Session UO8: HED Hydrodynamics

Results from MARBLE DT Experiments on the National Ignition Facility: Implosion of Foam-Filled Capsules for Studying Thermonuclear Burn in the Presence of Heterogeneous Mix

The MARBLE\footnote{T. J. Murphy {\it et al} J Phys:Conf Series {\bf 717}, 012072 (2016).} campaign on NIF investigates the effect of heterogeneous mix on thermonuclear burn for comparison to a probability distribution function (PDF) burn model.\footnote{J. R. Fincke, unpublished; J. R. Ristorcelli, Phys. Fluids 29, 020705 (2017).} MARBLE utilizes plastic capsules filled with deuterated plastic foam and tritium gas. The ratio of DT to DD neutron yield is indicative of the degree to which the foam and the gas atomically mix. Platform development experiments have been performed to understand the behavior of the foam and of the gas separately using two types of capsule. The first experiments using deuterated foam and tritium gas have been performed. Results of these experiments, and the implications for our understanding of thermonuclear burn in heterogeneously mixed separated reactant experiments will be discussed.   

Shock Propagation through Macro-Pore Engineered Foams

Shock propagation through macro-pore engineered foams has been studied to examine (1) if the pore size affects shock speed and (2) if spherical geometry of the void may induce turbulence. In the first experiment, three types of macro-pore engineered foams (\textless 1, 50, and 90 um in diameter) were used in shock tube experiments driven by the Omega laser. X-ray radiographic data indicates that shock speed through macro-pore engineered foams depends strongly on foam density, less on pore size. In the second experiment, a single foam-filled ``void'' in a diameter of 250 um was shocked by two opposing planar shocks, which were separated by 6.4 ns. While the first shock compressed a spherical foam-void without much turbulence, the second shock seems to increase a turbulent motion.   

Argon-Doped Capsule Implosion Experiments on the Shenguang-II Laser Facility

Argon is often doped in the hydrogen isotope capsule as the tracer for diagnosing the status of the hot spot in inertial confinement fusion implosion experiments. Implosion performance could be affected by the doped argon. For instance, it could bring about the concentration of the heavier argon ions in the center of hot spot, thus degrading the implosion performance. Moreover, implosion mix could be investigated by doping heavier elements in hydrogen isotope capsule, and the atomic-mix effects have been investigated in the pioneering studies. In this talk, we present the performance of argon-doped implosion experiments, in which D-D reaction was used for the substitute of D-T fuel. The experiments were conducted on the Shenguang-II laser facility. The doping-fraction of argon was set as 1{\%}, 2{\%} and 10{\%} (atomic fraction). The temperature and density of electrons are determined by the K-shell emission spectra of the highly-ionized argon. The size of hot spot was recorded by a time-resolving x-ray monochromatic imaging system. The neutron yield were detected by both BF$_{\mathrm{3}}$ and scintillator detectors. A strong correlation between argon x-ray line intensity and neutron yields have been found in the experiments, and the convergence ratios deduced from the hot-spot imaging agree well with numerical simulation for the difference doping fraction which brings about the change of the equations of states and radiative opacity.   

Interfacial mixing in high energy-density matter with a multiphysics kinetic model

We have extended a recently-developed multispecies, multitemperature BGK model [Haack et al. , J. Stat. Phys. (2017)] to include multiphysics capability that allows modeling of a wider range of plasma conditions. In particular, we have extended the model to describe one spatial dimension, and included a multispecies atomic ionization model, accurate collision physics across coupling regimes, self-consistent electric fields, and degeneracy in the electronic screening. We apply the new model to a warm dense matter scenario in which the ablator-fuel interface of an inertial confinement fusion target is heated, similar to a recent molecular dynamics study [Stanton et al., submitted to PRX], but for larger length and time scales and for much higher temperatures. From our numerical results we are able to explore a variety of phenomena, including hydrogen jetting, kinetic effects (non- Maxwellian and anisotropic distributions), plasma physics (size, persistence and role of electric fields) and transport (relative sizes of Fickean diffision, electrodiffusion and barodiffusion). As compared with the recent molecular dynamics work the kinetic model greatly extends the accessible physical domains we are able to model.   

