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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 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Coherent frequency combs from electrons colliding with a laser pulse

Highly coherent and powerful light sources capable of generating soft x-ray frequency combs are essential for high precision measurements and rigorous tests of fundamental physics. In this work, we derive the analytical conditions required for the emission of coherent radiation from an electron beam colliding with a laser pulse, modeled as a plane wave. These conditions are applied in a series of numerical simulations, where we show that a soft x-ray frequency comb can be produced if the electrons are regularly-spaced and sufficiently monoenergetic. High quality beams of this kind may be produced in the near future from laser-plasma interactions or linear accelerators. Furthermore, we highlight the advantageous role of employing few-cycle laser pulses in relaxing the stringent monoenergeticity requirements for coherent emission. The conditions derived here can also be used to optimize coherent emission in other frequency ranges, such as the terahertz domain.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Development of a Platform at the Matter in Extreme Conditions End Station for Characterization of Matter Heated by Intense Laser-Accelerated Protons

High intensity short-pulse lasers have made possible the generation of energetic proton beams, unlocking numerous applications in high energy density science. One such application is uniform and isochoric heating of materials to the warm dense matter (WDM) state. We have developed a new experimental platform to simultaneously create and probe warm dense matter at the Matter in Extreme Conditions (MEC) end station at the Linac Coherent Light Source (LCLS). The short pulse optical laser (delivering up to 1 J in 45 fs) and the ultra-bright LCLS x-ray laser with tunable frequency respectively deliver high power required to heat materials to WDM and precision-timed high-resolution x-rays to probe them. The laser-accelerated proton beam driven from a flat 1.5 μm Cu foil was first measured then directed to a secondary sample of Al or polypropylene, typically 300-400 μm away. The time evolution of the sample electron temperature was measured using streaked optical pyrometry, where we observed a peak temperature of 0.9 0.15 eV on the rear surface of an Al sample heated by the proton beam. Here, the simulations using the hybrid-PIC code LSP and the rad-hydro code HELIOS show that a measured proton beam can heat Al to approximately 4 eV and polypropylene to 1 eV if instead focused by a hemispherical Cu target. Through additional LSP simulations, we anticipate creating hotter warm dense matter states (20 eV) by increasing the laser energy to 10 J and keeping the other laser parameters fixed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Control of Large-Amplitude Combustion Oscillations Using Nanosecond Repetitively Pulsed Plasmas

This paper details the use of nanosecond repetitively pulsed discharges to attenuate combustion instabilities in a 14 kW swirl-stabilized methane/air combustor. The combustor exhibits large-amplitude pressure oscillations ranging from 1 to 4% of the mean pressure during which the flame exhibits bulk motion in each instability cycle, upstream and downstream, as revealed by high-speed chemiluminescence. Control is accomplished with an electrode comprising a pin anode at the centerline of the combustor, allowing a nanosecond spark to be generated in a region spanning close to the flame base, through the shear layers of the swirling flow and ending at the metallic combustor wall. The discharges are generated using 20 kV, 9 kHz pulses; and they correspond to about 120 W of mean power. This results in a suppression of the peak amplitude of the pressure oscillations by a factor of two to four, and 5 dB in the rms value. Using phase-averaged visualizations of the flame with and without plasma, we detail the sequence of flame motion in the course of the instability. With the plasma active, this reveals significant interactions between the flame and the plasma during the suppression. Finally, we present a state-space model of the thermoacoustic system, and we demonstrate open-loop control of the instabilities.

Engineering↗
DOE OSTI2023

X-ray Pump-Probe Measurements using a Laser-Plasma Accelerator (Final Report)

This project funded one graduate student, Mario Balcazar, to perform experiments on high power laser facilities to study the application of X-rays generated by laser wakefield accelerated electrons for advanced radiography, in particular X-ray phase contrast imaging of hydrodynamic shocks/instabilities. The work made use of the DOE’s LaserNetUS facilities. We performed dynamic phase-contrast X-ray imaging of the shock generated by a 200 ps duration laser pulse (E = 1 J, I = 10 15 Wcm –2 ) with a 30 µm diameter liquid target, with unprecedented spatio-temporal resolution. This includes multi-shock generation within the liquid jet and plasma instability formation. Innovative electron-beam radiography was used to probe the laser-plasma interplay finding evidence of bilateral heating of the water followed by strong electric field generation. These measurements help explain some of the discrepancies between simulation and experiment and pave the way to better plasma diagnostic systems in HED and ICF physics experiments. This work was performed in collaboration with researchers from Michigan, LLNL, LBL and Sandia National Laboratories, Queen’s University Belfast and Imperial College.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Femtosecond laser-induced formation of submicrometer spikes on a semiconductor substrate

