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V N Goncharov - One of the best experts on this subject based on the ideXlab platform.
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Fuel-shell interface instability growth effects on the performance of room temperature direct-drive implosions
Physics of Plasmas, 2019Co-Authors: S. C. Miller, P B Radha, J P Knauer, V. Yu. Glebov, C. J. Forrest, V N GoncharovAbstract:Performance degradation in direct-drive inertial confinement fusion implosions is caused by several effects, one of which is Rayleigh–Taylor (RT) instability growth during the Deceleration Phase. In room-temperature plastic target implosions, Deceleration-Phase RT growth is enhanced by the density discontinuity and finite Atwood number at the fuel–shell interface. In this paper, the Atwood number of the interface is systematically varied by altering the ratio of deuterium to tritium (D:T) within the DT gas fill. It is shown that the stability of the interface is best characterized by the effective Atwood number, which is primarily determined by radiation heating of the shell and not by the composition of the fuel. Both simulation and experimental data show that yield performance scales with the fraction of D and T present in the fuel and that the observed inferred ion temperature asymmetry ( Δ T i = T i max − T i min ), which indicates the presence of long-wavelength modes, has a small sensitivity to the different D:T ratios.Performance degradation in direct-drive inertial confinement fusion implosions is caused by several effects, one of which is Rayleigh–Taylor (RT) instability growth during the Deceleration Phase. In room-temperature plastic target implosions, Deceleration-Phase RT growth is enhanced by the density discontinuity and finite Atwood number at the fuel–shell interface. In this paper, the Atwood number of the interface is systematically varied by altering the ratio of deuterium to tritium (D:T) within the DT gas fill. It is shown that the stability of the interface is best characterized by the effective Atwood number, which is primarily determined by radiation heating of the shell and not by the composition of the fuel. Both simulation and experimental data show that yield performance scales with the fraction of D and T present in the fuel and that the observed inferred ion temperature asymmetry ( Δ T i = T i max − T i min ), which indicates the presence of long-wavelength modes, has a small sensitivity...
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impact of three dimensional hot spot flow asymmetry on ion temperature measurements in inertial confinement fusion experiments
Physics of Plasmas, 2018Co-Authors: R Betti, D Shvarts, O M Mannion, D Patel, V N Goncharov, K S Anderson, P B Radha, J P Knauer, A BoseAbstract:Three-dimensional (3-D) implosion asymmetries lead to significant variations in ion-temperature measurements in inertial confinement fusion experiments. We present an analytical method to generalize the physical properties of velocity variance in the Brysk ion-temperature model. This analysis provides a consistent explanation for the 3-D effects of inferred ion-temperature variations for various single modes and multimodes modeled by the Deceleration-Phase hydrocode DEC3D and the neutron transport code IRIS3D. The effect of the hot-spot flow asymmetry on variations in ion-temperature measurements is shown to be uniquely determined by a complete set of six hot-spot flow parameters. An approximated solution to the minimum inferred ion temperature is derived and shown to be close to the thermal ion temperature for low mode l = 1, which exhibits the largest anisotropic velocity variance in the single-mode spectrum. The isotropic velocity variance for low mode l = 2 is shown to result in the minimum inferred ion temperatures being well above the thermal ion temperature.Three-dimensional (3-D) implosion asymmetries lead to significant variations in ion-temperature measurements in inertial confinement fusion experiments. We present an analytical method to generalize the physical properties of velocity variance in the Brysk ion-temperature model. This analysis provides a consistent explanation for the 3-D effects of inferred ion-temperature variations for various single modes and multimodes modeled by the Deceleration-Phase hydrocode DEC3D and the neutron transport code IRIS3D. The effect of the hot-spot flow asymmetry on variations in ion-temperature measurements is shown to be uniquely determined by a complete set of six hot-spot flow parameters. An approximated solution to the minimum inferred ion temperature is derived and shown to be close to the thermal ion temperature for low mode l = 1, which exhibits the largest anisotropic velocity variance in the single-mode spectrum. The isotropic velocity variance for low mode l = 2 is shown to result in the minimum inferred i...
