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At least 1,261 records · Page 70
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

The role of hot electrons in the dynamics of a laser-driven strong converging shock

Experiments on strong shock excitation in spherical plastic targets conducted at the Omega Laser Facility are interpreted with the radiation–hydrodynamics code CHIC to account for parametric instabilities excitation and hot-electron generation. The effects of hot electrons on the shock-pressure amplification and upstream preheat are analyzed. In this study, it is demonstrated that both effects contribute to an increase in shock velocity. Comparison of the measured laser reflectivity and shock flash time with numerical simulations make it possible to reconstitute the time history of the ablation and shock pressures. Finally, consequences of this analysis for the shock-ignition target design are discussed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Weak-shock wave propagation in polymer-based particulate composites

Shock waves are common in polymer-based particulate composites that are subjected to intermediate to high-velocity impact loading. However, quantitative information on the spatial variation of stress, particle velocities, and energy dissipation during the formation and propagation of weak-shock waves is limited. In this paper, a systematic experimental study is conducted to understand the characteristics of weak-shocks in polymer-bonded particulate composites. Specimens made of polymer-bonded sugar were subjected to a projectile impact loading, at varying velocities, using a modified Hopkinson pressure bar apparatus. Full-field displacement and strains of the deformed samples were obtained with the help of an ultrahigh-speed imaging and digital image correlation technique. Using the full-field displacement data, the shock wave velocity, shock front thickness, and the full-field stress fields are calculated. From the spatial stress field and the strain rate data, the spatial energy dissipation profile is also estimated. The effect of impact velocity on the spatial stress profile, shock wave velocity, and energy dissipation are discussed.

42 ENGINEERING↗
DOE OSTI2019

Simulated refraction-enhanced X-ray radiography of laser-driven shocks

Refraction-enhanced x-ray radiography (REXR) is used to infer shock-wave positions of more than one shock wave, launched by a multiple-picket pulse in a planar plastic foil. This includes locating shock waves before the shocks merge, during the early time and the main drive of the laser pulse that is not possible with the velocity interferometer system for any reflector. Simulations presented in this paper of REXR show that it is necessary to incorporate refraction and attenuation of x rays along with the appropriate opacity and refractive-index tables to interpret experimental images. Simulated REXR shows good agreement with an experiment done on the OMEGA laser facility to image a shock wave. REXR can be applied to design multiple-picket pulses with a better understanding of the shock locations. Finally, this will be beneficial to obtain the required adiabats for inertial confinement fusion implosions.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Piston driven converging shock waves in a stiffened gas

We present that the problem of a one-dimensional (1D) cylindrically or spherically symmetric shock wave converging into an inviscid, ideal gas was first investigated by Guderley[Starke kugelige und zylinrische verdichtungsstosse in der nahe des kugelmitterpunktes bzw. Der zylinderachse,” Luftfahrtforschung 19, 302 (1942)]. In the time since, many authors have discussed the practical notion of how Guderley-like flows might be generated. One candidate is a constant velocity, converging “cylindrical or spherical piston,” giving rise to a converging shock wave in the spirit of its classical, planar counterpart. A limitation of pre-existing analyses along these lines is the restriction to flows in materials described by an ideal gas equation of state (EOS) constitutive law. This choice is of course necessary for the direct comparison with the classical Guderley solution, which also features an ideal gas EOS. However, the ideal gas EOS is limited in its utility in describing a wide variety of physical phenomena and, in particular, the shock compression of solid materials. This work is thus intended to provide an extension of previous work to a nonideal EOS. The stiff gas EOS is chosen as a logical starting point due to not only its close resemblance to the ideal gas law but also its relevance to the shock compression of various liquid and solid materials. Using this choice of EOS, the solution of a 1D planar piston problem is constructed and subsequently used as the lowest order term in a quasi-self-similar series expansion intended to capture both curvilinear and nonideal EOS effects. The solution associated with this procedure provides correction terms to the 1D planar solution so that the expected accelerating shock trajectory and nontrivially varying state variable profiles can be obtained. This solution is further examined in the limit as the converging shock wave approaches the 1D curvilinear origin. Lastly, given the stiff gas EOS is not otherwise expected to admit a Guderley-like solution when coupled to the inviscid Euler equations, this work thus provides the semianalytical limiting behavior of a flow that cannot be otherwise captured using self-similar analysis.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Kinetic simulations of piston-driven collisionless shock formation in magnetized laboratory plasmas

