WorldCat Identities

Metzler, N.

Overview
Works: 9 works in 9 publications in 1 language and 9 library holdings
Roles: Author
Publication Timeline
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Most widely held works by N Metzler
Nonlinear optical guiding in the separable beam limit by N Metzler( Book )

1 edition published in 1989 in English and held by 1 WorldCat member library worldwide

Direct Observation of Mass Oscillations due to Ablative Richtmyer-Meshkov Instability and Feedout in Planar Plastic Targets( )

1 edition published in 2002 in English and held by 0 WorldCat member libraries worldwide

Perturbations that seed Rayleigh-Taylor (RT) instability in laser-driven targets form during the early-time period. This time includes a shock wave transit from the front to the rear surface of the target, and a rarefaction wave transit in the opposite direction. During this time interval, areal mass perturbations caused by all sources of nonuniformity (laser imprint, surface ripple) are expected to oscillate. The first direct experimental observations of the areal mass oscillations due to ablative Richtmyer-Meshkov (RM) instability and feedout followed by the RT growth of areal mass modulation are discussed. The experiments were made with 40 to 99 mm thick planar plastic targets rippled either on the front or on the rear with a sine wave ripple with either 30 or 45 mm wavelength and with 0.5, 1 or 1.5 mm amplitude. Targets were irradiated with 4 ns long Nike KrF laser pulses at approximately 50 TW/cm2. The oscillations were observed with our novel diagnostic technique, a monochromatic x-ray imager coupled to a streak camera. For the ablative RM instability (front side ripple), the mass modulation amplitude was typically observed to grow, reach a peak, and then decrease, after which the exponential RT growth started. In some cases, one phase reversal due to the ablative RM instability was observed. For the feedout geometry (rear side ripple), in all cases two phase reversals were observed: a distinct half-oscillation was followed by the onset of the RT growth, resulting in a second phase reversal
Classical and Ablative Richtmyer-Meshkov Instability and Other ICF-Relevant Plasma Flows Diagnosed With Monochromatic X-Ray Imaging( )

1 edition published in 2007 in English and held by 0 WorldCat member libraries worldwide

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 RM-unstable 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
Direct Observation of Feedout-Related Mass Oscillations in Plastic Targets( )

1 edition published in 2001 in English and held by 0 WorldCat member libraries worldwide

Feedout means the transfer of mass perturbations from the rear to the front surface of a driven target. When a planar shock wave breaks out at a rippled rear surface of the target, a lateral pressure gradient drives sonic waves in a rippled rarefaction wave propagating back to the front surface. This process redistributes mass in the volume of the target, forming the feedout-generated seed for ablative Rayleigh-Taylor (RT) instability. We report the first direct experimental observation of areal mass oscillation associated with feedout, followed by the onset of exponential RT growth
Perturbation Evolution Started by Richtmyer-Meshkov Instability in Planar Laser Targets( )

1 edition published in 2006 in English and held by 0 WorldCat member libraries worldwide

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
Large-Scale High-Resolution Simulations of High Gain Direct-Drive Inertial Confinement Fusion Targets( )

1 edition published in 2004 in English and held by 0 WorldCat member libraries worldwide

Targets have been designed that produce moderate to high gain when directly driven by lasers. The intrinsic sensitivity of these targets to hydro instabilities is found using the FAST(2D) multidimensional radiation hydrocode [J.H. Gardner, A.J. Schmitt, J.P. Dahlburg, et al., Phys. Plasmas 5, 1935 (1998)], which simulates the simultaneous behavior of a large bandwidth (e.g., l = 2-256) of perturbations from compression to acceleration, and then to stagnation and burn. The development of the structure in these multi-mode simulations is benchmarked to theoretical analysis and single-mode calculations, which reveals the need to "renormalize" the simulation after compression. The simulations predict that a direct drive point design is expected to degrade significantly from its 1-D clean yield, yet still ignite and give appreciable gain. Simulations of high-gain pellets using a spike prepulse to inhibit Richtmyer-Meshkov growth show a considerable robustness, with high (> 100) gains possible even with nominal surface finishes and laser imprint
Shock Front Distortion and Richtmyer-Meshkov-like Growth Caused by a Small Pre-Shock Non-Uniformity( )

1 edition published in 2007 in English and held by 0 WorldCat member libraries worldwide

Response of a shock front to small pre-shock non-uniformities of density, pressure and velocity is studied theoretically and numerically. These pre-shock nonuniformities emulate imperfections of a laser target, due either to its manufacturing, like joints or feeding tubes, or to pre-shock perturbation seeding/growth, as well as density fluctuations in foam targets, "thermal layers" near heated surfaces, etc. Similarly to the shock-wave interaction with a small non-uniformity localized at a material interface which triggers a classical Richtmyer-Meshkov (RM) instability, interaction of a shock wave with periodic or localized pre-shock perturbations distributed in the volume distorts the shape of the shock front and can cause a RM-type instability growth. Explicit asymptotic formulae describing distortion of the shock front and the rate of RM-type growth are presented. These formulae are favorably compared both to the exact solutions of the corresponding initial-boundary-value problem and to numerical simulations. It is demonstrated that a small density modulation localized sufficiently close to a flat target surface produces the same perturbation growth as an "equivalent" ripple on the surface of a uniform target, characterized by the same initial areal mass modulation amplitude
Instability of a Planar Expansion Wave( )

1 edition published in 2005 in English and held by 0 WorldCat member libraries worldwide

An expansion wave is produced when an incident shock wave interacts with a surface separating a fluid from a vacuum. Such an interaction starts the feedout process that transfers perturbations from the rippled inner (rear) to the outer (front) surface of a target in inertial confinement fusion. Being essentially a standing sonic wave superimposed on a centered expansion wave, a rippled expansion wave in an ideal gas, like a rippled shock wave, typically produces decaying oscillations of all fluid variables. Its behavior, however, is different at large and small values of the adiabatic exponent gamma. At gamma> 3, the mass modulation amplitude delta-m in a rippled expansion wave exhibits a power-law growth with time alpha tau(beta), where beta = (gamma - 3)/(gamma - 1). This is the only example of a hydrodynamic instability whose law of growth, dependent on the equation of state, is expressed in a closed analytical form. The growth is shown to be driven by a physical mechanism similar to that of a classical Richtmyer-Meshkov instability. In the opposite extreme gamma - 1 much less than 1, delta-m exhibits oscillatory growth, approximately linear with time, until it reaches its peak value approximately (gamma - 1)^( - 1/2), and then starts to decrease. The mechanism driving the growth is the same as that of Vishniac's instability of a blast wave in a gas with low gamma. Exact analytical expressions for the growth rates are derived for both cases and favorably compared to hydrodynamic simulation results
Direct Observation of Mass Oscillations Due to Ablative Richtmyer-Meshkov Instability in Plastic Targets( )

1 edition published in 2002 in English and held by 0 WorldCat member libraries worldwide

We report the first direct experimental observation of the ablative Richtmyer-Meshkov instability. It manifests itself in oscillations of areal mass that occur during the shock transit time, which are caused by the rocket effect or dynamic overpressure characteristic of interaction between the laser absorption zone and the ablation front. With the 4 ns long Nike KrF laser pulse and our novel diagnostic technique (monochromatic x-ray imaging coupled to a streak camera) we were able to register a peak and a valley of the areal mass variation before the observed onset of the Rayleigh-Taylor growth
 
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