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Hydrodynamic growth of shell modulations in the Deceleration Phase of spherical direct-drive implosions
Physics of Plasmas, 2003Co-Authors: V. A. Smalyuk, V N Goncharov, P B Radha, J P Knauer, J. A. Delettrez, F. J. Marshall, D. D. Meyerhofer, Sonya B. Dumanis, V. Yu. Glebov, Susan ReganAbstract:The evolution of shell modulations was measured in targets with titanium-doped layers using differential imaging [B. Yaakobi et al., Phys. Plasmas 7, 3727 (2000)] near peak compression of direct-drive spherical implosions. Inner-shell modulations grow throughout the Deceleration Phase of the implosion due to the Rayleigh–Taylor instability with relative modulation levels of ∼20% at peak neutron production and ∼50% at peak compression (∼100 ps later) in targets with 1-mm-diam, 20-μm-thick shells filled with 4 atm of D3He gas. In addition, the shell modulations grow up to about 1.5 times due to Bell–Plesset convergent effects during the same period. At peak compression the inner part of the shell has a higher modulation level than other parts of the shell.
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rayleigh taylor instability in the Deceleration Phase of spherical implosion experiments
Physics of Plasmas, 2002Co-Authors: V. A. Smalyuk, V N Goncharov, J. A. Delettrez, F. J. Marshall, D. D. Meyerhofer, T. C. Sangster, S P Regan, R P J Town, B. YaakobiAbstract:The temporal evolution of inner-shell modulations, unstable during the Deceleration Phase of a laser-driven spherical implosion, has been measured through K-edge imaging [B. Yaakobi et al., Phys. Plasmas 7, 3727 (2000)] of shells with titanium-doped layers. The main study was based on the implosions of 1 mm diam, 20 μm thick shells filled with either 18 atm or 4 atm of D3He gas driven with 23 kJ, 1 ns square laser pulses on OMEGA [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)]. These targets have similar modulation levels at the beginning of the Deceleration Phase due to similar modulation growths in the acceleration Phase, but different modulation growths throughout the Deceleration Phase due to different fill pressures (convergence ratios). At peak compression, the measured inner surface, areal-density nonuniformity σrms levels were 23±5 % for more-stable 18 atm fill targets and 53±11 % for less-stable 4 atm fill targets. The inner-surface modulations grow throughout the Deceleration Phase due to Rayleigh–Taylor instability and Bell–Plesset convergence effects. The nonuniformity at peak compression is sensitive to the initial perturbation level as measured in implosions with different laser-smoothing conditions.
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Rayleigh–Taylor instability in the Deceleration Phase of spherical implosion experiments
Physics of Plasmas, 2002Co-Authors: V. A. Smalyuk, V N Goncharov, J. A. Delettrez, F. J. Marshall, D. D. Meyerhofer, Susan Regan, T. C. Sangster, Richard Town, B. YaakobiAbstract:The temporal evolution of inner-shell modulations, unstable during the Deceleration Phase of a laser-driven spherical implosion, has been measured through K-edge imaging [B. Yaakobi et al., Phys. Plasmas 7, 3727 (2000)] of shells with titanium-doped layers. The main study was based on the implosions of 1 mm diam, 20 μm thick shells filled with either 18 atm or 4 atm of D3He gas driven with 23 kJ, 1 ns square laser pulses on OMEGA [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)]. These targets have similar modulation levels at the beginning of the Deceleration Phase due to similar modulation growths in the acceleration Phase, but different modulation growths throughout the Deceleration Phase due to different fill pressures (convergence ratios). At peak compression, the measured inner surface, areal-density nonuniformity σrms levels were 23±5 % for more-stable 18 atm fill targets and 53±11 % for less-stable 4 atm fill targets. The inner-surface modulations grow throughout the Deceleration Phase due to Ra...
