The Experts below are selected from a list of 918 Experts worldwide ranked by ideXlab platform
Ke Lan - One of the best experts on this subject based on the ideXlab platform.
-
comparison of the laser spot movement inside cylindrical and spherical Hohlraums
Physics of Plasmas, 2017Co-Authors: Dong Yang, Ke Lan, Jie Liu, Wenyi Huo, Yaohua Chen, Guoli Ren, Zhiwen Yang, Liang GuoAbstract:Compared with cylindrical Hohlraums, the octahedral spherical Hohlraums have natural superiority in maintaining high radiation symmetry during the whole capsule implosion process in indirect drive inertial confinement fusion. However, the narrow space between laser beams and the hohlraum wall may disturb laser propagation inside the spherical hohlraum. In this work, the laser propagation inside the spherical hohlraum and cylindrical hohlraum is investigated experimentally by measuring laser spot movement at the SGIII-prototype laser facility. The experimental results show that the laser propagations inside the spherical hohlraum and the cylindrical hohlraum are totally different from each other due to different hohlraum structures. For the spherical hohlraum, although the laser energy is mainly deposited in the initial position of the laser spot during the whole laser pulse, some laser energies are absorbed by the ablated plasmas from the hohlraum wall. Because the laser beam is refracted by the thin plasmas near the laser entrance hole (LEH) region, the laser spot in the spherical hohlraum moves toward the opposite LEH. In contrast, the laser spot in the cylindrical hohlraum moves toward the LEH along the laser path due to the plasma expansion. When the laser is to be turned off, the accumulated plasmas near the LEH region in the cylindrical hohlraum absorb a majority of laser energy and hinder the laser arriving at the appointed position on the hohlraum wall.
-
experimental demonstration of low laser plasma instabilities in gas filled spherical Hohlraums at laser injection angle designed for ignition target
Physical Review E, 2017Co-Authors: Ke Lan, Xufei Xie, Wenyi Huo, Yaohua Chen, Guoli Ren, Dong Yang, C Y Zheng, Chuanlei Zhai, Liang Hao, Xiaoshi PengAbstract:Octahedral spherical Hohlraums with a single laser ring at an injection angle of 55^{∘} are attractive concepts for laser indirect drive due to the potential for achieving the x-ray drive symmetry required for high convergence implosions. Laser-plasma instabilities, however, are a concern given the long laser propagation path in such Hohlraums. Significant stimulated Raman scattering has been observed in cylindrical Hohlraums with similar laser propagation paths during the ignition campaign on the National Ignition Facility (NIF). In this Rapid Communication, experiments demonstrating low levels of laser-driven plasma instability (LPI) in spherical Hohlraums with a laser injection angle of 55^{∘} are reported and compared to that observed with cylindrical Hohlraums with injection angles of 28.5^{∘} and 55^{∘}, similar to that of the NIF. Significant LPI is observed with the laser injection of 28.5^{∘} in the cylindrical hohlraum where the propagation path is similar to the 55^{∘} injection angle for the spherical hohlraum. The experiments are performed on the SGIII laser facility with a total 0.35-μm incident energy of 93 kJ in a 3 nsec pulse. These experiments demonstrate the role of hohlraum geometry in LPI and demonstrate the need for systematic experiments for choosing the optimal configuration for ignition studies with indirect drive inertial confinement fusion.
-
Comparison of the laser spot movement inside cylindrical and spherical Hohlraums
PHYSICS OF PLASMAS, 2017Co-Authors: Li Zhichao, Ke Lan, Wenyi Huo, Yang Dong, Li Sanwei, Liu Jie, Ren Guoli, Chen Yao-hua, Yang Zhiwen, Guo LiangAbstract:Compared with cylindrical Hohlraums, the octahedral spherical Hohlraums have natural superiority in maintaining high radiation symmetry during the whole capsule implosion process in indirect drive inertial confinement fusion. However, the narrow space between laser beams and the hohlraum wall may disturb laser propagation inside the spherical hohlraum. In this work, the laser propagation inside the spherical hohlraum and cylindrical hohlraum is investigated experimentally by measuring laser spot movement at the SGIII-prototype laser facility. The experimental results show that the laser propagations inside the spherical hohlraum and the cylindrical hohlraum are totally different from each other due to different hohlraum structures. For the spherical hohlraum, although the laser energy is mainly deposited in the initial position of the laser spot during the whole laser pulse, some laser energies are absorbed by the ablated plasmas from the hohlraum wall. Because the laser beam is refracted by the thin plasmas near the laser entrance hole (LEH) region, the laser spot in the spherical hohlraum moves toward the opposite LEH. In contrast, the laser spot in the cylindrical hohlraum moves toward the LEH along the laser path due to the plasma expansion. When the laser is to be turned off, the accumulated plasmas near the LEH region in the cylindrical hohlraum absorb a majority of laser energy and hinder the laser arriving at the appointed position on the hohlraum wall. Published by AIP Publishing.National Natural Science Foundation of China [11405011, 11475033, 11305159]SCI(E)ARTICLE72
-
radiation flux study of spherical Hohlraums at the sgiii prototype facility
Physics of Plasmas, 2016Co-Authors: Xufei Xie, Ke Lan, Wenyi Huo, Yaohua Chen, Dong Yang, Liang Guo, Longfei Jing, Yunbao Huang, Xiaohua JiangAbstract:An octahedral spherical hohlraum is a promising candidate in target design for inertial confinement fusion study, because of its potential superiority in uniform radiation and efficient coupling [Lan et al., Phys. Plasmas 21, 010704 (2014)]. Before the experimental investigation for octahedral spherical hohlraum, an energetics experiment is accomplished on the Shenguang-III prototype laser facility by using spherical Hohlraums with two cylindrical laser entrance holes. Time evolution of the radiation temperature is obtained with flat response X-ray diode detectors at four different viewing angles with demonstrated repeatability of the measurements. The experimental observations are successfully explained by using a phenomenological model which considers not only the radiation flux contributed from the laser ablated and radiation ablated plasma from hohlraum wall, but also that contributed from the filling plasma inside the hohlraum. This method proves to be a simple but effective way to interpret the time...
