| In-Situ Measurements of Temperature Profiles and Plume Formation at the Surfaces of Samples Irradiated by a Picosecond Laser Pulse Train |
03 JUL 2003 |
53 pages |
| Authors:
J. Grun; R. Fischer; C. K. Manka; R. F. Wenzel; R. Cozzens; NAVAL RESEARCH LAB WASHINGTON DC BEAM PHYSICS BRANCH
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 | One-inch diameter samples of various materials, such as stainless steel, painted and unpainted aluminum, fused silica, and fiberglass composites, were irradiated by a train of picosecond-duration pulses from a free-electron laser at irradiances of 0.5 to 10 kW/cm2. These experiments were the first to examine the lethality of a train of picosecond-duration laser pulses in an irradiance regime relevant to high energy laser lethality, i.e., utilizing laser intensities that have ... |
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| Precision-Scale Explosion Experiments Using Laser-Driven Shocks |
13 MAR 98 |
15 pages |
| Authors:
J. Grun; J. R. Barthel; R. Burris; J. Crawford; K. Evans; NAVAL RESEARCH LAB WASHINGTON DC
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| The Naval Research Laboratory uses shock initiated by a powerful laser pulse to perform precision scale measurements of hydrodynamic phenomena relevant to nuclear and conventional explosions, and to supernovae. A pulse from NRL's 1.3-kJ Pharos III laser is focused onto the surface of a period sized piece of material placed in ambient gas. The laser heats the material to a few hundred eV creating a miniature ... |
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| Precursor-Shock in a Well-Characterized Thermal Layer |
22 DEC 97 |
28 pages |
| Authors:
J. Grun; R. Burris; G. Joyce; S. Slinker; J. Huba; NAVAL RESEARCH LAB WASHINGTON DC LASERPHYSICS SECTION
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| We present an experiment that measured the behavior of a shock precursor in a well-characterized, thin thermal layer above a 3000 deg K hot surface. A laser pulse focused onto a thin solid target produced the shock, eliminating interference from explosion products. Precursor and thermal layer characteristics were measured using spectroscopy, interferometry, and dark-field shadowgraphy. |
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| Structuring Processes in Expanding Laser-Produced Plasmas |
30 MAR 88 |
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| Authors:
B. H. Ripin; J. Grun; T. N. Lee; C. K. Manka; E. A. McLean; NAVAL RESEARCH LAB WASHINGTON DC
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 | A plasma expanding into a magnetic field and/or another plasma can undergo several instabilities which will cause spatial nonuniformities and large scale structure to develop. Potential structure forming instabilities include: various forms of the Rayleigh-Taylor or interchange instability, Kevin-Helmholtz instabilities. In addition, experimental geometric factors can also affect expansion uniformity. The phenomena reported here should be of interest to a broad range of disciplines. Keywords: Plasma, Rayleigh Taylor, Structure, Turbulence, ... |
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| Flash X Radiography of Laser-Accelerated Foils |
14 NOV 86 |
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| Authors:
R. R. Whitlock; S. P. Obenschain; J. Grun; J. A. Stamper; J. A. Sprague; NAVAL RESEARCH LAB WASHINGTON DC
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| 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 (1.05 micrometers focused to 3 to 6 times 10 to the 12th power W/cm2 in a millimeter diameter spot) has been studied by two-dimensional, flash x- radiography employing pinhole imaging and slitted crystal ... |
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| Control of Ion-Velocity Distributions in Laser-Target Interaction Experiments |
06 OCT 86 |
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| Authors:
J. Grun; R. Stellingwerf; B. H. Ripin; MISSION RESEARCH CORP ALBUQUERQUE NM
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| The width of ion velocity distributions from laser produced plasmas can be controlled experimentally by varying the size of the laser spot. The ion velocity width is determined primarily by whether the ions are mostly in the rarefraction or steady state regime. It is not dominated by the thermal distribution of the ions, as is often assumed. Keywords: Laser fusion; Plasma; Fusion; Laser plasma interactions; Ions; Ablation. |
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| Measurement of Areal Mass Variation in Rayleigh-Taylor Unstable Targets. |
14 JUN 1984 |
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| Authors:
J. Grun; M. H. Emery; M. J. Herbst; S. Kacenjar; C. Opal; NAVAL RESEARCH LAB WASHINGTON DC
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| We present the first measurements of Rayleigh Taylor caused mass redistribution resolved in two spatial dimensiona. Bubble and spike formation and two dimensional effects have been observed. Results are consistent with theory which claims that the Rayleigh Taylor growth rate is about 1/2 of classical. |
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| Magnetic Bubble Formation Produced by an Expanding Laser Plasma |
28 FEB 1984 |
27 pages |
| Authors:
S. T. Kacenjar; B. H. Ripin; J. A. Stamper; J. Grun; E. A. McLean; NAVAL RESEARCH LAB WASHINGTON DC
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| A magnetic depleted bubble resulting from the expansion of a laser- generated debris plasma into a low density magnetized background plasma is observed. A compressed magnetic field propagates slightly ahead of the debris plasma and has a thickness on the order of 1 cm. (Author) |