The present invention generally provides semiconductor substrates having submicron-sized surface features generated by irradiating the surface with ultra short laser pulses. In one aspect a method of processing a semiconductor substrate is disclosed that includes placing at least a portion of a surface of the substrate in contact with a fluid, and exposing that surface portion to one or more femtosecond pulses so as to modify the topography of that portion. The modification can include, e.g., generating a plurality of submicron-sized spikes in an upper layer of the surface.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Development of a broadband hard x-ray radiography platform for pulsed-power experiments

In this article, we develop and demonstrate a broadband hard x-ray radiography platform at the Zebra Pulsed Power Laboratory that integrates point-projection radiography, bremsstrahlung measurements, and hard x-ray pinhole imaging, designed to diagnose current-driven, cylindrically compressed matter. Initial laser-pulsed-power coupled experiments revealed that intense background radiation generated during 1 MA Zebra current shots overwhelmed laser-produced hard x-rays, obscuring radiographic images. Using combined spectral and spatial diagnostics, we identify energetic electrons accelerated by return currents as the dominant source of background hard x-rays, with electron energies inferred to be 3–4 MeV based on Monte Carlo simulations, and demonstrate mitigation through modifications to the radiation shielding and return-current configuration. The diagnostic platform was validated using a wire-pinch hard x-ray source, allowing radiographs of static 1-mm-diameter aluminum wires to be obtained while simultaneously measuring x-ray source spectra and spatial emission distributions within a single shot. Measured wire transmission profiles were quantitatively reconstructed using radiation transport simulations that incorporate an experimentally inferred two-temperature exponential x-ray spectrum from bremsstrahlung signal analysis and spatially distributed emission sources identified by pinhole imaging. Agreement between measured and simulated transmission profiles demonstrates the validity of the radiographic and x-ray source characterization approach, establishing this diagnostic platform as a promising tool for diagnosing magnetically driven, high-density plasmas relevant to warm dense matter and inertial fusion energy research.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

X-ray multi-probe data acquisition: A novel technique for laser pump x-ray transient absorption spectroscopy

We report the development and implementation of a novel data acquisition (DAQ) technique for synchrotron-based laser pump X-ray Transient Absorption (XTA) spectroscopy, called X-ray Multi-Probe DAQ (XMP DAQ). This technique utilizes high performance analog to digital converters and home-built software to efficiently measure and process the XTA signal from all x-ray pulses between laser excitations. XMP DAQ generates a set of time resolved x-ray absorption spectra at thousands of different pump–probe time delays simultaneously. Two distinct XMP DAQ schemes are deployed to accommodate different synchrotron storage ring filling patterns. Current Integration (CI) DAQ is a quasi-analog technique that implements a fitting procedure to extract the time resolved absorption intensity from the averaged fluorescence detector response. The fitting procedure eliminates issues associated with small drifts in the voltage baseline and greatly enhances the accuracy of the technique. Photon Counting (PC) DAQ is a binary technique that uses a time resolved histogram to calculate the XTA spectrum. While PC DAQ is suited to measure XTA data with closely spaced x-ray pulses (~10 ns) and a low count rate (<1 detected photon/pulse), CI DAQ works best for widely spaced pulses (tens of ns or greater) with a high count rate (>1 detected photon/pulse). XMP DAQ produces a two-dimensional XTA dataset, enabling efficient quantitative analysis of photophysical and photochemical processes from the sub-nanosecond timescale to 100 μs and longer.

47 OTHER INSTRUMENTATION↗
DOE OSTI2023

Numerical investigation of gas-filled multipass cells in the enhanced dispersion regime for clean spectral broadening and pulse compression

We show via numerical simulations that the regime of enhanced frequency chirp can be achieved in gas-filled multipass cells. Our results demonstrate that there exists a region of pulse and cell parameters for which a broad and flat spectrum with a smooth parabolic-like phase can be generated. This spectrum is compatible with clean ultrashort pulses, whose secondary structures are always below the 0.5% of its peak intensity such that the energy ratio (the energy contained within the main peak of the pulse) is above 98%. This regime makes multipass cell post-compression one of the most versatile schemes to sculpt a clean intense ultrashort optical pulse.

Segundo Staels, V. W. (ORCID:0000000200056157)↗
DOE OSTI2020

Long-wavelength-infrared laser filamentation in solids in the near-single-cycle regime

We experimentally demonstrate long-wavelength-infrared (LWIR) femtosecond filamentation in solids. Systematic investigations of supercontinuum (SC) generation and self-compression of the LWIR pulses assisted by laser filamentation are performed in bulk KrS-5 and ZnSe, pumped by ∼ <#comment/> 145 f s , 9 µm, 10 µJ pulses from an optical parametric chirped-pulse amplifier operating at 10 kHz of repetition rate. Multi-octave SC spectra are demonstrated in both materials. While forming stable single filament, 1.5 cycle LWIR pulses with 4.5 µJ output pulse energy are produced via soliton-like self-compression in a 5 mm thick KrS-5. The experimental results quantitatively agree well with the numerical simulation based on the unidirectional pulse propagation equation. This work shows the experimental feasibility of high-energy, near-single-cycle LWIR light bullet generation in solids.

