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Hydrodynamick instabilities on ICF capsules

Description: This article summarizes our current understanding of hydrodynamic instabilities as relevant to ICF. First we discuss classical, single mode Rayleigh-Taylor instability, and nonlinear effects in the evolution of a single mode. Then we discuss multimode systems, considering: (1) the onset of nonlinearity; (2) a second order mode coupling theory for weakly nonlinear effects, and (3) the fully nonlinear regime. Two stabilization mechanisms relevant to ICF are described next: gradient scale length and convective stabilization. Then we describe a model which is meant to estimate the weakly nonlinear evolution of multi-mode systems as relevant to ICF, given the short-wavelength stabilization. Finally, we discuss the relevant code simulation capability, and experiments. At this time we are quite optimistic about our ability to estimate instability growth on ICF capsules, but further experiments and simulations are needed to verify the modeling. 52 refs.
Date: June 7, 1991
Creator: Haan, S.W.
Partner: UNT Libraries Government Documents Department

Radiation transport between concentric spheres

Description: This is a note originally distributed in 1983. I am re-releasing it now, with a couple of words changed, so that it can be used for test problems, distributed more openly, and so forth. One could argue that it should be published, but I do not have time to reshape it into something I would regard as suitable for journal publication. A different derivation of the same result is being published in an appendix in D.W. Phillion and S.M. Pollaine, ``Dynamical Compensation of Irradiation Nonuniformities in a Spherical Hohlraum Illuminated with Tetrahedral Symmetry by Laser Beams,`` submitted to Phys. Plasmas.
Date: August 8, 1994
Creator: Haan, S. W.
Partner: UNT Libraries Government Documents Department

Hydrodynamic instability modeling for ICF

Description: The intent of this paper is to review how instability growth is modeled in ICF targets, and to identify the principal issues. Most of the material has been published previously, but is not familiar to a wide audience. Hydrodynamic instabilities are a key issue in ICF. Along with laser-plasma instabilities, they determine the regime in which ignition is possible. At higher laser energies, the same issues determine the achievable gain. Quantitative predictions are therefore of the utmost importance to planning the ICF program, as well as to understanding current Nova results. The key fact that underlies all this work is the stabilization of short wavelengths.
Date: March 31, 1993
Creator: Haan, S. W.
Partner: UNT Libraries Government Documents Department

Measuring Spherical Harmonic Coefficients on a Sphere

Description: The eigenfunctions of Rayleigh-Taylor modes on a spherical capsule are the spherical harmonics Y{sub l,m} These can be measured by measuring the surface perturbations along great circles and fitting them to the first few modes by a procedure described in this article. For higher mode numbers, it is more convenient to average the Fourier power spectra along the great circles, and then transform them to spherical harmonic modes by an algorithm derived here.
Date: May 16, 2003
Creator: Pollaine, S & Haan, S W
Partner: UNT Libraries Government Documents Department

Robustness Studies of Ignition Targets for the National Ignition Facility in Two Dimensions

Description: Inertial confinement fusion capsules are critically dependent on the integrity of their hot spots to ignite. At the time of ignition, only a certain fractional perturbation of the nominally spherical hot spot boundary can be tolerated and the capsule still achieve ignition. The degree to which the expected hot spot perturbation in any given capsule design is less than this maximum tolerable perturbation is a measure of the ignition margin or robustness of that design. Moreover, since there will inevitably be uncertainties in the initial character and implosion dynamics of any given capsule, all of which can contribute to the eventual hot spot perturbation, quantifying the robustness of that capsule against a range of parameter variations is an important consideration in the capsule design. Here, the robustness of the 300 eV indirect drive target design for the National Ignition Facility [J. D. Lindl, et al., Phys. Plasmas 11, 339 (2004)] is studied in the parameter space of inner ice roughness, implosion velocity, and capsule scale. A suite of two thousand two-dimensional simulations, run with the radiation hydrodynamics code Lasnex, is used as the data base for the study. For each scale, an ignition region in the two remaining variables is identified and the ignition cliff is mapped. In accordance with the theoretical arguments of Levedahl and Lindl [Nucl. Fusion 37, 165 (1997)] and Kishony and Shvarts [Phys. Plasmas 8, 4925 (2001)], the location of this cliff is fitted to a power law of the capsule implosion velocity and scale. It is found that the cliff can be quite well represented in this power law form, and, using this scaling law, an assessment of the overall (one- and two-dimensional) ignition margin of the design can be made. The effect on the ignition margin of an increase or decrease in the density ...
Date: November 7, 2007
Creator: Clark, D S; Haan, S W & Salmonson, J D
Partner: UNT Libraries Government Documents Department

