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Fabrication and testing of gas filled targets for large scale plasma experiments on Nova

Description: An experimental campaign on the Nova laser was started in July 1993 to study one st of target conditions for the point design of the National Ignition Facility (NIF). The targets were specified to investigate the current NIF target conditions--a plasma of {approximately}3 keV electron temperature and an electron density of {approximately}1.0 E + 21 cm{sup {minus}3}. A gas cell target design was chosen to confine as gas of {approximately}0.01 cm{sup 3} in volume at {approximately} 1 atmosphere. This paper will describe the major steps and processes necessary in the fabrication, testing and delivery of these targets for shots on the Nova Laser at LLNL.
Date: March 6, 1995
Creator: Stone, G.F.; Spragge, M.; Wallace, R.J. & Rivers, C.J.
Partner: UNT Libraries Government Documents Department

The design, performance, and application of an atomic-force microscope-based profilometer

Description: Rayleigh-Taylor instabilities during implosions of inertially confined fusion (ICF) capsules affect capsule performance. During acceleration, surface imperfections grow and can, if large enough, lead to an asymmetric implosion or even shell breakup. For this reason, characterizing the topography of target capsules is extremely important. We have developed a profilometer based on an atomic force microscope combined with a precision rotary air bearing. Averaged 1D surface height power spectra obtained with this instrument are converted to 2D mode spectra, which are used as input to hydrodynamic simulations. We describe the design of the system and its performance in terms of runout and repeatability. We also discuss the simulation of these measurements and the statistics involved in averaging 1D power spectra. Finally, we show the application of this measurement technique to capsules whose surfaces have been modified by laser ablation, resulting in a well-defined surface topography. This special case provides an excellent test for the system, since the expected results are exactly calculable.
Date: October 1, 1994
Creator: McEachern, R.L.; Moore, C.E. & Wallace, R.J.
Partner: UNT Libraries Government Documents Department

Evaulation of B{sub 4}C as an ablator material for NIF capsules. Revision 1

Description: Boron carbide (B{sub 4}C) is examined as a potential fuel container and ablator for implosion capsules on the National Ignition Facility (NIF). A capsule of pure B{sub 4}C encasing a layer of solid DT implodes stably and ignites with anticipated NIF x-ray drives, producing 18 MJ of energy. Thin films of B{sub 4}C were found to be resistant to oxidation and modestly transmitting in the infrared (IR), possibly enabling IR fuel characterization and enhancement for thin permeation barriers but not for full-thickness capsules. Polystyrene mandrels 0.5 mm in diameter were successfully coated with 0.15-2.0 micrometers of B{sub 4}C. Thickness estimated from optical density agreed well with those measured by scanning electron microscopy (SEM). The B{sub 4}C microstructure was columnar but finer than for Be made at the same conditions. B{sub 4}C is a very strong material, with a fiber tensile strength capable of holding NIF fill pressures at room temperature, but it is also very brittle, and microscopic flaws or grain structure may limit the noncryogenic fill pressure. Argon (Ar) permeation rates were measured for a few capsules that had been further coated with 5 micrometers of plasma polymer. The B{sub 4}C coatings tended to crack under tensile load. Some shells filled more slowly than they leaked, suggesting that the cracks open and close under opposite pressure loading. As observed earlier for Ti coatings, 0.15-micrometer layers of B{sub 4}C had better gas retention properties than 2-micrometer layers, possibly because of fewer cracks. Permeation and fill strength issues for capsules with a full ablator thickness of B{sub 4}C are unresolved. 21 refs., 6 figs.
Date: March 26, 1997
Creator: Burnham, A.K.; Alford, C.S.; Makowiecki, D.M.; Dittrich, T.R.; Wallace, R.J.; Honea, E.C. et al.
Partner: UNT Libraries Government Documents Department

