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On December 5, 2022, an indirect drive fusion implosion on the National Ignition Facility (NIF) achieved a target gain G_{target} of 1.5. This is the first laboratory demonstration of exceeding "scientific breakeven" (or G_{target}>1) where 2.05 MJ of 351 nm laser light produced 3.1 MJ of total fusion yield, a result which significantly exceeds the Lawson criterion for fusion ignition as reported in a previous NIF implosion [H. Abu-Shawareb et al. (Indirect Drive ICF Collaboration), Phys. Rev. Lett. 129, 075001 (2022)PRLTAO0031-900710.1103/PhysRevLett.129.075001]. This achievement is the culmination of more than five decades of research and gives proof that laboratory fusion, based on fundamental physics principles, is possible. This Letter reports on the target, laser, design, and experimental advancements that led to this result.

For more than half a century, researchers around the world have been engaged in attempts to achieve fusion ignition as a proof of principle of various fusion concepts. Following the Lawson criterion, an ignited plasma is one where the fusion heating power is high enough to overcome all the physical processes that cool the fusion plasma, creating a positive thermodynamic feedback loop with rapidly increasing temperature. In inertially confined fusion, ignition is a state where the fusion plasma can begin "burn propagation" into surrounding cold fuel, enabling the possibility of high energy gain. While "scientific breakeven" (i.e., unity target gain) has not yet been achieved (here target gain is 0.72, 1.37 MJ of fusion for 1.92 MJ of laser energy), this Letter reports the first controlled fusion experiment, using laser indirect drive, on the National Ignition Facility to produce capsule gain (here 5.8) and reach ignition by nine different formulations of the Lawson criterion.

Magnetically applied pressure-shear (MAPS) is a new experimental technique that provides a platform for direct measurement of material strength at extreme pressures. The technique employs an imposed quasi-static magnetic field and a pulsed power generator that produces an intense current on a planar driver panel, which in turn generates high amplitude magnetically induced longitudinal compression and transverse shear waves into a planar sample mounted on the drive panel. In order to apply sufficiently high shear traction to the test sample, a high strength material must be used for the drive panel. Molybdenum is a potential driver material for the MAPS experiment because of its high yield strength and sufficient electrical conductivity. To properly interpret the results and gain useful information from the experiments, it is critical to have a good understanding and a predictive capability of the mechanical response of the driver. In this work, the inelastic behavior of molybdenum under uniaxial compression and biaxial compression-shear ramp loading conditions is experimentally characterized. It is observed that an imposed uniaxial magnetic field ramped to approximately 10 T through a period of approximately 2500 µs and held near the peak for about 250 µs before being tested appears to anneal the molybdenum panel. In order to provide a physical basis for model development, a general theoretical framework that incorporates electromagnetic loading and the coupling between the imposed field and the inelasticity of molybdenum was developed. Based on this framework, a multi-axial continuum model for molybdenum under electromagnetic loading is presented. The model reasonably captures all of the material characteristics displayed by the experimental data obtained from various experimental configurations. In addition, data generated from shear loading provide invaluable information not only for validating but also for guiding the development of the material model for multiaxial loadings. [ABSTRACT FROM AUTHOR]

A magnetohydrodynamic loading technique was used to shocklessly compress beryllium to peak longitudinal stresses of 19-110 GPa and, subsequently, unload in order to determine both the compressive response and also the shear stress supported upon release. Loading strain rates were on the order of 106 s-1, while the unloading rates were nearly constant at 3×105 s-1. Velocimetry was used to monitor the ramp and release behavior of a beryllium/lithium fluoride window interface. After applying window corrections to infer in situ beryllium velocities, a Lagrangian analysis was employed to determine the material response. The Lagrangian wavespeed-particle velocity response is integrated to generate the stress-strain path, average change in shear stress over the elastic unloading, and estimates of the shear modulus at peak compression. These data are used to infer the pressure dependence of the flow strength at the unloading rate. Comparisons to several strength models reveal good agreement to 45 GPa, but the data indicate 20%-30% higher strength near 100 GPa. [ABSTRACT FROM AUTHOR]