X-ray backlit imaging measurement of in-flight pusher density for an indirect drive capsule implosion

Description: Both the efficiency of an implosion and the growth rate of hydrodynamic instability increase with the aspect ratio of an implosion. In order to study the physics of implosions with high Rayleigh-Taylor growth factors, we use doped ablators which should minimize x-ray preheat and shell decompression, and hence increase in-flight aspect ratio. We use x-ray backlighting techniques to image the indirectly-driven capsules. We record backlit 4.7 keV images of the full capsule throughout the implosion phase with 55 ps and 15 {mu}m resolution. We use these images to measure the in-flight aspect ratios for doped ablators, and we inferred the radial density profile as a function of time by Abel inverting the x-ray transmission profiles.
Date: May 6, 1996
Creator: Kalantar, D.H.; Haan, S.W. & Hammel, B.A.
Partner: UNT Libraries Government Documents Department

A review of the ablative stabilization of the Rayleigh-Taylor instability in regimes relevant to Inertial Confinement Region. Revision 1

Description: It has been recognized for many year`s that the most significant limitation of ICF is the Rayleigh-Taylor (R-T) instability. It limits the distance an ablatively driven shell can be moved to several times its initial thickness. Fortunately material flow through the unstable region at velocity v{sub A} reduces the growth rate to {radical}{sub 1+kL}/{sup kg} {minus}{beta}kv{sub A} with {beta} from 2-3. In recent years experiments using both x-ray drive and smoothed laser drive to accelerate foils have confirmed our understanding of the ablative R-T instability in planar geometry. The growth of small initial modulations on the foils is measured for growth factors up to 60 for direct drive and 80 for indirect drive. For x-ray drive large stabilization is evident. After some growth, the instability enters the non-linear phase when mode coupling and saturation are also seen and compare well with modeling. Normalized growth rates for direct drive are measured to be higher, but strategies for reduction by raising the isentrope are being investigated. For direct drive, high spatial frequencies are imprinted from the laser beam and amplified by the R-T instability. Modeling shows an understanding of this ``laser imprinting.``
Date: December 1, 1993
Creator: Kilkenny, J. D.; Glendinning, S. G. & Haan, S. W.
Partner: UNT Libraries Government Documents Department

Shock Timing Techniques for Ignition Capsules on the NIF

Description: Results from a series of shock trajectory measurements in planar liquid deuterium targets will set the pulse shape they use for ignition capsules at the National Ignition Facility. They discuss outstanding issues for this concept, in particular, ideas for certifying that the drive on a planar sample is the same as on a spherical capsule.
Date: September 2, 2003
Creator: Munro, D H; Haan, S W; Collins, G W & Celliers, P M
Partner: UNT Libraries Government Documents Department

Imploded Capsule Fuel Temperature and Density Measurement by Energy-Dependent Neutron Imaging

Description: Neutron imaging systems measure the spatial distribution of neutron emission from burning inertial confinement fusion (ICF) targets. These systems use a traditional pinhole geometry to project an image of the source onto a two-dimensional scintillator array, and a CCD records the resulting scintillation image. The recent history of ICF neutron images has produced images with qualities that have improved as the fusion neutron yields have increased to nearly 10{sup 14} neutrons. Anticipated future neutron yields in excess of 10{sup 16} at the National Ignition Facility and LMJ have raised the prospect of neuron imaging diagnostics which simultaneously probe several different characteristics of burning fusion targets. The new measurements rely on gated-image recording to select images corresponding to specific bands of neutron energies. Gated images of downscattered neutrons with energies from 5 to 8 MeV can emphasize regions of the target which contain DT fuel which is not burning. At the same time, gated images which select different portions of the 14-MeV spectral peak can produce spatial temperature maps of a burning target. Since the neutron production depends on the DT fuel density and temperature, simultaneous images of temperature and neutron emission can be combined to infer the an image of the source density using an Abel inversion method that is analogous to the method that has been used in x-ray imaging. Thus, with higher-yield sources, neutron imaging offers the potential to record simultaneously several critical features that characterize the performance of an ICF target: the neutron emission distribution, the temperature and density distributions, and the distribution of nonburning fuel within the target.
Date: September 28, 2005
Creator: Moran, M J; Koch, J; Landen, O L; Haan, S W; Barrera, C A & Morse, E C
Partner: UNT Libraries Government Documents Department