V. A. Smalyuk - One of the best experts on this subject based on the ideXlab platform.
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visualizing Deceleration Phase instabilities in inertial confinement fusion implosions using an enhanced self emission technique at the national ignition facility
Physics of Plasmas, 2018Co-Authors: Louisa Pickworth, V. A. Smalyuk, B. A. Hammel, Laura Robin Benedetti, D. K. Bradley, J. E. Field, S. W. Haan, H F Robey, L Berzak F Hopkins, R. HatarikAbstract:High-mode perturbations and low-mode asymmetries were measured in the Deceleration Phase of indirectly driven, deuterium gas filled inertial confinement fusion capsule implosions at convergence ratios of 10 to 15, using a new “enhanced emission” technique at the National Ignition Facility [E. M. Campbell et al., AIP Conf. Proc. 429, 3 (1998)]. In these experiments, a high spatial resolution Kirkpatrick-Baez microscope was used to image the x-ray emission from the inner surface of a high-density-carbon capsule's shell. The use of a high atomic number dopant in the shell enabled time-resolved observations of shell perturbations penetrating into the hot spot. This allowed the effects of the perturbations and asymmetries on degrading neutron yield to be directly measured. In particular, mix induced radiation losses of ∼400 J from the hot spot resulted in a neutron yield reduction of a factor of ∼2. In a subsequent experiment with a significantly increased level of short-mode initial perturbations, shown throu...
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Development of new platforms for hydrodynamic instability and asymmetry measurements in Deceleration Phase of indirectly driven implosions on NIF
Physics of Plasmas, 2018Co-Authors: Louisa Pickworth, V. A. Smalyuk, B. A. Hammel, Harry Robey, R. Tommasini, Laura Robin Benedetti, L. F. Berzak Hopkins, D. K. Bradley, M. Dayton, S. FelkerAbstract:Hydrodynamic instabilities and asymmetries are a major obstacle in the quest to achieve ignition at the National Ignition Facility (NIF) as they cause pre-existing capsule perturbations to grow and ultimately quench the fusion burn in experiments. This paper reviews the development of two new experimental techniques to measure high-mode instabilities and low-mode asymmetries in the Deceleration Phase of indirect drive inertial confinement fusion implosions. In the first innovative technique, self-emission from the hot spot was enhanced with an argon dopant to “self-backlight” the shell in-flight, imaging the perturbations in the shell near peak velocity. Experiments with pre-imposed two-dimensional perturbations showed hydrodynamic instability growth of up to 7000× in areal density. These experiments discovered unexpected three-dimensional structures originating from the capsule support structures. These new 3-D structures became one of the primary concerns for the indirect drive ICF program that requires their origin to be understood and their impact mitigated. In a second complementary technique, the inner surface of the decelerating shell was visualized in implosions using x-ray emission of a high-Z dopant added to the inner surface of the capsule. With this technique, low mode asymmetry and high mode perturbations, including perturbations seeded by the gas fill tube and capsule support structure, were quantified near peak compression. Using this doping method, the role of perturbations and radiative losses from high atomic number materials on neutron yield was quantified.Hydrodynamic instabilities and asymmetries are a major obstacle in the quest to achieve ignition at the National Ignition Facility (NIF) as they cause pre-existing capsule perturbations to grow and ultimately quench the fusion burn in experiments. This paper reviews the development of two new experimental techniques to measure high-mode instabilities and low-mode asymmetries in the Deceleration Phase of indirect drive inertial confinement fusion implosions. In the first innovative technique, self-emission from the hot spot was enhanced with an argon dopant to “self-backlight” the shell in-flight, imaging the perturbations in the shell near peak velocity. Experiments with pre-imposed two-dimensional perturbations showed hydrodynamic instability growth of up to 7000× in areal density. These experiments discovered unexpected three-dimensional structures originating from the capsule support structures. These new 3-D structures became one of the primary concerns for the indirect drive ICF program that requires...
