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Studying the stars on earth: astrophysics on intense lasers

Description: Lawrence Livermore National Laboratory in Livermore, California, is now performing significant astrophysics experiments on its huge Nova laser facility, and a similar effort has started at the Gekko laser facility at Osaka University in Japan. Our experiments on the Nova and Gekko lasers so far encourage us that our astrophysics work is already leading to a better understanding of the hydrodynamics of supernovae and astrophysical jets. The ability of large inertial confinement fusion lasers to recreate star-like conditions in the laboratory greatly improves our understanding of the heavens; for the first time in our history, we can study the stars up close on Earth.
Date: March 10, 1999
Creator: Remington, B. A.
Partner: UNT Libraries Government Documents Department

97-ERD-022 final report: Supernova on Nova

Description: This is the final year of the 3-year LDRD-ERD involving Lasers, D&NT, Physics, and ILSA to develope astrophysics experiments on intense lasers such as the Nova and Gekko lasers. During this 3 year period, we have developed a highly successful experiment probing the hydrodynamics of the explosion phase of core-collapse supernovae, which occurs during the first ~3 hours after core collapse. This was in collaboration with the Univ. of Arizona and CEA/Saclay. We also developed a very successful experiment to probe the hydrodynamics of the later time, young remnant phase, meaning the first ~10-20 years after core collapse. This was in collaboration with the Univ. of Michigan and Univ. of Colorado. Finally, we developed during the final year an exquisite experiment to probe the dynamics of radiative, high Mach number astrophysical jets, in collaboration with the Univ. of Maryland and Osaka Univ. Each experiment has received very high visibility, with a multitude of publications, both in the technical journals (most importantly, the astrophysical journals) and in the popular press. The attached publication list shows 25 papers published or submitted to technical journals, 5 articles appearing in the popular press (including a cover story of Sky and Telescope), and 65 conference presentations, ~10 of which were invited talks. The most important papers to come out of this effort was a comprehensive theory paper for Ap. J. establishing the rigorous scaling between laboratory laser experiments and the astrophysical subjects of interest: supernovae, supernova remnants, and jets; and a review article for Science covering this emerging subfield of Astrophysics on Intense Lasers. Since there are so many publications that have resulted from this LDRD project, only these two most important papers are attached. The rest are properly referenced, and can be found online or in the library. In anticipation of the closing of ...
Date: March 11, 1999
Creator: Remington, B. A.
Partner: UNT Libraries Government Documents Department

Progress on the physics of ignition for radiation driven inertial confinement fusion (ICF) targets

Description: Extensive modeling of proposed National Ignition Facility (NIF) ignition targets has resulted in a variety of targets using different materials in the fuel shell, using driving temperatures which range from 250-300 eV, and requiring energies from < 1 MJ up to the full 1. 8 MJ design capability of NIF. Recent Nova experiments have shown that hohlraum walls composed of a mixture of high-z materials could result in targets which require about 20% less energy. Nova experiments are being used to quantify benefits of beam smoothing in reducing stimulated scattering processes and laser beam filamentation for proposed gas-filled hohlraum targets on NIF. Use of Smoothing by Spectral Dispersion with 2-3 {Angstrom}of bandwidth results in <4-5% of Stimulated Raman Scattering and less than about 1% Stimulated Brillouin Scattering for intensities less than about 2x10{sup 15}W/cm{sup 2} for this type of hohlraum. The symmetry in Nova gas- filled hohlraums is affected by the gas fill. A large body of evidence now exists which indicates that this effect is due to laser beam filamentation which can be largely controlled by beam smoothing. We present here the firs 3-D simulations of hydrodynamic instability for the NIF point design capsule. These simulations, with the HYDRA radiation hydrodynamics code, indicate that spikes can penetrate up to 10 {mu}m into the 30{mu}m radius hot spot before ignition is quenched. Using capsules whose surface is modified by laser ablation, Nova experiments have been used to quantify the degradation of implosions subject to near NIF levels of hydrodynamic instability.
Date: September 1, 1996
Creator: Lindl, J.D. & Marinak, M.M.
Partner: UNT Libraries Government Documents Department