-
Progress in octahedral spherical hohlraum study
Elsevier, 2016Co-Authors: Ke Lan, Jie Liu, Xufei Xie, Wenyi Huo, Yaohua Chen, Guoli Ren, Chunyang Zheng, Dong YangAbstract:In this paper, we give a review of our theoretical and experimental progress in octahedral spherical hohlraum study. From our theoretical study, the octahedral spherical Hohlraums with 6 Laser Entrance Holes (LEHs) of octahedral symmetry have robust high symmetry during the capsule implosion at hohlraum-to-capsule radius ratio larger than 3.7. In addition, the octahedral spherical Hohlraums also have potential superiority on low backscattering without supplementary technology. We studied the laser arrangement and constraints of the octahedral spherical Hohlraums, and gave a design on the laser arrangement for ignition octahedral Hohlraums. As a result, the injection angle of laser beams of 50°–60° was proposed as the optimum candidate range for the octahedral spherical Hohlraums. We proposed a novel octahedral spherical hohlraum with cylindrical LEHs and LEH shields, in order to increase the laser coupling efficiency and improve the capsule symmetry and to mitigate the influence of the wall blowoff on laser transport. We studied on the sensitivity of the octahedral spherical Hohlraums to random errors and compared the sensitivity among the octahedral spherical Hohlraums, the rugby Hohlraums and the cylindrical Hohlraums, and the results show that the octahedral spherical Hohlraums are robust to these random errors while the cylindrical Hohlraums are the most sensitive. Up till to now, we have carried out three experiments on the spherical hohlraum with 2 LEHs on Shenguang(SG) laser facilities, including demonstration of improving laser transport by using the cylindrical LEHs in the spherical Hohlraums, spherical hohlraum energetics on the SGIII prototype laser facility, and comparisons of laser plasma instabilities between the spherical Hohlraums and the cylindrical Hohlraums on the SGIII laser facility. PACS codes: 52.70.La, 52.35.Tc, 47.40.Nm, Keywords: Indirect-drive inertial confinement fusion, Novel spherical hohlraum with 6 LEHs, High and robust radiation symmetry, High energy coupling efficiency, Theoretical study, Experiment
E L Dewald - One of the best experts on this subject based on the ideXlab platform.
-
understanding icf Hohlraums using nif gated laser entrance hole images
Physics of Plasmas, 2020Co-Authors: Hui Chen, O S Jones, L R Benedetti, N B Meezan, E L Dewald, N Izumi, J D Moody, D T Woods, S A Maclaren, N E PalmerAbstract:The newly available ns-gated laser-entrance-hole (LEH) imager on the National Ignition Facility provides routine, non-perturbative measurements of the x-ray emission from laser-heated plasmas inside the hohlraum as viewed at 19° to the hohlraum axis through one of its LEHs. Multiple images are acquired for a series of times and filter-selected x-ray energy bands within a single shot. The images provide time dependent data on phenomena including the effective radius of the LEH, the length of the gold-plasma “bubble” evolving off the interior wall surface heated by the outer beams, the evolving radius of the x-ray heated hohlraum wall, and the radius of the ablation front of the fusion capsule. These measurements are explained and illustrated with sample data. These techniques are then applied to understand hohlraum behavior as a function of gas fill. For Hohlraums with helium gas fill densities of 0.15 to 0.30 mg/cm3, synthetic images computed from simulations agree well with experimental gated LEH images when an inhibited heat transport model [Jones et al., Phys. Plasmas 24, 056312 (2017)] is used. This model can be adjusted to reproduce the expansion rate of the laser-heated plasma bubble in such a way as to improve agreement with the images. At the higher 0.6 mg/cc gas fill, the experimental images show more pronounced 3D features, resulting in slightly less good agreement with the 2D simulations.