Laboratory laser experiments offer a novel approach to studying magnetized collisionless shocks, and a common method in recent experiments is to drive shocks using a laser-ablated piston plasma. However, current experimental capabilities are still limited to spatio-temporal scales on the order of shock formation, making it challenging to distinguish piston and shock dynamics. We present quasi-1D particle-in-cell simulations of piston-driven, magnetized collisionless shock formation using the code psc , which includes a model of laser-driven plasmas that can be well-matched to experimental conditions. The simulations cover a range of upstream and ablation parameters and yield several robust signatures of shock formation that can provide a reference for experimental results.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Hugoniot states and optical response of soda lime glass shock compressed to 120 GPa

In contrast to relatively pure silica glass (fused silica-FS), commercial silica-rich glasses contain significant fractions of additional oxide components. In particular, soda-lime glass (SLG) consists of approximately 71% SiO 2 by weight, which raises the question: what is the effect of additional cations on the shock compression response of silica-rich glasses? To address this concern, plate impact experiments were conducted to determine the high-pressure Hugoniot states for shocked SLG (37 to 120 GPa) and compared with recently reported results on FS. Using laser interferometry, particle velocity profiles were measured at the impact surface and the SLG/LiF window interface. In all experiments, the transmitted profiles show a single shock wave, with no features indicative of a phase transformation. The Hugoniot states determined from the wave profiles are described well using a linear shock velocity–particle velocity relation. Interferometry measurements (using 1550-nm wavelength laser) at the impact surface show that SLG is transparent when shocked to 55 GPa, transparent for tens of nanoseconds after impact between 55 and 81 GPa, and opaque beyond 81 GPa. From impact surface measurements, a linear relationship between the apparent and true particle velocity was observed, resulting in a linear relationship between the refractive index (at 1550 nm) and density. At 120 GPa, the SLG density is nearly twice its ambient value, indicating that SLG can achieve highly dense amorphous states. When compared to FS, shocked SLG is much less compressible and likely does not transform to a crystalline phase. A plausible explanation for this difference is indicated.

58 GEOSCIENCES↗
DOE OSTI2020

Inflationary stimulated Raman scattering in shock-ignition plasmas

In the shock-ignition inertial confinement fusion scheme, high-intensity lasers propagate through an inhomogeneous coronal plasma, driving a shock designed to cause fuel ignition. During the high-intensity ignitor laser pulse, in the long scale length coronal plasma, back-scattered stimulated Raman scattering (SRS) is likely to be in the kinetic regime. In this work, we use one-dimensional particle-in-cell simulations to show that there is a non-linear frequency shift caused by kinetic effects, resulting in the growth of SRS in an inhomogeneous plasma far exceeding the predictions of fluid theory, the so-called inflationary SRS or iSRS. We find that iSRS occurs over a wide range of density scale lengths relevant to shock-ignition and other directly-driven inertial confinement fusion schemes. The presence of iSRS in shock-ignition plasmas has implications for the theoretical gains from shock-ignition inertial confinement fusion. Here, we quantify the intensity threshold for the onset of iSRS for shock-ignition relevant parameters.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2026

Hot electron preheat effects in two-photon polymerization plastic lattice laser-driven shock-tube experiments on the OMEGA laser

