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Measurements of MeV photon flashes in petawatt laser experiments

Description: Planar targets illuminated by the Petawatt laser system emit directed beams of photons with energies of MeVs. The laser pulses have durations of 0.5 or 5 psec, on target energies in excess of 100 joules, and focal-spot sizes that vary from 10 to 100 µm, producing peak intensities greater than 10<sup>19</sup> watts/cm<sup>;2</sup>. Arrays of PIN diodes, dosimeters and nuclear-activation detectors measure the angular distributions of photons with energies greater than 0.5 MeV. The PIN diodes, with 1 cm<sup>2</sup> by 500-µm sensitive volume, are housed in lead pigs with 2.5-cm thick walls. Measured emission intensities have been as high as 5x10<sup>13</sup> (gamma) MeV/steradian. The angular distributions are highly directed in forward directions, with significant variations on a shot-to-shot basis. Backward radiated intensities tend to be more than a decade lower than in forward direct
Date: November 10, 1998
Creator: Phillips, T.; Brown, C. G.; Cowan, T.; Hatchett, S.; Hunt, A.; Key, M. et al.
Partner: UNT Libraries Government Documents Department

Cluster ion beam polishing for inertial confinement fusion target capsules

Description: Targets for Inertial Confinement Fusion (ICF) typically consist of a hollow, spherical capsule filled with a mixture of hydrogen isotopes. Typically, these capsules are irradiated by short, intense pulses of either laser light (``direct drive``) or laser-generated. x-rays (``indirect drive``), causing them to implode This compresses and heats the fuel, leading to thermonuclear fusion. This process is highly sensitive to hydrodynamic (e.g., Rayleigh-Taylor) instabilities, which can be initiated by imperfections in the target. Thus, target capsules must be spherical and smooth One of the lead capsule designs for the National Ignition Facility, a 1.8 MJ laser being built at Livermore, calls for a 2-mm- diam capsule with a 150-{micro}m-thick copper-doped beryllium wall. These capsules can be fabricated by sputter depositing the metal onto a spherical plastic mandrel. This results in surfaces with measured Rq`s of 50 to 150 nm, as measured with an atomic force microscope For optimal performance the roughness should be below 10 nm rms We have begun studying the use of ion cluster beam polishing as a means of improving the surface finish of as-deposited capsules In this approach, a batch of capsules would be agitated in a bounce pan inside a vacuum chamber during exposure to the cluster beam. This would ensure a uniform beam dose around the capsule. We have performed preliminary experiments on both Be flats and on a stationary Be capsule On the capsule, the measured Rq went from 64 nm before polishing to 15 nm after This result was obtained without any effort at process optimization. Similar smoothing was observed on the planar samples
Date: June 9, 1998
Creator: McEachern, R.
Partner: UNT Libraries Government Documents Department

Ultrashort x-ray backlighters and applications

Description: Previously, using ultrashort laser pulses focused onto solid targets, we have experimentally studied a controllable ultrafast broadband radiation source in the extreme ultraviolet for time-resolved dynamical studies in ultrafast science [J. Workman, A. Maksimchuk, X. Llu, U. Ellenberger, J. S. Coe, C.-Y. Chien, and D. Umstadter, ``Control of Bright Picosecond X-Ray Emission from Intense Sub- Picosecond Laser-Plasma Interactions,`` Phys. Rev. Lett. 75, 2324 (1995)]. Once armed with a bright ultrafast broadband continuum x-ray source and appropriate detectors, we used the source as a backlighter to study a remotely produced plasma. The application of the source to a problem relevant to high-density matter completes the triad: creating and controlling, efficiently detecting, and applying the source. This work represented the first use of an ultrafast laser- produced x-ray source as a time-resolving probe in an application relevant to atomic, plasma and high-energy-density matter physics. Using the x-ray source as a backlighter, we adopted a pump-probe geometry to investigate the dynamic changes in electronic structure of a thin metallic film as it is perturbed by an ultrashort laser pulse. Because the laser deposits its energy in a skin depth of about 100 {Angstrom} before expansion occurs, up to gigabar pressure shock waves lasting picosecond in duration have been predicted to form in these novel plasmas. This raises the possibility of studying high- energy-density matter relevant to inertial confinement fusion (ICF) and astrophysics in small-scale laboratory experiments. In the past, time-resolved measurements of K-edge shifts in plasmas driven by nanosecond pulses have been used to infer conditions in highly compressed materials. In this study, we used 100-fs laser pulses to impulsively drive shocks into a sample (an untamped 1000 {Angstrom} aluminum film on 2000 {Angstrom} of parylene-n), measuring L-edge shifts.
Date: August 1, 1997
Creator: Umstadter, D., University of Michigan
Partner: UNT Libraries Government Documents Department