Supernova hydrodynamicas experiments using the Nova laser

Description: We are developing experiments using the Nova laser to investigate (1) compressible nonlinear hydrodynamic mixing relevant to the first few hours of the supernova (SN) explosion and (2) ejecta-ambient plasma interactions relevant to the early SN remnant phase. The experiments and astrophysical implications are discussed.
Date: July 1, 1997
Creator: Remington, B.A.; Glendinning, S.G. & Estabrook, K.
Partner: UNT Libraries Government Documents Department

Nova experiments to investigate hydrodynamic instabilities in the solid state

Description: Experiments were done to shock compress and accelerate copper foils at peak presssures of {approximately}3 Mbar above and below the melt temperature to study the effects of material strength on hydrodynamic instabilities. An x-ray drive generated in a hohlraum target was used to generate the shock wave profiles. The growth of a preimposed perturbation at an embedded interface is diagnosed by x-ray radiography. Results obtained using a high contrastshaped laser pulse show that the growth of the modulation is delayed compared to fluid simulations,which could be due to material strength stabilization. In contrast, when a copper foil is placed above the melt temperature at {gt}3 Mbar with a single shock, it melts upon compression and the modulation growth is consistent with fluid modeling. Experimental results from copper shocked to 3 Mbar both below and above the melt temperature are presented and compared with simulation.
Date: July 8, 1997
Creator: Kalantar, D.H.; Remington, B.A.; Chandler, E.A.; Colvin, J.D.; Griswold, D.L.; Turner, R.E. et al.
Partner: UNT Libraries Government Documents Department

Nonlinear Rayleigh-Taylor instability experiments in Nova

Description: We examined the progression of the Rayleigh-Taylor (RT) instability from an initial multimode perturbation. The RT experiments focused on the transition from the linear to non-linear regimes for perturbation growth at an embedded, or classical, interface. The multimode experiments have attempted to observe the process of bubble competition wherein neighboring structures either continue to rise or are washed downstream in the flow depending upon; their relative size. This competition is predicted to result in an inverse cascade at late times where progressively larger structures will begin to dominate the flow. Experiments to date have shown evidence of coupled modes arising, but have not yet accelerated the interface long enough to produce the several generations of coupling required for a true inverse cascade.
Date: June 16, 1997
Creator: Budil, K.S.; Remington, B.A.; Weber, S.V.; Perry, T.S. & Peyser, T.A.
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

Classical Rayleigh-Taylor instability experiments at Nova

Description: The evolution of the Rayleigh-Taylor (RT) instability at an embedded, or classical, interface is examined in a series of experiments at the Nova laserfacility .[reference for Nova] These experiments focused on the transition from the linear to nonlinear regimes for both single- and multimode initialperturbations. The development of a single mode at the embedded interface is compared to its evolution at an ablation front and the effect of ablativestabilization is experimentally demonstrated. The multimode experiments have shown evidence of the process of bubble competition, whereinneighboring structures either continue to rise or are washed downstream in the flow depending upon their relative size. The experiments with simulations performed with either the LASNEX are comparedcode [G. B.Zimmerman and W. L. Kruer, Comments Plasma Phys. Controlled Fusion 2,51 (1975).], a two-dimensional Lagrangian radiation-hydrodynamics code, or CALE [R. Tipton, reference for CALE], a two-dimensional arbitrary Lagrange-Eulerian radiation-hydrodynamics code.
Date: November 10, 1997
Creator: Budil, K. S.; Remington, B. A.; Weber, S. V.; Perry, T. S. & Peyser, T. A.
Partner: UNT Libraries Government Documents Department