We present simulations of Omega shock tube experiments designed to investigate hot electron preheat effects in 3D-printed, two-photon polymerization (2PP) plastic lattices. Preheat is inferred in the experiments from the expansion of a plastic witness disk embedded in the lattice. Using the Eulerian radiation-hydrodynamics code xRAGE, we model shock propagation and preheat from both radiative and hot electron energy sources to evaluate their relative impact. To simulate the transport of laser-generated hot electrons, the nonlocal electron heat transport model proposed by Schurtz, Nicolaï, and Busquet (SNB) is extended with a hot electron source term and an energy cascade algorithm. We explore how variations in ablator, lattice geometry, and laser drive affect the shock velocity and witness disk expansion. Simulations show that the inclusion of a 5 μm gold layer reduces shock pressure by 60% and shock speeds by 30%–40% but does not significantly reduce the hot electron preheat, and that different lattice geometries lead to enhanced shock velocities—up to 40% faster than in homogeneous foams. However, radiative and conductive preheat from classical mechanisms alone fail to match experiment. By including a hot electron source term, we reproduce experimental observables such as disk expansion rates and spatial radiographic features. We find that a hot electron population corresponding to 4%–8% of the incident laser energy with T hot = 50 keV produces expansion which agrees with the experimental data, suggesting hot electron preheat is the most plausible explanation.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2026

Investigating shock-induced chemical reactions in Ni+Al multilayers: A continuum-based mesoscale approach with Arrhenius kinetics and artificial thermal conduction

A new continuum-based mesoscale modeling approach for shock-induced chemical reactions (SICRs) in Ni+Al multilayers is demonstrated in Sandia’s shock physics hydrocode, CTH. The approach utilizes Arrhenius-type kinetics and artificial thermal conduction. Our work builds upon previous efforts to parameterize equations of state for Ni x Al y [J. Appl. Phys. 137, 075102 (2025)], as well as simulations of inert shocks in realistic 2D microstructures [J. Appl. Phys. 137, 225301 (2025)]. To calibrate the reaction kinetics, pairs of the reaction coordinate, R′, vs time are extracted from the molecular dynamics (MD) literature. Here, the MD-informed kinetics are used to simulate the dynamic evolution of pressure and temperature in 2D mesoscale simulations. Overall, the MD-informed kinetics obtained for planar interfaces are too slow, as initial reaction is not observed on a nanosecond time scale. Even with quasi-periodic shock focusing leading to the formation of so-called “hot-spots,” the hot spots are unable to grow and coalesce using the fitted Arrhenius rate constants. However, by increasing the rate constants by two orders of magnitude, SICRs are observed at a shock pressure near 30 GPa, which is supported by experiments. Consequently, these mesoscale simulations suggest that unresolved shear-based mechanical mixing might possibly account for the discrepancies in kinetic rates, with shock-generated intense perturbations, interfacial vortical flows, and elevated temperatures serving as favorable reaction conditions. Future work will calibrate a shear-dependent reaction rate from the MD simulations with realistic interfaces that are wavy, diffuse, and disordered.

Kittell, David E. [Sandia National Laboratories (S↗
DOE OSTI2012

AN ACTIVE GALACTIC NUCLEUS DRIVEN SHOCK IN THE INTRACLUSTER MEDIUM AROUND THE RADIO GALAXY 3C 310

We present results from a 57.6 ks Chandra observation of the cluster gas associated with the fat-double radio galaxy 3C 310. We find a surface brightness discontinuity in the gas outside the southern radio lobe that we attribute to a shock driven by the supersonic inflation of this lobe {approx}180 kpc from the nucleus. Modeling the surface brightness/density jump, the shock has Mach number 1.5-1.9, depending on the assumptions one makes about the density profile and the nature of the energy input. There are not sufficient counts in the image to detect conclusively the temperature jump associated with the shock. The total mechanical energy of the outburst is 5 Multiplication-Sign 10{sup 60} erg. Assuming a Mach 1.9 shock, the age of the outburst is {approx}100 million yrs, and the time-averaged power of the outburst is {approx}1.3 Multiplication-Sign 10{sup 45} erg s{sup -1}. The power input is 100 times greater than the radiative losses of the gas within the radius of the shock. Most importantly, the equivalent heat input due to the entropy increase is roughly 10% of the thermal energy of the gas to the radius of the shock. 3C 310 is another example where regular outbursts of the observed strength with a duty cycle of 0.1 could offset the radiative losses of the gas near the Bondi radius and regulate feedback. We also detect a cool filamentary X-ray arm along the eastern periphery of the southern radio lobe. This arm is probably composed of low-entropy gas dredged up in the inflation of the radio plasma, similar to features seen in M87.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