Supernova hydrodynamics experiments using the Nova laser

Description: We are developing experiments using the Nova laser to investigate two areas of physics relevant to core-collapse supernovae (SN): (1) compressible nonlinear hydrodynamic mixing and (2) radiative shock hydrodynamics. In the former, we are examining the differences between the 2D and 3D evolution of the Rayleigh-Taylor instability, an issue critical to the observables emerging from SN in the first year after exploding. In the latter, we are investigating the evolution of a colliding plasma system relevant to the ejecta-stellar wind interactions of the early stages of SN remnant formation. The experiments and astrophysical implications are discussed.
Date: April 1, 1997
Creator: Remington, B.A.; Glendinning, S.G.; Estabrook, K.; Wallace, R.J.; Rubenchik, A.; Kane, J. et al.
Partner: UNT Libraries Government Documents Department

Numerical analysis of spherically convergent Rayleigh-Taylor experiments on the Nova laser

Description: In the frame of a CEA/US DOE collaboration, convergent experiments have been done on the Nova laser. Numerical simulations with our 2D Lagrangian code FCI2 led the analysis and correctly reproduced the experimental data. From single mode 2D perturbations, ablation front Rayleigh-Taylor instability growth is computed. Moderate and high convergence ratios are addressed. The shrinking of the wavelength plays a prominent role for small convergence ratio and weakly nonlinear hydrodynamics.
Date: August 23, 1999
Creator: Cherfils, C; Galmiche, D; Glendinning, S G; Laffite, S; Remington, B A & Wallace, R J
Partner: UNT Libraries Government Documents Department

X-ray radiographic imaging of hydrodynamic phenomena in radiation driven materials -- shock propagation, material compression and shear flow. Revision 1

Description: One- and two-dimensional, time resolved x-ray radiographic imaging at high photon energy (5-7 keV) is used to study shock propagation, material motion and compression, and the effects of shear flow in solid density samples which are driven by x-ray ablation with the Nova laser. By backlighting the samples with x-rays and observing the increase in sample areal density due to shock compression, the authors directly measure the trajectory of strong shocks ({approx}40 Mbar) in flight, in solid density plastic samples. Doping a section of the samples with high-Z material (Br) provides radiographic contrast, allowing the measurement of the shock induced particle motion. Instability growth due to shear flow at an interface is investigated by imbedding a metal wire in a cylindrical plastic sample and launching a shock in the axial direction. Time resolved radiographic measurements are made with either a slit-imager coupled to an x-ray streak camera or a pinhole camera coupled to a gated microchannel plate detector, providing {approx} 10-{mu}m spatial and {approx} 100-ps temporal resolution.
Date: February 1, 1994
Creator: Hammel, B. A.; Kilkenny, J. D.; Munro, D.; Remington, B. A.; Kornblum, H. N.; Perry, T. S. et al.
Partner: UNT Libraries Government Documents Department

Measurements of Wall Stagnation in Gas-Filled ICF Hohlraums

Description: For ICF hohlraums driven by long pulses, such as will be needed for ignition on the NIF, the high-Z wall must be held back to avoid excessive laser spot motion and time-dependent symmetry swings. One means of accomplishing this is to fill the hohlraum with a low density, low-Z gas. We report on gas-wall interface characterization by axial x-ray backlighting and self-emission, on gas filled hohlraums fielded at the Omega facility. Up to 30 drive beams are fired, forming a single ring of illumination on the hohlraum wall to emulate the near 2D cylindrically symmetric NIF hohlraum drive conditions. We compare the observed motion with predictions. In addition, the gas-gold interface is Rayleigh-Taylor (R-T) unstable during deceleration. This R-T instability could be further exacerbated in NIF ignition hohlraums designed with intentionally roughened walls to provide smoothing of infrared heating used to prepare smooth DT ice layers in the capsule. We have therefore intentionally prepared initial perturbations on one half of the gold wall to quantify the amount of increased penetration, due to mix of the gold into the gas, at stagnation.
Date: August 22, 2003
Creator: Turner, R E; Eder, D C; Dewald, E L; Wallace, R J; Amendt, P A; Pollaine, S M et al.
Partner: UNT Libraries Government Documents Department