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| Introduction to the Laser-HANE Experiment and Summary of Low-Pressure Interaction Results |
22 FEB 1984 |
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| Authors:
B. H. Ripin; J. Grun; S. Kacenjar; E. A. McLean; J. A. Stamper; NAVAL RESEARCH LAB WASHINGTON DC
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| A brief overview of the NRL laser-target experiment which simulates the interactions involved in a HANE is presented. A burst of fast laser- produced-debris-ions stream into a low-density magnetized ambient plasma/gas. The interactions between these two plasma components are investigated under a variety of conditions. At ambient pressures below 150 mTorr we observed a magnetic bubble formation during the debris expansion; we found that the field is swept out of ... |
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| A Novel X-Ray Backlighting Method for Rayleigh-Taylor Instability Measurements on Ablatively Driven Targets |
17 FEB 1984 |
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| Authors:
J. Grun; S. Kacenjar; NAVAL RESEARCH LAB WASHINGTON DC
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| This document describes a face-on-x-ray backlighting method that does not require a dedicated laser beam and a separate x-ray source. This method is used to measure the lateral mass transfer characteristic of the Rayleigh-Taylor instability in ablatively accelerated, laser driven targets. (Author) |
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| Variation of Laser Absorption with Plasma Scalelength in Long- Scalelength Plasmas |
30 SEP 1983 |
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| Authors:
M. J. Herbst; J. Grun; J. Gardner; J. A. Stamper; F. C. Young; NAVAL RESEARCH LAB WASHINGTON DC
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| A short-pulse, high-intensity Nd-laser beam interacts with performed plasmas of variable scalelength. At the longest scalelength, absorption is limited by backscatter, despite increased collisional absorption. (Author) |
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| Prospects for Optical Probing of the Rayleigh-Taylor Instability in Ablatively-Accelerated Foil Targets |
21 JUN 1983 |
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| Authors:
J. A. Stamper; S. P. Obenschain; B. H. Ripin; E. A. McLean; J. Grun; NAVAL RESEARCH LAB WASHINGTON DC
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| Optical probing of non-uniformities is promising as a diagnostic of the Rayleigh-Taylor (R-T) instability. A study was made on an ablatively accelerated target which was designed to provide known initial conditions for the growth of the instability. Two diagnostic techniques were simultaneously used. A side-on, dark-field shadowgram (third harmonic) showed periodic structure in the steep-gradient region on the rear side of the accelerating target. The angular scatter pattern (second harmonic ... |
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| Experimental Methods for Studying the Rayleigh-Taylor Instability of Ablatively Accelerated Targets |
17 JUN 1983 |
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| Authors:
J. Grun; M. H. Emery; M. J. Herbst; E. A. McLean; S. P. Obenschain; NAVAL RESEARCH LAB WASHINGTON DC
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| The authors describe new diagnostic methods for the study of hydrodynamic instabilities in ablatively accelerated targets. These methods include face-on x-ray backlighting that does not require a backlighting laser beam (for growth rate measurement), and a tracer dot technique (for tracking ablation plasma flow). The targets in the experiments are periodically perturbed to provide initial conditions for the growth of the Rayleigh-Taylor instability. (Author) |
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| Laser-Plasma Interaction Experiments and Diagnostics at NRL (Naval Research Laboratory) |
11 MAY 1983 |
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| Authors:
B. H. Ripin; J. Grun; M. J. Herbst; S. T. Kacenjar; E. A. McLean; NAVAL RESEARCH LAB WASHINGTON DC
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| Laser plasma interaction experiments have now advanced to the point where very quantitative measurements are required to elucidate the physic issues important for laser fusion and other applications. Detailed time-resolved knowledge of the plasma density, temperature, velocity gradients, spatial structure, heat flow characteristics, radiation emission, etc, are needed over tremendou ranges of plasma density and temperature. Moreover, the time scales are very short, aggrevating the difficulty of the measurements further. ... |
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| Measurements of Laser Coupling and Plasma Profiles in Longer-Scalelength Plasmas |
30 SEP 1982 |
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| Authors:
M. J. Herbst; P. G. Burkhalter; J. Grun; S. P. Obenschain; J. A. Stamper; NAVAL RESEARCH LAB WASHINGTON DC
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| Novel configuration of our two-beam laser allows laser-coupling experiments to be performed in longer-scalelength plasmas (Ln approximately 250- 600 micrometer at nc/10), which better simulate reactor-sized pellet plasmas. Preliminary observations show increased backscatter, as expected, but also reveal large reductions in 2 omega 0 and high-energy x-ray emissions. The latter may indicate lessened importance of resonance absorption in longer-scalelength plasmas. Measurements of plasma profiles are at least as important as ... |
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| Ballistic Pendula for Measuring the Momentum of a Laser-Produced Plasma |
17 SEP 1982 |
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| Authors:
J. Grun; B. H. Ripin; NAVAL RESEARCH LAB WASHINGTON DC
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| We describe the use of a ballistic pendulum array to measure the momentum of a laser-produced plasma. An insitu calibration method is described and the pendulum results are compared to measurements made with other diagnostics. |
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| Laser-Ablative Acceleration of Targets to Near Inertial Fusion Conditions |
30 AUG 1982 |
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| Authors:
B. H. Ripin; S. E. Bodner; P. G. Burkhalter; H. Griem; J. Grun; NAVAL RESEARCH LAB WASHINGTON DC
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| NRL is investigating the physics issues involved in the direct illumination approach to laser fusion. Millimeter diameter planar targets are ablatively accelerated to speeds and conditions near those required of fusion pellet shells using 3-5 ns, 1.05 micrometer light from the PHAROS II laser. At 5 x 10 to the 13th power W/sq cm targets were accelerated to 160 km/sec with a velocity uniformity of + or - 7% through ... |
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| Flash X Radiography of Laser-Accelerated Targets |
30 AUG 1982 |
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| Authors:
R. R. Whitlock; S. P. Obenschain; J. Grun; NAVAL RESEARCH LAB WASHINGTON DC
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| Flash x radiography of ablatively accelerated planar foils has provided quantitative measurements and qualitative observations regarding several parameters of critical interest to direct illumination laser fusion. A 1.05 micron, 3.3 nsec driver beam was focused onto carbon foils in a large (0.7- 1 mm diameter) spot to reduce edge effects. From images produced by a backlighting x-ray flash, we have measured overall coupling efficiency, smoothing of laser nonuniformities, target velocity, ... |
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| Spot Spectroscopy: Local Spectroscopic Measurements within Laser- Produced Plasmas |
20 APR 1982 |
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| Authors:
M. J. Herbst; P. G. Burkhalter; J. Grun; R. R. Whitlock; M. Fink; NAVAL RESEARCH LAB WASHINGTON DC
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| Use of a locally embedded tracer in laser-irradiated solid targets yields a localized source of diagnostic x-ray line radiation in the blowoff plasma. This technique potentially eliminates problems of chord-integration over regions of varying density and temperature in an inhomogeneous plasma, and reduces complications due to plasma opacity effects in the interpretation of spectra. Spectra obtained in an experimental test of this new technique are of a quality superior to ... |
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| Ablative Acceleration of Planar Targets to High Velocities |
30 MAR 1982 |
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| Authors:
J. Grun; S. P. Obenschain; B. H. Ripin; R. R. Whitlock; E. A. McLean; NAVAL RESEARCH LAB WASHINGTON DC
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| Laser irradiated targets are ablatively accelerated to velocities near those required for fusion pellet implosions while remaining relatively cool and uniform. The target velocities and velocity profiles are measured using a double-foil method, which is described in detail. Also, the ablation plasma flow from the target surface is spatially resolved, and the scalings with absorbed irradiance of the ablation pressure, ablation velocity, and mass ablation rate are determined. Results are ... |
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| Ablated Plasma Flow from Planar Targets. |
13 MAR 1981 |
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| Authors:
M. J. Herbst; J. Grun; NAVAL RESEARCH LAB WASHINGTON DC
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| The experimentally observed flow of plasma ablated by a laser from a planar target resembles the nozzle flow of fluid from a circular orifice. This has implications for experimental simulations of spherical laser fusion pellets using planar targets and affects far field ion measurements in planar geometry experiments. (Author) |
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| Uniformity of Laser-Driven, Ablatively Accelerated Targets. |
12 MAR 1981 |
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| Authors:
S. P. Obenschain; B. H. Ripin; E. A. McLean; J. Grun; NAVAL RESEARCH LAB WASHINGTON DC
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| A double-target technique is used to measure the uniformity with which laser irradiated thin foil targets are ablatively accelerated. Studies of the effects of laser nonuniformities on the target acceleration reveal an increase in smoothing (symmetrization) with increasing laser intensity. Measurements of targets accelerated to velocities (160 km/sec) sufficient for pellet fusion implosions are presented and discussed. |
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| Characteristics of Ablation Plasma from Planar, Laser-Driven Targets. |
09 MAR 1981 |
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| Authors:
J. Grun; R. Decoste; B. H. Ripin; J. Gardner; NAVAL RESEARCH LAB WASHINGTON DC
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| The momentum, energy, and velocity characteristics of plasma ablating from planar targets irradiated by long Nd-laser pulses (4-nsec, < 10 to the 14th power W/sq cm) are measured and the dependence of ablation parameters upon absorbed irradiance is determined. Large laser spots are used in these experiments so that the results are not sensitive to boundary effects. (Author) |
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Reports by Author
