Targets for low-adiabat direct-drive-implosion experiments on OMEGA must meet rigorous specifications and tight tolerances on the diameter,wall thickness,wall-thickness uniformity,and presence of surface features.Of t...Targets for low-adiabat direct-drive-implosion experiments on OMEGA must meet rigorous specifications and tight tolerances on the diameter,wall thickness,wall-thickness uniformity,and presence of surface features.Of these,restrictions on the size and number of defects(bumps and depressions)on the surface are the most challenging.The properties of targets that are made using vapor-deposition and solution-based microencapsulation techniques are reviewed.Targets were characterized using confocal microscopy,bright-and dark-field microscopy,atomic force microscopy,electron microscopy,and interferometry.Each technique has merits and limitations,and a combination of these techniques is necessary to adequately characterize a target.The main limitation with the glow-discharge polymerization(GDP)method for making targets is that it produces hundreds of domes with a lateral dimension of 0.7-2 μm.Polishing these targets reduces the size of some but not all domes,but it adds scratches and grooves to the surface.Solution-made polystyrene shells lack the dome features of GDP targets but have hundreds of submicrometer-size voids throughout the wall of the target;a few of these voids can be as large as~12 μm at the surface.展开更多
The first hydrodynamic instability growth measurements with three-dimensional(3D) surface-roughness modulations were performed on CH shell spherical implosions at the National Ignition Facility(NIF) [G. H. Miller, E. ...The first hydrodynamic instability growth measurements with three-dimensional(3D) surface-roughness modulations were performed on CH shell spherical implosions at the National Ignition Facility(NIF) [G. H. Miller, E. I. Moses, and C. R. Wuest, Opt. Eng. 43, 2841(2004)]. The initial capsule outer-surface amplitudes were increased approximately four times, compared with the standard specifications, to increase the signal-to-noise ratio, helping to qualify a technique for measuring small 3D modulations. The instability growth measurements were performed using x-ray through-foil radiography based on time-resolved pinhole imaging. Averaging over 15 similar images significantly increased the signal-to-noise ratio, making possible a comparison with 3D simulations. At a convergence ratio of～2.4, the measured modulation levels were～3 times larger than those simulated based on the growth of the known imposed initial surface modulations. Several hypotheses are discussed, including increased instability growth due to modulations of the oxygen content in the bulk of the capsule. Future experiments will be focused on measurements with standard 3D ‘nativeroughness' capsules as well as with deliberately imposed oxygen modulations.展开更多
A unique approach for permeation filling of nonpermeable inertial confinement fusion target capsules with deuterium–tritium(DT) is presented. This process uses a permeable capsule coupled into the final target capsul...A unique approach for permeation filling of nonpermeable inertial confinement fusion target capsules with deuterium–tritium(DT) is presented. This process uses a permeable capsule coupled into the final target capsule with a 0.03-mmdiameter fill tube. Leak free permeation filling of glow-discharge polymerization(GDP) targets using this method have been successfully demonstrated, as well as ice layering of the target, yielding an inner ice surface roughness of 1-μm rms(root mean square). Finally, the measured DT ice-thickness profile for this experiment was used to validate a thermal model's prediction of the same thickness profile.展开更多
Experiments on the National Ignition Facility show that multi-dimensional effects currently dominate the implosion performance. Low mode implosion symmetry and hydrodynamic instabilities seeded by capsule mounting fea...Experiments on the National Ignition Facility show that multi-dimensional effects currently dominate the implosion performance. Low mode implosion symmetry and hydrodynamic instabilities seeded by capsule mounting features appear to be two key limiting factors for implosion performance. One reason these factors have a large impact on the performance of inertial confinement fusion implosions is the high convergence required to achieve high fusion gains.To tackle these problems, a predictable implosion platform is needed meaning experiments must trade-off high gain for performance. LANL has adopted three main approaches to develop a one-dimensional(1D) implosion platform where 1D means measured yield over the 1D clean calculation. A high adiabat, low convergence platform is being developed using beryllium capsules enabling larger case-to-capsule ratios to improve symmetry. The second approach is liquid fuel layers using wetted foam targets. With liquid fuel layers, the implosion convergence can be controlled via the initial vapor pressure set by the target fielding temperature. The last method is double shell targets. For double shells, the smaller inner shell houses the DT fuel and the convergence of this cavity is relatively small compared to hot spot ignition. However,double shell targets have a different set of trade-off versus advantages. Details for each of these approaches are described.展开更多
基金This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944the University of Rochester,and the New York State Energy Research and Development Authority.