A magnetic loading technique was used to study the strength of polycrystalline tantalum ramp compressed to peak stresses between 60 and 250GPa. Velocimetry was used to monitor the planar ramp compression and release of various tantalum samples. A wave profile analysis was then employed to determine the pressure-dependence of the average shear stress upon unloading at strain rates on the order of 105 s-1. Experimental uncertainties were quantified using a Monte Carlo approach, where values of 5% in the estimated pressure and 9-17% in the shear stress were calculated. The measured deviatoric response was found to be in good agreement with existing lower pressure strength data as well as several strength models. Significant deviations between the experiments and models, however, were observed at higher pressures where shear stresses of up to 5GPa were measured. Additionally, these data suggest a significant effect of the initial material processing on the high pressure strength. Heavily worked or sputtered samples were found to support up to a 30% higher shear stress upon release than an annealed material. [ABSTRACT FROM AUTHOR]

Unloading from a plastically deformed state has long been recognized as a sensitive measure of a material's deviatoric response. In the case of a ramp compression and unload, time resolved particle velocity measurements of a sample/window interface may be used to gain insight into the sample material's strength. Unfortunately, measurements of this type are often highly perturbed by wave interactions associated with impedance mismatches. Additionally, wave attenuation, the finite pressure range over which the material elastically unloads, and rate effects further complicate the analysis. Here, we present a methodology that overcomes these shortcomings to accurately calculate a mean shear stress near peak compression for experiments of this type. A new interpretation of the self-consistent strength analysis is presented and then validated through the analysis of synthetic data sets on tantalum to 250 GPa. The synthetic analyses suggest that the calculated shear stresses are within 3% of the simulated values obtained using both rate-dependent and rate-independent constitutive models. Window effects are addressed by a new technique referred to as the transfer function approach, where numerical simulations are used to define a mapping to transform the experimental measurements to in situ velocities. The transfer function represents a robust methodology to account for complex wave interactions and a dramatic improvement over the incremental impedance matching methods traditionally used. The technique is validated using experiments performed on both lithium fluoride and tantalum ramp compressed to peak stresses of 10 and 15 GPa, respectively. In each case, various windows of different shock impedance are used to ensure consistency within the transfer function analysis. The data are found to be independent of the window used and in good agreement with previous results. [ABSTRACT FROM AUTHOR]

In a previous study, the behavior of single crystal tantalum under ramp wave loading along the [100] and [110] orientations was characterized. The principal objective of the present study is to gain some insights on the observed single crystal behavior particularly on its precursor response and strong orientation dependence, and the implication of the macroscopic behavior on the possible underlying deformation mechanisms. The approach used to achieve this objective is through the material model development and numerical simulation. A continuum model developed in a previous work for polycrystalline tantalum was first modified to describe the experimental data and extract the material information associated with the data. A rigorous finite deformation single crystal model based on dislocation slip was then developed to gain physical insights into the possible deformation mechanisms. The slip systems considered were the {110}<111> and {112}<111> systems. Dislocation density and its evolution by nucleation or multiplication were incorporated as a key mechanism for describing the precursor behavior in both models. The orientation dependence was modeled through the assumption of anisotropic dislocation nucleation. In the continuum model, different nucleation rates were assumed for the [100] and [110] orientation. In the single crystal model, this anisotropy is assumed to be associated with the twinning/antitwinning asymmetry of the BCC crystals. The precursor for the [100] orientation is attributed mainly to the slips along the antitwinning direction and that for the [110] is to the slips along the twinning direction. The anisotropic dislocation nucleation leads to the orientation dependence of the rate sensitivity of single crystal Ta and the subsequent deformation behavior. Both models were demonstrated to be able to generate reasonably consistent results and to capture the observed material features. Through the developed models, a reasonable understanding was achieved for the evolution of stress, strain, strain rates, strength, temperature, and stress strain relations for single crystal tantalum under ramp wave loading and the possible correlation between the macroscopic behavior and microscopic deformation mechanisms. [ABSTRACT FROM AUTHOR]

