measurement technique, response of the satellite was studied by measuring the far-field diffraction pattern (FFDP) as a function of pulsewidth, wavelength, polarization, position in the FFDP, detector/processing techniques, and satellite orientation. The purpose of the pulsed laser testing was two-fold: (1) to characterize the satellite optical response with the detector and signal processing electronics currently used in most SLR stations using the portable laser ranging standard, and (2) to characterize the satellite response for various conditions using the highest bandwidth optical detector (streak camera) available for the next generation of satellite laser ranging (SLR) technology. The portable ranging standard employed multiple measurement devices and an optical calibration scheme to eliminate range-dependent and amplitude-dependent systematics. These precautions were taken to eliminate/minimize instrumental errors and provide maximum accuracy. For LAGEOS orbit (6000 Km), ground stations are located 34 to 38 Mu radians off the axis of the return signal from the satellite; therefore, an optical mask was used to restrict the field of view (FOV) of detection to this annular region of the FFDP. The two measurement techniques were implemented using an aperture sharing scheme and complemented each other by providing mutual verification.

Varghese, Thomas K.↗
DOE OSTI2015

Synthesis, crystal structure and photoluminescence of (Ba{sub 0.99}Eu{sub 0.01})Al{sub 3}Si{sub 4}N{sub 9}

Crystalline grains of (Ba{sub 0.99}Eu{sub 0.01})Al{sub 3}Si{sub 4}N{sub 9} were obtained from samples synthesized by heating mixtures of binary nitride powders at 2000 °C and 0.85 MPa of N{sub 2} gas. The fundamental reflections of electron diffraction (ED) and X-ray diffraction (XRD) measured for some grains could be indexed with orthorhombic cell parameters: a=10.028(2) Å, b=53.353(9) Å, and c=5.9215(11) Å. Streaks and diffuse lines along the b axis were observed in the ED and XRD photographs, indicating stacking faults. A statistical average structure was analyzed using the intensity data of the fundamental reflections with the space group Fdd2. Local structure models were presented based on the average structure. Similar streaks and diffuse lines with fundamental reflections indexed with monoclinic cell parameters: a=5.8376(4) Å, b=26.6895(12) Å, c=5.8393(3) Å, and β=118.8428(15)° were also observed in the XRD oscillation photographs of another grain. The mixture of the grains having the orthorhombic and monoclinic fundamental structures emitted blue–green light with a peak wavelength of 500 nm and a full width at half-maximum (FWHM) of 65 nm under 400 nm excitation. The emission intensity measured at 300 °C was 67.5% of the intensity measured at 25 °C. A broad excitation band ranged from about 260 nm to 475 nm with maximum intensity at around 290 nm, and 60% of the intensity was obtained by excitation at 400 nm. - Graphical abstract: Crystalline grains of (Ba{sub 0.99}Eu{sub 0.01})Al{sub 3}Si{sub 4}N{sub 9}, having orthorhombic and monoclinic fundamental structures and stacking faults, were obtained from samples synthesized at 2000 °C and 0.85 MPa of N{sub 2}. The grains emitted blue–green light with a peak wavelength of 500 nm and a full width at half-maximum (FWHM) of 65 nm under 400 nm excitation. The emission intensity measured at 300 °C was 67.5% of the intensity measured at 25 °C. - Highlights: • (Ba{sub 0.99}Eu{sub 0.01})Al{sub 3}Si{sub 4}N{sub 9} was synthesized at 2000 °C and 0.85 MPa of N{sub 2}. • Stacking faults of the crystal structure were shown by X-ray and electron diffraction. • Orthorhombic and monoclinic statistical average-structure models were presented. • Photoluminescence excitation and emission spectra were measured. • Thermal quenching of the emission intensities was characterized.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

EdgeAI: Machine learning via direct attached accelerator for streaming data processing at high shot rate x-ray free-electron lasers

We present a case for low batch-size inference with the potential for adaptive training of a lean encoder model. We do so in the context of a paradigmatic example of machine learning as applied in data acquisition at high data velocity scientific user facilities such as the Linac Coherent Light Source-II x-ray Free-Electron Laser. We discuss how a low-latency inference model operating at the data acquisition edge can capitalize on the naturally stochastic nature of such sources. We simulate the method of attosecond angular streaking to produce representative results whereby simulated input data reproduce high-resolution ground truth probability distributions. By minimizing the mean-squared error between the decoded output of the latent representation and the ground truth distributions, we ensure that the encoding layers and resulting latent representation maintains full fidelity for any downstream task, be it classification or regression. We present throughput results for data-parallel inference of various batch sizes, some with throughput exceeding 100 k images per second. We also show in situ training below 10 s per epoch for the full encoder–decoder model as would be relevant for streaming and adaptive real-time data production at our nation’s scientific light sources.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2022

Density reconstruction in convergent high-energy-density systems using x-ray radiography and Bayesian inference