文摘Targets for low-adiabat direct-drive-implosion experiments on OMEGA must meet rigorous specifications and tight tolerances on the diameter,wall thickness,wall-thickness uniformity,and presence of surface features.Of these,restrictions on the size and number of defects(bumps and depressions)on the surface are the most challenging.The properties of targets that are made using vapor-deposition and solution-based microencapsulation techniques are reviewed.Targets were characterized using confocal microscopy,bright-and dark-field microscopy,atomic force microscopy,electron microscopy,and interferometry.Each technique has merits and limitations,and a combination of these techniques is necessary to adequately characterize a target.The main limitation with the glow-discharge polymerization(GDP)method for making targets is that it produces hundreds of domes with a lateral dimension of 0.7-2 μm.Polishing these targets reduces the size of some but not all domes,but it adds scratches and grooves to the surface.Solution-made polystyrene shells lack the dome features of GDP targets but have hundreds of submicrometer-size voids throughout the wall of the target;a few of these voids can be as large as~12 μm at the surface.
基金performed under the auspices of the U.S.Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344
文摘The first hydrodynamic instability growth measurements with three-dimensional(3D) surface-roughness modulations were performed on CH shell spherical implosions at the National Ignition Facility(NIF) [G. H. Miller, E. I. Moses, and C. R. Wuest, Opt. Eng. 43, 2841(2004)]. The initial capsule outer-surface amplitudes were increased approximately four times, compared with the standard specifications, to increase the signal-to-noise ratio, helping to qualify a technique for measuring small 3D modulations. The instability growth measurements were performed using x-ray through-foil radiography based on time-resolved pinhole imaging. Averaging over 15 similar images significantly increased the signal-to-noise ratio, making possible a comparison with 3D simulations. At a convergence ratio of～2.4, the measured modulation levels were～3 times larger than those simulated based on the growth of the known imposed initial surface modulations. Several hypotheses are discussed, including increased instability growth due to modulations of the oxygen content in the bulk of the capsule. Future experiments will be focused on measurements with standard 3D ‘nativeroughness' capsules as well as with deliberately imposed oxygen modulations.
基金supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944the University of Rochester+1 种基金the New York State Energy Research and Development Authoritysponsored by an agency of the US Government
文摘A unique approach for permeation filling of nonpermeable inertial confinement fusion target capsules with deuterium–tritium(DT) is presented. This process uses a permeable capsule coupled into the final target capsule with a 0.03-mmdiameter fill tube. Leak free permeation filling of glow-discharge polymerization(GDP) targets using this method have been successfully demonstrated, as well as ice layering of the target, yielding an inner ice surface roughness of 1-μm rms(root mean square). Finally, the measured DT ice-thickness profile for this experiment was used to validate a thermal model's prediction of the same thickness profile.
文摘Experiments on the National Ignition Facility show that multi-dimensional effects currently dominate the implosion performance. Low mode implosion symmetry and hydrodynamic instabilities seeded by capsule mounting features appear to be two key limiting factors for implosion performance. One reason these factors have a large impact on the performance of inertial confinement fusion implosions is the high convergence required to achieve high fusion gains.To tackle these problems, a predictable implosion platform is needed meaning experiments must trade-off high gain for performance. LANL has adopted three main approaches to develop a one-dimensional(1D) implosion platform where 1D means measured yield over the 1D clean calculation. A high adiabat, low convergence platform is being developed using beryllium capsules enabling larger case-to-capsule ratios to improve symmetry. The second approach is liquid fuel layers using wetted foam targets. With liquid fuel layers, the implosion convergence can be controlled via the initial vapor pressure set by the target fielding temperature. The last method is double shell targets. For double shells, the smaller inner shell houses the DT fuel and the convergence of this cavity is relatively small compared to hot spot ignition. However,double shell targets have a different set of trade-off versus advantages. Details for each of these approaches are described.