In a previous study by Asay et al. [J. Appl. Phys. 106, 073515 (2009)], the inelastic response of annealed and cold-rolled pure polycrystalline tantalum at intermediate strain rates was characterized with ramp wave loading to peak longitudinal stresses of 17 GPa. It was found that the annealed Ta at strain rates of about 106/s exhibited pronounced elastic overshoot, followed by rapid stress relaxation and the amplitude of the elastic precursor depicted essentially no dependence on sample thickness for samples with controlled initial properties, in contrast to the precursor attenuation typically observed in shock wave experiments. The precursor for the cold-rolled sample was more dispersive and did not exhibit the characteristics depicted by the annealed samples. A principal objective of the present study was to gain some insights into this behavior and its implication on the deformation mechanisms for tantalum. Another objective was to gain a fundamental understanding of the dynamic inelasticity of polycrystalline tantalum, its evolution with the processing history, and the resultant thermomechanical behavior. The approach used to achieve these objectives was to first develop a material model that captured the observed material characteristics and then to use numerical simulations of dynamic experiments to gain additional insights into the observed material behavior. The constitutive model developed is based on the concept of dislocation generation and motion. Despite its simplicity, the model works quite well for both sets of data and serves a valuable tool to achieve the research objectives. The tantalum studied here essentially exhibits a strong rate sensitivity and this behavior is modeled through the low dislocation density and the strong stress dependence of the dislocation velocity. For the annealed material, the mobile dislocation density is assumed to be essentially zero in the model. This low dislocation density combined with strong stress dependence of dislocation velocity results in a metastable elastic response and a precursor that shows little attenuation. The increase of mobile dislocations through the cold-rolling process leads to a less rate-sensitive behavior for the cold-rolled tantalum and also the disappearance of the precursor behavior observed for the annealed samples. Both the low dislocation density and the strong rate dependence of the dislocation velocity may be related to the low mobility of the screw dislocations in bcc metals. This low mobility results from its extended, three-dimensional core structure. [ABSTRACT FROM AUTHOR]

A magnetic loading technique was used to ramp load single-crystal [100] lithium fluoride specimens to peak stresses of 5–114 GPa. Wave analysis of in situ particle velocity profiles was used to estimate the compressive strength of LiF at peak stress. It was found that the strength increased with peak stress and showed two distinct regions of hardening; the first is believed to be governed by strain hardening and the second by pressure hardening. The quasielastic strain obtained from the initial part of the unloading was shown to saturate at about 1.3% for peak stresses greater than approximately 30 GPa. Over the studied pressure range, the measured strength of LiF varied from its initial value of 0.08 to about 1.1 GPa at the highest compressed state of 114 GPa. Comparison of the measured strength to results from two strength models showed good agreement. It was demonstrated that the strength of LiF introduces systematic error of about 10% when used as an interferometer window for measurements of material strength in isentropic compression experiments. [ABSTRACT FROM AUTHOR]

A magnetic loading technique was used to study the strength of pure, annealed, and cold-rolled polycrystalline tantalum under planar ramp loading at strain rates of ∼106/s. Both the initial yield strength and the flow strength after compression to peak loading stresses of 18 GPa were determined. For sample thicknesses ranging from 0.5–6.0 mm, it was found that the elastic limit of ∼3.2 GPa, corresponding to a yield strength of 1.6 GPa, for annealed Ta was sharply defined and essentially independent of sample thickness. After elastic yielding, relaxation of the longitudinal stress occurred for sample thicknesses greater than ∼0.5 mm, approaching an asymptotic value of ∼1.6 GPa. Two different purities of annealed Ta showed no difference in initial yield strength. Cold-rolling annealed Ta to 26% plastic strain resulted in a more dispersed elastic precursor with an amplitude of about 1.6 GPa and with no stress relaxation after yielding. Analysis of unloading wave profiles from the peak loading states allowed determination of the flow stress, which increased to about 0.9 GPa for annealed Ta and 1.3 GPa for cold-rolled Ta at peak stresses of 17–18 GPa. [ABSTRACT FROM AUTHOR]

