Hydrodynamic instability experiments allow access to material properties at extreme conditions, where strain rates exceed 105 s−1 and pressures reach 100 GPa. Current hydrodynamic instability experimental methods require in-flight radiography to image the instability growth at high pressure and high strain rate, limiting the facilities where these experiments can be performed. An alternate approach, recovering the sample after loading, allows measurement of the instability growth with profilometry. Tantalum samples were manufactured with different 2D and 3D initial perturbation patterns and dynamically compressed by a blast wave generated by laser ablation. The samples were recovered from peak pressures between 30 and 120 GPa and strain rates on the order of 107 s−1, providing a record of the growth of the perturbations due to hydrodynamic instability. These records are useful validation points for hydrocode simulations using models of material strength at high strain rate. Recovered tantalum samples were analyzed, providing an estimate of the strength of the material at high pressure and strain rate.

Additive manufacturing (AM) is enabling the fabrication of materials with engineered lattice structures at the micron scale. These mesoscopic structures fall between the length scale associated with the organization of atoms and the scale at which macroscopic structures are constructed. Dynamic compression experiments were performed to study the emergence of behavior owing to the lattice periodicity in AM materials on length scales that approach a single unit cell. For the lattice structures, both bend and stretch dominated, elastic deflection of the structure was observed ahead of the compaction of the lattice, while no elastic deformation was observed to precede the compaction in a stochastic, random structure. The material showed lattice characteristics in the elastic response of the material, while the compaction was consistent with a model for compression of porous media. The experimental observations made on arrays of 4 × 4 × 6 lattice unit cells show excellent agreement with elastic wave velocity calculations for an infinite periodic lattice, as determined by Bloch wave analysis, and finite element simulations.

Measurements of silver K-shell and bremsstrahlung emission from thin-foil laser targets as a function of laser prepulse energy are presented. The silver targets were chosen as a potential 22 keV backlighter source for the National Ignition Facility Experiments. The targets were irradiated by the Titan laser with an intensity of 8 × 1017 W/cm2 with 40 ps pulse length. A secondary nanosecond timescale laser pulse with controlled, variable energy was used to emulate the laser prepulse. Results show a decrease in both Kα and bremsstrahlung yield with increasing artificial prepulse. Radiation hydrodynamic modeling of the prepulse interaction determined that the preplasma and intact target fraction were different in the three prepulse energies investigated. Interaction of the short pulse laser with the resulting preplasma and target was then modeled using a particle-in-cell code PSC which explained the experimental results. The relevance of this work to future Advanced Radiographic Capability laser x-ray backlighter sources is discussed.

Periodic sensitivity calibration of imaging plates (IP) is crucial for quantitative understanding of x-ray data obtained at the National Ignition Facility (NIF). To test the x-ray sensitivity of the IPs and the scanners, we developed an x-ray exposure station based on radioactive isotopes (55Fe, 109Cd, and 241Am). This apparatus provides a convenient setup for a periodical test of the IP's and the scanners. On NIF implosion experiments with deuterium-tritium mixture fuel, the neutrons produced in the capsule hit the imaging plates and impose background signal. Therefore it is also important to know the neutron sensitivity of the IPs. The sensitivity for 14 MeV neutrons was measured on high neutron yield shots at the OMEGA laser facility. The measured sensitivities were compared with the results of Monte Carlo simulations.

The National Ignition Facility (NIF) is capable of creating new and novel high-energy-density (HED) systems relevant to astrophysics. Specifically, a system could be created that studies the effects of a radiative shock on a hydrodynamically unstable interface. These dynamics would be relevant to the early evolution after a core-collapse supernova of a red supergiant star. Prior to NIF, no HED facility had enough energy to perform this kind of experiment. The experimental target will include a 340 μm predominantly plastic ablator followed by a low-density SiO2 foam. The interface will have a specific, machined pattern that will seed hydrodynamic instabilities. The growth of the instabilities in a radiation-dominated environment will be observed. This experiment requires a ≥300 eV hohlraum drive and will be diagnosed using point projection pinhole radiography, which have both been recently demonstrated on NIF.

