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Observation of Rayleigh–Taylor growth to short wavelengths on Nike (1999)

Pawley, C. J. ; Bodner, S. E. ; Dahlburg, J. P. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Physics of Plasmas 6 (1999), S. 565-570

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ISSN: 1089-7674

Quelle: AIP Digital Archive

Thema: Physik

Notizen: The uniform and smooth focal profile of the Nike KrF laser [S. Obenschain et al., Phys. Plasmas 3, 2098 (1996)] was used to ablatively accelerate 40 μm thick polystyrene planar targets with pulse shaping to minimize shock heating of the compressed material. The foils had imposed small-amplitude sinusoidal wave perturbations of 60, 30, 20, and 12.5 μm wavelength. The shortest wavelength is near the ablative stabilization cutoff for Rayleigh–Taylor growth. Modification of the saturated wave structure due to random laser imprint was observed. Excellent agreement was found between the two-dimensional simulations and experimental data for most cases where the laser imprint was not dominant. © 1999 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.873201

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2

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Growth of pellet imperfections and laser imprint in direct drive inertial confinement fusion targets : The 42nd annual meeting of the division of plasma physics of the American Physical Society and the 10th international congress on plasma physics (2001)

Schmitt, Andrew J. ; Velikovich, A. L. ; Gardner, J. H. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Physics of Plasmas 8 (2001), S. 2287-2295

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ISSN: 1089-7674

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Simple hydrodynamic models for describing the Richtmyer–Meshkov (RM) growth and the Rayleigh–Taylor (RT) instability are tested by simulation. The RM sharp boundary model predictions are compared with numerical simulations of targets with surface perturbations or stationary intensity perturbations. Agreement is found in the overall trends, but the specific behavior can be significantly different. RM growth of imprint from optically smoothed lasers is also simulated and quantified. The results are used to calculate surface perturbations, growth factors, and laser imprint efficiencies. These in turn are used with standard RT growth formulas to predict perturbation growth in multimode simulations of compression and acceleration of planar and spherical targets. The largest differences between prediction and theory occur during ramp-up of the laser intensity, where RT formulas predict more growth than seen in the simulations. © 2001 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.1360709

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3

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Direct drive acceleration of planar liquid deuterium targets : The 40th annual meeting of the division of plasma physics of the american physical society (1999)

Sethian, J. D. ; Bodner, S. E. ; Colombant, D. G. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Physics of Plasmas 6 (1999), S. 2089-2094

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ISSN: 1089-7674

Quelle: AIP Digital Archive

Thema: Physik

Notizen: The Nike laser (∼2–3 kJ, ∼1014 W/cm2) has been used to ablatively accelerate planar liquid deuterium targets. These experiments are designed to test some aspects of a high gain direct drive target design. The target consists of a low-density foam that is filled with liquid deuterium and covered with a thin polyimide membrane. The measured target trajectory agrees well with one-dimensional (1D) simulations. The growth of the areal mass modulations were measured with a new, 1.26 keV x-ray backlighter. The modulations appear later and grow to a smaller amplitude when the foot of the laser pulse is made spatially smoother. A thin layer of gold on the front of the target reduces the modulations. The results are compared with 2D modeling.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.873498

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4

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Effects of thin high-Z layers on the hydrodynamics of laser-accelerated plastic targets : Review,Tutorial and Invited Papers from the 43rd Annual Meeting of the APS Division of Plasma Physics (2002)

Obenschain, S. P. ; Colombant, D. G. ; Karasik, M. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Physics of Plasmas 9 (2002), S. 2234-2243