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Visualizing Deceleration-Phase instabilities in inertial confinement fusion implosions using an “enhanced self-emission” technique at the National Ignition Facility
Physics of Plasmas, 2018Co-Authors: Louisa Pickworth, V. A. Smalyuk, B. A. Hammel, Harry Robey, Laura Robin Benedetti, L. F. Berzak Hopkins, D. K. Bradley, J. E. Field, S. W. Haan, R. HatarikAbstract:High-mode perturbations and low-mode asymmetries were measured in the Deceleration Phase of indirectly driven, deuterium gas filled inertial confinement fusion capsule implosions at convergence ratios of 10 to 15, using a new “enhanced emission” technique at the National Ignition Facility [E. M. Campbell et al., AIP Conf. Proc. 429, 3 (1998)]. In these experiments, a high spatial resolution Kirkpatrick-Baez microscope was used to image the x-ray emission from the inner surface of a high-density-carbon capsule's shell. The use of a high atomic number dopant in the shell enabled time-resolved observations of shell perturbations penetrating into the hot spot. This allowed the effects of the perturbations and asymmetries on degrading neutron yield to be directly measured. In particular, mix induced radiation losses of ∼400 J from the hot spot resulted in a neutron yield reduction of a factor of ∼2. In a subsequent experiment with a significantly increased level of short-mode initial perturbations, shown throu...
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Experimental techniques for measuring Rayleigh?Taylor instability in inertial confinement fusion
Physica Scripta, 2012Co-Authors: V. A. SmalyukAbstract:Rayleigh–Taylor (RT) instability is one of the major concerns in inertial confinement fusion (ICF) because it amplifies target modulations in both acceleration and Deceleration Phases of implosion, which leads to shell disruption and performance degradation of imploding targets. This article reviews experimental results of the RT growth experiments performed on OMEGA laser system, where targets were driven directly with laser light. RT instability was studied in the linear and nonlinear regimes. The experiments were performed in acceleration Phase, using planar and spherical targets, and in Deceleration Phase of spherical implosions, using spherical shells. Initial target modulations consisted of two-dimensional (2D) pre-imposed modulations, and 2D and three-dimensional (3D) modulations imprinted on targets by the nonuniformities in laser drive. In planar geometry, the nonlinear regime was studied using 3D modulations with broadband spectra near nonlinear saturation levels. In acceleration-Phase, the measured modulation Fourier spectra and nonlinear growth velocities are in good agreement with those predicted by Haan's model (Haan 1989 Phys. Rev. A 39 5812). In a real-space analysis, the bubble merger was quantified by a self-similar evolution of bubble size distributions (Oron et al 2001 Phys. Plasmas 8 2883). The 3D, inner-surface modulations were measured to grow throughout the Deceleration Phase of spherical implosions. RT growth rates are very sensitive to the drive conditions, therefore they can be used to test and validate drive physics in hydrodynamic codes used to design ICF implosions. Measured growth rates of pre-imposed 2D target modulations below nonlinear saturation levels were used to validate nonlocal thermal electron transport model in laser-driven experiments.
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Hydrodynamic growth of shell modulations in the Deceleration Phase of spherical direct-drive implosions
Physics of Plasmas, 2003Co-Authors: V. A. Smalyuk, V N Goncharov, P B Radha, J P Knauer, J. A. Delettrez, F. J. Marshall, D. D. Meyerhofer, Sonya B. Dumanis, V. Yu. Glebov, Susan ReganAbstract:The evolution of shell modulations was measured in targets with titanium-doped layers using differential imaging [B. Yaakobi et al., Phys. Plasmas 7, 3727 (2000)] near peak compression of direct-drive spherical implosions. Inner-shell modulations grow throughout the Deceleration Phase of the implosion due to the Rayleigh–Taylor instability with relative modulation levels of ∼20% at peak neutron production and ∼50% at peak compression (∼100 ps later) in targets with 1-mm-diam, 20-μm-thick shells filled with 4 atm of D3He gas. In addition, the shell modulations grow up to about 1.5 times due to Bell–Plesset convergent effects during the same period. At peak compression the inner part of the shell has a higher modulation level than other parts of the shell.