Measurement of RT amplitudes and wavelengths of laser driven plates

Description: A laser drive plate, that is a dense solid plate drive by a laser heated, lower density plasma, is inherently Raleigh-Taylor (R-T) unstable, We have previously indicated that observed surface perturbation on the plate are probably R-T instabilities, initiated by the mode structure of the driving laser beam. Using a semi- transparent impact target viewed with a polarized Epi-Illuminated Confocal Streak Microscope, has allowed us to measure the amplitude and growth of the instability.
Date: October 16, 1997
Creator: Frank, A.M. & Gillespie, C.H.
Partner: UNT Libraries Government Documents Department

Radiation MHD modeling of a proposed dynamic hohlraum

Description: In this paper we report 2D radiation magnetohydrodynamic simulations of a dynamic hohlraum target designed to be driven by the Z accelerator at Sandia National Laboratory, Albuquerque New Mexico. Z generates currents up 20 MA with a rise time of 100 ns and peak electrical power of 40 TW. In this design we attempt to reduce the effects of magneto-Rayleigh Taylor (RT) modes by using a distributed initial density profile. Earlier work showed that ``tailoring`` the initial density profile could reduce the sheath acceleration and the number of e-foldings that the RT instability grows during the implosion . As the sheath moves in radially, fresh material is swept up or ``snow plowed``, providing a back pressure that counters the J x B force. A special profile can be found in which the unstable outer surface of the sheath implodes at constant velocity, reducing the classical growth rate to zero, although residual Richtmeyer-Meshkov type instability (instability of the snow-plow shock front) may be present. In practice, it is hard to create tailored initial density profiles due to the difficulty of machining and otherwise manipulating very low density materials. It becomes easier to manufacture these complex targets as the current, energy and load mass increase with large drivers. Z is the first fast pulse power device with enough energy to consider loads of this type.
Date: July 1, 1997
Creator: Hammer, J.H.; De Groot, J.S.; Tabak, M.; Toor, A. & Zimmerman, G.B.
Partner: UNT Libraries Government Documents Department

Representative surface profile power spectra from capsules used in NOVA and Omega implosion experiments

Description: Typical surface profile power spectra of capsules used in Nova and Omega implosion experiments are presented. All Nova capsules are essentially identical in size and composition; their differences reflect small shell-to-shell variations. Differences among the Omega capsule power spectra can be attributed to changes in material properties with doping and (very importantly) differences in processing experience. These capsule power spectra accurately reflect past and current production, but are only a starting point for future capabilities.
Date: October 20, 1998
Creator: Cook, R. C.; McEachern, R. L. & Stephens, R.
Partner: UNT Libraries Government Documents Department

New approaches to the preparation of P(alpha)MS beads as mandrels for NIF-scale target capsules

Description: We report on a new method using heated density gradient columns for preparing spherical poly({alpha} - methylstyrene) (P{alpha}MS) bead mandrels for inertial confinement fusion spherical shell targets. Using 1,2 propane diol/glycerol mixtures, stable density gradient columns for supporting P{alpha}MS beads can be prepared at temperatures as high as 150 {degrees}C. At these temperatures plasticized commercial beads become fluid and spherical, however loss of the plasticizer and very low molecular weight components of the bead due to limited solubility in the column fluid leads to surface finish problems. We also present results on P{alpha}MS beads prepared in an aqueous bath batch mode. Using these techniques beads with maximum out-of-rounds less than 5 {micro}m have been produced.
Date: October 20, 1998
Creator: Buckley, S R; Cook, R C; Fearon, E & Letts, S A
Partner: UNT Libraries Government Documents Department