Observations of Plasmons in Warm Dense Matter

Description: We present the first collective x-ray scattering measurements of plasmons in solid-density plasmas. The forward scattering spectra of a laser-produced narrow-band x-ray line from isochorically heated beryllium show that the plasmon frequency is a sensitive measure of the electron density. Dynamic structure calculations that include collisions and detailed balance match the measured plasmon spectrum indicating that this technique will enable new applications to determine the equation of state and compressibility of dense matter.
Date: September 5, 2006
Creator: Glenzer, S H; Landen, O L; Neumayer, P; Lee, R W; Widmann, K; Pollaine, S W et al.
Partner: UNT Libraries Government Documents Department

Nonlinear mixing behavior of the three-dimensional Rayleigh-Taylor instability at a decelerating interface.

Description: We report results from the first experiments to explore the evolution of the Rayleigh-Taylor (RT) instability from intentionally three-dimensional (3D) initial conditions at an embedded, decelerating interface in a high-Reynolds-number flow. The experiments used {approx}5 kJ of laser energy to produce a blast wave in polyimide and/or brominated plastic having an initial pressure of {approx}50 Mbars. This blast wave shocked and then decelerated the perturbed interface between first material and a lower-density, C foam. This caused the formation of a decelerating interface with an Atwood number {approx}2/3, producing a long-term positive growth rate for the RT instability. The initial perturbations were a 3D perturbation in an ''egg-crate'' pattern with feature spacings of 71 {micro}m in two orthogonal directions and peak-to-valley amplitudes of 5 {micro}m. The resulting RT spikes were observed to overtake the shock waves at the undisturbed, ''free-fall'' rate, and to subsequently deliver material from behind the interface to the forward shock. This result is unanticipated by prior simulations and models.
Date: March 19, 2004
Creator: Robey, H; Remington, B; Edwards, M; Perry, T; Wallace, R J; Louis, H et al.
Partner: UNT Libraries Government Documents Department

High convergence implosion symmetry in cylindrical hohlraums

Description: High convergence, hohlraum-driven implosions will require control of time-integrated drive asymmetries to 1% levels for ignition to succeed on the NIF. We review how core imaging provides such asymmetry measurement accuracy for the lowest order asymmetry modes, and describe recent improvements in imaging techniques that should allow detection of higher order asymmetry modes. We also present a simple analytic model explaining how the sensitivity of symmetry control to beam pointing scales as we progress from single ring per side Nova cylindrical hohlraum illumination geometries to NIF-like multiple rings per side Omega hohlraum illumination geometries and ultimately to NIF-scale hohlraums.
Date: September 1, 1999
Creator: Amendt, P A; Bradley, D K; Hammel, B A; Landen, O L; Suter, L J; Turner, R E et al.
Partner: UNT Libraries Government Documents Department

Laser driven hydrodynamic instability experiments. Revision 1

Description: An extensive series of experiments has been conducted on the Nova laser to measure hydrodynamic instabilities in planar foils accelerated by x-ray ablation. Single mode experiments allow a measurement of the fundamental growth rates from the linear well into the nonlinear regime. Two-mode foils allow a first direct observation of mode coupling. Surface-finish experiments allow a measurement of the evolution of a broad spectrum of random initial modes.
Date: February 17, 1993
Creator: Remington, B. A.; Weber, S. V.; Haan, S. W.; Kilkenny, J. D.; Glendinning, S. G.; Wallace, R. J. et al.
Partner: UNT Libraries Government Documents Department

Measurement of the Absolute Hohlraum Wall Albedo Under Ignition Foot Drive Condition

Description: We present the first measurements of the absolute albedos of hohlraums made from gold or from high-Z mixtures. The measurements are performed over the range of radiation temperatures (70-100 eV) expected during the foot of an indirect-drive temporally-shaped ignition laser pulse, where accurate knowledge of the wall albedo (i.e. soft x-ray wall re-emission) is most critical for determining capsule radiation symmetry. We find that the gold albedo agrees well with calculations using the super transition array opacity model, potentially providing additional margin for ICF ignition.
Date: August 26, 2003
Creator: Jones, O S; Glenzer, S H; Suter, L J; Turner, R E; Campbell, K M; Dewald, E L et al.
Partner: UNT Libraries Government Documents Department