-
Using Laser Entrance Hole Shields to Increase Coupling Efficiency in Indirect Drive Ignition Targets for the National Ignition Facility (NIF) Using Laser Entrance Hole Shields to Increase Coupling Efficiency in Indirect Drive Ignition Targets for the Nati
2020Co-Authors: D A Callahan, O S Jones, E L Dewald, D E Hinkel, N Izumi, P A Amendt, O L Landen, S W Haan, J D Lindl, S M PollaineAbstract:Abstract: 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 ~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, ~ 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 ~ 10 MJ of yield. In the current designs, which are not completely optimized, the addition of the LEH shields saves ~ 95 kJ of energy (about 10%) over Hohlraums without LEH shields. Introduction
-
first demonstration of improved capsule implosions by reducing radiation preheat in uranium vs gold Hohlraums
Physics of Plasmas, 2018Co-Authors: E L Dewald, J E Field, N B Meezan, S Khan, R Tommasini, O L Landen, A S Moore, R Rygg, D B Sayre, A J MackinnonAbstract:In indirectly-driven Inertial Confinement Fusion (ICF) implosions, supra-thermal M-band (>2 keV) radiation from principally 4–3 resonance line transitions generated during laser irradiation at the peak power of Au hohlraum walls can preheat the fusion capsule and reduce compressional pressure. Higher Z, un-lined depleted uranium (DU) Hohlraums were used for the first time in ICF implosions on the National Ignition Facility (NIF) to reduce M-band radiation levels while keeping the total radiation flux similar to Au Hohlraums. First implosions in DU demonstrate an increase in in-flight density (+15%) of high density carbon capsules, and hence in stagnated hot spot temperature (+15%), hot spot x-ray (+200%) and fusion neutron yields (+100%) compared to Au Hohlraums. We show analytically that these changes are consistent with the observed 40% reduction in M-band x-ray flux in DU, and are in agreement with 2D hydrodynamic simulations. This result had a major impact on ICF research on the NIF where a significant fraction of high neutron yield implosions are currently using un-lined DU Hohlraums.In indirectly-driven Inertial Confinement Fusion (ICF) implosions, supra-thermal M-band (>2 keV) radiation from principally 4–3 resonance line transitions generated during laser irradiation at the peak power of Au hohlraum walls can preheat the fusion capsule and reduce compressional pressure. Higher Z, un-lined depleted uranium (DU) Hohlraums were used for the first time in ICF implosions on the National Ignition Facility (NIF) to reduce M-band radiation levels while keeping the total radiation flux similar to Au Hohlraums. First implosions in DU demonstrate an increase in in-flight density (+15%) of high density carbon capsules, and hence in stagnated hot spot temperature (+15%), hot spot x-ray (+200%) and fusion neutron yields (+100%) compared to Au Hohlraums. We show analytically that these changes are consistent with the observed 40% reduction in M-band x-ray flux in DU, and are in agreement with 2D hydrodynamic simulations. This result had a major impact on ICF research on the NIF where a significan...
-
fusion energy output greater than the kinetic energy of an imploding shell at the national ignition facility
Physical Review Letters, 2018Co-Authors: Le S Pape, E L Dewald, L Berzak F Hopkins, L Divol, S D Bhandarkar, L R Bennedetti, T Bunn, Juergen Biener, J Crippen, D T CaseyAbstract:: A series of cryogenic, layered deuterium-tritium (DT) implosions have produced, for the first time, fusion energy output twice the peak kinetic energy of the imploding shell. These experiments at the National Ignition Facility utilized high density carbon ablators with a three-shock laser pulse (1.5 MJ in 7.5 ns) to irradiate low gas-filled (0.3 mg/cc of helium) bare depleted uranium Hohlraums, resulting in a peak hohlraum radiative temperature ∼290 eV. The imploding shell, composed of the nonablated high density carbon and the DT cryogenic layer, is, thus, driven to velocity on the order of 380 km/s resulting in a peak kinetic energy of ∼21 kJ, which once stagnated produced a total DT neutron yield of 1.9×10^{16} (shot N170827) corresponding to an output fusion energy of 54 kJ. Time dependent low mode asymmetries that limited further progress of implosions have now been controlled, leading to an increased compression of the hot spot. It resulted in hot spot areal density (ρr∼0.3 g/cm^{2}) and stagnation pressure (∼360 Gbar) never before achieved in a laboratory experiment.
-
performance of beryllium targets with full scale capsules in low fill 6 72 mm Hohlraums on the national ignition facility
Physics of Plasmas, 2017Co-Authors: Andrei N Simakov, J L Kline, G A Kyrala, E L Dewald, J E Ralph, A B Zylstra, D C Wilson, Eric Loomis, R Tommasini, D J StrozziAbstract:When used with 1.06-mm beryllium (Be) capsules on the National Ignition Facility, gold Hohlraums with the inner diameter of 5.75 mm and helium gas fill density of 1.6 mg/cm3 exhibit significant drive degradation due to laser energy backscatter (of order 14%–17%) and “missing” X-ray drive energy (about 32% during the main pulse). Also, hard to simulate cross-beam energy transfer (CBET) must be used to control the implosion symmetry. Larger, 6.72-mm Hohlraums with fill densities ≤0.6 mg/cm3 generally offer improved drive efficiency, reduced hot-electron preheat, and better control of the implosion symmetry without CBET. Recently, we carried out an exploratory campaign to evaluate performance of 1.06-mm Be capsules in such Hohlraums and determine optimal hohlraum parameters. Specifically, we performed a hohlraum fill-density scan with a three-shock, 9.5-ns laser pulse and found that an appropriate axial laser repointing and azimuthal outer-quad splitting resulted in significantly improved hohlraum energetics...
