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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Ionization Waves During the Subnanosecond Breakdown Initiated by Runaway Electrons in High-Pressure Nitrogen and Air

The experimental investigations of a subnanosecond breakdown initiated by runaway electrons in air and nitrogen at the pressures within 0.013–0.4 MPa are performed. The temporal development patterns of the discharge plasma glow in different regions of the discharge gap are registered with a fast photodiode, a four-channel ICCD-camera, and an ultrafast streak camera. It is shown that the breakdown occurs in the form of ionization waves propagating from the electrode with a small radius of curvature. It is found that a runaway electron beam behind the anode foil at the nitrogen and air pressure ~0.1 MPa is detected with the collector at the point of time corresponding to the maximum gap voltage.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Iso-oriented monolayer α-MoO 3 (010) films epitaxially grown on SrTiO 3 (001)

The ability to synthesis well-ordered two-dimensional materials under ultra-high vacuum and directly characterize them by other techniques in-situ can greatly advance our current understanding on their physical and chemical properties. In this paper, we demonstrate that iso-oriented α-MoO3 films with as low as single monolayer thickness can be reproducibly grown on SrTiO3(001) substrates by molecular beam epitaxy ( (010)MoO3 || (001)STO, [100]MoO3 || [100]STO or [010]STO) through a self-limiting process. While one in-plane lattice parameter of the MoO3 is very close to that of the SrTiO3 (aMoO3 = 3.96 Å, aSTO = 3.905 Å), the lattice mismatch along other direction is large (~5%, cMoO3 = 3.70 Å), which leads to relaxation as clearly observed from the splitting of streaks in reflection high-energy electron diffraction (RHEED) patterns. A narrow range in the growth temperature is found to be optimal for the growth of monolayer α-MoO3 films. Increasing deposition time will not lead to further increase in thickness, which is explained by a balance between deposition and thermal desorption due to the weak van der Waals force between α-MoO3 layers. Lowering growth temperature after the initial iso-oriented α-MoO3 monolayer leads to thicker α-MoO3(010) films with excellent crystallinity.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2018

Time-Resolved Thomson Scattering on Laboratory Plasma Jets

In this study, Thomson scattering measurements were performed on plasma jets created from a 15-μm-thick radial Al foil load on a 1-MA pulsed power machine. The laser used for these measurements has a maximum energy of 10 J at 526.5 nm. Using the full energy, however, significantly heats the 5x10¹⁸ cm⁻³ jet by inverse bremsstrahlung, creating a density bubble in the jet. To measure the evolving plasma parameters of this laser-heated jet, a streak camera was used to record the scattered spectrum, resulting in the sub-ns time-resolved Thomson scattering. Analysis of the streak camera image showed that the electron temperature of the jet was about 25 eV prior to the laser pulse. The laser then heated the plasma to 80-100 eV within about 2 ns. The electron temperature then stabilized for about 0.5 ns prior to falling at the end of the laser pulse. Jets made from a radial Ti foil showed more heating by the laser than the Al jets, going from 50 to over 150 eV, and heating was detected even when only 1 J of laser energy was used. Also, the ion-acoustic peaks in the scattered spectrum from the Ti jets were significantly narrower than those from Al jets, a result of several possible differences in the plasma created from these two materials.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Investigations of plasma evolution in Laser Ablation Z-Pinch Experiments using Time-Resolved Optical Spectroscopy

In this dissertation, investigations of the temporal evolution of magnetically driven plasmas are presented. These studies were carried at the Nevada Terawatt Facility using the Zebra pulsed-power accelerator to magnetically compress and confine a cylindrical plasma column. Important parameters needed to characterize these laboratory plasmas include magnetic field strength and orientation, as well as electron number density and temperature. To fully understand the characteristics of a plasma, accurate experimental measurement of these parameters is essential. To determine the electron temperature, the Boltzmann plot method was used. Simulated spectra from PrismSPECT were compared to experimental measurements in order to measure electron number density and temperature early in the pinched plasma formation. Simultaneously, Mach-Zehnder laser interferometry was used to provide complementary measurements of the electron number density. A novel method, streaked Zeeman-induced Magnetic Splitting optical spectroscopy, was developed to measure time- and space-resolved magnetic field strengths in these hot, dense plasmas. This technique has also been applied to diagnose the magnetic field strengths in laser ablation Z-pinch experiments, wherein a pulsed power driver pinches a laser ablated plume.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Temporal resolution limit estimation of x-ray streak cameras using a CsI photocathode

