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Glize, K.

Publications and source records attributed to Glize, K..

10 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

X-ray phase-contrast imaging of strong shocks on OMEGA EP

The ongoing improvement in laser technology and target fabrication is opening new possibilities for diagnostic development. An example is x-ray phase-contrast imaging (XPCI), which serves as an advanced x-ray imaging diagnostic in laser-driven experiments. In this work, we present the results of the XPCI platform that was developed at the OMEGA EP Laser-Facility to study multi-Mbar single and double shocks produced using a kilojoule laser driver. Two-dimensional radiation-hydrodynamic simulations agree well with the shock progression and the spherical curvature of the shock fronts. It is demonstrated that XPCI is an excellent method to determine with high accuracy the front position of a trailing shock wave propagating through an expanding CH plasma that was heated by a precursor Mbar shock wave. Furthermore, the interaction between the rarefaction wave and the shock wave results in a clear signature in the radiograph that is well reproduced by radiation-hydrodynamic simulations.

47 OTHER INSTRUMENTATION↗
DOE OSTI2024

Optimization Methodology of Polar Direct-Drive Illumination for the National Ignition Facility

Improved laser illumination uniformity drives shocks and implosions to create more extreme high energy density environments. Predominantly, the geometry of experiments that can be performed is dictated by the layout of beams at laser facilities, limiting inter-facility and multiscale investigations. This Letter presents the first automated, algorithmic approach for generating illumination configurations for high energy density experiments. The method is demonstrated in comparison to a polar direct drive solid target experiment at the National Ignition Facility. The new illumination configuration is simulated to create greater than ×3 higher peak pressure and almost ×2 higher density by maintaining better shock uniformity. Furthermore, the optimization process is performed with reduced computational expense and isotropic plasma profiles, while accounting for the impact of cross-beam energy transfer.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Effect of overlapping laser beams and density scale length in laser-plasma instability experiments on OMEGA EP

Experiments have been conducted on the OMEGA EP laser facility to study the effect of density scale length and overlapping beam geometry on laser-plasma instabilities near and below the quarter-critical density. Experiments were conducted in both planar geometry (density scale length L n ~ 190 to 300 μm) and spherical geometry (L n ~ 150 μm) with up to four overlapping beams and were designed to have overlapped intensities and density scale lengths comparable to OMEGA spherical experiments, but with many fewer beams. In comparison with previous experiments on OMEGA and National Ignition Facility, it is confirmed that shorter density scale lengths favor the two-plasmon decay (TPD) instability, while longer density scale lengths favor stimulated Raman scattering (SRS). In addition, for experiments at the same scale length and overlapped laser intensity, higher single-beam intensities favor SRS, while a larger number of overlapping beams favor TPD.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Development of an x-ray radiography platform to study laser-direct-drive energy coupling at the National Ignition Facility

A platform has been developed to study laser-direct-drive energy coupling at the National Ignition Facility (NIF) using a plastic sphere target irradiated in a polar-direct-drive geometry to launch a spherically converging shock wave. To diagnose this system evolution, eight NIF laser beams are directed onto a curved Cu foil to generate Heα line emission at a photon energy of 8.4 keV. These x rays are collected by a 100-ps gated x-ray imager in the opposing port to produce temporally gated radiographs. The platform is capable of acquiring images during and after the laser drive launches the shock wave. A backlighter profile is fit to the radiographs, and the resulting transmission images are Abel inverted to infer radial density profiles of the shock front and to track its temporal evolution. Here, the measurements provide experimental shock trajectories and radial density profiles that are compared to 2D radiation-hydrodynamic simulations using cross-beam energy transfer and nonlocal heat-transport models.