Drive development for an \textasciitilde 10 Mbar Rayleigh-Taylor strength experiment on the National Ignition Facility

Strength can be inferred by the amount a Rayleigh-Taylor surface deviates from classical growth when subjected to acceleration. If the acceleration is great enough, even materials highly resistant to deformation will flow. We use the National Ignition Facility (NIF) to create an acceleration profile that will cause sample metals, such as Mo or Cu, to reach peak pressures of \textasciitilde 10 Mbar without inducing shock melt. To create such a profile we shock release a stepped density reservoir across a large gap with the stagnation of the reservoir on the far side of the gap resulting in the desired pressure drive history. Low density steps (foams) are a necessary part of this design and have been studied in the last several years on the Omega and NIF facilities. We will present computational and experimental progress that has been made on the \textasciitilde 10 Mbar drive designs -- including recent drive shots carried out at the NIF.   

Modeling and simulations of radiative blast wave driven Rayleigh-Taylor instability experiments

Recent experiments at the National Ignition Facility measured the growth of Rayleigh-Taylor RT instabilities driven by radiative blast waves, relevant to astrophysics and other HEDP systems. We constructed a new Buoyancy-Drag (BD) model, which accounts for the ablation effect on both bubble and spike. This ablation effect is accounted for by using the potential flow model ]Oron et al PoP 1998], adding another term to the classical BD formalism: $\beta $\textit{Du}$_{A}/u$, where $\beta $ the Takabe constant, $D$ the drag term, $u_{A}$ the ablation velocity and $u $the instability growth velocity. The model results are compared with the results of experiments and 2D simulations using the CRASH code, with nominal radiation or reduced foam opacity (by a factor of 1000). The ablation constant of the model, $\beta_{b/s}$, for the bubble and for the spike fronts, are calibrated using the results of the radiative shock experiments.   

Experiments of the highly non-linear Rayleigh-Taylor instability regime and dependence on Atwood Number

Potential flow models predict that a Rayleigh-Taylor unstable system will reach a terminal velocity (and constant Froude number) at low Atwood numbers. Numerical simulations predict a re-acceleration phase of Rayleigh-Taylor Instability (RTI) and higher Froude number at late times. To observe this effect, we are conducting a series of experiments at OMEGA 60 to measure single-mode RTI growth at low and high Atwood numbers and late times. X-ray radiographs spanning 40$+$ ns capture the evolution of these systems. Experimental design challenges and initial results are discussed here. This work is funded by the Lawrence Livermore National Laboratory under subcontract B614207, and was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract No. DE-AC52-07NA27344.   

Coupled Hydrodynamic Instability Growth on Oblique Interfaces with a Reflected Rarefaction

Hydrodynamic instabilities play an important role in the evolution of inertial confinement fusion and astrophysical phenomena. Three of the Omega-EP long pulse beams (10 ns square pulse, $\sim$14 kJ total energy, 1.1 mm spot size) drive a supported shock across a heavy-to-light, oblique, interface. Single- and double-mode initial conditions seed coupled Richtmyer-Meshkov (RM), Rayleigh-Taylor (RT), and Kelvin-Helmholtz (KH) growth. At early times, growth is dominated by RM and KH, whereas at late times a rarefaction from laser turn-off reaches the interface, leading to decompression and RT growth. The addition of a thirty degree tilt does not alter mix width to within experimental error bars, even while significantly altering spike and bubble morphology. The results of single and double-mode experiments along with simulations using the multi-physics hydro-code RAGE will be presented. This work performed under the auspices of the U.S. Department of Energy by LANL under contract DE-AC52-06NA25396. This work is funded by the NNSA-DS and SC-OFES Joint Program in High-Energy-Density Laboratory Plasmas, grant number DE-NA0002956. This material is partially supported by DOE Office of Science Graduate Student Research (SCGSR) program.   

High-Energy-Density Shear Flow and Instability Experiments

High-energy-density shear experiments have been performed by LANL at the OMEGA Laser Facility and National Ignition Facility (NIF). The experiments have been simulated using the LANL radiation-hydrocode RAGE and have been used to assess turbulence models’ ability to function in the high-energy-density, inertial- fusion-relevant regime. Beginning with the basic configuration of two counter-oriented shock-driven flows of $\geq$ 100 km/s, which initiate a strong shear instability across an initially solid-density, 20 $\mu$m thick Al plate, variations of the experiment to details of the initial conditions have been performed. These variations have included increasing the fluid densities (by modifying the plate material from Al to Ti and Cu), imposing sinusoidal seed perturbations on the plate, and directly modifying the plate's intrinsic surface roughness. Radiography of the unseeded layer has revealed the presence of emergent Kelvin-Helmholtz structures which may be analyzed to infer fluid-mechanical properties including turbulent energy density.   