EFFECTS OF PERPENDICULAR DIFFUSION ON ENERGETIC PARTICLES ACCELERATED BY THE INTERPLANETARY CORONAL MASS EJECTION SHOCK

In this work, based on a numerical solution of the focused transport equation, we obtained the intensity and anisotropy time profiles of solar energetic particles (SEPs) accelerated by an interplanetary shock in the three-dimensional Parker magnetic field. The shock is treated as a moving source of energetic particles with an assumed particle distribution function. We computed the time profiles of particle flux and anisotropy as measured by an observer at 1 AU, equatorial plane, and various longitudes with respect to the shock propagation direction. With perpendicular diffusion, energetic particles can cross magnetic field lines. Particles may be detected before the observer's field line is connected to the shock. After the observer's field line breaks from the shock front, the observer still can see more particles are injected into its field line. Our simulations show that the particle onset time, peak time, peak intensity, decay rate, and duration of SEP event could be significantly influenced by the effect of perpendicular diffusion. The anisotropy with perpendicular diffusion is almost the same as that without perpendicular diffusion, but there is an obvious difference at the moment when the observer's field line begins to be connected to the shock.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

LOW-VELOCITY SHOCKS TRACED BY EXTENDED SiO EMISSION ALONG THE W43 RIDGES: WITNESSING THE FORMATION OF YOUNG MASSIVE CLUSTERS

The formation of high-mass stars is tightly linked to that of their parental clouds. Here, we focus on the high-density parts of W43, a molecular cloud undergoing an efficient event of star formation. Using a column density image derived from Herschel continuum maps, we identify two high-density filamentary clouds, called the W43-MM1 and W43-MM2 ridges. Both have gas masses of 2.1 × 10{sup 4} M{sub ☉} and 3.5 × 10{sup 4} M{sub ☉} above >10{sup 23} cm{sup -2} and within areas of ∼6 and ∼14 pc{sup 2}, respectively. The W43-MM1 and W43-MM2 ridges are structures that are coherent in velocity and gravitationally bound, despite their large velocity dispersion measured by the N{sub 2}H{sup +} (1-0) lines of the W43-HERO IRAM large program. Another intriguing result is that these ridges harbor widespread (∼10 pc{sup 2}) bright SiO (2-1) emission, which we interpret to be the result of low-velocity shocks (≤10 km s{sup –1}). We measure a significant relationship between the SiO (2-1) luminosity and velocity extent and show that it distinguishes our observations from the high-velocity shocks associated with outflows. We use state-of-the-art shock models to demonstrate that a small percentage (10%) of Si atoms in low-velocity shocks, observed initially in gas phase or in grain mantles, can explain the observed SiO column density in the W43 ridges. The spatial and velocity overlaps between the ridges of high-density gas and the shocked SiO gas suggest that ridges could be forming via colliding flows driven by gravity and accompanied by low-velocity shocks. This mechanism may be the initial conditions for the formation of young massive clusters.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