Symmetry Experiments on Omega with LMJ like Multiple Beam Cones Irradation

Description: We carried out a set of experiments on the Omega laser facility at Rochester with Laser MegaJoule (LMJ) like indirect drive irradiation. We studied the irradiation non-uniformity with the foam ball radiography technique and the implosion symmetry with (D{sub 2} + Argon) filled capsules core emission. Cylindrical ''Nova scale 1'' thin wall hohlraums were used. Forty of the Omega beams, arranged in three cones on each side of the hohlraum (5, 5, and lo), were used to create the X-ray drive. Eight additional beams were used on a Ti source to radiograph the foam balls. The shaped laser pulse was about 3 ns duration. The radiation drive was measured on each shot. The images were recorded with a 5 prn resolution Gated X-ray Imager coupled to a CCD camera.
Date: July 17, 2000
Creator: Richard, A L; Jadaud, J P; Dague, N; Monteil, M C; Turner, R E; Bradley, D et al.
Partner: UNT Libraries Government Documents Department

Experimental Testbed for the Study of Hydrodynamic Issues in Supernovae

Description: More than a decade after the explosion of SN 1987A, unresolved discrepancies still remain in attempts to numerically simulate the mixing processes initiated by the passage of a very strong shock through the layered structure of the progenitor star. Numerically computed velocities of the radioactive {sup 56}Ni and {sup 56}CO, produced by shock-induced explosive burning within the silicon layer for example, are still more than 50% too low as compared with the measured velocities. In order to resolve such discrepancies between observation and simulation, an experimental testbed has been designed on the Omega Laser for the study of hydrodynamic issues of importance to supernovae (SNe). In this paper, we present results from a series of scaled laboratory experiments designed to isolate and explore several issues in the hydrodynamics of SN explosions. The results of the experiments are compared with numerical simulations and are generally found to be in reasonable agreement.
Date: October 9, 2000
Creator: Robey, H F; Kane, J O; Remington, B A; Drake, R P; Hurricane, O A; Louis, H et al.
Partner: UNT Libraries Government Documents Department

Indirect-Drive Time Dependent Symmetry Diagnosis at NIF-Scale

Description: The scaling to NIF of current techniques used to infer the time-dependent flux asymmetries for indirectly-driven capsules is reviewed. We calculate that the projected accuracy for detecting the lowest mode asymmetries by a variety of techniques now meet the requirements for symmetry tuning for ignition. The scaling to NIF has also motivated the implementation of new, more efficient and hence less perturbative backlighting techniques which have recently provided high quality symmetry data during validation tests at the Omega facility.
Date: October 27, 1999
Creator: Landen, O.L; Bradley, D.K.; Pollaine, S.M.; Amendt, P.A.; Glendinning, S.G.; Suter, L.J. et al.
Partner: UNT Libraries Government Documents Department

Experimental measurements of hydrodynamic instabilities on NOVA of relevance to astrophysics

Description: Large lasers such as Nova allow the possibility of achieving regimes of high energy densities in plasmas of millimeter spatial scales and nanosecond time scales. In those plasmas where thermal conductivity and viscosity do not play a significant role, the hydrodynamic evolution is suitable for benchmarking hydrodynamics modeling in astrophysical codes. Several experiments on Nova examine hydrodynamically unstable interfaces. A typical Nova experiment uses a gold millimeter-scale hohlraum to convert the laser energy to a 200 eV blackbody source lasting about a nanosecond. The x-rays ablate a planar target, generating a series of shocks and accelerating the target. The evolving area1 density is diagnosed by time-resolved radiography, using a second x-ray source. Data from several experiments are presented and diagnostic techniques are discussed.
Date: September 11, 1998
Creator: Budil, K S; Cherfils, C; Drake, R P; Farley, D; Glendinning, S G; Kalantar, D H et al.
Partner: UNT Libraries Government Documents Department

