Laser-Driven Radiography Experiments at TRIDENT
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Tobias, Benjamin John↗
Engineering topics
Johnson, Randall Philip
Publications and source records attributed to Johnson, Randall Philip.
Quantification of uncertainty in photon source spot size inference during laser-driven radiography experiments at TRIDENT
Images of the R2DTO resolution target were obtained during laser-driven-radiography experiments performed at the TRIDENT laser facility, and analysis of these images using the Bayesian Inference Engine (BIE) determines a most probable full-width half maximum (FWHM) spot size of 78 μm. However, significant uncertainty prevails due to variation in the measured detector blur. Propagating this uncertainty in detector blur through the forward model results in an interval of probabilistic ambiguity spanning approximately 35-195 μm when the laser energy impinges on a thick (1 mm) tantalum target. In other phases of the experiment, laser energy is deposited on a thin (~100 nm) aluminum target placed 250 μm ahead of the tantalum converter. When the energetic electron beam is generated in this manner, upstream from the bremsstrahlung converter, the inferred spot size shifts to a range of much larger values, approximately 270-600 μm FWHM. This report discusses methods applied to obtain these intervals as well as concepts necessary for interpreting the result within a context of probabilistic quantitative inference.
47 OTHER INSTRUMENTATION↗
Laser-plasmas in the relativistic-transparency regime: science and applications
Laser-plasma interactions in the novel regime of relativistically induced transparency (RIT) have been harnessed to generate intense ion beams efficiently with average energies exceeding 10 MeV/nucleon (>100 MeV for protons) at “table-top” scales in experiments at the LANL Trident Laser. By further optimization of the laser and target, the RIT regime has been extended into a self-organized plasma mode. This mode yields an ion beam with much narrower energy spread while maintaining high ion energy and conversion efficiency. This mode involves self-generation of persistent high magnetic fields (~10 4 T, according to particle-in-cell simulations of the experiments) at the rear-side of the plasma. These magnetic fields trap the laser-heated multi-MeV electrons, which generate a high localized electrostatic field (~0.1 TV/m). After the laser exits the plasma, this electric field acts on a highly structured ion-beam distribution in phase space to reduce the energy spread, thus separating acceleration and energy-spread reduction. Thus, ion beams with narrow energy peaks at up to 18 MeV/nucleon are generated reproducibly with high efficiency (≈5%). The experimental demonstration has been done with 0.12 PW, high-contrast, 0.6 ps Gaussian 1.053 μm laser pulses irradiating planar foils up to 250 nm thick at 2–8 × 10 20 W/cm 2 . These ion beams with co-propagating electrons have been used on Trident for uniform volumetric isochoric heating to generate and study warm-dense matter at high densities. These beam plasmas have been directed also at a thick Ta disk to generate a directed, intense point-like Bremsstrahlung source of photons peaked at ~2 MeV and used it for point projection radiography of thick high density objects. In addition, prior work on the intense neutron beam driven by an intense deuterium beam generated in the RIT regime has been extended. Neutron spectral control by means of a flexible converter-disk design has been demonstrated, and the neutron beam has been used for point-projection imaging of thick objects. Finally, we discuss the plans and prospects for further improvements and applications.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Strength and viscosity effects on perturbed shock front stability in metals
Here, computational modeling and experimental measurements on metal samples subject to a laser-driven, ablative Richtmyer-Meshkov instability showed differences between viscosity and strength effects. In particular, numerical and analytical solutions, coupled with measurements of fed-through perturbations, generated by perturbed shock fronts onto initially flat surfaces, show promise as a validation method for models of deviatoric response in the post shocked material. Analysis shows that measurements of shock perturbation amplitudes at low sample thickness-to-wavelength ratios are not enough to differentiate between strength and viscosity effects, but that surface displacement data of the fed-through fed-thru perturbations appears to resolve the ambiguity. Additionally, analytical and numerical results show shock front perturbation evolution dependence on initial perturbation amplitude and wavelength is significantly different in viscous and materials with strength, suggesting simple experimental geometry changes should provide data supporting one model or the other.
36 MATERIALS SCIENCE↗
Trident Laser Building Layout
This is a picture of the Trident Laser Building layout and other descriptors.
99 GENERAL AND MISCELLANEOUS↗
Trident Utility Requirements
This document lists the requirements for the Trident Utility building.
99 GENERAL AND MISCELLANEOUS↗
Neutron imaging with the short-pulse laser driven neutron source at the TRIDENT Laser Facility
Emerging approaches to short-pulse laser-driven neutron production offer a possible gateway to compact, low cost, and intense broad spectrum sources for a wide variety of applications. They are based on energetic ions, driven by an intense short-pulse laser, interacting with a converter material to produce neutrons via breakup and nuclear reactions. Recent experiments performed with the high-contrast laser at the Trident laser facility of Los Alamos National Laboratory have demonstrated a laser-driven ion acceleration mechanism operating in the regime of relativistic transparency, featuring a volumetric laser-plasma interaction. This mechanism is distinct from previously studied ones that accelerate ions at the laser-target surface. The Trident experiments produced an intense beam of deuterons with an energy distribution extending above 100 MeV. This deuteron beam, when directed at a beryllium converter, produces a forward-directed neutron beam with ~5x10 9 n/sr, in a single laser shot, primarily due to deuteron breakup. The neutron beam has a pulse duration on the order of a few nanoseconds with an energy distribution extending from a few hundreds of keV to almost 80 MeV. For the experiments on neutron-source spot-size measurements, our gated neutron imager was setup to select neutrons in the energy range of 2.5 to 35 MeV. The spot size of neutron emission at the converter was measured by two different imaging techniques, using a knife-edge and a penumbral aperture, in two different experimental campaigns. The neutron-source spot size is measured ~1 mm for both experiments. The measurements and analysis reported here give a spatial characterization for this type of neutron source for the first time. In addition, the forward modeling performed provides an empirical estimate of the spatial characteristics of the deuteron ion-beam. Finally, these experimental observations, taken together, provide essential yet unique data to benchmark and verify theoretical work into the basic acceleration mechanism, which remains an ongoing challenge.
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