R Betti - One of the best experts on this subject based on the ideXlab platform.
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impact of three dimensional hot spot flow asymmetry on ion temperature measurements in inertial confinement fusion experiments
Physics of Plasmas, 2018Co-Authors: R Betti, D Shvarts, O M Mannion, D Patel, V N Goncharov, K S Anderson, P B Radha, J P Knauer, A BoseAbstract:Three-dimensional (3-D) implosion asymmetries lead to significant variations in ion-temperature measurements in inertial confinement fusion experiments. We present an analytical method to generalize the physical properties of velocity variance in the Brysk ion-temperature model. This analysis provides a consistent explanation for the 3-D effects of inferred ion-temperature variations for various single modes and multimodes modeled by the Deceleration-Phase hydrocode DEC3D and the neutron transport code IRIS3D. The effect of the hot-spot flow asymmetry on variations in ion-temperature measurements is shown to be uniquely determined by a complete set of six hot-spot flow parameters. An approximated solution to the minimum inferred ion temperature is derived and shown to be close to the thermal ion temperature for low mode l = 1, which exhibits the largest anisotropic velocity variance in the single-mode spectrum. The isotropic velocity variance for low mode l = 2 is shown to result in the minimum inferred ion temperatures being well above the thermal ion temperature.Three-dimensional (3-D) implosion asymmetries lead to significant variations in ion-temperature measurements in inertial confinement fusion experiments. We present an analytical method to generalize the physical properties of velocity variance in the Brysk ion-temperature model. This analysis provides a consistent explanation for the 3-D effects of inferred ion-temperature variations for various single modes and multimodes modeled by the Deceleration-Phase hydrocode DEC3D and the neutron transport code IRIS3D. The effect of the hot-spot flow asymmetry on variations in ion-temperature measurements is shown to be uniquely determined by a complete set of six hot-spot flow parameters. An approximated solution to the minimum inferred ion temperature is derived and shown to be close to the thermal ion temperature for low mode l = 1, which exhibits the largest anisotropic velocity variance in the single-mode spectrum. The isotropic velocity variance for low mode l = 2 is shown to result in the minimum inferred i...
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effects of residual kinetic energy on yield degradation and ion temperature asymmetries in inertial confinement fusion implosions
Physics of Plasmas, 2018Co-Authors: K. M. Woo, R Betti, D Shvarts, O M Mannion, D Patel, A Bose, R Yan, P Y Chang, Ronald M EpsteinAbstract:The study of Rayleigh–Taylor instability in the Deceleration Phase of inertial confinement fusion implosions is carried out using the three-dimensional (3-D) radiation-hydrodynamic Eulerian parallel code DEC3D. We show that the yield-over-clean is a strong function of the residual kinetic energy (RKE) for low modes. Our analytical models indicate that the behavior of larger hot-spot volumes observed in low modes and the consequential pressure degradation can be explained in terms of increasing the RKE. These results are derived using a simple adiabatic implosion model of the Deceleration Phase as well as through an extensive set of 3-D single-mode simulations using the code DEC3D. The effect of the bulk velocity broadening on ion temperature asymmetries is analyzed for different mode numbers l=1–12. The jet observed in low mode l=1 is shown to cause the largest ion temperature variation in the mode spectrum. The vortices of high modes within the cold bubbles are shown to cause lower ion temperature variat...
