High-speed gated x-ray imagers (invited)

Kilkenny, J. D.; Bell, P. M.; Hanks, R. L.; Power, G.D.; Turner, R. E.; Wiedwald, J. D.

doi:10.1063/1.1140115

Cited by 51 publications

(13 citation statements)

References 3 publications

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“…16 A 4ϫ4 pinhole array with pinhole diameters of ϳ7 m projects 16 images spaced ϳ55 ps apart with a magnification of 12 onto 4 microchannel plate strip lines. Two different pinholes cameras were used.…”

Section: Experimental Geometrymentioning

confidence: 99%

Rayleigh–Taylor instability evolution in ablatively driven cylindrical implosions

et al. 1997

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The Rayleigh-Taylor instability is an important limitation in inertial confinement fusion capsule designs. Significant work both theoretically and experimentally has been done to demonstrate the stabilizing effects of material flow through the unstable region. The experimental verification has been done predominantly in planar geometry. Convergent geometry introduces effects not present in planar geometry such as shell thickening and accelerationless growth of modal amplitudes ͑e.g., Bell-Plesset growth͒. Amplitude thresholds for the nonlinear regime are reduced, since the wavelength of a mode m decreases with convergence ϳR/m, where R is the radius. Convergent effects have been investigated using an imploding cylinder driven by x-ray ablation on the NOVA laser ͓J. L. Emmet, W. F. Krupke, and J. B. Trenholme, Sov. J. Quantum Electron. 13, 1 ͑1983͔͒. By doping sections of the cylinder with opaque materials, in conjunction with x-ray backlighting, the growth and feedthrough of the perturbations from the ablation front to the inner surface of the cylinder for various initial modes and amplitudes from early time through stagnation was measured. Mode coupling of illumination asymmetries with material perturbations is observed, as well as phase reversal of the perturbations from near the ablation front to the inner surface of the cylinder. Perturbation growth is observed due to convergence and compressibility alone, without the effects of acceleration, and scales as ϳ1/R, where is the mass density. Imaging is performed with an x-ray pinhole camera coupled to a gated microchannel plate detector.

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Section: Experimental Geometrymentioning

confidence: 99%

Rayleigh–Taylor instability evolution in ablatively driven cylindrical implosions

et al. 1997

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“…Part of the X-rays are absorbed by the outer layer of the capsule, located at the center of the hohlraum, which is ablated and therefore generates a spherically-symmetric rocket reaction that compresses the capsule. The radiographs of the imploding capsule, viewed along an equatorial (i.e., perpendicular to the hohlraum axis) line of sight, are imaged by an array of pinholes, 20 lm to 25 lm in diameter, and recorded on a gated X-ray detector, 11 Invited speaker. c) Electronic mail: tommasini2@llnl.gov patches on opposite sides of the hohlraum walls.…”

Section: Experiments Descriptionmentioning

confidence: 99%

Tent-induced perturbations on areal density of implosions at the National Ignition Facilitya)

et al. 2015

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Areal density non-uniformities seeded by time-dependent drive variations and target imperfections in Inertial Confinement Fusion (ICF) targets can grow in time as the capsule implodes, with growth rates that are amplified by instabilities. Here, we report on the first measurements of the perturbations on the density and areal density profiles induced by the membranes used to hold the capsule within the hohlraum in indirect drive ICF targets. The measurements are based on the reconstruction of the ablator density profiles from 2D radiographs obtained using pinhole imaging coupled to area backlighting, as close as 150 ps to peak compression. Our study shows a clear correlation between the modulations imposed on the areal density and measured neutron yield, and a 3Â reduction in the areal density perturbations comparing a high-adiabat vs. low-adiabat pulse shape. V C 2015 AIP Publishing LLC. [http://dx.

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“…The implosion trajectory was diagnosed with a fourframe x-ray framing camera. 308,309 A sequence of images of a cryogenic target implosion is shown in Fig. 8-12(a), covering both the implosion and disassembly phases.…”

Section: B Cryogenic Implosionsmentioning

confidence: 99%

Direct-drive inertial confinement fusion: A review

et al. 2015

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The direct-drive, laser-based approach to inertial confinement fusion (ICF) is reviewed from its inception following the demonstration of the first laser to its implementation on the present generation of high-power lasers. The review focuses on the evolution of scientific understanding gained from target-physics experiments in many areas, identifying problems that were demonstrated and the solutions implemented. The review starts with the basic understanding of laser–plasma interactions that was obtained before the declassification of laser-induced compression in the early 1970s and continues with the compression experiments using infrared lasers in the late 1970s that produced thermonuclear neutrons. The problem of suprathermal electrons and the target preheat that they caused, associated with the infrared laser wavelength, led to lasers being built after 1980 to operate at shorter wavelengths, especially 0.35 μm—the third harmonic of the Nd:glass laser—and 0.248 μm (the KrF gas laser). The main physics areas relevant to direct drive are reviewed. The primary absorption mechanism at short wavelengths is classical inverse bremsstrahlung. Nonuniformities imprinted on the target by laser irradiation have been addressed by the development of a number of beam-smoothing techniques and imprint-mitigation strategies. The effects of hydrodynamic instabilities are mitigated by a combination of imprint reduction and target designs that minimize the instability growth rates. Several coronal plasma physics processes are reviewed. The two-plasmon–decay instability, stimulated Brillouin scattering (together with cross-beam energy transfer), and (possibly) stimulated Raman scattering are identified as potential concerns, placing constraints on the laser intensities used in target designs, while other processes (self-focusing and filamentation, the parametric decay instability, and magnetic fields), once considered important, are now of lesser concern for mainline direct-drive target concepts. Filamentation is largely suppressed by beam smoothing. Thermal transport modeling, important to the interpretation of experiments and to target design, has been found to be nonlocal in nature. Advances in shock timing and equation-of-state measurements relevant to direct-drive ICF are reported. Room-temperature implosions have provided an increased understanding of the importance of stability and uniformity. The evolution of cryogenic implosion capabilities, leading to an extensive series carried out on the 60-beam OMEGA laser [Boehly et al., Opt. Commun. 133, 495 (1997)], is reviewed together with major advances in cryogenic target formation. A polar-drive concept has been developed that will enable direct-drive–ignition experiments to be performed on the National Ignition Facility [Haynam et al., Appl. Opt. 46(16), 3276 (2007)]. The advantages offered by the alternative approaches of fast ignition and shock ignition and the issues associated with these concepts are described. The lessons learned from target-physics and implosion experiments are taken into account in ignition and high-gain target designs for laser wavelengths of 1/3 μm and 1/4 μm. Substantial advances in direct-drive inertial fusion reactor concepts are reviewed. Overall, the progress in scientific understanding over the past five decades has been enormous, to the point that inertial fusion energy using direct drive shows significant promise as a future environmentally attractive energy source.

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High-speed gated x-ray imagers (invited)

Cited by 51 publications

References 3 publications

Rayleigh–Taylor instability evolution in ablatively driven cylindrical implosions

Rayleigh–Taylor instability evolution in ablatively driven cylindrical implosions

Tent-induced perturbations on areal density of implosions at the National Ignition Facilitya)

Direct-drive inertial confinement fusion: A review

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