N B Meezan - One of the best experts on this subject based on the ideXlab platform.
-
low mode implosion symmetry sensitivity in low gas fill nif cylindrical Hohlraums
Physics of Plasmas, 2021Co-Authors: N Izumi, N B Meezan, D A Callahan, J D Moody, L Divol, O L Landen, D T Woods, Hui Chen, M Hohenberger, A L KritcherAbstract:Achieving an efficient capsule implosion in National Ignition Facility indirect-drive target experiments requires symmetric hohlraum x-ray drive for the duration of the laser pulse. This is commonly achieved using two-sided two-cone laser irradiation of cylindrical Hohlraums that, in principle, can zero the time average of all spherical harmonic asymmetry modes <6 as well as the time dependence of the usually dominant mode 2. In practice, experimental evidence indicates that maintaining symmetric drive becomes limited late in the pulse due to the inward expansion of the hohlraum wall and outward expansion of the capsule ablator plasmas impairing the propagation of the inner-cone laser beams. This effect is enhanced in Hohlraums employing low gas-fill, now used almost exclusively as these provide the highest performing implosions and reduce Stimulated Brillouin and Raman backscatter losses, since the gas plasma provides less back pressure to limit blow-in of the hohlraum wall and capsule ablator plasmas. In order to understand this dynamic behavior, we combined multi-keV X-ray imaging of the wall and imploded fuel plasmas as we changed a single parameter at a time: hohlraum gas-fill, laser outer cone picket energy, radius of high density carbon capsules used, and laser beam polar and azimuthal pointing geometry. We developed a physics-based multi-parameter experimental scaling to explain the results that extend prior scalings and compare those to radiation hydrodynamic simulations to develop a more complete picture of how hohlraum, capsule, and laser parameters affect pole vs equator drive symmetry.
-
foam lined hohlraum inertial confinement fusion experiments on the national ignition facility
Physical Review E, 2020Co-Authors: A S Moore, N B Meezan, J L Milovich, S D Bhandarkar, S Johnson, Ricardo Heredia, Theodore F Baumann, Monika M Biener, H Chen, L DivolAbstract:Experiments on the National Ignition Facility (NIF) to study Hohlraums lined with a 20-mg/cc $400\text{\ensuremath{-}}\ensuremath{\mu}\mathrm{m}$-thick ${\mathrm{Ta}}_{2}{\mathrm{O}}_{5}$ aerogel at full scale (hohlraum diameter = 6.72 mm) are reported. Driven with a 1.6-MJ, 450-TW laser pulse, the performance of the foam liner is diagnosed using implosion hot-spot symmetry measurements of the high-density carbon (HDC) capsule and measurement of inner beam propagation through a thin-wall $8\text{\ensuremath{-}}\ensuremath{\mu}\mathrm{m}$ Au window in the hohlraum. Results show an improved capsule performance due to laser energy deposition further inside the hohlraum, leading to a modest increase in x-ray drive and reduced preheat due to changes in the x-ray spectrum when the foam liner is included. In addition, the outer cone bubble uniformity is improved, but the predicted improvement in inner beam propagation to improve symmetry control is not realized for this foam thickness and density.
-
evidence of restricted heat transport in national ignition facility Hohlraums
Physics of Plasmas, 2020Co-Authors: N B Meezan, O S Jones, N Izumi, M B Schneider, D T Woods, Hui Chen, H A Scott, D A Liedahl, George B Zimmerman, J D MoodyAbstract:We present experimental evidence of restricted electron thermal conduction in the high-Z coronal plasma regions of laser-driven Hohlraums on the National Ignition Facility. Four separate measurements, three of which are direct observations of Hohlraum dynamics, corroborate this finding. (1) The velocity of the coronal plasma ablated and heated by the outer-cone laser beams is determined by time-dependent imaging of the gold plasma plume, or “bubble.” The velocities of the incoming plume (perpendicular to the Hohlraum axis) are consistent with high-fidelity 2D radiation-hydrodynamic simulations using flux-limited thermal electron conduction with a flux multiplier f = 0.03. Simulations using f = 0.15, which is very nearly classical Spitzer–Harm transport, predict plume velocities slower than measured. (2) Specific features in time-resolved images of the Hohlraum wall at an angle of 19 ° are also more consistent with f = 0.03 simulations compared to f = 0.15. (3) Spectroscopic tracers were added to the Hohlraum wall in the outer-beam bubble region. The ratios of hydrogen-like to helium-like line emission are sensitive to the electron temperature of the bubble. The hydrogen-like to helium-like ratios extracted from the time-integrated spectra of manganese and cobalt tracers from two observation angles are consistent with f = 0.03 and not with f = 0.15. (4) The time of peak capsule emission, or “bang time,” an integrated measurement, is also more consistent with f = 0.03 than with f = 0.15. While these findings do not identify the causes of restricted thermal conduction in Hohlraums, they motivate future experiments to test specific hypotheses and focus on model development in the regions of the plasma exhibiting restricted transport.