Plate impact experiments were conducted to produce two and three step shock wave loadings in [100] ultrapure, lithium fluoride (LiF) crystals to examine the role of loading history on optical window response in laser interferometry measurements. Peak compressive stresses ranged between 5.0 and 17.5 GPa, and the window response was characterized by measuring the difference between the apparent and actual velocities of reflecting surfaces by using a velocity interferometer. In some experimental configurations, this velocity correction was obtained independently from the projectile velocity. Our results show that the velocity correction in [100] lithium fluoride windows can be described in all cases by a single linear relation, Δu=(0.2739±0.0016)u. Because this correction is independent of the loading history, it is applicable to arbitrary loading, which includes ramp-wave or shockless compression. By using the velocity correction and the measured particle and shock velocities, we have also determined the density dependence of the refractive index for [100] lithium fluoride at 532 nm to be n=(1.2769±0.0024)+(0.0443±0.000 82)ρ. [ABSTRACT FROM AUTHOR]

A magnetic loading technique was used to ramp load pure aluminum and 6061 aluminum alloy to peak stresses of approximately 29 GPa. The peak loading rate was approximately 106/s, followed by unloading from peak stress at a rate of about 105/s. The pure aluminum samples had impurity levels ranging from about 10 ppm to 0.5 wt % and average grain sizes in the range of 144–454 μm. The 6061 alloy was prepared in either the T6 condition with grain sizes of 5–50 μm, or in the T0 or T6 heat treatment condition with a grain size of about 40 μm. A wave profile technique was used to estimate the compressive strength during unloading. It was found that the compressive strength estimated during unloading increased with peak stress for all materials and that the change in strength was insensitive to initial material properties. This observation is in agreement with previous results obtained from shock loading of the same materials [H. Huang and J. R. Asay, J. Appl. Phys. 98, 033524 (2005)] and suggests that the deformation mechanisms, which govern strength properties at high strain rates, are similar for the two cases. It was also found that the quasielastic strain occurring during unloading saturated at about 2% in 6061-T6 alloy for peak stresses in the range of 10–50 GPa. The change in quasielastic strain was found to be similar for pure aluminum and 6061 alloys. [ABSTRACT FROM AUTHOR]

Plate-impact experiments were performed to examine the influence of grain size on the dynamic tensile (or spall) behavior of shocked polycrystalline aluminum. Ultrapure and commercially pure 1050 aluminum plates were cold rolled to 80% strain and heat treated under predetermined conditions to produce recrystallized samples with average grain sizes varying between 49 and 453 μm. Well-characterized samples were subjected to plane wave loading at peak compressive stresses of 4 and 21 GPa, and free-surface velocity profiles were obtained using velocity interferometry. At 4 GPa, the observed pullback velocity, a characteristic feature of the spall response, was similar for different grain sizes of 1050 and ultrapure Al, suggesting that the preferential failure mode is intragranular. At 21 GPa, the spall response (i.e., the pullback velocity and the signal structure) depended on the alloy content; the pullback velocity of ultrapure Al increased with increase in grain size, while it remained constant for 1050 Al. In addition, the structure of pullback signals showed a well-defined change in slope for different grain size samples in ultrapure Al, while no such feature was observed for 1050 Al. For the grain sizes examined, the σHEL was nearly independent of the grain size for 1050 Al and beyond a certain grain size for ultrapure Al. [ABSTRACT FROM AUTHOR]

Ramp wave experiments on the Sandia Z accelerator provide a different approach to study the rapid compression response of materials at pressures, temperatures, and stress or strain rates not attainable in conventional shock experiments. Due to its shockless nature, the ramp wave experiment is often termed as an isentropic (or quasi-isentropic) compression experiment (ICE) and the analysis of ICE has been focused on determination of the isentropes. One objective of the current study is to show that ramp wave experiment can be used as a much more general material characterization tool for studying material behavior under high strain rates and pressures. The second objective is to suggest practical methodology to design the experiment and analyze experimental data. Numerical simulations were used to achieve these objectives. It is demonstrated that the ramp wave experiment is essentially a controlled-strain-rate material test. The strain rate can be varied through the rise time and shape of the ramp wave. The resultant stress-strain relation is a specific relation for a specific strain-rate history. The isentrope, which is a limiting case of such relations, may be approximated through a very low strain-rate loading path. Because of the rate dependence of the material behavior, each material point experiences different strain-rate loading paths. Lagrangian analysis requires information pertinent to a local Lagrangian material point. This information may be obtained through a pair of wave profiles measured at two very close, but essentially the same, Lagrangian points. [ABSTRACT FROM AUTHOR]

