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Stoupin, S. (ORCID:0000000226225270)

Publications and source records attributed to Stoupin, S. (ORCID:0000000226225270).

6 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Thermonuclear performance variability near ignition at the National Ignition Facility

We describe our current understanding of the variability and degradation mechanisms observed through a series of five indirectly driven inertial fusion implosions fielded at the National Ignition Facility in the fall of 2021, four of which attempted to reproduce the first experiment to achieve Lawson's criterion for ignition with a thermonuclear yield of 1.35 MJ on August 8, 2021. A large number of absolutely calibrated (imaging, time-resolved, and spectrally resolved) x-ray and neutron diagnostics are fielded on the NIF along multiple lines of sight for each experiment. This allows for a reconstruction of the DT fuel and ablator mix injected into the hotspot around peak burn. We show that nuclear yield variations are well reproduced by numerical modeling when the measured low mode asymmetries and mix mass are included. Furthermore, these observed perturbations during burn are linked to small variations in laser delivery and capsule defects. Stringent specifications are then set to achieve robust ignition with the implosion design studied in this paper.

Divol, L. (ORCID:0000000269699898)↗
DOE OSTI2022

Crystal response measurement of the x-ray transmission crystals used by the Imaging Spectroscopy Snout at the National Ignition Facility

The Imaging Spectroscopy Snout (ISS) used at the National Ignition Facility is able to simultaneously collect neutron pinhole images, 1D spatially resolved x-ray spectra, and time resolved x-ray pinhole images. To measure the x-ray spectra, the ISS can be equipped with up to four different transmission crystals, each offering different energy ranges from ∼7.5 to ∼12 keV and different resolutions. Characterizing and calibrating such instruments is of paramount importance in order to extract meaningful results from experiments. More specifically, we characterized different ISS transmission-type alpha-Quartz crystals by measuring their responses as a function of photon energy, from which we inferred the angle-integrated reflectivity for each crystal’s working reflections. These measurements were made at the Lawrence Livermore National Laboratory calibration station dedicated to the characterization of x-ray spectrometers. The sources used covered a wide x-ray range—from a few to 30 keV; the source diameter was ∼0.6 mm. The experimental results are discussed alongside theoretical calculations using the pyTTE model.

Dozieres, M. (ORCID:0000000286401459)↗
DOE OSTI2022

X-ray source characterization and sample heating on x-ray diffraction experiments at the National Ignition Facility

X-ray diffraction is a powerful measurement technique for determining material properties, and it is now possible to perform these experiments at pressures exceeding 1 TPa [Rygg et al., Rev. Sci. Instrum. 91, 043902 (2020)] at the National Ignition Facility (NIF). The x-ray source for these experiments is the quasi-monochromatic Heα emission from metal foils heated to multi-keV temperatures. A critical aspect for understanding the sample's thermodynamic state is the amount of heating caused by absorption of the probe x-rays. In this work, we characterize the performance of the Ge foil x-ray source over more than 60 NIF x-ray diffraction experiments. We use this information to constrain the level of diffraction sample heating from the x-ray source and discuss the impact on the thermodynamic state.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

A Monte Carlo technique to model performance of streak camera-based time-resolving x-ray spectrometers

A Monte Carlo technique has been developed to simulate the expected signal and the statistical noise of x-ray spectrometers that use streak cameras to achieve the time resolution required for ultrafast diagnostics of laser-generated plasmas. The technique accounts for statistics from both the photons incident on the streak camera’s photocathode and the electrons emitted by the photocathode travelling through the camera’s electron optics to the sensor. We use the technique to optimize the design of a spectrometer, which deduces the temporal history of electron temperature of the hotspot in an inertial confinement fusion implosion from its hard x-ray continuum emission spectra. The technique is general enough to be applied to any instrument using an x-ray streak camera.

Stoupin, S. (ORCID:0000000226225270)↗
DOE OSTI2021

The multi-optics high-resolution absorption x-ray spectrometer (HiRAXS) for studies of materials under extreme conditions

We report the development of a high-resolution spectrometer for extended x-ray absorption fine structure (EXAFS) studies of materials under extreme conditions. A curved crystal and detector in the spectrometer are replaceable such that a single body is employed to perform EXAFS measurements at different x-ray energy intervals of interest. Two configurations have been implemented using toroidal crystals with Ge 311 reflection set to provide EXAFS at the Cu K-edge (energy range 8.9–9.8 keV) and Ge 400 reflection set to provide EXAFS at the Ta L3-edge (9.8–10.7 keV). Key performance characteristics of the spectrometer were found to be consistent with design parameters. The data generated at the National Ignition Facility have shown an ≃3 eV spectral resolution for the Cu K-edge configuration and ≃6 eV for the Ta L3-edge configuration.

Stoupin, S. (ORCID:0000000226225270)↗