Radiation-hydrodynamic Simulations of the Impact of Instabilities and Asymmetries on Inertial Confinement Fusion PDF Download
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Author: Kristopher McGlinchey
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Category :
Languages : en
Pages :
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Author: Kristopher McGlinchey
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Category :
Languages : en
Pages :
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Author: Samuel Carl Miller
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Category :
Languages : en
Pages : 169
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"Performance degradation in laser direct-drive (LDD) inertial confinement fusion (ICF) implosions is caused by several effects, including Rayleigh-Taylor (RT) and Richtmyer-Meshkov (RM) hydrodynamic instability growth. RT instability growth occurs in both the acceleration and deceleration phases of implosions. The first half of this thesis examines the evolution of internal perturbations that create seeds for instability growth during shock-transit (or early-time), while the second half describes the perturbation evolution during shell deceleration. During shock-transit, perturbations from shell material density modulations and isolated defects plant seeds at various interfaces such as the ablation front and material interfaces. These seeds can become amplified due to secular feedout growth and shock-induced vorticity and will grow exponentially during the acceleration phase due to ablative RT. A comprehensive understanding of this evolution is essential to characterize the impact of internal defects on inflight shell integrity. Through detailed simulations and analysis, this thesis identifies several key physical processes that play a role in the evolution of perturbations created by these defects throughout the early stage of implosions. Simulations also predict that significant shell mass modulations develop during shell acceleration. The use of low density ablator materials (foam) is suggested as a potential mitigation strategy to reduce the effects created by these defects. To perform this detailed study of internal defect evolution, two new high-fidelity physics codes were developed to track characteristic wave propagation in the ICF context using low-noise, low-dissipation, high-order spatial accuracy solution methods. Modern high performance computing (HPC) systems have becoming increasingly complex, and adapting existing or new software to fully utilize them is a significant development challenge. Each code in this thesis examines the feasibility of different approaches: a modern design in a well-known HPC-centric language (Fortran), and a new language (Julia), which emphasizes developer productivity and shows the potential to be well-suited for HPC workloads. Mass modulations at the ablation front, which grow during the acceleration phase, feed through to the inner surface of the shell and create seeds for deceleration phase RT growth at the inner surface. Deceleration instability growth was studied using laser direct drive implosions of room-temperature plastic targets. Perturbation growth in such implosions is enhanced by the density discontinuity and finite Atwood number at the fuel-shell interface. The magnitude of this density discontinuity can be controlled by changing the fuel composition (D:T, or ratio of deuterium to tritium). However, this thesis demonstrates that the stability of the interface is best characterized by the effective Atwood number, which is primarily determined by material densities at distances on the order of perturbation wavelength on either side of the interface, rather than the density ratio at the interface. Since the densities at these distances are defined not by fuel composition, but radiation heating of the shell, both simulation and experimental data show that target performance is insensitive to different D:T ratios"--Pages ix -x
Author: Ka Ming Woo
Publisher:
ISBN:
Category :
Languages : en
Pages : 244
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"Hydrodynamic instability is one of the primary sources of degrading the fusion yields in inertial confinement fusion (ICF) experiments. The presence of non-uniformities during the hot spot formation leads to dominant experimental signatures of implosion asymmetries. The physical mechanism of how hydrodynamic instabilities manifest themselves in experimental observable plays an important role to interpret three-dimensional (3-D) effects on ICF experimental data. In the first part of the thesis, we describe the development of a 3-D radiation hydrodynamic Eulerian spherical moving-mesh parallel code DEC3D to model the deceleration-phase Rayleigh-Taylor instability. The new code implements advanced modern numerical methods including the high-resolution shock-capturing technique the piecewise parabolic method for hydrodynamics, the macro-zoning technique to treat small time-step problems of the spherical mesh, and the integration of HYPRE to solve the implicit multi-group radiation diffusion. A single mode and multi-mode simulation database was established to study the relations between 3-D hydrodynamic effects and implosion asymmetries. In the second part of the thesis, two comprehensive physical models were developed: (1) to explain the effects of the residual kinetic energy on the degradation of fusion yields and hot-spot pressures, and the property of larger hot-spot volumes for low modes, and (2) to explain the effects of 3-D hot-spot ow asymmetries on the variations of ion-temperature measurements. An analytical method of velocity variance decomposition was developed to infer the minimum ion temperatures and explain the physical mechanism of larger apparent ion temperatures than the true thermal ion temperatures."--Pages xiii-xiv.
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Category :
Languages : en
Pages : 10
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Inertial confinement fusion (ICF) implosions, whether real or ideal, are subject to a variety of hydrodynamic instabilities that amplify small departures from spherical symmetry. Asymmetric implosions departing from spherical symmetry can lead to the breakup of the imploding shell or the creation of hydrodynamic turbulence. In an effort to understand the evolution of the asymmetries, perturbation seeds with both velocity and surface displacements have been introduced at the boundary of two different density media to model analytical Rayleigh-Taylor instability growth. Growth of perturbed amplitudes has been studied in linear and late-time nonlinear regimes. Simulated linear growth rates and nonlinear bubble velocities are in good agreement with theoretical values for Atwood numbers that are close to unity (relevant to ICF applications).