BROAD N{sub 2}H{sup +} EMISSION TOWARD THE PROTOSTELLAR SHOCK L1157-B1

We present the first detection of N{sub 2}H{sup +} toward a low-mass protostellar outflow, namely, the L1157-B1 shock, at ∼0.1 pc from the protostellar cocoon. The detection was obtained with the IRAM 30 m antenna. We observed emission at 93 GHz due to the J = 1-0 hyperfine lines. Analysis of this emission coupled with HIFI CHESS multiline CO observations leads to the conclusion that the observed N{sub 2}H{sup +}(1-0) line originated from the dense (≥10{sup 5} cm{sup –3}) gas associated with the large (20''-25'') cavities opened by the protostellar wind. We find an N{sub 2}H{sup +} column density of a few 10{sup 12} cm{sup –2} corresponding to an abundance of (2-8) × 10{sup –9}. The N{sub 2}H{sup +} abundance can be matched by a model of quiescent gas evolved for more than 10{sup 4} yr, i.e., for more than the shock kinematical age (≅2000 yr). Modeling of C-shocks confirms that the abundance of N{sub 2}H{sup +} is not increased by the passage of the shock. In summary, N{sub 2}H{sup +} is a fossil record of the pre-shock gas, formed when the density of the gas was around 10{sup 4} cm{sup –3}, and then further compressed and accelerated by the shock.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

A magnetohydrodynamic model of the M87 jet. II. Self-consistent quad-shock jet model for optical relativistic motions and particle acceleration

We describe a new paradigm for understanding both relativistic motions and particle acceleration in the M87 jet: a magnetically dominated relativistic flow that naturally produces four relativistic magnetohydrodynamic (MHD) shocks (forward/reverse fast and slow modes). We apply this model to a set of optical super- and subluminal motions discovered by Biretta and coworkers with the Hubble Space Telescope during 1994-1998. The model concept consists of ejection of a single relativistic Poynting jet, which possesses a coherent helical (poloidal + toroidal) magnetic component, at the remarkably flaring point HST-1. We are able to reproduce quantitatively proper motions of components seen in the optical observations of HST-1 with the same model we used previously to describe similar features in radio very long baseline interferometry observations in 2005-2006. This indicates that the quad relativistic MHD shock model can be applied generally to recurring pairs of super/subluminal knots ejected from the upstream edge of the HST-1 complex as observed from radio to optical wavelengths, with forward/reverse fast-mode MHD shocks then responsible for observed moving features. Moreover, we identify such intrinsic properties as the shock compression ratio, degree of magnetization, and magnetic obliquity and show that they are suitable to mediate diffusive shock acceleration of relativistic particles via the first-order Fermi process. We suggest that relativistic MHD shocks in Poynting-flux-dominated helical jets may play a role in explaining observed emission and proper motions in many active galactic nuclei.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Self-sustained asymmetry of lepton-number emission: a new phenomenon during the supernova shock-accretion phase in three dimensions

During the stalled-shock phase of our three-dimensional, hydrodynamical core-collapse simulations with energy-dependent, three-flavor neutrino transport, the lepton-number flux (ν {sub e} minus ν-bar {sub e}) emerges predominantly in one hemisphere. This novel, spherical-symmetry breaking neutrino-hydrodynamical instability is termed LESA for 'Lepton-number Emission Self-sustained Asymmetry'. While the individual ν {sub e} and ν-bar {sub e} fluxes show a pronounced dipole pattern, the heavy-flavor neutrino fluxes and the overall luminosity are almost spherically symmetric. Initially, LESA seems to develop stochastically from convective fluctuations. It exists for hundreds of milliseconds or more and persists during violent shock sloshing associated with the standing accretion shock instability. The ν {sub e} minus ν-bar {sub e} flux asymmetry originates predominantly below the neutrinosphere in a region of pronounced proto-neutron star (PNS) convection, which is stronger in the hemisphere of enhanced lepton-number flux. On this side of the PNS, the mass accretion rate of lepton-rich matter is larger, amplifying the lepton-emission asymmetry, because the spherical stellar infall deflects on a dipolar deformation of the stalled shock. The increased shock radius in the hemisphere of less mass accretion and minimal lepton-number flux ( ν-bar {sub e} flux maximum) is sustained by stronger convection on this side, which is boosted by stronger neutrino heating due to 〈ϵ{sub ν-bar{sub e}}〉>〈ϵ{sub ν{sub e}}〉. Asymmetric heating thus supports the global deformation despite extremely nonstationary convective overturn behind the shock. While these different elements of the LESA phenomenon form a consistent picture, a full understanding remains elusive at present. There may be important implications for neutrino-flavor oscillations, the neutron-to-proton ratio in the neutrino-heated supernova ejecta, and neutron-star kicks, which remain to be explored.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

A powerful double radio relic system discovered in PSZ1 G108.18-11.53: evidence for a shock with non-uniform Mach number?