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ISSN: 1089-7674

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Experimental results and simulations that study the effects of thin metallic layers with high atomic number (high-Z) on the hydrodynamics of laser accelerated plastic targets are presented. These experiments employ a laser pulse with a low-intensity foot that rises into a high-intensity main pulse. This pulse shape simulates the generic shape needed for high-gain fusion implosions. Imprint of laser nonuniformity during start up of the low intensity foot is a well-known seed for hydrodynamic instability. Large reductions are observed in hydrodynamic instability seeded by laser imprint when certain minimum thickness gold or palladium layers are applied to the laser-illuminated surface of the targets. The experiment indicates that the reduction in imprint is at least as large as that obtained by a 6 times improvement in the laser uniformity. Simulations supported by experiments are presented showing that during the low intensity foot the laser light can be nearly completely absorbed by the high-Z layer. X rays originating from the high-Z layer heat the underlying lower-Z plastic target material and cause large buffering plasma to form between the layer and the accelerated target. This long-scale plasma apparently isolates the target from laser nonuniformity and accounts for the observed large reduction in laser imprint. With onset of the higher intensity main pulse, the high-Z layer expands and the laser light is transmitted. This technique will be useful in reducing laser imprint in pellet implosions and thereby allow the design of more robust targets for high-gain laser fusion. © 2002 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.1464541

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5

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Measurements of laser-imprinted perturbations and Rayleigh–Taylor growth with the Nike KrF laser : The 38th annual meeting of the Division of Plasma Physics (DPP) of the American Physical Society (1997)

Pawley, C. J. ; Gerber, K. ; Lehmberg, R. H. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Physics of Plasmas 4 (1997), S. 1969-1977

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ISSN: 1089-7674

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Nike is a 56 beam Krypton Fluoride (KrF) laser system using Induced Spatial Incoherence (ISI) beam smoothing with a measured focal nonuniformity 〈ΔI/I〉 of 1% rms in a single beam [S. Obenschain et al., Phys. Plasmas 3, 1996 (2098)]. When 37 of these beams are overlapped on the target, we estimate that the beam nonuniformity is reduced by 37, to (ΔI/I)≅0.15% (excluding short-wavelength beam-to-beam interference). The extraordinary uniformity of the laser drive, along with a newly developed x-ray framing diagnostic, has provided a unique facility for the accurate measurements of Rayleigh–Taylor amplified laser-imprinted mass perturbations under conditions relevant to direct-drive laser fusion. Data from targets with smooth surfaces as well as those with impressed sine wave perturbations agree with our two-dimensional (2-D) radiation hydrodynamics code that includes the time-dependent ISI beam modulations. A 2-D simulation of a target with a 100 Å rms randomly rough surface finish driven by a completely uniform beam gives final perturbation amplitudes similar to the experimental data for the smoothest laser profile. These results are promising for direct-drive laser fusion.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.872560

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6

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The Nike KrF laser facility: Performance and initial target experiments (1996)

Obenschain, S. P. ; Bodner, S. E. ; Colombant, D. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Physics of Plasmas 3 (1996), S. 2098-2107

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ISSN: 1089-7674

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Krypton-fluoride (KrF) lasers are of interest to laser fusion because they have both the large bandwidth capability ((approximately-greater-than)THz) desired for rapid beam smoothing and the short laser wavelength (1/4 μm) needed for good laser–target coupling. Nike is a recently completed 56-beam KrF laser and target facility at the Naval Research Laboratory. Because of its bandwidth of 1 THz FWHM (full width at half-maximum), Nike produces more uniform focal distributions than any other high-energy ultraviolet laser. Nike was designed to study the hydrodynamic instability of ablatively accelerated planar targets. First results show that Nike has spatially uniform ablation pressures (Δp/p〈2%). Targets have been accelerated for distances sufficient to study hydrodynamic instability while maintaining good planarity. In this review we present the performance of the Nike laser in producing uniform illumination, and its performance in correspondingly uniform acceleration of targets. © 1996 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.871661

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7

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Large area electron beam pumped krypton fluoride laser amplifier (1997)

Sethian, J. D. ; Obenschain, S. P. ; Gerber, K. A. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Review of Scientific Instruments 68 (1997), S. 2357-2366