100 Femtosecond laser absorption in solid density targets

Description: Experimental short pulse lasers are rapidly approaching energy levels where target irradiances exceeding 10{sup 20} W/CM{sup 2} are routinely achievable. These high intensity levels will open up a new class of solid target interaction physics where relativistic effects must be included and non-traditional absorption mechanisms become significant. However much remains to be understood of the absorption physics at lower intensities where classical absorption is dominated by collisional and resonance absorption. If attention is paid to producing clean laser pulses that do not significantly pre-pulse interact with the target, it is possible to produce plasmas of sufficiently short scale length that near-solid density interactions are observable at intensities exceeding 10{sup 18} W/CM{sup 2} for 100 fs laser irradiation. We report here extensions to our previous efforts at normal incidence that expand our observations to non-normal angles including the effect of polarization for several target materials. Between 10{sup 13} W/CM{sup 2} and 10{sup 14} W/CM{sup 2} we observe that the target absorption retains a signature of the intra-band atomic transitions. At higher intensities a more material independent ion-electron collisional absorption and short scale length resonance absorption dominate. P - polarized absorption in short scale length plasmas has been observed to exceed 60 percent.
Date: October 8, 1996
Creator: Price, D.F.; More, R.M.; Walling, R.S. & Stewart, R.E.
Partner: UNT Libraries Government Documents Department

Mandrel development update

Description: We report on the progress since January, 1998, in preparing polymer mandrels by microencapsulation for NIF scale ICF capsules that meet the required symmetry and surface finish requirements. During that time we successfully completed our FY98 DOE TDF4.1 milestone of improving the mandrel low mode to meet NIF requirements. A number of batches of 2 mm microencapsulated poly(a- methylstyrene) shells have been produced with mode 2 out-of-rounds of less than 2 {micro}m. Detailed characterization for these and other batches is presented. We have found that the key to reducing mode 2 out-of-round is the density matching of the composite oil/inner core water microencapsulated shell preform to the supporting bath. Density matching of the inner core water to the oil phase seems to be less important, perhaps because core centering is accomplished by other physical means. Shell roughness over the very important mode 10 to 100 region is still too high by at least a decade in power, and work aimed at improving this is the task for FY99. In addition to basic sphericity results we also report on a number of experiments designed to elucidate the fundamental scientific issues. In most cases the experiments reported are but starting points that will be followed up during FY99. Lastly we note that no effort has been placed on optimizing the overcoating and thermal decomposition steps, which must follow the successful microencapsulation step. Based upon GA� s experience with smaller scale shells we are hopeful that these steps will not degrade capsule symmetry and surface finish. This question should be answered at least in part during FY99 as GA begins to supply finished 2 mm CH mandrels for the polyimide and Be ablator development work.
Date: February 1, 1999
Creator: Buckley, S; Cook, B; Hassel, A & Takagi, M
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

Sputter deposited beryllium fuel capsules for NIF

Description: The objective of our effort is to systematically study the properties of films produced under different conditions, with an emphasis on improving surface morphology and microstructure while studying permeability and capsule strength. We have made extensive use of atomic force and electron microscopy to determine the microstructure of the films, along with composition probes (mainly x-ray fluorescence) to quantify the chemical structure. Our studies can be roughly divided into three categories. First, there are those in which the effects of substrate biasing have been investigated. This includes varying the substrate voltage from 0 to 120 V and applying an intermittent bias. Next there are studies of Be combined with boron, a non-soluble dopant Because of it`s low Z this dopant is of particular interest for x-ray related applications. Finally, there are experiments in which pulses of nitrogen are admitted to the vacuum chamber during deposition. The layers of nitride formed tended to disrupt the growth of Be grains, leading to a more fine-grained microstructure. For all these studies, we have most often used hollow plastic spheres for our substrate material. However, there have been some samples deposited on glass spheres or silicon flats.
Date: February 12, 1998
Creator: Alford, C.S.
Partner: UNT Libraries Government Documents Department

Measurements of direct drive laser imprint in thin foils by XUV radiography using an X-ray laser backlighter

Description: In direct drive inertial confinement fusion, the residual speckle pattern remaining after beam smoothing plays an important role in the seeding of instabilities at the ablation front. We have used an x-ray laser as an XUV backlighter to characterize the imprinted modulation in thin foils for smoothing by random phase plate and spectral dispersion at both 0.35 pm and 0.53 pm irradiation, and induced spatial incoherence at 0.53 pm irradiation. We also demonstrate measurements of the modulation due to a single mode optical imprint generated by a narrow slit interference pattern, and modification of the imprint with a superposed smooth irradiation to study time dependence of the imprinting process. 8 refs., 10 figs.
Date: November 1, 1996
Creator: Kalantar, D.H.; Key, M.H. & DaSilva, L.B.
Partner: UNT Libraries Government Documents Department