Diffuse radio emission in the form of radio haloes and relics has been found in a number of merging galaxy clusters. These structures indicate that shock and turbulence associated with the merger accelerate electrons to relativistic energies. We report the discovery of a radio relic + radio halo system in PSZ1 G108.18-11.53 (z = 0.335). This cluster hosts the second most powerful double radio relic system ever discovered. We observed PSZ1 G108.18-11.53 with the Giant Meterwave Radio Telescope and the Westerbork Synthesis Radio Telescope. We obtained radio maps at 147, 323, 607 and 1380 MHz. We also observed the cluster with the Keck telescope, obtaining the spectroscopic redshift for 42 cluster members. From the injection index, we obtained the Mach number of the shocks generating the two radio relics. For the southern shock, we found $M$ = 2.33 $+0.19\atop{-0.26}$ while the northern shock Mach number goes from $M$2.20 $+0.07\atop{-0.14}$ in the north part down to $M$ = 200 $+0.03\atop{-0.08}$ in the southern region. Finally, if the relation between the injection index and the Mach number predicted by diffusive shock acceleration theory holds, this is the first observational evidence for a gradient in the Mach number along a galaxy cluster merger shock.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Weak collisionless shocks mediated by ion gyroviscosity

Collisionless shocks are ubiquitous in space and astrophysical plasmas, and they are essential dynamical features of these systems. Lacking Coulomb collisions, these shocks are mediated by the anomalous dissipation provided by nonlinear plasma instabilities. By numerically resolving the structure of a steady-state, ion gyroviscous shock, we show that ion gyroviscosity, alone, can produce weak (M≲1.1, where M is the sonic Mach number) shocks in a collisionless, magnetized plasma. We emphasize that this effect does not require an appeal to plasma microturbulence. Moreover, while most collisionless systems may be unsuitable to support purely gyroviscous shocks, we argue that gyro-viscous heating may be an overlooked mechanism, generally; and it may be a key driver within magnetohydrodynamic shocks at large. In conclusion, representative examples include the plasma environments produced on the plasma liner experiment and the magnetized liner inertial fusion platforms.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Effects of Initial Condition Spectral Content on Shock Driven-Turbulent Mixing

The mixing of materials due to the Richtmyer-Meshkov instability and the ensuing turbulent behavior is of intense interest in a variety of physical systems including inertial confinement fusion, combustion, and the final stages of stellar evolution. Extensive numerical and laboratory studies of shock-driven mixing have demonstrated the rich behavior associated with the onset of turbulence due to the shocks. Here we report on progress in understanding shock-driven mixing at interfaces between fluids of differing densities through three-dimensional (3D) numerical simulations using the RAGE code in the implicit large eddy simulation context. We consider a shock-tube configuration with a band of high density gas (SF 6 ) embedded in low density gas (air). Shocks with a Mach number of 1.26 are passed through SF 6 bands, resulting in transition to turbulence driven by the Richtmyer-Meshkov instability. The system is followed as a rarefaction wave and a reflected secondary shock from the back wall pass through the SF 6 band. We apply a variety of initial perturbations to the interfaces between the two fluids in which the physical standard deviation, wave number range, and the spectral slope of the perturbations are held constant, but the number of modes initially present is varied. By thus decreasing the density of initial spectral modes of the interface, we find that we can achieve as much as 25% less total mixing at late times. This has potential direct implications for the treatment of initial conditions applied to material interfaces in both 3D and reduced dimensionality simulation models.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