Nonlinear Rayleigh-Taylor and Richtmyer-Meshkov mixing experiments at Nova

Description: The evolution of the Rayleigh-Taylor (RT) and Richtmyer-Meshkov (RM) instabilities in the nonlinear regime of growth was investigated in indirect-drive experiments on the Nova laser. The RT experiments investigated the evolution of both single- and multimode perturbations at an embedded interface, isolated from the effects of ablation. This ``classical`` geometry allows short wavelength ({lambda} {approximately} 10-20 {micro}m) perturbations to grow strongly, in marked contrast to prior results at an ablation front. The RM experiments studied singly- and doubly-shocked perturbed interfaces in both face-on and side-on geometries. (U)
Date: September 15, 1997
Creator: Budil, K.S.; Remington, B.A.; Weber, S.V.; Farley, D.R.; Murray, S. & Peyser, T.A.
Partner: UNT Libraries Government Documents Department

Laser imprint and implications for direct drive ignition with the National Ignition Facility

Description: For direct drive ICF, nonuniformities in laser illumination can seed ripples at the ablation front in a process called imprint. Such nonuniformities will grow during the capsule implosion and can penetrate the capsule shell impede ignition, or degrade burn. We have simulated imprint for a number of experiments on tile Nova laser. Results are in generally good agreement with experimental data. We leave also simulated imprint upon National Ignition Facility (NIF) direct drive ignition capsules. Imprint modulation amplitude comparable to the intrinsic surface finish of {approximately}40 nm is predicted for a laser bandwidth of 0.5 THz. Ablation front modulations experience growth factors up to several thousand, carrying modulation well into the nonlinear regime. Saturation modeling predicts that the shell should remain intact at the time of peak velocity, but penetration at earlier times appears more marginal.
Date: July 9, 1996
Creator: Weber, S.V.; Glendinning, S.G.; Kalantar, D.H.; Remington, B.A. & Rothenberg, J.E.
Partner: UNT Libraries Government Documents Department

Petawatt laser system and targeting performance

Description: We recently demonstrated the production of 1.25 PW of peak power in the Nova/Petawatt Laser Facility, generating > 600 J in < 450 fs. Results of the first focused irradiance tests, at 500 J and deployment of a novel targeting system will be presented.
Date: April 30, 1997
Creator: Pennington, D.M.; Perry, M.D. & Britten, J.A.
Partner: UNT Libraries Government Documents Department

Hard x-ray production from high intensity laser solid interactions

Description: Intense laser (> 10{sup 21} W/cm{sup 2}) driven hard x-ray sources offer a new alternative to conventional electron accelerator bremsstrahlung sources. These laser driven sources offer considerable simplicity in design and cost advantage for multiple axis views and have the potential for much higher spatial and temporal resolution than is achievable with accelerator sources We have begun a series of experiments using the Petawatt Laser system at LLNL to determine the potential of these sources for radiography applications Absolutely calibrated spectra extending to 20 MeV and high resolution radiographs through a {rho}r{>=}150 gm/cm{sup 2} have been obtained The physics of these sources and the scaling relationships and laser technology required to provide the dose levels necessary for radiography applications will be discussed Diagnostics of the laser produced electrons and photons will be addressed
Date: June 3, 1998
Creator: Sefcik, J. A.
Partner: UNT Libraries Government Documents Department

The status of the ICF target physics program at Lawrence Livermore National Laboratory

Description: Calculations of x-ray driven igniting implosions require several critical parameters which have been separately tested on Nova, viz., acceptable levels of SBS and SRS from plasmas equivalent to the plasmas in igniting hohlraums, quantitative understanding of radiation temperature in gas-filled hohlraums, demonstration of control of drive symmetry in gas-filled hohlraums, low levels of seeding of hydrodynamic instabilities from surfaces, especially cryogenic deuterium tritium ice, and quantitative understanding of the mix of cold fuel into a hot spot in high growth factor implosions. 14 refs.
Date: June 14, 1996
Creator: Kilkenny, J.D.; Bernat, t.P. & Hammel, B.A.
Partner: UNT Libraries Government Documents Department