47 OTHER INSTRUMENTATION↗
DOE OSTI2022

Role of hot electrons in shock ignition constrained by experiment at the National Ignition Facility

Shock ignition is a scheme for direct drive inertial confinement fusion that offers the potential for high gain with the current generation of laser facility; however, the benefits are thought to be dependent on the use of low adiabat implosions without laser–plasma instabilities reducing drive and generating hot electrons. A National Ignition Facility direct drive solid target experiment was used to calibrate a 3D Monte Carlo hot-electron model for 2D radiation-hydrodynamic simulations of a shock ignition implosion. The α = 2.5 adiabat implosion was calculated to suffer a 35% peak areal density decrease when the hot electron population with temperature T ℎ = 55 keV and energy E ℎ = 13 kJ was added to the simulation. Optimizing the pulse shape can recover ~1/3 of the peak areal density lost due to a change in shock timing. Here, despite the harmful impact of laser–plasma instabilities, the simulations indicate shock ignition as a viable method to improve performance and broaden the design space of near ignition high adiabat implosions.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Measuring magnetic fields in laser-driven coils with dual-axis proton deflectometry

Abstract By driving hot electrons between two metal plates connected by a wire loop, high power lasers can generate multi-tesla, quasi-static magnetic fields in miniature coil targets. Many experiments involving laser-coil targets rely on proton deflectometry directed perpendicular to the coil axis to extract a measurement of the magnetic field. In this paper, we show that quantitative measurements using perpendicular probing are complicated by the presence of GV m −1 electric fields in the target that develop on sub-ns timescales. Probing parallel to the coil axis with fiducial grids is shown to reliably separate the electric and magnetic field measurements, giving current estimates of I ≈ 5 kA in 1 mm- and 2 mm-diameter wire loops. An analytic model of proton deflection in electric and magnetic fields is used to benchmark results from the particle-in-cell code and help deconvolve the magnetic and electric field deflections. Results are used to motivate a new experimental scheme that combines a single-plate target with axial proton probing and direct current measurements. This scheme has several important advantages over the traditional target and diagnostic set-up, enabling the robust measurement of coil magnetic fields and plasma properties, as well as making it easier to validate different theoretical models at a range of laser intensities.

Bradford, P. (ORCID:0000000296186342)↗
DOE OSTI2020

Preparations for a European R&D roadmap for an inertial fusion demo reactor

A European consortium of 15 laboratories across nine nations have worked together under the EUROFusion Enabling Research grants for the past decade with three principle objectives. These are: (a) investigating obstacles to ignition on megaJoule-class laser facilities; (b) investigating novel alternative approaches to ignition, including basic studies for fast ignition (both electron and ion-driven), auxiliary heating, shock ignition, etc.; and (c) developing technologies that will be required in the future for a fusion reactor. This paperr presents a brief overview of these activities, along with new calculations relates the concept of auxiliary heating of inertial fusion targets, and provides possible future directions of research and development for the updated European Roadmap that is due at the end of 2020. This article is part of a discussion meeting issue ‘Prospects for high gain inertial fusion energy (part 2)’.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Stimulated Raman scattering mechanisms and scaling behavior in planar direct-drive experiments at the National Ignition Facility

Stimulated Raman scattering (SRS) has been investigated comprehensively in planar-geometry experiments at the National Ignition Facility at conditions relevant to the corona of inertial con finement fusion (ICF) ignition-scale direct-drive targets. These experiments at measured electron temperatures of 4 to 5 keV, simulated density scale lengths Ln of 400 to 700 um, and laser intensities at the quarter-critical density of up to 1.5 x 10 15 W/cm 2 have determined SRS thresholds and the scaling behavior of SRS for various beam geometries. Several SRS mechanisms, including saturated absolute SRS near the quarter-critical density and additional SRS, including near-backscatter or sidescatter at lower densities, have been identi fied. Correlation of time-dependent SRS at densities ~0.15 to 0.21 of the critical density with hot-electron signatures, as well as the magnitudes of these signatures across different experiments, is observed. Additional modeling work is needed to de nitively identify the density region in which hot electrons are generated, and will guide SRS and hot-electron preheat mitigation strategies for direct-drive-ignition designs.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Proton deflectometry of a capacitor coil target along two axes

A developing application of laser-driven currents is the generation of magnetic fields of picosecond–nanosecond duration with magnitudes exceeding $B=10~\text{T}$. Single-loop and helical coil targets can direct laser-driven discharge currents along wires to generate spatially uniform, quasi-static magnetic fields on the millimetre scale. Here, we present proton deflectometry across two axes of a single-loop coil ranging from 1 to 2 mm in diameter. Comparison with proton tracking simulations shows that measured magnetic fields are the result of kiloampere currents in the coil and electric charges distributed around the coil target. Using this dual-axis platform for proton deflectometry, robust measurements can be made of the evolution of magnetic fields in a capacitor coil target.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