A Monte Carlo model is developed and implemented to calculate the characteristics of x-ray induced secondary electron (SE) emission from a CsI photocathode used in an x-ray streak camera. Time distributions of emitted SEs are investigated with an incident x-ray energy range from 1 to 30 keV and a CsI thickness range from 100 to 1000 nm. Simulation results indicate that SE time distribution curves have little dependence on the incident x-ray energy and CsI thickness. The calculated time dispersion within the CsI photocathode is about 70 fs, which should be the temporal resolution limit of x-ray streak cameras that use CsI as the photocathode material.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

Single shot time stamping of ultrabright radio frequency compressed electron pulses

We demonstrate a method of time-stamping Radio Frequency compressed electron bunches for Ultrafast Electron Diffraction experiments in the sub-pC regime. We use an in-situ ultra-stable photo-triggered streak camera to directly track the time of arrival of each electron pulse and correct for the timing jitter in the radio frequency synchronization. We show that we can correct for timing jitter down to 30 fs root-mean-square with minimal distortion to the diffraction patterns, and performed a proof-of-principle experiment by measuring the ultrafast electron-phonon coupling dynamics of silicon.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Attosecond time–energy structure of X-ray free-electron laser pulses

Here, the time–energy information of ultrashort X-ray free-electron laser pulses generated by the Linac Coherent Light Source is measured with attosecond resolution via angular streaking of neon 1s photoelectrons. The X-ray pulses promote electrons from the neon core level into an ionization continuum, where they are dressed with the electric field of a circularly polarized infrared laser. This induces characteristic modulations of the resulting photoelectron energy and angular distribution. From these modulations we recover the single-shot attosecond intensity structure and chirp of arbitrary X-ray pulses based on self-amplified spontaneous emission, which have eluded direct measurement so far. We characterize individual attosecond pulses, including their instantaneous frequency, and identify double pulses with well-defined delays and spectral properties, thus paving the way for X-ray pump/X-ray probe attosecond free-electron laser science.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

Experimental demonstration of attosecond pump–probe spectroscopy with an X-ray free-electron laser

Pump–probe experiments with subfemtosecond resolution are the key to understanding electronic dynamics in quantum systems. Here we demonstrate the generation and control of subfemtosecond pulse pairs from a two-colour X-ray free-electron laser. By measuring the delay between the two pulses with an angular streaking diagnostic, we characterize the group velocity of the X-ray free-electron laser and show control of the pulse delay down to 270as. Here, we confirm the application of this technique to a pump–probe measurement in core-ionized para-aminophenol. These results reveal the ability to perform pump–probe experiments with subfemtosecond resolution and atomic site specificity.

47 OTHER INSTRUMENTATION↗
DOE OSTI2016

Recording Vavilov – Cherenkov radiation in a linear accelerator using a picosecond streak camera

Using a picosecond image converter camera with a linear sweep (PS-1/S1 streak camera developed at GPI RAS, Moscow), we have measured temporal parameters of Vavilov – Cherenkov radiation pulses. The radiation was generated by relativistic electrons passing through a quartz cone mounted on the axis of a vacuum chamber of a linear accelerator, which is a part of the VEPP-5 injection complex at the Budker Institute of Nuclear Physics, Siberian Branch of the Russian Academy of Sciences (BINP SB RAS, Novosibirsk). The data obtained in these experiments provide an insight into the processes of formation of electron bunches and their ‘quality’ in a linear accelerator prior to injection of electrons into the accumulator-cooler. A conclusion is made regarding the advisability of streak camera application in tuning the linear accelerators for optimisation of electron bunch parameters. (Vavilov – Cherenkov radiation)