Plastic ablator ignition capsule design for the National Ignition Facility

Description: The National Ignition Campaign, tasked with designing and fielding targets for fusion ignition experiments on the National Ignition Facility (NIF), has carried forward three complementary target designs for the past several years: a beryllium ablator design, a plastic ablator design, and a high-density carbon or synthetic diamond design. This paper describes current simulations and design optimization to develop the plastic ablator capsule design as a candidate for the first ignition attempt on NIF. The trade-offs in capsule scale and laser energy that must be made to achieve a comparable ignition probability to that with beryllium are emphasized. Large numbers of 1-D simulations, meant to assess the statistical behavior of the target design, as well as 2-D simulations to assess the target's susceptibility to Rayleigh-Taylor growth are presented.
Date: December 1, 2009
Creator: Clark, D S; Haan, S W; Hammel, B A; Salmonson, J D; Callahan, D A & Town, R P
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

3D HYDRA Simulations of NIF Targets

Description: The performance of NIF target designs is simulated in three dimensions using the HYDRA multiphysics radiation hydrodynamics code. In simulations of a cylindrical NIF hohlraum that include an imploding capsule, the motion of the wall material inside the hohlraum shows a high degree of axisymmetry. Laser radiation is able to propagate through the entrance hole for the required duration of the pulse. Gross hohlraum energetics in the simulation mirror the results from an axisymmetric simulation. A simulation of a copper-doped beryllium ablator NIF capsule carried out over large solid angle resolved the full spectrum of the most dangerous modes that grow from surface roughness. Hydrodynamic instabilities evolve into the weakly nonlinear regime. There is no evidence of low mode jetting driven by nonlinear mode coupling.
Date: October 20, 2000
Creator: Marinak, M M; Kerbel, G D; Gentile, N A; Jones, O; Pollaine, S; Dittrich, T R et al.
Partner: UNT Libraries Government Documents Department

Inference of ICF Implosion Core Mix using Experimental Data and Theoretical Mix Modeling

Description: The mixing between fuel and shell materials in Inertial Confinement Fusion (ICF) implosion cores is a current topic of interest. The goal of this work was to design direct-drive ICF experiments which have varying levels of mix, and subsequently to extract information on mixing directly from the experimental data using spectroscopic techniques. The experimental design was accomplished using hydrodynamic simulations in conjunction with Haan's saturation model, which was used to predict the mix levels of candidate experimental configurations. These theoretical predictions were then compared to the mixing information which was extracted from the experimental data, and it was found that Haan's mix model performed well in predicting trends in the width of the mix layer. With these results, we have contributed to an assessment of the range of validity and predictive capability of the Haan saturation model, as well as increased our confidence in the methods used to extract mixing information from experimental data.
Date: April 30, 2008
Creator: Welser-Sherrill, L; Haynes, D A; Mancini, R C; Cooley, J H; Tommasini, R; Golovkin, I E et al.
Partner: UNT Libraries Government Documents Department

High resolution simulations of ignition capsule designs for the National Ignition Facility

