Session CO04: HED: Hydrodynamic Instabilities and Mixing

Live

MARBLE is a separated reactants campaign to investigate the effects of heterogeneous mix on thermonuclear burn. In MARBLE experiments, a two-shock implosion compresses Si-doped plastic capsules filled with fully deuterated divinylbenzene foam and HT or ArT gas fills. Embedded in the foam are engineered voids of known sizes and locations, which allow for control over heterogeneity prior to hydrodynamic mixing. The ratio of DT to DD neutron yield is measured, from which properties of the mix can be deduced. The MARBLE team successfully demonstrated for the first time control over heterogeneity and quantitatively assessed effects of mix on thermonuclear burn. These data enable validation of mix {\&} burn models in multi-physics codes such as the LANL xRAGE code.   

Live

The Marble\footnote{T J Murphy {\it et al,} J Phys:Conf Series {\bf 717}, 012072 (2016).} campaign on NIF quantifies 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mix on thermonuclear burn for comparison to a probability distribution function (PDF) burn model.\footnote{J R Fincke, unpublished; J R Ristorcelli, Phys Fluids 29, 020705 (2017).} MARBLE utilizes plastic capsules filled with deuterated plastic foam and tritium-containing gas. Recent experiments, which utilized an argon-tritium gas mixture, show the expected decrease in DT/DD yield ratio with non-uniform initial foam morphology, while previous experiments with a hydrogen-tritium gas mixture did not.\footnote{T J Murphy {\it et al} submitted to High Energy. Dens. Phys.}   

Live

The quest for controlled fusion energy has been ongoing for over a half century. The attraction of inertial confinement fusion (ICF) is the enormous energy that is potentially available in fusion fuels and the view of fusion as a safe, clean energy source. Understanding how the development of material mixing impacts thermonuclear reaction rates is of particular importance to achieving energy gain in ICF. The MARBLE campaign at Los Alamos National Laboratory (LANL) is a series of ICF experiments employing plastic foams with engineered macro-pores designed to investigate heterogeneous material mixing during laser driven shock implosions. Accurately modeling the dynamics of these foams is challenging for radiation-hydrodynamics codes due to the complex geometry that stresses multi-material modeling of equation of state (EOS) opacity, thermal conduction, and thermonuclear burn. We employed xRAGE, a LANL Eulerian radiation-hydrodynamics code, to perform the simulations and study the material effects and shock propagation in comparison with the results of companion MARBLE Void Collapse experiments performed on the OMEGA laser at the Laboratory for Laser Energetics (LLE). Our simulations are in good agreement with the experimental shock wave speeds. We will present the conditions necessary for accurate simulation of these experiments and discuss modeling implications.   

Live

We describe a platform with an open geometry in which the laser-produced plasma plumes will collide to produce high density, hot, often turbulent regions such that turbulent mix and thermonuclear reactions can occur. To examine the dynamic process of the turbulent mix as well as the feasibility of achieving measurable thermonuclear reactions, we have studied several configurations using 2D and 3D simulations, including V-shaped wedges and cones. Furthermore, different spatial arrangements of low Z and high Z material can be arranged. This platform is quite versatile in including various amounts of the mix, initiating different flow instabilities, and studying the transition from laminar to turbulent flows. We will present our analysis of several simulated platforms, demonstrate the feasibility of various measurements, and discuss their relevance in constraining the mix models.   

Live

Diffusive particle acceleration in shocks is a likely source of cosmic rays. To be consistent with observations, acceleration by this method requires that local magnetic fields are amplified above the mean interstellar field. It has been proposed that the passage of cosmic rays through the background plasma could self-consistently amplify the fields through the development of magneto-collisional instabilities. The TDYNO platform has been developed, in which rapid magnetic field amplification to near equipartition with the turbulent fluid motions has been demonstrated, through the action of the turbulent dynamo. This subsonic, stochastically magnetized plasma provides an opportunity to study physics relevant to the interstellar medium. Here, we present results from experiments which adapt this target platform to study magneto-collisional instabilities driven by kA/mm$^{2}$ current densities.   