Characterization of X-ray streak cameras for use on Nova

Description: There are many different types of measurements that require a continuous time history of x-ray emission that can be provided with an x-ray streak camera. In order to properly analyze the images that are recorded with the x-ray streak cameras operated on Nova, it is important to account for the streak characterization of each camera. We have performed a number of calibrations of the streak cameras both on the bench as well as with Nova disk target shots where we use a time modulated laser intensity profile (self-beating of the laser) on the target to generate an x-ray comb. We have measured the streak camera sweep direction and spatial offset, curvature of the electron optics, sweep rate, and magnification and resolution of the electron optics.
Date: September 1, 1996
Creator: Kalantar, D.H.; Bell, P.M.; Costa, R.L.; Hammel, B.A.; Landen, O.L.; Orzechowski, T.J. et al.
Partner: UNT Libraries Government Documents Department

Design and reality for NIF ignition targets

Description: Advances in ICF experiments and modeling have led to improved understanding of the growth of instabilities during capsule implosion and the effects on capsule performance. This has led to more refined specifications on the characteristics of igniting capsules, all of which have solid D-T fuel layers. These specifications involve a trade-off between the interior ice surface structure, outer capsule surface structure, and time-dependent drive asymmetry.
Date: May 31, 1996
Creator: Bernat, T.P.
Partner: UNT Libraries Government Documents Department

Improved gas-filled hohlraum performance on Nova with beam smoothing

Description: Gas-filled hohlraums are presently the base line ignition target design for the National Ignition Facility. Initial Nova experiments on gas-filled hohlraums showed that radiation temperature was reduced due to SBS and SRS scattering losses and that implosion symmetry had shifted compared with vacuum hohlraums and calculations. Subsequent single beam experiments imaging thermal x-ray emission showed the shift is due to laser-plasma heating dynamics and filarnentation in a flowing plasma. Experiments using a single beam have shown that scattering losses and effects of filamentation are reduced when the beam is smoothed with an random phase plate (RPP) or kinoform phase plate (KPP). Scattering is further reduced to less than 5% of the incident laser energy when SSD is added.
Date: December 2, 1997
Creator: Kauffman, R.L.; Powers, L.V. & Dixit, S.N.
Partner: UNT Libraries Government Documents Department

Equation of state measurements of D2 on Nova

Description: In this paper we describe principle Hugoniot measurements of liquid D{sub 2} up to P = 2.1 Mbar. We compressed liquid D{sub 2} with a Nova-laser-driven shock wave launched from an aluminum pusher. The Al/D{sub 2} interface and the shock front in the D{sub 2} are observed with temporally resolved radiography, to determine particle speed U{sub p}, shock speed U{sub s}, and the ratio of final density to initial density {rho}/{rho}{sub 0}. The pressure is calculated. These absolute EOS data reveal a compressibility comparable to the dissociation model.
Date: July 1, 1997
Creator: Collins, G.W.; Da Silva, L.B. & Celliers, P.
Partner: UNT Libraries Government Documents Department

Spatial resolution of gated x-ray pinhole cameras

Description: The new camera FXI was investigated. Spatial resolution, or its Fourier transform, the modulation transfer function (MTF), is critical for quantitative interpretation of recent hydrodynamic instability data taken on the Nova laser. We have taken data corresponding to backlit straight edges, pinholes, and grids, both on the bench and {ital in}{ital situ} on Nova. For both the pinhole and edge data, the MTF at all wavelengths of interest can be deduced from a single image. Grids are of more limited usefulness, giving the MTF value only at the spatial period of the grid. These different techniques for characterizing the MTF of gated x-ray pinhole cameras are discussed, with results specific to the FXI presented.
Date: May 15, 1996
Creator: Robey, H.F.; Budil, K.S. & Remington, B.A.
Partner: UNT Libraries Government Documents Department

High-energy 4{omega} probe laser for laser-plasma experiments at nova

Description: For the characterization of inertial confinement fusion plasmas we implemented a high-energy 4{omega} probe laser at the Nova laser facility. A total energy of > 50 Joules at 4{omega}, a focal spot size of order 100 {micro}m, and a pointing accuracy of 100 {micro}m was demonstrated for target shots. This laser provides intensities of up to 3 x 10{sup 14}W cm{sup -2} and therefore fulfills high-power requirements for laser-plasma interaction experiments. The 4{omega} probe laser is now routinely used for Thomson scattering. Successful experiments were performed in gas-filled hohlraums at electron densities of n{sub e} > 2 X 10{sup 21}cm{sup -3} which represents the highest density plasma so far being diagnosed with Thomson scattering.
Date: June 2, 1998
Creator: Glenzer, S. H., LLNL
Partner: UNT Libraries Government Documents Department