Micromachining of inertial confinement fusion targets

Description: Many experiments conducted on today`s largest inertial confinement fusion drive lasers require target components with sub-millimeter dimensions, precisions of a micron or less and surface finishes measured in nanometers. For metal and plastic, techniques using direct machining with diamond tools have been developed that yield the desired parts. New techniques that will be discussed include the quick-flip locator, a magnetically held kinematic mount that has allowed the direct machining of millimeter-sized beryllium hemishells whose inside and outside surface are concentric to within 0.25 micron, and an electronic version of a tracer lathe which has produced precise azimuthal variations of less than a micron.
Date: December 31, 1996
Creator: Gobby, P.L.; Salzer, L.J. & Day, R.D.
Partner: UNT Libraries Government Documents Department

NIF capsule design update

Description: We describe several ignition capsule designs, for use in the National Ignition Facility. We will compare these designs for ablator efficiency, ignition margin, implosion and stability performance. This study includes capsule designs driven by x-ray drive profiles with both 300 eV and 250 eV peak temperatures. All of the 300 eV designs are tuned to implode the DT fuel in a nearly identical manner. Capsule designs consist of an ablator material (CH with Br dopant; Be with Cu dopant; and B{sub 4}C) encasing a layer of solid DT. The dopants alter material opacities sufficiently to (1) shield the DT fuel from preheat effects; and (2) develop an ablation front density profile favorable to implosion stability. B{sub 4}C has sufficient opacity at 300 eV that a dopant is not necessary. Issues relating to material properties and fabrication will be described.
Date: October 1, 1996
Creator: Dittrich, T.R.; Haan, S.W.; Pollaine, S.; Burnham, A.K. & Strobel, G.L.
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

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

Sputter-deposited Be ablators for NIF target capsules

Description: We have performed a series of preliminary experiments to determine whether sputter deposition of doped Be is a practical route to producing NIF target capsules with Be ablators. Films ranging in thickness from 7 to {approximately} 120 {micro}m have been deposited on spherical polymer mandrels using a bounce pan to ensure uniform coating. With no voltage bias applied to the pan, relatively porous coatings were formed that were highly permeable to hydrogen. The surface finish of these films ranged from {approximately}250 nm rms for 13-{micro}m-thick films to a minimum of {approximately}75 nm rms for an 80-{micro}m-thick film. Application of a voltage bias was found to significantly modify the film morphology. At a bias of 120 V, 7-{micro}m-thick films with a dense, fine-grained microstructure were produced. These capsules had a reflective surface with a 50 nm rms roughness. Finally, to demonstrate the ability to produce a graded dopant profile, a coating was produced in which the concentration of added Cu was varied from 2.5 atom % at the beginning to zero after 40 {micro}m of deposition.
Date: March 26, 1997
Creator: McEachern, R.; Clford, C.; Cook, R.; Makowiecki, E. & Wallace, R.
Partner: UNT Libraries Government Documents Department

Some aspects of the hydrodynamics of the microencapsulation route to NIF mandrels

Description: Spherical plastic shells for use as mandrels for the fabrication of ICF (Inertial Confinement Fusion) target capsules can be produced by solution-based microencapsulation techniques. The specifications for these mandrels in terms of sphericity are extremely rigorous, and it is clear that various aspects of the solution hydrodynamics associated with their production are important in controlling the quality of the final product. This paper explores what we know (and need to know) about the hydrodynamics of the microencapsulation process in order to lay the foundation for process improvements as well as identify inherent limits.
Date: October 20, 1998
Creator: Gresho, P M
Partner: UNT Libraries Government Documents Department

Analysis of integrating sphere performance for IR enhanced DT layering

Description: Absorbed IR energy can supplement the beta decay energy from DT ice to improve the driving force toward uniform layers. A significant problem with this approach has been to deliver the added IR energy with sufficient uniformity to enhance rather than destroy the uniformity of the ice layers. Computer modeling has indicated that one can achieve {approximately}1% uniformity in the angular variation of the absorbed power using an integrating sphere containing holes large enough to allow external inspection of the ice layer uniformity. The power required depends on the integrating sphere size, a 25 mm diameter sphere requires {approximately}35 mW of IR to deposit as much energy in the ice as the 50 mW/cm{sup 3}(35 pW total) received from tritium decay in DT. Power absorbed in the plastic can cause unacceptable ice-layer non-uniformities for the integrating sphere design considered here.
Date: June 1, 1997
Creator: Stephens, R.B., & Collins, G.W.
Partner: UNT Libraries Government Documents Department