Qu, Shizhen↗
DOE OSTI2023

Study of The Compression of an Imploding Plasma and the Magnetic- Field Flux Using Advanced, Non-Intrusive, Spectroscopic Techniques

The main motivation of the project was to measure the magnetic field in pulsed power driven plasma compression using advanced non-intrusive spectroscopic techniques. The strength of the project is that it encompasses a combination of laboratory experiments with diagnostics for both the magnetic field and plasma properties and computational modeling. The following issues were addressed: (1) Plasma and magnetic field dynamics, (2) Field compression and diffusion, (3) Energy balance in the system, (4) Onset of instabilities, and (5) Correlation of the plasma and field evolutions with the initial conditions. The unique feature of the research was the use of advanced spectroscopy to measure both the magnetic field and various plasma properties in multiple locations using both side-on and end-on views, simultaneously. The experimental system allowed for imploding different gas mixtures (which facilitated local measurements) and for flexibility in modifying the initial conditions. Two current generators were used with significantly different current rise times (200 ns and 1.6 µs) but at the same current level of 400 kA. The slower pulsed power generator (at rise time 1.6 µs) was based at the Weizmann Institute of Science (WIS) and imploded plasma into which an axial magnetic field (up to 1 T) was initially embedded. The faster current rise time generator (at rise time 200 ns) based at University of California San Diego (UCSD) was used for plasma parameter studies initially, with collaborative efforts we successfully implemented the advanced spectroscopy techniques at UC San Diego. One graduate student (Nick Aybar) and a postdoctoral scholar (Maylis Dozeries) were trained. They both are based at the Lawrence Livermore National Laboratory now.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Enhanced cutoff energies for direct and rescattered strong-field photoelectron emission of plasmonic nanoparticles

Abstract The efficient generation, accurate detection, and detailed physical tracking of energetic electrons are of applied interest for high harmonics generation, electron-impact spectroscopy, and femtosecond time-resolved scanning tunneling microscopy. We here investigate the generation of photoelectrons (PEs) by exposing plasmonic nanostructures to intense laser pulses in the infrared (IR) spectral regime and analyze the sensitivity of PE spectra to competing elementary interactions for direct and rescattered photoemission pathways. Specifically, we measured and numerically simulated emitted PE momentum distributions from prototypical spherical gold nanoparticles (NPs) with diameters between 5 and 70 nm generated by short laser pulses with peak intensities of 8.0 × 10 12 and 1.2 × 10 13 W/cm 2 , demonstrating the shaping of PE spectra by the Coulomb repulsion between PEs, accumulating residual charges on the NP, and induced plasmonic electric fields. Compared to well-understood rescattering PE cutoff energies for strong-field photoemission from gaseous atomic targets (10× the ponderomotive energy), our measured and simulated PE spectra reveal a dramatic cutoff-energy increase of two orders of magnitude with a significantly higher contribution from direct photoemission. Our findings indicate that direct PEs reach up to 93 % of the rescattered electron cutoff energy, in contrast to 20 % for gaseous atoms, suggesting a novel scheme for the development of compact tunable tabletop electron sources.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Pulsed Magnet Power Systems at NSLS-II

The National Synchrotron Light Source - II (NSLS-II) is a 3 GeV X-ray user facility with 29 beamlines. The NSLS-II pulsed power system consists of an event generator for timely injection and extraction of beam in the transport line from linac to booster at 170 MeV, and from booster to storage ring at 3 GeV. We will discuss current pulsed power systems and the future upgrades/improvements on those systems.

43 PARTICLE ACCELERATORS↗
DOE OSTI2021

Seed source for plasma compression in the long wavelength infrared

Two color laser pulses are used to form an air plasma and generate broadband infrared radiation suitable as a seed for backward Raman amplification of CO 2 laser pulses. Broadband radiation in the atmospheric window from 8-14 microns is observed. The infrared radiation is characterized using a long wavelength grating spectrometer specially designed to accept an ionizing laser filament at its input plane. The LWIR yield is greatly enhanced by chirping the drive pulse. Unidirectional pulse propagation simulations suggest that this is due in part to the dependence of the nonlinear refractive index on the pulse