Reshock and release experiments were performed on single crystal aluminum along three orientations and on polycrystalline 1050 aluminum with 50 μm grain size at shock stresses of 13 and 21 GPa to investigate the mechanisms for previously observed quasielastic recompression behavior. Particle velocity profiles obtained during reshocking both single crystals and polycrystalline aluminum from initial shock stresses of 13–21 GPa show similar quasielastic recompression behavior. Quasielastic release response is also observed in all single crystals, but the magnitude of the effect is crystal orientation dependent, with [111] and [110] exhibiting more ideal elastic-plastic release for unloading from the shocked state than for the [100] orientation and polycrystalline aluminum. The quasielastic response of 1050 aluminum is intermediate to that of the [100] and [111] orientations. Comparison of the wave profiles obtained for both unloading and reloading of single crystals and polycrystalline 1050 aluminum from shocked states suggests that the observed quasielastic response of polycrystalline aluminum results from the averaging response of single crystals for shock propagation along different orientations, and that the response of 1050 aluminum with large grain boundaries is not significantly different from the results obtained on single crystal aluminum. The yield strength of the single crystals and 1050 aluminum is found to increase with shock stress, which is consistent with previous results [H. Huang and I. R. Asay, J. Appl. Phys. 98, 033524 (2005)]. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) mesoscale simulations of planar shock compression, followed by either reloading or unloading, are presented to examine and understand the quasielastic response observed experimentally in shocked polycrystalline aluminum. The simulations included a realistic representation of the grain ensembles in polycrystalline samples to identify heterogeneous deformation features deemed important to model the continuum measurements. The simulations were carried out using a 2D Lagrangian finite element code (ISP-TROTP) that incorporated elastic-plastic deformation in grain interiors and utilized a contact/cohesive methodology to analyze the response of finite strength grain boundaries. Local heterogeneous response due to mesoscale features was quantified by calculating appropriate material variables along in situ Lagrangian tracer lines and comparing the temporal variation of their mean values with results from 2D continuum simulations. A series of initial calculations ruled out effects due to finite element size and width of the representative volume element used in our simulations. Simulations using a variety of heterogeneities were performed to identify the heterogeneities that were most important for simulating the experimentally observed quasielastic response. These were inclusions, hardened grain boundaries, and microporosity. Mesoscale simulations incorporating these effects demonstrate that the shock-deformed state in polycrystalline aluminum is strongly heterogeneous with considerable variations in lateral stresses. The simulated velocity profiles for a representative reloading and unloading experimental configuration were found to agree well with experimental data, and suggest that hardened grain boundaries are the most likely source of mesoscale heterogeneities in shocked 6061-T6 aluminum. The calculated shear strength and shear stresses were also found to be in good agreement with the reported experimental values. [ABSTRACT FROM AUTHOR]

The effects of shock loading on compressive yield strength are presented for several aluminum materials. These include commercially pure aluminum 1060, ultrapure aluminum, pure aluminum single crystal of [100] and [111] orientations, and aluminum alloy 6061-T6. The yield strength of these materials was measured by a cyclic shock loading technique in which the sample was first shocked to longitudinal stresses ranging from 4 to 22 GPa, followed by complete release and then reshocked to final states of 4–31 GPa. The results reveal that the yield strength of 6061-T6 alloy, as determined through measurement of its Hugoniot elastic limit during reshocking, remains unchanged after first shock loading and release. In contrast, the yield strength of all pure aluminum materials was found to increase during reshocking. In addition, plastic strain hardening was observed in all reshock wave profiles after the initial elastic response, as observed through substantially higher reshock wave speeds. This results in substantially higher reshock Hugoniot stresses than predicted by the original Hugoniot of aluminum at the same compression. The compressive yield strength at the reshock Hugoniot stress was estimated by comparing the first and second Hugoniot states and correcting for thermal effects. The results suggest that strain hardening during second shock compression is independent of first shock amplitudes over the range of 6–22 GPa and appears to saturate for a first shock stress greater than 6 GPa. The temperature correction for the Hugoniot mean stress shows that the increased temperature produced by second shock compression significantly reduces the flow strength during reshocking and makes the resultant strength strongly dependent on loading history. [ABSTRACT FROM AUTHOR]