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ISSN: 1089-7623

Quelle: AIP Digital Archive

Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik

Notizen: Nike is a recently completed multi-kilojoule krypton fluoride (KrF) laser that has been built to study the physics of direct drive inertial confinement fusion. This paper describes in detail both the pulsed power and optical performance of the largest amplifier in the Nike laser, the 60 cm amplifier. This is a double pass, double sided, electron beam-pumped system that amplifies the laser beam from an input of 50 J to an output of up to 5 kJ. It has an optical aperture of 60 cm × 60 cm and a gain length of 200 cm. The two electron beams are 60 cm high × 200 cm wide, have a voltage of 640 kV, a current of 540 kA, and a flat top power pulse duration of 250 ns. A 2 kG magnetic field is used to guide the beams and prevent self-pinching. Each electron beam is produced by its own Marx/pulse forming line system. The amplifier has been fully integrated into the Nike system and is used on a daily basis for laser-target experiments. © 1997 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.1148118

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8

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Flash x radiography of laser-accelerated foils (1987)

Whitlock, R. R. ; Obenschain, S. P. ; Grun, J. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 61 (1987), S. 131-141

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: The successful compression of laser-driven pellets to thermonuclear ignition depends on the stability and uniformity of the motion with which dense shells can be imploded. The motion of planar foils accelerated by the Pharos II laser has been studied by two-dimensional, flash x radiography employing pinhole imaging and slitted crystal imaging. The acceleration was driven by a 3–5-ns duration, 1.05-μm laser focused to 3–6×1012 W/cm2 in a millimeter diameter spot, while a second laser beam of shorter duration produced the x-ray flash for imaging purposes. The x-ray images obtained clearly show that the planar foil targets are ablatively accelerated to velocities of 3×106 cm/s while maintaining a density above 3% of solid. The axial extent of the accelerated, high-density material has been observed to be as small as 25% of the distance traveled. The sides of accelerated portions of the foil connect smoothly to the stationary regions removed from the laser illumination. This connection apparently isolates the rear surface from the hot ablation plasma and helps explain the low rear surface temperatures which have been observed. The overall appearance of the accelerated foil is localized and nearly planar at early times when it has moved distances small compared to its diameter. The x-radiographic results are in general agreement with two-dimensional hydrodynamic simulations and with earlier Naval Research Laboratory studies of target motion, ablation pressures, and symmetrization employing other diagnostics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.338845

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9

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Increased x-ray conversion efficiency from gold plasmas irradiated with spatially and temporally incoherent light (1991)

Kania, D. R. ; Kruer, W. L. ; Bell, P. ; [weitere]

New York, NY : American Institute of Physics (AIP)

Physics of Fluids 3 (1991), S. 1496-1500

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ISSN: 1089-7666

Quelle: AIP Digital Archive

Thema: Physik

Notizen: The efficiency with which 1.05 μm laser light is converted into x rays with energy less than 1.5 keV in high Z materials (gold) is increased by approximately 20% with the use of spatially and temporally incoherent light when compared to a nominal, high-powered laser beam with an identical average irradiance of 1014 W/cm2. This effect is not a result of increased laser light absorption, laser bandwidth, nor reduced hot electron generation for the incoherent light, but is probably due to the change in the short scale length (∼100 μm) laser light intensity distribution in the target plane. The absolute levels of stimulated scattering and hot electron generation were small in all cases. Incoherent illumination reduced stimulated Brillouin scattering levels from 1.1% to 0.2% and, similarly, hot electron generation was decreased from 0.1% to 0.07%.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.859717

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Reduction of 3ω0/2 emission from laser-produced plasmas with broad bandwidth, induced spatial incoherence at 0.53 μm (1991)

Peyser, T. A. ; Manka, C. K. ; Obenschain, S. P. ; [weitere]

New York, NY : American Institute of Physics (AIP)

Physics of Fluids 3 (1991), S. 1479-1484

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ISSN: 1089-7666

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Measurements of the 3ω0/2 emission from laser-irradiated targets at 0.53 μm were made at three angles over a wide range of laser bandwidths with and without induced spatial incoherence (ISI) echelons. The 3ω0/2 emission was found to be correlated with hard x rays but not Raman spectra, suggesting that the 3ω0/2 radiation was due to two-plasmon decay. Reduction of both 3ω0/2 emission and the accompanying hard x rays by ISI required five to ten times larger bandwidths than needed to suppress stimulated Raman scattering and stimulated Brillouin scattering.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.859715

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