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hydrodynamic scaling of the Deceleration Phase rayleigh taylor instability
Physics of Plasmas, 2015Co-Authors: A Bose, K. M. Woo, Ryan Nora, R BettiAbstract:The scaling of the Deceleration Phase of inertial fusion direct-drive implosions is investigated for OMEGA and National Ignition Facility (NIF)-size targets. It is shown that the Deceleration-Phase Rayleigh–Taylor instability (RTI) does not scale hydro-equivalently with implosion size. This is because ablative stabilization resulting from thermal conduction and radiation transport in a spherically converging geometry is different on the two scales. As a consequence, NIF-scale implosions show lower hot-spot density and mass ablation velocity, allowing for higher RTI growth. On the contrary, stabilization resulting from density-gradient enhancement, caused by reabsorption of radiation emitted from the hot spot, is higher on NIF implosions. Since the RTI mitigation related to thermal conduction and radiation transport scale oppositely with implosion size, the degradation of implosion performance caused by the Deceleration RTI is similar for NIF and OMEGA targets. It is found that a minimum threshold for the no-α Lawson ignition parameter of χΩ ≈ 0.2 at the OMEGA scale is required to demonstrate hydro-equivalent ignition at the NIF scale for symmetric direct-drive implosions.
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Analytical model of the ablative Rayleigh-Taylor instability in the Deceleration Phase
Physics of Plasmas, 2005Co-Authors: J. Sanz, R BettiAbstract:A sharp boundary model for the Deceleration Phase of imploding capsules in inertial confinement fusion, in both direct and indirect drive, has been developed. The model includes heat conduction, local α-particle energy deposition, and shell compressibility effects. A differential equation for the temporal evolution of the modal amplitude interface is obtained. It is found that the α-particle energy has a strong influence on the evolution of the low l modes, via the compressibility of the shell. The modes are damped by vorticity convection, fire polishing, and α-particle energy deposition. The existence of a cutoff l number arises from the high blow of velocity into the hot region (rocket effect) if density gradient scale length effects are taken into account at the interface. The differential equation for the modal amplitude is used as a postprocessor to the results of 1D-SARA code [J. J. Honrubia, J. Quant. Spectrosc. Radiat. Transfer. 49, 491 (1993)] in a typical capsule for indirect-drive ignition desi...
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Deceleration Phase of inertial confinement fusion implosions
Physics of Plasmas, 2002Co-Authors: R Betti, V N Goncharov, K S Anderson, D. D. Meyerhofer, R.l. Mccrory, S. Skupsky, Richard TownAbstract:A model for the Deceleration Phase and marginal ignition of imploding capsules is derived by solving a set of ordinary differential equations describing the hot-spot energy balance and the shell dynamics including the return shock propagation. It is found that heat flux leaving the hot spot goes back in the form of internal energy and PdV work of the material ablated off the inner-shell surface. Though the hot-spot temperature is reduced by the heat conduction losses, the hot-spot density increases due to the ablated material in such a way that the hot-spot pressure is approximately independent of heat conduction. For hot-spot temperatures exceeding approximately 7 keV, the ignition conditions are not affected by heat conduction losses that are recycled into the hot spot by ablation. Instead, the only significant internal energy loss is due to the hot-spot expansion tamped by the surrounding shell. The change of adiabat induced by the shock is also calculated for marginally igniting shells, and the relati...
A Bose - One of the best experts on this subject based on the ideXlab platform.