Collapsing Radiative Shocks in Argon Gas on the Omega Laser

Description: A number of astrophysical systems involve radiative shocks that collapse spatially in response to energy lost through radiation. Supernova remnants are an example of systems that cool enough to radiatively collapse. This is believed to produce thin, dense shells that are Vishniac unstable. This type of instability may be responsible for the convoluted structure of supernova remnants such as the Cygnus Loop. We are conducting experiments on the Omega laser intended to produce such collapsing shocks and to study their evolution. The experiments use the laser to accelerate a thin slab of driving material (beryllium) through 1.1 ATM of argon gas ({approx}2 mg/cc) at {approx}100 km/sec. The simulations also predict that the dense layer will be pushed ahead of the dense beryllium by the leading edge of the expansion of this material. The experiment is diagnosed in two ways. X-ray radiography has detected the presence of the dense shocked layer. These data indicate that the shock velocity is {approx}100 km/s. A unique, side-on application of the VISAR (Velocity Interferometer System for Any Reflector) technique is used to detect frequency shifts from ionization and any reflections from the edge of the dense shocked layer.
Date: November 1, 2003
Creator: Reighard, A B; Drake, R P; Dannenberg, K; Perry, T S; Robey, H A; Remington, B A et al.
Partner: UNT Libraries Government Documents Department

Measurement of the absolute hohlraum wall albedo under ignition foot drive conditions

Description: We present the first measurements of the absolute albedos of hohlraums made from gold or from high-Z mixtures. The measurements are performed over the range of radiation temperatures (70-100 eV) expected during the foot of an indirect-drive temporally-shaped ignition laser pulse, where accurate knowledge of the wall albedo (i.e. soft x-ray wall re-emission) is most critical for determining capsule radiation symmetry. We find that the gold albedo agrees well with calculations using the super transition array opacity model, potentially providing additional margin for ICF ignition.
Date: November 25, 2003
Creator: Suter, L J; Wallace, R J; Hammel, B A; Weber, F A; Landen, O L; Campbell, K M et al.
Partner: UNT Libraries Government Documents Department

Hard X-ray and Hot Electron Environment in Vacuum Hohlraums at NIF

Description: Time resolved hard x-ray images (hv > 9 keV) and time integrated hard x-ray spectra (hv = 18-150 keV) from vacuum hohlraums irradiated with four 351 nm wavelength NIF laser beams are presented as a function of hohlraum size and laser power and duration. The hard x-ray images and spectra provide insight into the time evolution of the hohlraum plasma filling and the production of hot electrons. The fraction of laser energy detected as hot electrons (f{sub hot}) and a comparison to a filling model are presented.
Date: September 22, 2005
Creator: McDonald, J. W.; Suter, L. J.; Landen, O. L.; Foster, J. M.; Celeste, J. R.; Holder, J. P. et al.
Partner: UNT Libraries Government Documents Department

Laser Coupling to Reduced-Scale Targets at the Early Light Program of the National Ignition Facility

Description: A platform for analysis of material properties under extreme conditions, where a sample is bathed in radiation with a high temperature, is under development. This hot environment is produced with a laser by depositing maximum energy into a small, high-Z can. Such targets were recently included in an experimental campaign using the first four of the 192 beams of the National Ignition Facility, under construction at the University of California Lawrence Livermore National Laboratory. These targets demonstrate good laser coupling, reaching a radiation temperature of 340 eV. In addition, there is a unique wavelength dependence of the Raman backscattered light that is consistent with Brillouin backscatter of Raman forward scatter [A. B. Langdon and D. E. Hinkel, Physical Review Letters 89, 015003 (2002)]. Finally, novel diagnostic capabilities indicate that 20% of the direct backscatter from these reduced-scale targets is in the polarization orthogonal to that of the incident light.
Date: November 18, 2004
Creator: Hinkel, D E; Schneider, M B; Baldis, H A; Bower, D; Campbell, K M; Celeste, J R et al.
Partner: UNT Libraries Government Documents Department