Author:
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ISBN:
Category :
Languages : en
Pages : 84
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Author: National Research Council
Publisher: National Academies Press
ISBN: 0309270626
Category : Science
Languages : en
Pages : 119
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In the fall of 2010, the Office of the U.S. Department of Energy's (DOE's) Secretary for Science asked for a National Research Council (NRC) committee to investigate the prospects for generating power using inertial confinement fusion (ICF) concepts, acknowledging that a key test of viability for this concept-ignition -could be demonstrated at the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory (LLNL) in the relatively near term. The committee was asked to provide an unclassified report. However, DOE indicated that to fully assess this topic, the committee's deliberations would have to be informed by the results of some classified experiments and information, particularly in the area of ICF targets and nonproliferation. Thus, the Panel on the Assessment of Inertial Confinement Fusion Targets ("the panel") was assembled, composed of experts able to access the needed information. The panel was charged with advising the Committee on the Prospects for Inertial Confinement Fusion Energy Systems on these issues, both by internal discussion and by this unclassified report. A Panel on Fusion Target Physics ("the panel") will serve as a technical resource to the Committee on Inertial Confinement Energy Systems ("the Committee") and will prepare a report that describes the R&D challenges to providing suitable targets, on the basis of parameters established and provided to the Panel by the Committee. The Panel on Fusion Target Physics will prepare a report that will assess the current performance of fusion targets associated with various ICF concepts in order to understand: 1. The spectrum output; 2. The illumination geometry; 3. The high-gain geometry; and 4. The robustness of the target design. The panel addressed the potential impacts of the use and development of current concepts for Inertial Fusion Energy on the proliferation of nuclear weapons information and technology, as appropriate. The Panel examined technology options, but does not provide recommendations specific to any currently operating or proposed ICF facility.
Author:
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Category :
Languages : en
Pages : 20
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This report discusses topics on hydrodynamics instabilities in inertial confinement: linear analysis of Rayleigh-Taylor instability; ablation-surface instability; bubble rise in late-stage Rayleigh-Taylor instability; and saturation and multimode interactions in intermediate-stage Rayleigh-Taylor instability.
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Languages : en
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"Reduced" (i.e., simplified or approximate) ion-kinetic (RIK) models in radiation-hydrodynamic simulations permit a useful description of inertial-confinement-fusion (ICF) implosions where kinetic deviations from hydrodynamic behavior are important. For implosions in or near the kinetic regime (i.e., when ion mean free paths are comparable to the capsule size), simulations using a RIK model give a detailed picture of the time- and space-dependent structure of imploding capsules, allow an assessment of the relative importance of various kinetic processes during the implosion, enable explanations of past and current observations, and permit predictions of the results of future experiments. The RIK simulation method described here uses moment-based reduced kinetic models for transport of mass, momentum, and energy by long-mean-free-path ions, a model for the decrease of fusion reactivity owing to the associated modification of the ion distribution function, and a model of hydrodynamic turbulent mixing. The transport models are based on local gradient-diffusion approximations for the transport of moments of the ion distribution functions, with coefficients to impose flux limiting or account for transport modification. After calibration against a reference set of ICF implosions spanning the hydrodynamic-to-kinetic transition, the method has useful, quantifiable predictive ability over a broad range of capsule parameter space. Calibrated RIK simulations show that an important contributor to ion species separation in ICF capsule implosions is the preferential flux of longer-mean-free-path species out of the fuel and into the shell, leaving the fuel relatively enriched in species with shorter mean free paths. Also, the transport of ion thermal energy is enhanced in the kinetic regime, causing the fuel region to have a more uniform, lower ion temperature, extending over a larger volume, than implied by clean simulations. We expect that the success of our simple approach will motivate continued theoretical research into the development of first-principles-based, comprehensive, self-consistent, yet useable models of kinetic multispecies ion behavior in ICF plasmas.
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Category :
Languages : en
Pages : 11
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To model ignition in a National Ignition Facility (NIF) capsule implosion, the authors must understand the behavior of instabilities that can cause breakup of the pellet shell. During a capsule implosion, shocks that transit the shell cause growth of perturbations at the surface or at an interface because of a Richtmyer-Meshkov type of instability. Following shock breakout, or earlier for a shaped pulse, the low-density ablated plasma accelerates the pusher, and the ablation front is Rayleigh-Taylor (RT) unstable. Ablation and finite density gradients have the effect of stabilizing the short wavelength modes. Unstable modes present on the outer surface grow and feed through to the inner surface. Once the shell encounters the rebounding shock from the capsule center, it decelerates and the inner surface becomes RT unstable. If perturbations grow large enough, pusher material mixes into the core, degrading implosion performance. Capsule designs for the NIF depend on ablative stabilization and saturation to prevent perturbations initially present on the capsule surface from growing large enough to quench ignition. Here, the authors examine the first simulations and experiments to study the effect of 3-D perturbation shape on instability growth and saturation in indirectly driven targets. The first section discusses HYDRA, the radiation hydrodynamics code developed for these simulations. The subsequent section examines 3-D shape effects in single-mode perturbations in planar foil simulations and experiments. A discussion of the evolution of multimode perturbations on planar foils is followed by a discussion of 3-D simulations of instability growth in Nova capsule implosions.
Author: Thomas J. McCarville
Publisher:
ISBN:
Category : Hydrodynamics
Languages : en
Pages : 380
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