Modeling of laser-driven hydrodynamics experiments

Correct interpretation of hydrodynamics experiments driven by a laser-produced shock depends strongly on an understanding of the time-dependent effect of the irradiation conditions on the flow. In this talk, we discuss the modeling of such experiments using the RAGE radiation-hydrodynamics code. The focus is an instability experiment consisting of a period of relatively-steady shock conditions in which the Richtmyer-Meshkov process dominates, followed by a period of decaying flow conditions, in which the dominant growth process changes to Rayleigh-Taylor instability. The use of a laser model is essential for capturing the transition.   

Results from a thin layer Richtmyer-Meshkov Experiment at OMEGA

The Richtmyer-Meshkov (RM) instability can degrade heating of the fuel in inertial confinement fusion (ICF) capsules where a multi-layer spherical capsule is ablatively driven. The RM hydrodynamic instability occurs when an impulsive force (or shock) impinges and amplifies imperfections at an interface with disparate densities. Any defects on the ablator or between layers in an ICF capsule will grow due to the RM instability and may lead to further degrading hydrodynamic instabilities. The linear instability can be driven into a non-linear regime and even become turbulent if it is subject to more shocks. The \textit{Mshock} campaign is studying this evolution in a planar multi-interface, multi-shock geometry analogous to an ICF implosion. The campaign uses a beryllium shock tube with low density CH foams and a thin high density CHI layer to study the layer's growth rate and the amount of mix expected based on the interface initial conditions. A smooth, coherent mode and broadband mode on the CHI layer provide a broad comparison of mix conditions for simulations. Results from experiments at the OMEGA facility in a simple shock and re-shock configuration and comparisons with the BHR Reynold's stress model are presented.   

Laser-driven Mach waves for gigabar-range shock experiments

Mach reflection offers possibilities for generating planar, supported shocks at higher pressures than are practical even with laser ablation. We have studied the formation of Mach waves by algebraic solution and hydrocode simulation for drive pressures at much than reported previously, and for realistic equations of state. We predict that Mach reflection continues to occur as the drive pressure increases, and the pressure enhancement increases monotonically with drive pressure even though the ``enhancement spike'' characteristic of low-pressure Mach waves disappears. The growth angle also increases monotonically with pressure, so a higher drive pressure seems always to be an advantage. However, there are conditions where the Mach wave is perturbed by reflections. We have performed trial experiments at the Omega facility, using a laser-heated halfraum to induce a Mach wave in a polystyrene cone. Pulse length and energy limitations meant that the drive was not maintained long enough to fully support the shock, but the results indicated a Mach wave of 25-30 TPa from a drive pressure of 5-6 TPa, consistent with simulations. A similar configuration should be tested at the NIF, and a Z-pinch driven configuration may be possible.   

Using NIF to Test Theories of High-Pressure, High-Rate Plastic Flow in Metals

Precisely controlled plasmas are playing key roles both as pump and probe in experiments to understand the strength of solid metals at high energy density (HED) conditions. In concert with theoretical advances, these experiments have enabled a predictive capability to model material strength at Mbar pressures and high strain rates [1]. Here we describe multiscale strength models developed for tantalum starting with atomic bonding and extending up through the mobility of individual dislocations, the evolution of dislocation networks and so on until the ultimate material response at the scale of an experiment [2]. Experiments at the National Ignition Facility (NIF) probe strength in metals ramp compressed to 1-8 Mbar [3]. The model is able to predict 1 Mbar experiments without adjustable parameters [3]. The combination of experiment and theory has shown that solid metals can behave significantly differently at HED conditions [3]. We also describe recent studies of lead compressed to 3-5 Mbar. [1] R.E. Rudd et al., MRS Bulletin 35, 999 (2010). [2] N.R. Barton et al., J. Appl. Phys. 109, 073501 (2011).[3] H.-S. Park et al., Phys. Rev. Lett. 114, 065502 (2015).   

Numerical analysis of Melting Phenomenon on plates drving by large pulse current

Characteristic properties of materials under high pressure, such as isentropic compression lines, are very important, which can be investigated through pulsed intense magnetic field and magnetic force generated by large-current facilities. However, due to the strong Ohmic heating caused by the intense current flowing through the loads, the load material undergoes a series of phase transitions including melting, vaporization and even ionization into plasmas. Therefore, estimation and prediction of the ablation condition of the loading surface play an extremely important role in load design and fulfillment of physical goals of large facilities. In this work, the melting of an aluminum plate under a 30 MA loading current is investigated using the MDSC2 code, which is based on Burgess' resistivity model and Linderman's melting criteria. For aluminum plates of different thicknesses, temporal variation of the ablation layer as well as typical physical quantities (i.e. density, temperature, pressure, etc.) during the late time at the interface between the ablation and non-ablation regions are obtained.