-
understanding icf Hohlraums using nif gated laser entrance hole images
Physics of Plasmas, 2020Co-Authors: Hui Chen, O S Jones, L R Benedetti, N B Meezan, E L Dewald, N Izumi, J D Moody, D T Woods, S A Maclaren, N E PalmerAbstract:The newly available ns-gated laser-entrance-hole (LEH) imager on the National Ignition Facility provides routine, non-perturbative measurements of the x-ray emission from laser-heated plasmas inside the hohlraum as viewed at 19° to the hohlraum axis through one of its LEHs. Multiple images are acquired for a series of times and filter-selected x-ray energy bands within a single shot. The images provide time dependent data on phenomena including the effective radius of the LEH, the length of the gold-plasma “bubble” evolving off the interior wall surface heated by the outer beams, the evolving radius of the x-ray heated hohlraum wall, and the radius of the ablation front of the fusion capsule. These measurements are explained and illustrated with sample data. These techniques are then applied to understand hohlraum behavior as a function of gas fill. For Hohlraums with helium gas fill densities of 0.15 to 0.30 mg/cm3, synthetic images computed from simulations agree well with experimental gated LEH images when an inhibited heat transport model [Jones et al., Phys. Plasmas 24, 056312 (2017)] is used. This model can be adjusted to reproduce the expansion rate of the laser-heated plasma bubble in such a way as to improve agreement with the images. At the higher 0.6 mg/cc gas fill, the experimental images show more pronounced 3D features, resulting in slightly less good agreement with the 2D simulations.
-
first demonstration of improved capsule implosions by reducing radiation preheat in uranium vs gold Hohlraums
Physics of Plasmas, 2018Co-Authors: E L Dewald, J E Field, N B Meezan, S Khan, R Tommasini, O L Landen, A S Moore, R Rygg, D B Sayre, A J MackinnonAbstract:In indirectly-driven Inertial Confinement Fusion (ICF) implosions, supra-thermal M-band (>2 keV) radiation from principally 4–3 resonance line transitions generated during laser irradiation at the peak power of Au hohlraum walls can preheat the fusion capsule and reduce compressional pressure. Higher Z, un-lined depleted uranium (DU) Hohlraums were used for the first time in ICF implosions on the National Ignition Facility (NIF) to reduce M-band radiation levels while keeping the total radiation flux similar to Au Hohlraums. First implosions in DU demonstrate an increase in in-flight density (+15%) of high density carbon capsules, and hence in stagnated hot spot temperature (+15%), hot spot x-ray (+200%) and fusion neutron yields (+100%) compared to Au Hohlraums. We show analytically that these changes are consistent with the observed 40% reduction in M-band x-ray flux in DU, and are in agreement with 2D hydrodynamic simulations. This result had a major impact on ICF research on the NIF where a significant fraction of high neutron yield implosions are currently using un-lined DU Hohlraums.In indirectly-driven Inertial Confinement Fusion (ICF) implosions, supra-thermal M-band (>2 keV) radiation from principally 4–3 resonance line transitions generated during laser irradiation at the peak power of Au hohlraum walls can preheat the fusion capsule and reduce compressional pressure. Higher Z, un-lined depleted uranium (DU) Hohlraums were used for the first time in ICF implosions on the National Ignition Facility (NIF) to reduce M-band radiation levels while keeping the total radiation flux similar to Au Hohlraums. First implosions in DU demonstrate an increase in in-flight density (+15%) of high density carbon capsules, and hence in stagnated hot spot temperature (+15%), hot spot x-ray (+200%) and fusion neutron yields (+100%) compared to Au Hohlraums. We show analytically that these changes are consistent with the observed 40% reduction in M-band x-ray flux in DU, and are in agreement with 2D hydrodynamic simulations. This result had a major impact on ICF research on the NIF where a significan...
Wenyi Huo - One of the best experts on this subject based on the ideXlab platform.
-
comparison of the laser spot movement inside cylindrical and spherical Hohlraums
Physics of Plasmas, 2017Co-Authors: Dong Yang, Ke Lan, Jie Liu, Wenyi Huo, Yaohua Chen, Guoli Ren, Zhiwen Yang, Liang GuoAbstract:Compared with cylindrical Hohlraums, the octahedral spherical Hohlraums have natural superiority in maintaining high radiation symmetry during the whole capsule implosion process in indirect drive inertial confinement fusion. However, the narrow space between laser beams and the hohlraum wall may disturb laser propagation inside the spherical hohlraum. In this work, the laser propagation inside the spherical hohlraum and cylindrical hohlraum is investigated experimentally by measuring laser spot movement at the SGIII-prototype laser facility. The experimental results show that the laser propagations inside the spherical hohlraum and the cylindrical hohlraum are totally different from each other due to different hohlraum structures. For the spherical hohlraum, although the laser energy is mainly deposited in the initial position of the laser spot during the whole laser pulse, some laser energies are absorbed by the ablated plasmas from the hohlraum wall. Because the laser beam is refracted by the thin plasmas near the laser entrance hole (LEH) region, the laser spot in the spherical hohlraum moves toward the opposite LEH. In contrast, the laser spot in the cylindrical hohlraum moves toward the LEH along the laser path due to the plasma expansion. When the laser is to be turned off, the accumulated plasmas near the LEH region in the cylindrical hohlraum absorb a majority of laser energy and hinder the laser arriving at the appointed position on the hohlraum wall.