X-ray radiography is a technique frequently used to diagnose convergent high-energy-density (HED) systems, such as inertial confinement fusion implosion, and provides unique information that is not available through self-emission measurements. In this work, we investigate the scope and limits of that information using a radiography simulation combined with the Bayesian inference workflow. The accuracy of density reconstruction from simulated radiographs of spherical implosions driven with 27 kJ laser energy is assessed, including the increase or decrease in accuracy due to the addition of Lagrangian marker layers, Poisson noise, and improved prior information. This work is the first to present the full uncertainty distributions inferred from radiography analysis in HED systems and demonstrates the importance of constructing the full posterior probability density, as opposed to a point estimate, due to the modal structure of the likelihood surface introduced by typical experimental noise sources. This general methodology can be used both for robust analysis of radiographic data and for an improved design of radiography experiments by modeling the full experimental system.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Spatiotemporal imaging of plasmonic fields near nanoparticles below the diffraction limit

Optically induced collective conduction-electron oscillations can generate intense plasmonic fields near metallic nanoparticles. Here, we suggest a method for reconstructing such nanoplasmonic fields with nanometer spatial and sub-femtosecond temporal resolution from streaked photoemission spectra. Applying this imaging scheme to Au nanospheres, we demonstrate the accurate spatiotemporal reconstruction of the plasmonic near-field distribution in comparison with the directly calculated plasmonic field.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2011

Characterization of high-current electron beam interaction with metal targets

The process of electron beam interaction with metal targets was characterized using electrical and optical diagnostics. Electron beams with current density of 5-10 A/cm{sup 2}, electron energy up to 120 keV, pulse duration up to 200 {mu}s, and cross-sectional area of 8-30 cm{sup 2} at the target surface were generated by GESA I and GESA II facilities. Streak imaging of the target surface specular reflectivity was used to determine the onset of melting and re-solidification of the target surface. Using time- and space-resolved schlieren imaging, the evolution of surface irregularities was studied. Experimental and numerical investigations of the neutral flow evaporated from the target surface showed a neutral density of {approx}10{sup 19} cm{sup -3} in the vicinity of the target and neutral velocities up to 2 x 10{sup 5} cm/s. Framing and streak images of visible light emission were used to study the temporal evolution of the target surface plasma and vapors. Time- and space-resolved spectroscopy was applied to determine the surface plasma density and temperature, which were found to be {approx}10{sup 14} cm{sup -3} and {<=}1 eV, respectively. Because of this small plasma density, electric fields in the plasma sheath are not sufficient to cause electrohydrodynamic instability of the liquid target surface. However, hydrodynamic instabilities due to the intense neutral flow observed in experimental and numerical studies are likely to be responsible for the growth of wavelike irregularities.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Experimental demonstration of novel beam characterization using a polarizable X-band transverse deflection structure

The PolariX TDS (Polarizable X-Band Transverse Deflection Structure) is an innovative TDS-design operating in the X-band frequency-range. The design gives full control of the streaking plane, which can be tuned in order to characterize the projections of the beam distribution onto arbitrary transverse axes. This novel feature opens up new opportunities for detailed characterization of the electron beam. In this paper we present first measurements of the Polarix TDS at the FLASHForward beamline at DESY, including three-dimensional reconstruction of the charge-density distribution of the bunch and slice emittance measurements in both transverse directions. The experimental results open the path toward novel and more extensive beam characterization in the direction of multi-dimensional-beam-phase-space reconstruction.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2012

Characteristic x-ray emission from undermines plasmas irradiated by ultra-intense lasers

Between FY09 and FY11 we have conducted more than a dozen three-week experimental campaigns at high-power laser facilities around the world to investigate laser-channeling through x-ray and optical imaging and the conversion from laser-energy to xrays. We have performed simultaneous two-wavelength x-ray imaging (K-alpha and He-alpha) to distinguish the hot-plasma region (hot-spot) from the laser-produced electrons (K-alpha). In addition, we have initiated a new collaboration with SNL and have performed first shots on the 100 TW beamlet chamber to commission a fast x-ray streak camera to be used to investigate the temporal evolution of our K-alpha sources. We also collaborated on campaigns at the Rutherford Appleton Laboratory (UK) and the LANL Trident laser to employ laser produced x-ray sources for Thomson scattering off dense matter.

60 APPLIED LIFE SCIENCES↗
NASA NTRS1980

Artificial aurora conjugate to a rocket-borne electron accelerator

An accelerator intended to send electron beams upward along an L = 1.24 magnetic field line was flown from a rocket launched from Kauai, Hawaii, on October 15, 1972. Though the intent was to produce several hundred observable auroral streaks in the Southern Hemisphere, imaging instruments operated there aboard jet aircraft detected only a single aurora. Produced by a 0.155-A beam of energy 22.8 keV, the aurora was of expected brightness and had a diameter (210 + or - 50 m) somewhat larger than expected and an altitude (top 116 + or - 2 km; bottom 92 + or - 2 km) higher than expected.