Description: Ignition capsule designs for the National Ignition Facility (NIF) [G. H. Miller, E. I. Moses, and C. R. Wuest, Opt. Eng. 443, 2841 (2004)] have continued to evolve in light of improved physical data inputs, improving simulation techniques, and - most recently - experimental data from a growing number of NIF sub-ignition experiments. This paper summarizes a number of recent changes to the cryogenic capsule design and some of our latest techniques in simulating its performance. Specifically, recent experimental results indicated harder x-ray drive spectra in NIF hohlraums than were predicted and used in previous capsule optimization studies. To accommodate this harder drive spectrum, a series of high-resolution 2-D simulations, resolving Legendre mode numbers as high as two thousand, were run and the germanium dopant concentration and ablator shell thicknesses re-optimized accordingly. Simultaneously, the possibility of cooperative or nonlinear interaction between neighboring ablator surface defects has motivated a series of fully 3-D simulations run with the massively parallel HYDRA code. These last simulations include perturbations seeded on all capsule interfaces and can use actual measured shell surfaces as initial conditions. 3-D simulations resolving Legendre modes up to two hundred on large capsule sectors have run through ignition and burn, and higher resolution simulations resolving as high as mode twelve hundred have been run to benchmark high-resolution 2-D runs. Finally, highly resolved 3-D simulations have also been run of the jet-type perturbation caused by the fill tube fitted to the capsule. These 3-D simulations compare well with the more typical 2-D simulations used in assessing the fill tube's impact on ignition. Coupled with the latest experimental inputs from NIF, our improving simulation capability yields a fuller and more accurate picture of NIF ignition capsule performance.
Date: February 17, 2011
Creator: Clark, D S; Haan, S W; Cook, A W; Edwards, M J; Hammel, B A; Koning, J M et al.
Partner: UNT Libraries Government Documents Department

Inference of ICF implosion core mix using experimental data and theoretical mix modeling

Description: The mixing between fuel and shell materials in Inertial Confinement Fusion (lCF) implosion cores is a current topic of interest. The goal of this work was to design direct-drive ICF experiments which have varying levels of mix, and subsequently to extract information on mixing directly from the experimental data using spectroscopic techniques. The experimental design was accomplished using hydrodynamic simulations in conjunction with Haan's saturation model, which was used to predict the mix levels of candidate experimental configurations. These theoretical predictions were then compared to the mixing information which was extracted from the experimental data, and it was found that Haan's mix model predicted trends in the width of the mix layer as a function of initial shell thickness. These results contribute to an assessment of the range of validity and predictive capability of the Haan saturation model, as well as increasing confidence in the methods used to extract mixing information from experimental data.
Date: January 1, 2009
Creator: Sherrill, Leslie Welser; Haynes, Donald A; Cooley, James H; Sherrill, Manolo E; Mancini, Roberto C; Tommasini, Riccardo et al.
Partner: UNT Libraries Government Documents Department

Ignition Capsules with Aerogel-Supported Liquid DT Fuel For The National Ignition Facility

Description: For high repetition-rate fusion power plant applications, capsules with aerogel-supported liquid DT fuel can have much reduced fill time compared to {beta}-layering a solid DT fuel layer. The melting point of liquid DT can be lowered once liquid DT is embedded in an aerogel matrix, and the DT vapor density is consequently closer to the desired density for optimal capsule design requirement. We present design for NIF-scale aerogel-filled capsules based on 1-D and 2-D simulations. An optimal configuration is obtained when the outer radius is increased until the clean fuel fraction is within 65-75% at peak velocity. A scan (in ablator and fuel thickness parameter space) is used to optimize the capsule configurations. The optimized aerogel-filled capsule has good low-mode robustness and acceptable high-mode mix.
Date: October 25, 2011
Creator: Ho, D D; Salmonson, J D; Clark, D S; Lindl, J D; Haan, S W; Amendt, P et al.
Partner: UNT Libraries Government Documents Department

Measurement of the in-flight pusher density of an indirect drive capsule implosion core using x-ray backlighting

Description: Both the efficiency of an implosion and the growth rate of hydrodynamic instability increase with the aspect ratio of an implosion. In order to study the physics of implosions with high Rayleigh-Taylor growth factors, we use doped ablators which should minimize x-ray preheat and shell decompression, and hence increase in- flight aspect ratio. We use x-ray backlighting techniques to image the indirectly-driven capsules. We record backlit 4.7 KeV images of the full capsule throughout the implosion phase with 55 ps and 15{mu}m resolution. We use these images to measure the in-flight aspect ratios for doped ablators, and we infer the radial density profile as a function of time by Abel inverting the transmission profiles.
Date: May 30, 1996
Creator: Kalantar, D.H.; Haan, S.W.; Hammel, B.A.; Keane, C.J.; Landen, O.L. & Munro, D.H.
Partner: UNT Libraries Government Documents Department