-
experimental demonstration of low laser plasma instabilities in gas filled spherical Hohlraums at laser injection angle designed for ignition target
Physical Review E, 2017Co-Authors: Ke Lan, Xufei Xie, Wenyi Huo, Yaohua Chen, Guoli Ren, Dong Yang, C Y Zheng, Chuanlei Zhai, Liang Hao, Xiaoshi PengAbstract:Octahedral spherical Hohlraums with a single laser ring at an injection angle of 55^{∘} are attractive concepts for laser indirect drive due to the potential for achieving the x-ray drive symmetry required for high convergence implosions. Laser-plasma instabilities, however, are a concern given the long laser propagation path in such Hohlraums. Significant stimulated Raman scattering has been observed in cylindrical Hohlraums with similar laser propagation paths during the ignition campaign on the National Ignition Facility (NIF). In this Rapid Communication, experiments demonstrating low levels of laser-driven plasma instability (LPI) in spherical Hohlraums with a laser injection angle of 55^{∘} are reported and compared to that observed with cylindrical Hohlraums with injection angles of 28.5^{∘} and 55^{∘}, similar to that of the NIF. Significant LPI is observed with the laser injection of 28.5^{∘} in the cylindrical hohlraum where the propagation path is similar to the 55^{∘} injection angle for the spherical hohlraum. The experiments are performed on the SGIII laser facility with a total 0.35-μm incident energy of 93 kJ in a 3 nsec pulse. These experiments demonstrate the role of hohlraum geometry in LPI and demonstrate the need for systematic experiments for choosing the optimal configuration for ignition studies with indirect drive inertial confinement fusion.
-
first experimental comparisons of laser plasma interactions between spherical and cylindrical Hohlraums at sgiii laser facility
Matter and Radiation at Extremes, 2017Co-Authors: Yaohua Chen, Xufei Xie, Wenyi Huo, Guoli Ren, Dong Yang, C Y Zheng, Chuanlei Zhai, Liang Hao, Jie LiuAbstract:We present our recent laser-plasmas instability (LPI) comparison experiment at the SGIII laser facility between the spherical and cylindrical Hohlraums. Three kinds of filling are considered: vacuum, gas-filling with or without a capsule inside. A spherical hohlraum of 3.6 mm in diameter, and a cylindrical hohlraum of 2.4 mm × 4.3 mm are used. The capsule diameter is 0.96 mm. A flat-top laser pulse with 3 ns duration and up to 92.73 kJ energy is used. The experiment has shown that the LPI level in the spherical hohlraum is close to that of the outer beam in the cylindrical hohlraum, while much lower than that of the inner beam. The experiment is further simulated by using our 2-dimensional radiation hydrodynamic code LARED-Integration, and the laser back-scattering fraction and the stimulated Raman scatter (SRS) spectrum are post-processed by the high efficiency code of laser interaction with plasmas HLIP. According to the simulation, the plasma waves are strongly damped and the SRS is mainly developed at the plasma conditions of electron density from 0.08 nc to 0.1 nc and electron temperature from 1.5 keV to 2.0 keV inside the Hohlraums. However, obvious differences between the simulation and experiment are found, such as that the SRS back-scattering is underestimated, and the numerical SRS spectrum peaks at a larger wavelength and at a later time than the data. These differences indicate that the development of a 3D radiation hydrodynamic code, with more accurate physics models, is mandatory for spherical hohlraum study. We present our recent laser-plasmas instability (LPI) comparison experiment at the SGIII laser facility between the spherical and cylindrical Hohlraums. Three kinds of filling are considered: vacuum, gas-filling with or without a capsule inside. A spherical hohlraum of 3.6 mm in diameter, and a cylindrical hohlraum of 2.4 mm × 4.3 mm are used. The capsule diameter is 0.96 mm. A flat-top laser pulse with 3 ns duration and up to 92.73 kJ energy is used. The experiment has shown that the LPI level in the spherical hohlraum is close to that of the outer beam in the cylindrical hohlraum, while much lower than that of the inner beam. The experiment is further simulated by using our 2-dimensional radiation hydrodynamic code LARED-Integration, and the laser back-scattering fraction and the stimulated Raman scatter (SRS) spectrum are post-processed by the high efficiency code of laser interaction with plasmas HLIP....