43 PARTICLE ACCELERATORS↗
DOE OSTI2016

Wakefields of a Beam near a Single Plate in a Flat Dechirper

At linac-based, X-ray free electron lasers (FELs), there is interest in streaking the beam by inducing the transverse wakes in a flat dechirper, by passing the beam near to one of its two jaws. For LCLS-II - as has already been done for LCLS-I - this way of using the dechirper will e.g. facilitate two-color and fresh slice schemes of running the FEL. With the beam a distance from the near wall of say b ~ 0.25 mm and from the far wall by ≳ 5 mm, the second wall will no longer affect the results. The physics will be quite different from the two plate case: with two plates the impedance has a resonance spike whose frequency depends on the plate separation 2a; in the single plate case this parameter no longer exists. Formulas for the longitudinal, dipole, and quadrupole wakes for a beam off-axis between two dechirper plates, valid for the range of bunch lengths of interest in an X-ray FEL, are given in reference 3. By taking the proper limit, we can obtain the corresponding wakes for a beam close to one dechirper plate and far from the other. This is the task we perform in this note.

43 PARTICLE ACCELERATORS↗
DOE OSTI2017

Modelling K shell spectra from short pulse heated buried microdot targets

K shell X-ray emission measurements have been used to diagnose plasma conditions in short-pulse heated buried microdot targets on the Orion high power laser. These experiments have been used to validate simulations of short pulse laser-solid interaction that combine hybrid PIC modelling of the laser absorption with radiation-hydrodynamics simulations including an electron transport model. Comparison of these simulations with streaked K shell spectroscopy show the importance of including radial gradients in fitting the spectra. An example is presented of the emission of sulphur from a 50 µm diameter microdot sample buried in a plastic foil. Previously agreement between simulation and experiment was obtained only by treating the absorbed energy, electron temperature and beam divergence as fitting parameters. Overall, the good agreement obtained in this work used the measured laser energy and laser pulse length and calculated the laser-solid target interaction from first principles.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Time-Resolved Electron-Bunch Diagnostics Using Transverse Wakefields

The development of future free electron lasers (FELs) requires reliable time-resolved measurement of variable ultra-short electron-bunchs characteristics. A possible technique is to streak the bunch in the transverse direction by means of time-dependent external fields. In this paper we explore the possible use of self-generated electromagnetic fields *. A passive deflector, consisting of a dielectric-lined waveguide, is used to produce wakefields that impart a time-dependent transverse kick to the relativistic electron bunch passing off-axis. We investigate the technique and its performances and explore its possible application at the Fermilab Accelerator Science & Technology (FAST) facility.

43 PARTICLE ACCELERATORS↗
NASA NTRS1980

Circular Scan Streak Tube Development

A streak tube having circular scan was designed, built and tested. Continuous circular scan, easily derived from out of phase sine waves applied to the conventional deflection plates, permits the timing of pulses traveling long baselines. At the tube's output a circular array of 720 elements is scanned to provide 30 to 40 picosecond resolution. Initial difficulties with electron bombarded silicon arrays were circumvented by using microchannel plates within the streak tube to provide the needed electronic amplification and digital sensitivity and coupling the 720 element arrays to the electron beam by means of a phosphor on a fiber optics. Two ceramic body tubes with S-20 photocathodes were tested and delivered.

Nevin, S.↗
DOE OSTI2014

Electron diffraction study of the sillenites Bi{sub 12}SiO{sub 20}, Bi{sub 25}FeO{sub 39} and Bi{sub 25}InO{sub 39}: Evidence of short-range ordering of oxygen-vacancies in the trivalent sillenites

We present an electron diffraction study of three sillenites, Bi{sub 12}SiO{sub 20}, Bi{sub 25}FeO{sub 39}, and Bi{sub 25}InO{sub 39} synthesized using the solid-state method. We explore a hypothesis, inspired by optical studies in the literature, that suggests that trivalent sillenites have additional disorder not present in the tetravalent compounds. Electron diffraction patterns of Bi{sub 25}FeO{sub 39} and Bi{sub 25}InO{sub 39} show streaks that confirm deviations from the ideal sillenite structure. Multi-slice simulations of electron-diffraction patterns are presented for different perturbations to the sillenite structure - partial substitution of the M site by Bi{sup 3+}, random and ordered oxygen-vacancies, and a frozen-phonon model. Although comparison of experimental data to simulations cannot be conclusive, we consider the streaks as evidence of short-range ordered oxygen-vacancies.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Improving the off-axis spatial resolution and dynamic range of the NIF X-ray streak cameras (invited)