Davis, T. N.↗
DOE OSTI2015

SU-E-T-325: Dosimetric Impact Due to FlexiShield in Electronic Brachytherapy (eBx) of Breast IORT: A Phantom Study

Purpose: To evaluate dosimetric change of eBx plan due to Flexishield. Methods: To simulate a clinically difficult case (skin spacing < 1 cm and touching chest wall), prostheses breast tissue phantom overlaid Xoft spherical balloon applicator. To minimize significant metal streak artifact, megavoltage CT (MVCT) scan was acquired using helical TomoTherapy HiART. Two sets of MVCT images were taken with/without FlexiShield for 15 cases: 4 for small (3–4 cm), 4 for medium (4–5 cm) and 7 for large (5–6 cm) balloon. Total 30 MVCT scans were obtained with 50 % contrast to improve image contrast of balloon relative to breast tissue phantom. Balloon deformation was measured in anterior-posterior (AP) and lateral (LAT) dimensions in the middle of balloon. Skin spacing was also evaluated. Treatment plan was made based on each MVCT scan and two balloon surface doses (AP and LAT directions) and skin dose were compared between plans with/without FlexiShield. Results: The balloon was deformed due to pressure from both FlexiShield (skin side) and FlexiShield mini (chest wall side). Mean ± standard deviation (maximum) value was 1.5 ± 1.0 mm (3.3 mm) for AP compression and 0.4 ± 0.3 mm (1.1 mm) for LAT expansion. Balloon surface dose was increased by 1.8 ± 1.2 Gy (4.9 Gy) at AP point and decreased by 0.4 ± 0.4 Gy (1.3 Gy) at LAT point. Skin spacing was constantly reduced by 1.1 ± 0.8 mm (3 mm). Skin surface dose was increased by 1.5 ± 0.8 Gy (3.3 Gy) and its relative increase was 17.9 ± 9.3% (39.6%). Conclusion: FlexiShield deforms the balloon and reduces skin spacing, thereby resulting in higher dose in AP direction, lower dose in LAT direction, and elevated skin dose compared to the plan without FlexiShield. In the clinic, this balloon deformation and corresponding dose variation should be considered.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2021

Laser absorption measurements of electron density in nanosecond-scale atmospheric pressure pulsed plasmas

We report on time-resolved measurements of electron number density by continuous-wave laser absorption in a low-energy nanosecond-scale laser-produced spark in atmospheric pressure air. Laser absorption is a result of free-free and bound-free electron excitation, with the absorption coefficient modeled and evaluated using estimates of the time-variation in electron temperature and probe laser absorption path length. Plasma electron number densities are determined to be as high as n e = 7 x 10 19 cm -3 , and decay to 1/e of their peak values over a period of about 50 ns following plasma formation using a 20 mJ, 10 ns pulse width frequency-doubled Nd:YAG laser. The measured plasma densities at later times are shown to be in reasonable agreement with Stark broadening measurements of the 3s[ 5 S o ]-3p[ 5 P] electronic transition in atomic oxygen at 777 nm. This study provides support for the use of such continuous wave laser absorption for time resolved electron density measurements in low energy spark discharges in air, provided that an estimate of the electron temperature and laser path length can be made by accompanying diagnostics.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Toward streaked collective Thomson scattering measurements on an extreme ultraviolet plasma light source

Here we show through forward modeling calculations that streaked collective Thomson scattering measurements are feasible on laser-produced tin plasmas generated under conditions relevant for extreme ultraviolet lithography. Using a 532 nm probe laser beam, the feasibility of simultaneous measurements of electron plasma wave (EPW) and ion acoustic wave (IAW) spectra is investigated. Absolute photon counts for laser scattering off both waves are calculated. Probe laser electron heating and bremsstrahlung background radiation effects are accounted for. While a large spatiotemporal region can be successfully probed based on the IAW feature, only one measurement location can be accessed through the EPW as a result of the low signal to noise ratio. A portable/traveling tabletop system is proposed.

47 OTHER INSTRUMENTATION↗
DOE OSTI2011

A flexible apparatus for attosecond photoelectron spectroscopy of solids and surfaces

We describe an apparatus for attosecond photoelectron spectroscopy of solids and surfaces, which combines the generation of isolated attosecond extreme-ultraviolet (XUV) laser pulses by high harmonic generation in gases with time-resolved photoelectron detection and surface science techniques in an ultrahigh vacuum environment. This versatile setup provides isolated attosecond pulses with photon energies of up to 140 eV and few-cycle near infrared pulses for studying ultrafast electron dynamics in a large variety of surfaces and interfaces. The samples can be prepared and characterized on an atomic scale in a dedicated flexible surface science end station. The extensive possibilities offered by this apparatus are demonstrated by applying attosecond XUV pulses with a central photon energy of {approx}125 eV in an attosecond streaking experiment of a xenon multilayer grown on a Re(0001) substrate.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