43 PARTICLE ACCELERATORS↗
DOE OSTI2023

Plasma flows during the ablation stage of an over-massed pulsed-power-driven exploding planar wire array

We characterize the plasma flows generated during the ablation stage of an over-massed exploding planar wire array, fielded on the COBRA pulsed-power facility (1 MA peak current, 250 ns rise time). The planar wire array is designed to provide a driving magnetic field (80–100 T) and current per wire distribution (about 60 kA), similar to that in a 10 MA cylindrical exploding wire array fielded on the Z machine. Over-massing the arrays enables continuous plasma ablation over the duration of the experiment without implosion. The requirement to over-mass on the Z machine necessitates wires with diameters of 75–100μm, which are thicker than wires usually fielded on wire array experiments. To test ablation with thicker wires, we perform a parametric study by varying the initial wire diameter between 33 and 100 μm. The largest wire diameter (100 μm) array exhibits early closure of the cathode-wire gap, while the gap remains open over the duration of the experiment for wire diameters between 33 and 75 μm. Laser plasma interferometry and time-gated extreme-ultraviolet (XUV) imaging are used to probe the plasma flows ablating from the wires. The plasma flows from the wires converge to generate a pinch, which appears as a fast-moving (V≈100kms−1) column of increased plasma density (n¯e≈2×1018cm−3) and strong XUV emission. Finally, we compare the results with three-dimensional resistive-magnetohydrodynamic (MHD) simulations performed using the code GORGON, the results of which reproduce the dynamics of the experiment reasonably well.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Filming movies of attosecond charge migration in single molecules with high harmonic spectroscopy

Electron migration in molecules is the progenitor of chemical reactions and biological functions after light-matter interaction. Following this ultrafast dynamics, however, has been an enduring endeavor. Here we demonstrate that, by using machine learning algorithm to analyze high-order harmonics generated by two-color laser pulses, we are able to retrieve the complex amplitudes and phases of harmonics of single fixed-in-space molecules. These complex dipoles enable us to construct movies of laser-driven electron migration after tunnel ionization of N 2 and CO 2 molecules at time steps of 50 attoseconds. Moreover, the angular dependence of the migration dynamics is fully resolved. By examining the movies, we observe that electron holes do not just migrate along the laser polarization direction, but may swirl around the atom centers. Our result establishes a general scheme for studying ultrafast electron dynamics in molecules, paving a way for further advance in tracing and controlling photochemical reactions by femtosecond lasers.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Regular and in-plane skyrmions and antiskyrmions from boundary instabilities

We formulate a theory of skyrmion and antiskyrmion generation using magnetic field and charge current pulses. We show that the topological defect can be created at an edge of a system with Dzyaloshinskii-Moriya interaction (DMI) as well as at a boundary between regions with different DMI. We consider both perpendicular and in-plane (also known as magnetic bimerons) versions of skyrmions and antiskyrmions. We show that the magnetization twist in the vicinity of an edge or a boundary is described by a kink solution, the presence of which can instigate the generation of topological defects. We study the collective excitations of magnetization analytically and numerically, and demonstrate that under application of magnetic field and charge current pulses the magnon modes localized near boundaries can develop instabilities leading to the formation of skyrmions or antiskyrmions. As a result, due to the skyrmion and antiskyrmion Hall effects, a properly chosen current direction can push the topological defects away from the boundary, thus facilitating their generation.

36 MATERIALS SCIENCE↗
DOE OSTI2023

A New Analytical Expression for Estimating the Adiabatic Temperature Rise in Lithium-Ion Batteries During High-Power Pulses

A coupled, thermal-electrochemical model is used to explain why the Joule heating assumption (i.e., I 2 R) does not provide a good representation of the temperature rise during high power pulses in lithium-ion batteries, even in cases where the reversible heat generation can be neglected. The poor agreement occurs because the internal resistance changes during the pulse due to the opposing effects of mass transport in the electrolyte, which raises the resistance, and heat generation (temperature rise), which lowers the resistance. These insights are used to propose a new analytical expression for predicting the temperature rise during adiabatic pulses with limited experimental and physical data. The expression accounts for thermal effects using a Taylor series expansion of an Arrhenius-type equation. It accounts for transport effects using an approximate solution to the one-dimensional diffusion equation. The new expression is shown to accurately estimate the simulated, adiabatic temperature rise across a range of loadings (1 to 4 mAh cm -2 ) and C-rates (1C to 10C) for cells containing LiNi 0.5 Mn 0.3 Co 0.2 O 2 positive electrodes and graphite negative electrodes. In conclusion, it is also shown to accurately estimate the experimental, adiabatic temperature rise measured for cells with LiFePO 4 positive electrodes and mesocarbon negative electrodes with minimal changes to the fitted parameters.

25 ENERGY STORAGE↗