We report simulations and experiments that demonstrate an increase in spatial resolution of the NIF core diagnostic x-ray streak cameras by at least a factor of two, especially off axis. A design was achieved by using a corrector electron optic to flatten the field curvature at the detector plane and corroborated by measurement. In addition, particle in cell simulations were performed to identify the regions in the streak camera that contribute the most to space charge blurring. These simulations provide a tool for convolving synthetic pre-shot spectra with the instrument function so signal levels can be set to maximize dynamic range for the relevant part of the streak record.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2017

Double-shot MeV electron diffraction and microscopy

Here in this paper, we study by numerical simulations a time-resolved MeV electron scattering mode where two consecutive electron pulses are used to capture the evolution of a material sample on 10 ps time scales. The two electron pulses are generated by illuminating a photocathode in a radiofrequency photogun by two short laser pulses with adjustable delay. A streak camera/deflecting cavity is used after the sample to project the two electron bunches on two well separated regions of the detector screen. By using sufficiently short pulses, the 2D spatial information from each snapshot can be preserved. This “double-shot” technique enables the efficient capture of irreversible dynamics in both diffraction and imaging modes. Finally, in this work, we demonstrate both modes in start-to-end simulations of the UCLA Pegasus MeV microscope column.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Time-resolved and multiple-angle Thomson scattering on gas-puff Z-Pinch plasmas at pinch time

A 526.5 nm Thomson scattering diagnostic laser enables probing of the plasma conditions of neon gas-puff z-pinch implosions with temporal resolution. Splitting the laser into two 2.5 J pulses, both 2.3 ns in duration and separated by 4 ns, allows observation of sub-nanosecond time-resolved spectra for a total time of 7 ns. Collection optics were set at 90° and 30° to the laser, observing the same on-axis scattering volume with a radial extent of 0.4 mm. The spectra from both angles were collected by using the same streak camera, using a coupling system that allowed us to obtain temporal, spectral, and angular resolution in the same image. By comparing the ion-acoustic spectra from the two angles, we determined electron temperature and a range of possible electron densities. Measurements made in the 1-3 ns period before pinch time show best fit (determined by a least-squares method) electron densities of around 2 × 10 19 cm -3 , increasing to 1.5 × 10 20 cm -3 in the 3 ns following the start of the x-ray burst (t = 0 ns) from the pinch. The electron temperature increases from 300 eV to 500 eV at t = 0 ns before decreasing to below 300 eV after pinch time. With the present parameters (probe beam, collection angles, and electron temperature and density), this diagnostic method is too insensitive to electron density to provide more than a constraint on that parameter. Plasma regimes in which this technique could determine electron density with some precision are calculated.

47 OTHER INSTRUMENTATION↗
DOE OSTI2018

Time-Resolved Thomson Scattering on Gas-Puff Z-Pinch Plasmas at Pinch Time

The conditions and dynamics of neon gas puff Z-pinch plasmas at pinch time are studied on a pulsed power generator with a current rise time of approximately 200-ns and 0.9-mA peak current. Radial tailoring of the gas puff massdensity profile using a triple-nozzle coaxial valve (two annular gas liners and a central jet) allows production of both more stable and less stable (with regard to the magneto-Rayleigh– Taylor instability) Z-pinch implosions. A 526.5-nm, 10-J Thomson scattering diagnostic laser enables probing of the flow dynamics and plasma conditions of these implosions with both spatial and temporal resolutions. The 2.2-ns laser pulse scatters from the plasma electrons and is carried by one optical fiber to a visible light streak camera, and by a bundle of optical fibers to a time-gated camera, both after spectral dispersion by 750-mm spectrometers. The streak camera, with a 10-ns full streak time, provides subnanosecond resolution of the evolution of the pinch plasma parameters through stagnation. The timegated camera provides spatially resolved spectra (across a field of view of 6.1 mm) at the same time as the streak. Scattering spectra suggest that temperatures are high at stagnation, with the ion temperature as much as three times higher than the electron temperature. Furthermore, we consider the possibility of nonthermal explanations for the broad scattering spectra and high effective ion temperature, including collisionality, implosion velocity distributions (velocity gradients), and small-scale hydrodynamic motion.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