Inertial confinement fusion target component fabrication and technology development support: Annual report, October 1, 1995--September 30, 1996

Description: On December 30, 1990, the U.S. Department of Energy entered into a contract with General Atomics (GA) to be the Inertial Confinement Fusion (ICF) Target Component Fabrication and Technology Development Support contractor. In September 1995 this contract ended and a second contract was issued for us to continue this ICF target support work. This report documents the technical activities of the period October 1, 1995 through September 30, 1996. During this period, GA and our partners WJ Schafer Associates (WJSA) and Soane Technologies, Inc. (STI) were assigned 14 formal tasks in support of the Inertial Confinement Fusion program and its five laboratories. A portion of the effort on these tasks included providing direct {open_quotes}Onsite Support{close_quotes} at Lawrence Livermore National Laboratory (LLNL), Los Alamos National Laboratory (LANL), and Sandia National Laboratory Albuquerque (SNLA). We fabricated and delivered over 800 gold-plated hohlraum mandrels to LLNL, LANL and SNLA. We produced nearly 1,200 glass and plastic target capsules for LLNL, LANL, SNLA and University of Rochester/Laboratory for Laser Energetics (UR/LLE). We also delivered over 100 flat foil targets for Naval Research Lab (NRL) and SNLA in FY96. This report describes these target fabrication activities and the target fabrication and characterization development activities that made the deliveries possible. The ICF program is anticipating experiments at the OMEGA laser and the National Ignition Facility (NIF) which will require capsules containing cryogenic layered D{sub 2} or deuterium-tritium (DT) fuel. We are part of the National Cryogenic Target Program to create and demonstrate viable ways to generate and characterize cryogenic layers. Substantial progress has been made on ways to both create and characterize viable layers. During FY96, significant progress was made in the design of the OMEGA Cryogenic Target System that will field cryogenic targets on OMEGA.
Date: February 1, 1997
Creator: Hoppe, M.
Partner: UNT Libraries Government Documents Department

High speed imaging of Raleigh-Taylor instabilities in laser driven plates

Description: Recent improvements and modifications of the imaging techniques have identified and provided measurements of Raleigh-Taylor (R-T) instabilities that occur in these events. The microscope system in the LLNL Micro Detonics Facility, was converted to an epi-illuminated polarization configuration. A double pulse nanosecond illuminator and a second independently focusable frame camera were also added to the system. A laser driven plate, that is a dense solid driven by a laser heated, lower density plasma, is inherently R-T unstable. The plates are aluminum, deposited on the ends of optical fibers. They are launched by a YAG Laser pulse traveling down the fiber. Plate velocities are several kilometers per second and characteristic dimensions of the instabilities are a few to tens of microns. Several techniques were used to examine the plates, the most successful being specularly reflecting polarization microscopy looking directly at the plate as it flies toward the camera. These images gave data on the spatial frequencies of the instabilities but could not give the amplitudes. To measure the amplitude of the instability a semi- transparent witness plate was placed a known distance from the plate. As above, the plate was observed using the polarization microscope but using the streak camera as the detector. Both the launch of the plate and its impact into the witness plate are observed on the streak record. Knowing the plate velocity function from earlier velocimetry measurements and observing the variations in the arrival time across the plate, the amplitude of the instability can be calculated.
Date: October 1, 1996
Creator: Frank, A.M.; Gillespie, C.H. & Trott, W.M.
Partner: UNT Libraries Government Documents Department

Cryogenic D-T fuel layers formed in 1mm spheres by beta-layering

Description: Solid D-T fuel smoothly layered on the interior of spherical capsules is required for all inertial confinement fusion ignition target designs. One process for forming these layers, beta-layering, has been studied in surrogate geometries such as open cylinders or tori to allow accurate characterization of the DT surfaces. We present the first results from beta layering in 1 mm spherical containers, such as will be used in upcoming Omega experiments. These results are also directly relevant to ignition capsules for the National Ignition Facility. We find that layers can form with roughness as small as 1.2 microns rms, and that results are strongly dependent upon freezing rate as well as layer thickness.
Date: October 15, 1998
Creator: Bernat, T P; Burmann, J; Collins, G W; Kozioziemski, B; Mapoles, E R; Pipes, J et al.
Partner: UNT Libraries Government Documents Department