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impact of three dimensional hot spot flow asymmetry on ion temperature measurements in inertial confinement fusion experiments
Physics of Plasmas, 2018Co-Authors: R Betti, D Shvarts, O M Mannion, D Patel, V N Goncharov, K S Anderson, P B Radha, J P Knauer, A BoseAbstract:Three-dimensional (3-D) implosion asymmetries lead to significant variations in ion-temperature measurements in inertial confinement fusion experiments. We present an analytical method to generalize the physical properties of velocity variance in the Brysk ion-temperature model. This analysis provides a consistent explanation for the 3-D effects of inferred ion-temperature variations for various single modes and multimodes modeled by the Deceleration-Phase hydrocode DEC3D and the neutron transport code IRIS3D. The effect of the hot-spot flow asymmetry on variations in ion-temperature measurements is shown to be uniquely determined by a complete set of six hot-spot flow parameters. An approximated solution to the minimum inferred ion temperature is derived and shown to be close to the thermal ion temperature for low mode l = 1, which exhibits the largest anisotropic velocity variance in the single-mode spectrum. The isotropic velocity variance for low mode l = 2 is shown to result in the minimum inferred ion temperatures being well above the thermal ion temperature.Three-dimensional (3-D) implosion asymmetries lead to significant variations in ion-temperature measurements in inertial confinement fusion experiments. We present an analytical method to generalize the physical properties of velocity variance in the Brysk ion-temperature model. This analysis provides a consistent explanation for the 3-D effects of inferred ion-temperature variations for various single modes and multimodes modeled by the Deceleration-Phase hydrocode DEC3D and the neutron transport code IRIS3D. The effect of the hot-spot flow asymmetry on variations in ion-temperature measurements is shown to be uniquely determined by a complete set of six hot-spot flow parameters. An approximated solution to the minimum inferred ion temperature is derived and shown to be close to the thermal ion temperature for low mode l = 1, which exhibits the largest anisotropic velocity variance in the single-mode spectrum. The isotropic velocity variance for low mode l = 2 is shown to result in the minimum inferred i...
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effects of residual kinetic energy on yield degradation and ion temperature asymmetries in inertial confinement fusion implosions
Physics of Plasmas, 2018Co-Authors: K. M. Woo, R Betti, D Shvarts, O M Mannion, D Patel, A Bose, R Yan, P Y Chang, Ronald M EpsteinAbstract:The study of Rayleigh–Taylor instability in the Deceleration Phase of inertial confinement fusion implosions is carried out using the three-dimensional (3-D) radiation-hydrodynamic Eulerian parallel code DEC3D. We show that the yield-over-clean is a strong function of the residual kinetic energy (RKE) for low modes. Our analytical models indicate that the behavior of larger hot-spot volumes observed in low modes and the consequential pressure degradation can be explained in terms of increasing the RKE. These results are derived using a simple adiabatic implosion model of the Deceleration Phase as well as through an extensive set of 3-D single-mode simulations using the code DEC3D. The effect of the bulk velocity broadening on ion temperature asymmetries is analyzed for different mode numbers l=1–12. The jet observed in low mode l=1 is shown to cause the largest ion temperature variation in the mode spectrum. The vortices of high modes within the cold bubbles are shown to cause lower ion temperature variat...
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Hydrodynamic scaling of the Deceleration-Phase Rayleigh–Taylor instability
Physics of Plasmas, 2015Co-Authors: A Bose, K. M. Woo, Ryan Nora, Riccardo BettiAbstract:The scaling of the Deceleration Phase of inertial fusion direct-drive implosions is investigated for OMEGA and National Ignition Facility (NIF)-size targets. It is shown that the Deceleration-Phase Rayleigh–Taylor instability (RTI) does not scale hydro-equivalently with implosion size. This is because ablative stabilization resulting from thermal conduction and radiation transport in a spherically converging geometry is different on the two scales. As a consequence, NIF-scale implosions show lower hot-spot density and mass ablation velocity, allowing for higher RTI growth. On the contrary, stabilization resulting from density-gradient enhancement, caused by reabsorption of radiation emitted from the hot spot, is higher on NIF implosions. Since the RTI mitigation related to thermal conduction and radiation transport scale oppositely with implosion size, the degradation of implosion performance caused by the Deceleration RTI is similar for NIF and OMEGA targets. It is found that a minimum threshold for the no-α Lawson ignition parameter of χΩ ≈ 0.2 at the OMEGA scale is required to demonstrate hydro-equivalent ignition at the NIF scale for symmetric direct-drive implosions.