EP shots) supported the Indirect Drive Inertial Confinement Fusion Campaign. The remaining 67% (175 OMEGA-only shots and 150 EP-only shots) were dedicated to experiments for High-Energy-Density Physics. Highlights of the various HED and ICF-ID campaigns are summarized in the following reports. In addition to these experiments, LLNL Principal Investigators (PIs) led a variety of Laboratory Basic Science campaigns using OMEGA and EP, including 80 target shots using just OMEGA, 68 shots using just EP, and 7 Joint shots using both lasers together. The highlights of these are also summarized, following the ICF and HED campaigns. Overall, LLNL PIs led a total of 636 shots at LLE in FY 2019. In addition, LLNL PIs supported 7 NLUF shots on Omega and 32 NLUF shots on EP in collaboration with the academic community.

In recent years a powerful experimental tool has been added to the arsenal at the disposal of the materials scientist investigating materials response at extreme regimes of strain rates, temperatures, and pressures: laser compression. This technique has been applied successfully to mono-, poly-, and nanocrystalline metals and the results have been compared with predictions from analytical models and molecular dynamics simulations. Special flash x-ray radiography and flash x-ray diffraction, combined with laser shock propagation, are yielding the strength of metals at strain rates on the order of 107–108 s−1 and resolving details of the kinetics of phase transitions. A puzzling result is that experiments, analysis, and simulations predict dislocation densities that are off by orders of magnitude. Other surprises undoubtedly await us as we explore even higher pressure/strain rate/temperature regimes enabled by the National Ignition Facility.

Polycrystalline and monocrystalline (〈100〉 and 〈110〉) vanadium was subjected to shock compression followed by tensile wave release to study spall and fragmentation behavior. The shock pulse was generated by a direct laser drive at energy levels ranging from 11 to 440Jmm–2 (laser beam irradiated area 1.12mm2) and initial pulse durations of 3 and 8ns (approximate initial pressures between 10 and 250GPa). Glass and polycarbonate shields placed at a specific distance behind the vanadium targets were used to collect and analyze the ejected fragments in order to evaluate and quantify the extent of damage. The effects of target thickness, laser energy, polycrystallinity and pulse duration were studied. Calculations show melting at a pressure threshold of ∼150GPa, which corresponds to a laser energy level of ∼180Jmm–2. Consistent with the analytical predictions, the recovered specimens and fragments show evidence of melting at the higher energy levels. Spalling in the polycrystals occurred by a ductile tearing mechanism that favored grain boundaries. In the monocrystals it occurred by a mixture of cleavage fracture along the {010} planes and ductile dimple fracture. This lower spall strength in polycrystals contradicts predictions from the Hall–Petch equation. Experimentally obtained fragment sizes were compared with predictions from the Grady–Kipp model. The spall strength of vanadium under laser loading conditions was calculated from both VISAR pull-back signals and using the spall thickness. It was found to be considerably higher than predictions from gas gun experiments, the monocrystals showing a higher value than polycrystals. This higher spall strength is suggestive of a strong time dependence of the phenomenon, consistent with the nucleation and growth kinetics of voids and the strain rate sensitivity embedded in the Grady theory.

Measurements of K alpha radiation yield and x-ray bremsstrahlung emission from thin-foil silver targets are presented. The targets were irradiated by a short pulse laser with intensities from 5 X 10(16) to 10(18) W/cm(2) at 40 ps. Single hit charge-coupled device detectors, differential filter-stack detectors, and a crystal spectrometer were used to investigate the angular distribution of the K alpha and bremsstrahlung x-rays. This study is the first to use a broadband detector to estimate the absolute numbers of K alpha photons and to determine K alpha to bremsstrahlung ratios. The relevance of this work in the context of x-ray diffraction and x-ray radiography is discussed. (C) 2010 American Institute of Physics. [doi:10.1063/1.3473822]

Using the Janus LLNL and Omega facilities, we are using laser energy to generate shock and quasi-isentropic compression of monocrystalline, polycrystalline, and nanocrystalline FCC and BCC metallic specimens(Cu, Ni, V). We have investigated the internal defects generated by experimental and computational (MD) means. By comparing experimentally observed and computationally predicted structures we can obtain new insights into the fundamental deformation mechanisms. We have also investigated the mechanisms of spall initiation, propagation, and fragmentation.

