Direct Observation of Feedout-Related Mass Oscillations in Plastic Targets

Aglitskiy, Y.; Velikovich, A. L.; Karasik, M.; Serlin, V.; Pawley, C. J.; Schmitt, A. J.; Obenschain, S. P.; Mostovych, A. N.; Gardner, John; Metzler, N.

doi:10.1103/physrevlett.87.265002

Cited by 41 publications

(34 citation statements)

References 17 publications

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“…This trend is illustrated in Fig. 1(b [6][7][8]19 on the foam side of the target. For this target, the classical RM growth continues for only 0.6 ns after the incident shock wave hits the foam-plastic interface.…”

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confidence: 70%

“…Solid plastic is less compressible by the transmitted shock wavecompression ratio of no more than 3 -and therefore a larger value of is appropriate; 10,18 we take here Side-on measurements of the interfacial modulation amplitude x in laser-driven solid targets are difficult, but the total mass modulation amplitude m is directly measurable by the face-on radiographic diagnostics. [6][7][8][9]13 Time history of m is plotted in Transition to an accelerated target provides additional complications. After the target starts to accelerate, the classical RM interfacial growth must evolve into RT.…”

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confidence: 99%

“…[6][7][8] Our experiments were performed with the Nike KrF laser, 19 248 L nm. The 4 ns long laser pulse, with or without a ~5%, 3 ns foot was focused to a spot 750 m in diameter, producing intensity up to 50 TW/cm 2 .…”

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confidence: 99%

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Perturbation evolution started by Richtmyer-Meshkov instability in planar laser targets

et al. 2006

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The first observations of the interaction of the Richtmyer-Meshkov (RM) instability with reflected shock and rarefaction waves in laser-driven targets are reported.The RM growth is started by a shock wave incident upon a rippled interface between low-density foam and solid plastic. Subsequent interaction of secondary rarefaction and/or shock waves arriving from the ablation front and the rear surface of the target with the RM-unstable interface stops the perturbation growth and reverses its direction. The ensuing exponential Rayleigh-Taylor growth thus can sometimes proceed with an inverted phase.

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Perturbation evolution started by Richtmyer-Meshkov instability in planar laser targets

et al. 2006

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“…2 The presence of such distorted fronts in inertial-confinement-fusion (ICF) pellets is significant because they provide small "seeds" that at early times grow as a result of the ablative RichtmyerMeshkov (RM) instability. 3,4 Later, once the target shell begins to accelerate, the ablative Rayleigh-Taylor (RT) instability takes effect and small non-uniformities at the ablation surface grow initially with time t as e ct , where c is the growth rate. 5 Eventually, these perturbations form nonlinear bubble-and-spike structures that can quench thermonuclear ignition by mixing large amounts of ablator material into the hot spot.…”

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confidence: 99%

Numerical simulations of the ablative Rayleigh-Taylor instability in planar inertial-confinement-fusion targets using the FastRad3D code

et al. 2016

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The ablative Rayleigh-Taylor (RT) instability is a central issue in the performance of laser-accelerated inertial-confinement-fusion targets. Historically, the accurate numerical simulation of this instability has been a challenging task for many radiation hydrodynamics codes, particularly when it comes to capturing the ablatively stabilized region of the linear dispersion spectrum and modeling ab initio perturbations. Here, we present recent results from two-dimensional numerical simulations of the ablative RT instability in planar laser-ablated foils that were performed using the Eulerian code FastRad3D. Our study considers polystyrene, (cryogenic) deuterium-tritium, and beryllium target materials, quarter- and third-micron laser light, and low and high laser intensities. An initial single-mode surface perturbation is modeled in our simulations as a small modulation to the target mass density and the ablative RT growth-rate is calculated from the time history of areal-mass variations once the target reaches a steady-state acceleration. By performing a sequence of such simulations with different perturbation wavelengths, we generate a discrete dispersion spectrum for each of our examples and find that in all cases the linear RT growth-rate γ is well described by an expression of the form γ=α [kg/(1+ϵ kLm)]1/2−βkVa, where k is the perturbation wavenumber, g is the acceleration of the target, Lm is the minimum density scale-length, Va is the ablation velocity, and ϵ is either one or zero. The dimensionless coefficients α and β in the above formula depend on the particular target and laser parameters and are determined from two-dimensional simulation results through the use of a nonlinear curve-fitting procedure. While our findings are generally consistent with those of Betti et al. (Phys. Plasmas 5, 1446 (1998)), the ablative RT growth-rates predicted in this investigation are somewhat smaller than the values previously reported for the same target and laser parameters. It is speculated that differences in the equation-of-state and opacity models are largely responsible for the discrepancy. Resolution of this issue awaits the development of better experimental diagnostics capable of measuring small-wavelength (5–20 μm) perturbation growth due to the ablative RT instability in the linear regime.

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“…The most advanced modeling is still limited in resolution and relies upon both physical and numerical assumptions and simplifications whose adequacy needs to be constantly tested. For this reason, experimental verification of the codes and validation of the underlying physical models in the ICF-relevant physical conditions has been an area of active study in all the major centers of laser fusion research for the last decades, see [7][8][9][10][11][12][13][14][15] and references therein.…”

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confidence: 99%

Classical and ablative Richtmyer–Meshkov instability and other ICF-relevant plasma flows diagnosed with monochromatic x-ray imaging

et al. 2008

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Abstract. In inertial confinement fusion (ICF) and high-energy density physics (HEDP), the most important manifestations of the hydrodynamic instabilities and other mixing processes involve lateral motion of the accelerated plasmas. In order to understand the experimental observations and to advance the numerical simulation codes to the point of predictive capability, it is critically important to accurately diagnose the motion of the dense plasma mass. The most advanced diagnostic technique recently developed for this purpose is the monochromatic x-ray imaging that combines large field of view with high contrast, high spatial resolution and large throughput, ensuring high temporal resolution at large magnification. Its application made it possible for the experimentalists to observe for the first time important hydrodynamic effects that trigger compressible turbulent mixing in laser targets, such as ablative Richtmyer-Meshkov (RM) instability, feedout, interaction of a RMunstable interface with rarefaction waves. It also helped to substantially improve the accuracy of diagnosing many other important plasma flows, ranging from laser-produced jets to electromagnetically driven wires in a Z-pinch, and to test various methods suggested for mitigation of the Rayleigh-Taylor instability. We will review the results obtained with the aid of this technique in ICF-HEDP studies at the Naval Research Laboratory and the prospects of its future applications.

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Direct Observation of Feedout-Related Mass Oscillations in Plastic Targets

Cited by 41 publications

References 17 publications

Perturbation evolution started by Richtmyer-Meshkov instability in planar laser targets

Perturbation evolution started by Richtmyer-Meshkov instability in planar laser targets

Numerical simulations of the ablative Rayleigh-Taylor instability in planar inertial-confinement-fusion targets using the FastRad3D code

Classical and ablative Richtmyer–Meshkov instability and other ICF-relevant plasma flows diagnosed with monochromatic x-ray imaging

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