-
Comparison of the laser spot movement inside cylindrical and spherical Hohlraums
PHYSICS OF PLASMAS, 2017Co-Authors: Li Zhichao, Ke Lan, Wenyi Huo, Yang Dong, Li Sanwei, Liu Jie, Ren Guoli, Chen Yao-hua, Yang Zhiwen, Guo LiangAbstract:Compared with cylindrical Hohlraums, the octahedral spherical Hohlraums have natural superiority in maintaining high radiation symmetry during the whole capsule implosion process in indirect drive inertial confinement fusion. However, the narrow space between laser beams and the hohlraum wall may disturb laser propagation inside the spherical hohlraum. In this work, the laser propagation inside the spherical hohlraum and cylindrical hohlraum is investigated experimentally by measuring laser spot movement at the SGIII-prototype laser facility. The experimental results show that the laser propagations inside the spherical hohlraum and the cylindrical hohlraum are totally different from each other due to different hohlraum structures. For the spherical hohlraum, although the laser energy is mainly deposited in the initial position of the laser spot during the whole laser pulse, some laser energies are absorbed by the ablated plasmas from the hohlraum wall. Because the laser beam is refracted by the thin plasmas near the laser entrance hole (LEH) region, the laser spot in the spherical hohlraum moves toward the opposite LEH. In contrast, the laser spot in the cylindrical hohlraum moves toward the LEH along the laser path due to the plasma expansion. When the laser is to be turned off, the accumulated plasmas near the LEH region in the cylindrical hohlraum absorb a majority of laser energy and hinder the laser arriving at the appointed position on the hohlraum wall. Published by AIP Publishing.National Natural Science Foundation of China [11405011, 11475033, 11305159]SCI(E)ARTICLE72
-
First experimental comparisons of laser-plasma interactions between spherical and cylindrical Hohlraums at SGIII laser facility
Elsevier, 2017Co-Authors: Yaohua Chen, Xufei Xie, Wenyi Huo, Guoli Ren, Chunyang Zheng, Dong Yang, Chuanlei Zhai, Liang Hao, Jie LiuAbstract:We present our recent laser-plasmas instability (LPI) comparison experiment at the SGIII laser facility between the spherical and cylindrical Hohlraums. Three kinds of filling are considered: vacuum, gas-filling with or without a capsule inside. A spherical hohlraum of 3.6 mm in diameter, and a cylindrical hohlraum of 2.4 mm × 4.3 mm are used. The capsule diameter is 0.96 mm. A flat-top laser pulse with 3 ns duration and up to 92.73 kJ energy is used. The experiment has shown that the LPI level in the spherical hohlraum is close to that of the outer beam in the cylindrical hohlraum, while much lower than that of the inner beam. The experiment is further simulated by using our 2-dimensional radiation hydrodynamic code LARED-Integration, and the laser back-scattering fraction and the stimulated Raman scatter (SRS) spectrum are post-processed by the high efficiency code of laser interaction with plasmas HLIP. According to the simulation, the plasma waves are strongly damped and the SRS is mainly developed at the plasma conditions of electron density from 0.08 nc to 0.1 nc and electron temperature from 1.5 keV to 2.0 keV inside the Hohlraums. However, obvious differences between the simulation and experiment are found, such as that the SRS back-scattering is underestimated, and the numerical SRS spectrum peaks at a larger wavelength and at a later time than the data. These differences indicate that the development of a 3D radiation hydrodynamic code, with more accurate physics models, is mandatory for spherical hohlraum study
L Divol - One of the best experts on this subject based on the ideXlab platform.
-
low mode implosion symmetry sensitivity in low gas fill nif cylindrical Hohlraums
Physics of Plasmas, 2021Co-Authors: N Izumi, N B Meezan, D A Callahan, J D Moody, L Divol, O L Landen, D T Woods, Hui Chen, M Hohenberger, A L KritcherAbstract:Achieving an efficient capsule implosion in National Ignition Facility indirect-drive target experiments requires symmetric hohlraum x-ray drive for the duration of the laser pulse. This is commonly achieved using two-sided two-cone laser irradiation of cylindrical Hohlraums that, in principle, can zero the time average of all spherical harmonic asymmetry modes <6 as well as the time dependence of the usually dominant mode 2. In practice, experimental evidence indicates that maintaining symmetric drive becomes limited late in the pulse due to the inward expansion of the hohlraum wall and outward expansion of the capsule ablator plasmas impairing the propagation of the inner-cone laser beams. This effect is enhanced in Hohlraums employing low gas-fill, now used almost exclusively as these provide the highest performing implosions and reduce Stimulated Brillouin and Raman backscatter losses, since the gas plasma provides less back pressure to limit blow-in of the hohlraum wall and capsule ablator plasmas. In order to understand this dynamic behavior, we combined multi-keV X-ray imaging of the wall and imploded fuel plasmas as we changed a single parameter at a time: hohlraum gas-fill, laser outer cone picket energy, radius of high density carbon capsules used, and laser beam polar and azimuthal pointing geometry. We developed a physics-based multi-parameter experimental scaling to explain the results that extend prior scalings and compare those to radiation hydrodynamic simulations to develop a more complete picture of how hohlraum, capsule, and laser parameters affect pole vs equator drive symmetry.