Our research focused on obtaining a fundamental understanding of the source and properties of EMP at the Titan PW(petawatt)-class laser facility. The project was motivated by data loss and damage to components due to EMP, which can limit diagnostic techniques that can be used reliably at short-pulse PW-class laser facilities. Our measurements of the electromagnetic fields, using a variety of probes, provide information on the strength, time duration, and frequency dependence of the EMP. We measure electric field strengths in the 100's of kV/m range, durations up to 100 ns, and very broad frequency response extending out to 5 GHz and possibly beyond. This information is being used to design shielding to mitigate the effects of EMP on components at various laser facilities. We showed the need for well-shielded cables and oscilloscopes to obtain high quality data. Significant work was invested in data analysis techniques to process this data. This work is now being transferred to data analysis procedures for the EMP diagnostics being fielded on the National Ignition Facility (NIF). In addition to electromagnetic field measurements, we measured the spatial and energy distribution of electrons escaping from targets. This information is used as input into the 3D electromagnetic code, EMSolve, which calculates time dependent electromagnetic fields. The simulation results compare reasonably well with data for both the strength and broad frequency bandwidth of the EMP. This modeling work required significant improvements in EMSolve to model the fields in the Titan chamber generated by electrons escaping the target. During dedicated Titan shots, we studied the effects of varying laser energy, target size, and pulse duration on EMP properties. We also studied the effect of surrounding the target with a thick conducting sphere and cube as a potential mitigation approach. System generated EMP (SGEMP) in coaxial cables does not appear to be a significant at Titan. Our results are directly relevant to planned short-pulse ARC (advanced radiographic capability) operation on NIF.

Fragmentation is a fundamental material process that naturally spans spatial scales from microscopic to macroscopic. We developed a mathematical framework using an innovative combination of hierarchical material modeling (HMM) and adaptive mesh refinement (AMR) to connect the continuum to microstructural regimes. This framework has been implemented in a new multi-physics, multi-scale, 3D simulation code, NIF ALE-AMR. New multi-material volume fraction and interface reconstruction algorithms were developed for this new code, which is leading the world effort in hydrodynamic simulations that combine AMR with ALE (Arbitrary Lagrangian-Eulerian) techniques. The interface reconstruction algorithm is also used to produce fragments following material failure. In general, the material strength and failure models have history vector components that must be advected along with other properties of the mesh during remap stage of the ALE hydrodynamics. The fragmentation models are validated against an electromagnetically driven expanding ring experiment and dedicated laser-based fragmentation experiments conducted at the Jupiter Laser Facility. As part of the exit plan, the NIF ALE-AMR code was applied to a number of fragmentation problems of interest to the National Ignition Facility (NIF). One example shows the added benefit of multi-material ALE-AMR that relaxes the requirement that material boundaries must be along mesh boundaries.

We are developing an experimental platform that can compress materials quasi-isentropically to very high pressures at ultrahigh strain rates. This laser driven, ramped (shockless) drive is used to study material properties such as strength, equation of state, phase, and phase transition kinetics under extreme conditions. We have achieved a ramped, shockless drive up to 2 Mbar on the Omega laser using both direct laser illumination and indirect x-ray illumination. In order to probe high-Z materials under extreme pressures, we are also developing high energy x-ray backlighters, 17 to 100 keV, created by high intensity (>1018 W/cm2) short pulse lasers (1 to 50 ps) such as the Titan laser at LLNL. Using a micro-wire embedded in a low-Z substrate, we have obtained radiographs with better than 10 ?m spatial resolution. This paper will show designs of isentropic platforms that can reach >10 Mbar on the NIF laser, using both direct and indirect drive configurations.

Chemical engineering at the University of Newcastle has introduced a “Systems Thinking” approach in response to the changing needs of today's young engineers, particularly in relation to sustainable development and interaction with the wider community. The basic concepts are reinforced to the students in the form of case studies. The activities cover a broad range of traditional chemical engineering principles, including fluid mechanics, heat and mass transfer, process flowsheeting, and design. The case studies have the additional dimensions of life cycle modelling, environmental impact assessment, and direct interaction with the broader community. In this paper, two examples, involving Building Design and On-Site Water Management, are presented, including a brief description, desired learning outcomes, results and general observations. Generally, it was found that the case studies provided an excellent framework for establishing a systems approach to arriving at solutions, and acted as a focus for quantitative analysis using the various tools taught during the course. Most importantly, the material presented assisted students to understand the practices which contribute to the transition to a sustainable society.