A series of plate-impact spall experiments was conducted to study the spall strength of seven microstructural conditions of aluminum, including three grain sizes of 6061 Al alloy, both ultrapure and commercially pure (1060) polycrystalline aluminum, and single-crystal Al with two different orientations, over the stress range of 4–22 GPa. The pullback velocity, which is a characteristic signature of spall strength, is observed to depend on initial microstructure, impact stress, pulse duration, and loading rate. The pullback velocity generally increases over the stress range of 4–14 GPa and achieves a maximum as the impact stress approaches 22 GPa. The pullback velocity of [100] single-crystal Al is higher than that for both polycrystalline samples and [111] single-crystal samples, indicating that grain orientation strongly affects material response. Experimental results also show that the spall behavior is strongly dependent on sample thickness, while the effect of shock pulse duration was observed to be less significant. Comparison among three 6061 materials indicates that the observed differences depend on initial yield strength. The results also show that initial microstructures and impurities have a diminishing effect on the pullback velocity at stresses near 22 GPa. However, initial properties are observed to have a pronounced effect on the detailed structure of the pullback velocity profile at all stress levels. In particular, an interesting feature, i.e., a sharp slope during pullback followed by a distinct transition to a slower slope, is consistently observed. The occurrence of this change in slope is observed to depend on impact stress, loading rate, and grain size. [ABSTRACT FROM AUTHOR]

Measurements of the high-pressure compressive strength are presented for several aluminum alloys shocked to 22 GPa. Five well-characterized aluminum materials were studied, including 6061 alloy with three average grain sizes (50, 30, and <5 μm), pure aluminum 1060 (99.5% Al) with a 180-μm grain size, and ultrapure aluminum (99.9998% Al) with a 300-μm grain size. The purpose of these experiments was to investigate deformation mechanisms responsible for the apparently anomalous quasielastic recompression previously observed and to determine how the shock-induced yield strength varies with initial properties. The yield strength was estimated using combined reshock and release techniques previously developed. These results show that quasielastic recompression occurs for all materials investigated and is independent of grain size and impurity level. The shear stress and the shear strength at the shocked state were estimated from the reshock and release wave profiles. These results are consistent with previous investigations and suggest that the shear stress at the Hugoniot state is less than the yield strength. This is thought responsible for the observed quasielastic recompression. The present data, together with other reported measurements, illustrate that the yield strength of aluminum increases with applied shock stress to 90 GPa. The Steinberg-Guinan strength model [Steinberg, Cochran, and Guinan, J. Appl. Phys. 51, 1498 (1980)] was used to describe these data and was found to represent the overall data trend with increasing stress, but is not an accurate representation. The collective data suggest that the increase in strength at shock states, ΔY(ΔY=Yyield-YHEL), increases with applied stress and plastic strain. A strength model was developed to describe this increase, which fits the data accurately to 55 GPa and reveals that ΔY increases with shock stress in three distinct regions. It also strongly indicates that metallurgical properties, such as impurities and grain size, influence the ambient yield strength, but not the change in strength, which appears to be controlled by the shock-deformed aluminum matrix and possibly grain boundaries. [ABSTRACT FROM AUTHOR]