-
foam lined hohlraum inertial confinement fusion experiments on the national ignition facility
Physical Review E, 2020Co-Authors: A S Moore, N B Meezan, J L Milovich, S D Bhandarkar, S Johnson, Ricardo Heredia, Theodore F Baumann, Monika M Biener, H Chen, L DivolAbstract:Experiments on the National Ignition Facility (NIF) to study Hohlraums lined with a 20-mg/cc $400\text{\ensuremath{-}}\ensuremath{\mu}\mathrm{m}$-thick ${\mathrm{Ta}}_{2}{\mathrm{O}}_{5}$ aerogel at full scale (hohlraum diameter = 6.72 mm) are reported. Driven with a 1.6-MJ, 450-TW laser pulse, the performance of the foam liner is diagnosed using implosion hot-spot symmetry measurements of the high-density carbon (HDC) capsule and measurement of inner beam propagation through a thin-wall $8\text{\ensuremath{-}}\ensuremath{\mu}\mathrm{m}$ Au window in the hohlraum. Results show an improved capsule performance due to laser energy deposition further inside the hohlraum, leading to a modest increase in x-ray drive and reduced preheat due to changes in the x-ray spectrum when the foam liner is included. In addition, the outer cone bubble uniformity is improved, but the predicted improvement in inner beam propagation to improve symmetry control is not realized for this foam thickness and density.
-
application of cross beam energy transfer to control drive symmetry in icf implosions in low gas fill Hohlraums at the national ignition facility
Physics of Plasmas, 2020Co-Authors: L Pickworth, L R Benedetti, T Doppner, D E Hinkel, J E Ralph, P M Celliers, L Divol, B Bachmann, L Masse, Hui ChenAbstract:Cross beam energy transfer (CBET), invoked by setting a wavelength difference, Δλ, between inner and outer beam cones, can be used to increase the drive on the waist in indirectly driven inertial confinement fusion experiments at the National Ignition Facility (NIF). Historically, hot spot symmetry control in capsule implosions in high (≥0.9 mg/cm3 4He) gas fill Hohlraums was enabled by substantial CBET. However, these implosion designs suffered from inflight symmetry swings, high SRS backscatter on the inner cones, and significant hot electron generation posing a threat to DT fuel preheat. Subsequent experiments in larger, low (≤0.6 mg/cm3 4He) gas fill Hohlraums demonstrated round implosions by varying the inner cone fraction throughout the laser drive at Δλ = 0 A while keeping backscatter and hot electron generation very low. To enable driving larger capsules at a given Hohlraum size, additional tools for implosion symmetry control are required. With this goal in mind, this paper presents a detailed experimental study of using CBET in low gas fill Hohlraums near NIF's current peak power capability. We find a ∼2.5× higher sensitivity of the P2 Legendre mode with respect to Δλ changes compared to that of high gas fill designs. We attribute this observation to the fact that backscatter remains very low and that CBET remains in a linear regime, as suggested by simulations. As a result, a much smaller Δλ of order 1 A is sufficient for sustaining implosion symmetry while keeping laser-to-Hohlraum coupling high and hot electron generation very low. While this study used plastic ablator capsules, our findings can be generalized to other ablator materials and, hence, show great promise for using wavelength detuning as a strong lever for implosion symmetry control in future low gas fill designs that require smaller case to capsule ratios in order to increase the energy coupled to the capsule.
-
fusion energy output greater than the kinetic energy of an imploding shell at the national ignition facility
Physical Review Letters, 2018Co-Authors: Le S Pape, E L Dewald, L Berzak F Hopkins, L Divol, S D Bhandarkar, L R Bennedetti, T Bunn, Juergen Biener, J Crippen, D T CaseyAbstract:: A series of cryogenic, layered deuterium-tritium (DT) implosions have produced, for the first time, fusion energy output twice the peak kinetic energy of the imploding shell. These experiments at the National Ignition Facility utilized high density carbon ablators with a three-shock laser pulse (1.5 MJ in 7.5 ns) to irradiate low gas-filled (0.3 mg/cc of helium) bare depleted uranium Hohlraums, resulting in a peak hohlraum radiative temperature ∼290 eV. The imploding shell, composed of the nonablated high density carbon and the DT cryogenic layer, is, thus, driven to velocity on the order of 380 km/s resulting in a peak kinetic energy of ∼21 kJ, which once stagnated produced a total DT neutron yield of 1.9×10^{16} (shot N170827) corresponding to an output fusion energy of 54 kJ. Time dependent low mode asymmetries that limited further progress of implosions have now been controlled, leading to an increased compression of the hot spot. It resulted in hot spot areal density (ρr∼0.3 g/cm^{2}) and stagnation pressure (∼360 Gbar) never before achieved in a laboratory experiment.
-
symmetry control in subscale near vacuum Hohlraums
Physics of Plasmas, 2016Co-Authors: D Turnbull, N B Meezan, L Berzak F Hopkins, A B Zylstra, Le S Pape, L Divol, A J Mackinnon, O L Landen, H G RinderknechtAbstract:Controlling the symmetry of indirect-drive inertial confinement fusion implosions remains a key challenge. Increasing the ratio of the hohlraum diameter to the capsule diameter (case-to-capsule ratio, or CCR) facilitates symmetry tuning. By varying the balance of energy between the inner and outer cones as well as the incident laser pulse length, we demonstrate the ability to tune from oblate, through round, to prolate at a CCR of 3.2 in near-vacuum Hohlraums at the National Ignition Facility, developing empirical playbooks along the way for cone fraction sensitivity of various laser pulse epochs. Radiation-hydrodynamic simulations with enhanced inner beam propagation reproduce most experimental observables, including hot spot shape, for a majority of implosions. Specular reflections are used to diagnose the limits of inner beam propagation as a function of pulse length.