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hydrodynamic scaling of the Deceleration Phase rayleigh taylor instability
Physics of Plasmas, 2015Co-Authors: A Bose, K. M. Woo, Ryan Nora, R BettiAbstract:The scaling of the Deceleration Phase of inertial fusion direct-drive implosions is investigated for OMEGA and National Ignition Facility (NIF)-size targets. It is shown that the Deceleration-Phase Rayleigh–Taylor instability (RTI) does not scale hydro-equivalently with implosion size. This is because ablative stabilization resulting from thermal conduction and radiation transport in a spherically converging geometry is different on the two scales. As a consequence, NIF-scale implosions show lower hot-spot density and mass ablation velocity, allowing for higher RTI growth. On the contrary, stabilization resulting from density-gradient enhancement, caused by reabsorption of radiation emitted from the hot spot, is higher on NIF implosions. Since the RTI mitigation related to thermal conduction and radiation transport scale oppositely with implosion size, the degradation of implosion performance caused by the Deceleration RTI is similar for NIF and OMEGA targets. It is found that a minimum threshold for the no-α Lawson ignition parameter of χΩ ≈ 0.2 at the OMEGA scale is required to demonstrate hydro-equivalent ignition at the NIF scale for symmetric direct-drive implosions.
B. Yaakobi - One of the best experts on this subject based on the ideXlab platform.
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rayleigh taylor instability in the Deceleration Phase of spherical implosion experiments
Physics of Plasmas, 2002Co-Authors: V. A. Smalyuk, V N Goncharov, J. A. Delettrez, F. J. Marshall, D. D. Meyerhofer, T. C. Sangster, S P Regan, R P J Town, B. YaakobiAbstract:The temporal evolution of inner-shell modulations, unstable during the Deceleration Phase of a laser-driven spherical implosion, has been measured through K-edge imaging [B. Yaakobi et al., Phys. Plasmas 7, 3727 (2000)] of shells with titanium-doped layers. The main study was based on the implosions of 1 mm diam, 20 μm thick shells filled with either 18 atm or 4 atm of D3He gas driven with 23 kJ, 1 ns square laser pulses on OMEGA [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)]. These targets have similar modulation levels at the beginning of the Deceleration Phase due to similar modulation growths in the acceleration Phase, but different modulation growths throughout the Deceleration Phase due to different fill pressures (convergence ratios). At peak compression, the measured inner surface, areal-density nonuniformity σrms levels were 23±5 % for more-stable 18 atm fill targets and 53±11 % for less-stable 4 atm fill targets. The inner-surface modulations grow throughout the Deceleration Phase due to Rayleigh–Taylor instability and Bell–Plesset convergence effects. The nonuniformity at peak compression is sensitive to the initial perturbation level as measured in implosions with different laser-smoothing conditions.
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Rayleigh–Taylor instability in the Deceleration Phase of spherical implosion experiments
Physics of Plasmas, 2002Co-Authors: V. A. Smalyuk, V N Goncharov, J. A. Delettrez, F. J. Marshall, D. D. Meyerhofer, Susan Regan, T. C. Sangster, Richard Town, B. YaakobiAbstract:The temporal evolution of inner-shell modulations, unstable during the Deceleration Phase of a laser-driven spherical implosion, has been measured through K-edge imaging [B. Yaakobi et al., Phys. Plasmas 7, 3727 (2000)] of shells with titanium-doped layers. The main study was based on the implosions of 1 mm diam, 20 μm thick shells filled with either 18 atm or 4 atm of D3He gas driven with 23 kJ, 1 ns square laser pulses on OMEGA [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)]. These targets have similar modulation levels at the beginning of the Deceleration Phase due to similar modulation growths in the acceleration Phase, but different modulation growths throughout the Deceleration Phase due to different fill pressures (convergence ratios). At peak compression, the measured inner surface, areal-density nonuniformity σrms levels were 23±5 % for more-stable 18 atm fill targets and 53±11 % for less-stable 4 atm fill targets. The inner-surface modulations grow throughout the Deceleration Phase due to Ra...