Adiabatic release measurements were performed on aluminum (6061-T6) from ∼240- to500-GPa(∼2.4–5 Mbar) states on the principal Hugoniot. Using a magnetically accelerated flyer plate technique, capable of launching macroscopic aluminum flyer plates (approximately 12×25 mm in lateral dimension and ∼300 μm in thickness) to velocities in excess of 20 km/s, direct impact experiments were performed on a low shock impedance, 200-mg/cc silica aerogel to determine the aerogel Hugoniot in the pressure range of ∼30–75 GPa. Release experiments were then performed in which the aerogel was mounted onto an aluminum base plate, and the initial shock in the base plate was transmitted to the aerogel sample. Given the measured aerogel shock velocities from the release experiments and the measured aerogel Hugoniot from the direct impact experiments, release states on release adiabats of aluminum were ascertained. The results were compared to several equation of state models for aluminum, and a rigorous statistical analysis was performed. The statistical analysis enabled the suitability of these various models in describing the release response of hot, liquid states to be determined. This study enhances our understanding of the release response of aluminum for high-pressure states on the Hugoniot and lends confidence to the use of aluminum as a standard material in impedance-matching experiments. [ABSTRACT FROM AUTHOR]

Hugoniot measurements were performed on aluminum (6061-T6) in the stress range of 100–500 GPa (1–5 Mbar) using a magnetically accelerated flyer plate technique. This method of flyer plate launch utilizes the high currents, and resulting magnetic fields produced at the Sandia Z Accelerator to accelerate macroscopic aluminum flyer plates (approximately 12×25 mm in lateral dimension and ∼300 μm in thickness) to velocities in excess of 20 km/s. This technique was used to perform plate-impact shock-wave experiments on aluminum to determine the high-stress equation of state (EOS). Using a near-symmetric impact method, Hugoniot measurements were obtained in the stress range of 100–500 GPa. The results of these experiments are in excellent agreement with previously reported Hugoniot measurements of aluminum in this stress range. The agreement at lower stress, where highly accurate gas gun data exist, establishes the magnetically accelerated flyer plate technique as a suitable method for generating EOS data. Furthermore, the present results exhibit increased accuracy over the previous techniques used to obtain data in the higher-stress range. This improved accuracy enhances our understanding of the response of aluminum to 500 GPa, and lends increased confidence to the use of aluminum as a standard material in future impedance matching experiments. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Isentropic compression experiments (ICE) on Sandia National Laboratories' Z Accelerator are used to make continuous measurements of the index of refraction in single crystal Z-cut sapphire as the longitudinal stress is gradually increased to 20 GPa (uniaxial strain of about ∼3.9%). A planar, ramp compression wave, generated by a large magnetic field, propagates through a planar copper base plate. Part of the rear surface of the base plate is a free surface and part is covered with a sapphire window. Comparisons are made of velocity histories measured simultaneously at the free surface and at the copper/sapphire interface using a velocity interferometer system for any reflector (VISAR). This is sufficient to determine the index of refraction of the sapphire continuously as a function of density. Perturbations to the compression waves caused by interactions with the free surface and with the sapphire are accounted for by backward or forward solutions to the equations of motion. The effect of the unsteady nature of the compression wave in sapphire on the interferometry measurements is also taken into account. Results validate the interpretation of VISAR measurements on continuous loading experiments performed with optical windows. The measured index of refraction of sapphire agrees with previous studies validating this experimental technique and showing that it is useful for studying other materials for which index of refraction data do not exist. In addition, measured compression isentropes for copper and sapphire compare favorably with existing theoretical models. [ABSTRACT FROM AUTHOR]

Isentropic compression experiments (ICE) have been performed on the Z accelerator facility at Sandia National Laboratory. We describe the experimental design that used large magnetic fields to slowly compress samples to pressures in excess of 400 kbar. Velocity wave profile measurements were analyzed to yield isentropic compression equations of state (EOS). The method can also yield material strength properties. We describe magnetohydronamic simulations and results of experiments that used the "square short" configuration to compress copper and discuss ICE EOS experiments that have been performed with this method on tantalum, molybdenum, and beryllium. [ABSTRACT FROM AUTHOR]

Focuses on a study that examined the shock-induced luminescence from lithium niobate. Use of narrowband filters and photomultiplier tubes; Mechanism for light emission in lithium niobate; Difference between the X-cut quartz data and lithium niobate; Comparison of the plot of peak radiance versus stress and a plot of the energy dissipated versus stress.