Developing beam phasing on the Nova laser

Description: We are presently adding the capability to irradiate indirectly-driven Nova targets with two rings of illumination inside each end of the hohlraum for studies of time-dependent second Legendre (P2) and time- integrated fourth Legendre (P4) flux asymmetry control. The rings will be formed with specially designed kinoform phase plates (KPPs), which will direct each half of each beam into two separate rings that are nearly uniform azimuthally. The timing and temporal pulse shape of the outer rings will be controlled independently from those of the inner rings, allowing for phasing of the pulse shapes to control time dependent asymmetry. Modifications to the incident beam diagnostics (IBDS) will enable us to verify that acceptable levels of power balance among the contributing segments of each ring have been achieved on each shot. Current techniques for precision beam pointing and timing are expected to be sufficiently accurate for these experiments. We present a design for an affordable retrofit to achieve beam phasing on Nova, results of a simplified demonstration, and calculations highlighting the anticipated benefits.
Date: March 10, 1997
Creator: Ehrlich, R.B.; Amendt, P.A.; Dixit, S.N.; Hammel, B.A.; Kalantar, D.H.; Pennington, D.M. et al.
Partner: UNT Libraries Government Documents Department

The Petawatt laser system

Description: We recently demonstrated the production of over a petawatt of peak power in the Nova/Petawatt Laser Facility, generating > 600 J in {approximately} 440 fs. The Petawatt Laser Project was initiated to develop the capability to test the fast ignitor concept for inertial confinement fusion (ICF), and to provide a unique capability in high energy density physics. The laser was designed to produce near kJ pulses with a pulse duration adjustable between 0.5 and 20 ps. At the shortest pulse lengths, this laser is expected to surpass 10 21 W/cm 2 when focused later this year. Currently, this system is limited to 600 J pulses in a 46.3-cm beam. Expansion of the beam to 58 cm, with the installation of 94-cm gratings, will enable 1 kJ operation. Target experiments with petawatt pulses will be possible either integrated with Nova in the 10 beam target chamber or as a stand alone system in an independent, dedicated chamber. Focusing the beam onto a target will be accomplished using an on axis parabolic mirror. The design of a novel targeting system enabling the production of ultrahigh contrast pulses and an easily variable effective focal length is also described.
Date: March 11, 1997
Creator: Pennington, D.M.; Perry, M.D. & Stuart, B.C.
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

Engineering the Petawatt Laser into Nova

Description: The engineering process of integrating the Petawatt (10{sup 15} watts) laser system into the existing 30 kJ (UV) Nova laser at Lawrence Livermore National Laboratory (LLNL) is described in detail. The nanosecond-long, chirped Petawatt laser pulse is initially generated in a separate master oscillator room and then injected into one of Nova`s 10 beamlines. There, the pulse is further amplified and enlarged to {approximately}{phi}60 cm, temporally compressed under vacuum to <500 fs using large diameter diffraction gratings, and then finally focused onto targets using a parabolic mirror. The major Petawatt components are physically large which created many significant engineering challenges in design, installation and implementation. These include the diffraction gratings and mirrors, vacuum compressor chamber, target chamber, and parabolic focusing mirror. Other Petawatt system components were also technically challenging and include: an injection beamline, transport spatial filters, laser diagnostics, alignment components, motor controls, interlocks, timing and synchronization systems, support structures, and vacuum systems. The entire Petawatt laser system was designed, fabricated, installed, and activated while the Nova laser continued its normal two-shift operation. This process required careful engineering and detailed planning to prevent experimental downtime and to complete the project on schedule.
Date: December 23, 1997
Creator: Tietbohl, G.L.; Bell, P.M. & Hamilton, R.M.
Partner: UNT Libraries Government Documents Department