Live

\newline \indent We present results from experiments at the National Ignition Facility (NIF) that are part of developing a platform for performing high-resolution radiography of hydrodynamic experiments. The purpose of the experiments is to observe the nonlinear Rayleigh-Taylor instability evolution of a single mode perturbation with enough resolution to capture the turbulent transition. This presents a challenge in our High-Energy-Density (HED) experiments, since the largest length scale associated with turbulence in this regime is expected to be on the order of a few microns. \newline \indent To achieve a 3~$\mu$m resolution, we have taken a comprehensive approach of not only addressing the spatial resolution of the optic and detectors used, but also the need to minimize motion blur in our platform. Here we discuss our approach and show the first experimental images obtained on our path to 3~$\mu$m imaging of a HED hydrodynamic platform at the NIF.   

Live

The study of metal ejecta interactions has broad applicability to fields ranging from particle dynamics modeling to materials physics [1]. Recent experiments at laser facilities have begun to study ejecta formation [2], but there exist few examples of ejecta interaction studies. We present the first movies of ejecta-ejecta interactions from experiments performed on the OMEGA and EP lasers. Lasers drive shocks through two tin metal foils with planar trenches carved into their back sides. As the shocks break out, the trench features invert to form planar jets of micron-sized ejecta moving towards each other at speeds of several km/s. We use point-projection radiography to image the interacting jets. Jets emerging from tin releasing into solid are observed to have areal densities and volume fractions of 0.5 mg cm-2 and 0.25{\%}, respectively, whereas jets emerging from tin releasing into liquid have densities and volume fractions nearly three times greater. We discuss the observed interaction dynamics for both conditions. [1] W. T. Buttler et al., J. Dyn. Behav. Mater. 3(2), 151--155 (2017). [2] T. de Ress\'{e}guier et al., J. Appl. Phys. 124, 065106 (2018).   

Live

A laser pointing for an azimuthal uniform cylindrical implosion is determined empirically from x-ray self-emission images of the implosion end-on. The images are decomposed into cylindrical harmonics to determine the degree of uniformity and to measure the transfer of imposed laser intensity modes onto the cylinder. Two cases, one with an imposed mode-5 perturbation and another that is the most azimuthally uniform are compared. Despite a mode-5 persisting for the latter case, the implosion is measured to be uniform to within the resolvable features of the x-ray image. The growth of the modes for the imposed mode-5 case over time demonstrate that mode-5 growth occurs throughout the entire acceleration of the cylindrical shell, with exceptions in the case of shell defects that seed either mode-4 or mode-6 growth. Mode growth is independent of shell thickness and shell outer diameter. In all cases, there is no measurable mode-10 growth, despite the mode-10 amplitude increasing by a factor of 4 from the mode-5 pointing to the uniform pointing.   

Live

Turbulent mixing is believed to play a key role in a number of high energy density plasma systems including being the driver of magnetic field amplification in astrophysical dynamos, and having possibly deleterious effect in inertial confinement fusion, etc. Turbulent mixing has also defied direct observation in the high temperature ($>\sim$keV), long lasting ($>\sim$ns) and large volume ($>\sim$mm$^3$) regimes that overlap these applications. Here, we introduce a new experimental scheme to study turbulent mixing in these conditions that are uniquely accessible on the OMEGA EP laser. Our new scheme extends a proven design to create keV, mm$^3$, ns-duration turbulent plasma with the addition of mid-Z tracer elements, e.g., copper; chlorine, etc. to the target. These tracers, once they are entrained into the turbulent plasma following initiation, become strong, and crucially, distinguishable emission sources to x-ray imaging and spectroscopic instrumentation. Synthetic instrumentation of FLASH simulated plasma reveal the onset and progress of turbulent mixing from the structure of the plasma's self emission.   

Live

The LANL HED Hydro team has adapted our Omega RM/RT instability platform to study the effects of heating on a shocked interface similar to what might occurring in the inner shell of a double shell type design. The interface can be heated before, after or during shock and reshock using the Omega laser, and can easily be adapted to larger facilities such as the NIF. The current design allows for heating of one or two high density interfaces separated by low density foam. The materials can be chosen over a wide variety of densities and atomic numbers and heated from several eV up to around 100 eV, depending on material thickness and composition. Strong shocks can then interact with these layers from either end of the shock tube. Platform details and results of the heating tests on various layers will be presented.   