Design of ignition targets for the National Ignition Facility

Description: This is a brief update on the work being done to design ignition targets for the National Ignition Facility. Updates are presented on three areas of current activity : improvements in modeling, work on a variety of targets spanning the parameter space of possible ignition targets ; and the setting of specifications for target fabrication and diagnostics. Highlights of recent activity include : a simulation of the Rayleigh-Taylor instability growth on an imploding capsule, done in 3D on a 72{degree} by 72{degree} wedge, with enough zones to resolve modes out to 100 ; and designs of targets at 250eV and 350eV, as well as the baseline 300 eV ; and variation of the central DT gas density, which influences both the Rayleigh-Taylor growth and the smoothness of the DT ice layer.
Date: November 1, 1999
Creator: Haan, S.W.; Dittrich, T.R.; Marinak, M.M. & Hinkel, D.E.
Partner: UNT Libraries Government Documents Department

3D HYDRA simulations of NIF targets

Description: The performance of NIF target designs is simulated in three dimensions using the HYDRA multiphysics radiation hydrodynamics code. In simulations of a cylindrical NIF hohlraum that include an imploding capsule, all relevant hohlraum features and the detailed laser illumination pattern, the motion of the wall material inside the hohlraum shows a high degree of axisymmetry. Laser light is able to propagate through the entrance hole for the required duration of the pulse. Gross hohlraum energetics mirror the results from an axisymmetric simulation. A NIF capsule simulation resolved the full spectrum of the most dangerous modes that grow from surface roughness. Hydrodynamic instabilities evolve into the weakly nonlinear regime. There is no evidence of anomalous low mode growth driven by nonlinear mode coupling.
Date: October 30, 2000
Creator: Marinak, M M; Kerbel, G D; Gentile, N A; Jones, O; Munro, D; Pollaine, S et al.
Partner: UNT Libraries Government Documents Department

TuPo2.XX SYMMETRY TUNING OF NIF IGNITION TARGETS

Description: We present the results of a study in which we reduced the calculated intrinsic radiation asymmetry of a particular indirectly-driven cryogenic DT ignition target design through a series of two-dimensional and three-dimensional radiation hydrodynamic calculations of the integrated hohlraum/capsule system. We reduced the amplitude of the time-dependent P{sub 2} Legendre mode of the radiation flux onto the capsule by adjusting the beam pointing and changing the amount of laser power in the outer cone of beams relative to that in the inner cone of beams. In addition, we reduced the amplitude of a significant Y{sub 44} mode that peaks early in time by adjusting the relative pointing of the 23.5 and 30 inner cone beams.
Date: November 11, 2003
Creator: Jones, O S; Marinak, M M; Amendt, P A; Pollaine, S M; Herrmann, M C; Haan, S W et al.
Partner: UNT Libraries Government Documents Department

Using Laser Entrance Hole Shields to Increase Coupling Efficiency in Indirect Drive Ignition Targets for the National Ignition Facility (NIF)

Description: Coupling efficiency, the ratio of the capsule absorbed energy to the driver energy, is a key parameter in ignition targets. The hohlraum originally proposed for NIF coupled {approx}11% of the absorbed laser energy to the capsule as x-rays. We describe here a second generation of hohlraum target which has higher coupling efficiency, {approx}16%. Because the ignition capsule's ability to withstand 3D effects increases rapidly with absorbed energy, the additional energy can significantly increase the likelihood of ignition. The new target includes laser entrance hole (LEH) shields as a principal method for increasing coupling efficiency while controlling symmetry in indirect-drive ICF. The LEH shields are high Z disks placed inside the hohlraum to block the capsule's view of the cold LEHs. The LEH shields can reduce the amount of laser energy required to drive a target to a given temperature via two mechanisms: (1) keeping the temperature high near the capsule pole by putting a barrier between the capsule and the pole, (2) because the capsule pole does not have a view of the cold LEHs, good symmetry requires a shorter hohlraum with less wall area. Current integrated simulations of this class of target couple 140 kJ of x-rays to a capsule out of 865 kJ of absorbed laser energy and produce {approx}10 MJ of yield. In the current designs, which are not completely optimized, the addition of the LEH shields saves {approx}95 kJ of energy (about 10%) over hohlraums without LEH shields.
Date: November 3, 2005
Creator: Callahan, D A; Amendt, P A; Dewald, E L; Haan, S W; Hinkel, D E; Izumi, N et al.
Partner: UNT Libraries Government Documents Department