Live

Correctly modeling hydrodynamic instabilities often requires simultaneously treating structures that occur on different length scales, which can be challenging for simulations to handle. In this talk, we will discuss recent results from a high-energy-density experiment intended to measure multimode instability growth, as well as current efforts to model it using simulations. Multimode, for our purposes, refers to a repeatable, 2D initial seed perturbation consisting of \textgreater 10 modes organized into a finite band in Fourier space. The experiment drives a shock across a material interface, at which the perturbation has been machined. To model the resulting growth, we can use a combination of mesh-resolved structure with a mix model (BHR) in order to capture different scales in the instability, where the choice becomes particularly important when treating structure that does not neatly fit into either a regime of fully-developed turbulence nor full coherent modal growth. In particular, we present initial results using a modal model to initialize BHR, applied to this experiment.   

Live

A shock incident on an interface between two materials will deposit vorticity baroclinically. This vorticity will typically cause any perturbations on the pre-shock interface to grow. Many models of the post-shock perturbation evolution assume an infinite sound speed, whereas in the High-Energy-Density (HED) regime the sounds speeds near the interface are often on the order of the characteristic velocities of the perturbation evolution. In this talk, we will present an experimental scheme designed to quickly create a strong, localized vorticity distribution in a system with a finite sound speed. The motion of a tracer extended away from that localized vorticity then allows one to infer when different parts of the experiment learn about the created vorticity distribution. This should yield information about the sound speeds present near the post-shock interface, and could eventually be used to constrain post-shock thermodynamic states along the interface in HED Richtmyer-Meshkov experiments. This work conducted under the auspices of the U.S. DOE by LANL under contract 89233218CNA000001.   

Live

The presence of multiple shocks interacting with multiple material interfaces is ubiquitous in ICF, but is often poorly validated in these complex systems. The LANL NIF MShock campaign is developing a capability to study RM/RT growth in the multiple layer, multiple-shock regime. We recently demonstrated the novel ability to generate two successive shocks from the same direction in a planar target. Successive shock interaction with an interface has unique outcomes, compared to traditional reshock, which have never been experimentally isolated. The relative direction of the shock to the interface density gradient affects the direction of vorticity deposition and controls the possibility of interface phase inversion. Across all parameters, successive shocks span from the simplest physics of multiple shocks (no phase inversions and co-directional vorticity addition) to the most complicated dynamics (two phase inversions and counter-acting vorticity deposition). We present results of the first experiments studying successive shock interaction with a single perturbed interface. Initial experiments with two cases of different A/$\lambda $ show observed perturbation growth matches predictions that post-2nd shock the smaller A/$\lambda $ case re-inverts and the larger A/$\lambda $ case continues to grow.   

Live

A numerical design study was performed to explore the parameter space of multiple co-propagating planar shock interactions in a laser-driven shock-tube on the National Ignition Facility (NIF). The experiment geometry is unique in that it is capable of producing a wide range of multiple co- or counter-propagating shock / material interface interactions in a planar geometry with interfacial perturbations at a diagnosable scale. Integrated hohlraum / shock-tube package simulations were performed using both HYDRA and xRAGE, and comparison between the two shows good agreement on the trajectory of unstable interfaces. Comparisons are made with both experimental data [1] and previous simulations [2] from this platform. The parameter space of possible shock interactions is very rich and allows for the study of multi-shock instability growth from the incompressible limit to strongly compressible conditions. [1] E. C. Merritt et al., ``Results of the first same-sided successive-shock HED instability experiments'', abstract submitted to APS DPP (2020). [2] C. A. Di Stefano et al., ``First experimental measurement of two co-propagating shocks interacting with an unstable interface'', submitted to Phys. Rev. Lett (2020).   

On Demand

We present a numerical study of laser-driven shock interaction with a single deformable particle embedded in a polystyrene target for post-shock pressures up to 50 GPa. Numerical simulations are carried out using multi-physics radiation-hydrodynamics code FLASH that solves Euler's equations for compressible flow. We model the particle using a modified ideal gas equation state to mitigate the overestimation of compressibility in the code. We present the time evolution of pressure field, wave patterns in the flow and particle compression. Particle deformation is quantitatively characterized using time evolution of characteristic length scales of particle interface. Additionally, the motion of lagrangian tracers inside the particle is used to understand the inviscid momentum transfer from the shocked medium into the particle. The particle is accelerated to a considerable velocity as it gets traversed by the shock front. Finally, the study is carried out to investigate the flow field and the particle response for various combinations of particle sizes, particle densities and host-particle shock-impedance ratios.