Hydrodynamic instabilities such as the Rayleigh–Taylor(RT)and Richtmyer–Meshkov instabilities disrupt inertial confinement fusion(ICF)implosions through the growth of 3D perturbations.Growth of these 3D imperfection...Hydrodynamic instabilities such as the Rayleigh–Taylor(RT)and Richtmyer–Meshkov instabilities disrupt inertial confinement fusion(ICF)implosions through the growth of 3D perturbations.Growth of these 3D imperfections at the interfaces of an ICF capsule during implosion lead to mixing between materials that is detrimental to performance.These instabilities have been studied extensively in planar geometry,but such experiments lack the effects of convergence in spherical implosions.While several studies have been performed in spherical geometry,these often lack a direct means to measure perturbation growth.Experiments in cylindrical geometry include convergence effects while maintaining direct diagnostic access.Although cylinders have less compression than spheres,they do provide an excellent platform to validate modeling for convergent geometries.The problem with previous cylindrical implosion experiments was that the convergence ratios were limited to∼4.With the National Ignition Facility(NIF),larger cylindrical targets can be driven to convergences of 10–15 while maintaining a large enough final diameter to measure perturbation growth.This paper reviews the design process used to both benchmark radiation hydrodynamics codes and enable 1D post-processed simulations to explore design space to separate compression effects from acceleration/deceleration RT instability.Results from 1D simulations suggest that cylindrical implosions on the NIF can produce high-convergence experiments to validate RT instability growth for ICF implosions.展开更多
Experiments have identified the Rayleigh–Taylor(RT)instability as one of the greatest obstacles to achieving inertial confinement fusion.Consequently,mitigation strategies to reduce RT growth and fuel–ablator mixing...Experiments have identified the Rayleigh–Taylor(RT)instability as one of the greatest obstacles to achieving inertial confinement fusion.Consequently,mitigation strategies to reduce RT growth and fuel–ablator mixing in the hotspot during the deceleration phase of the implosion are of great interest.In this work,the effect of seed magnetic fields on deceleration-phase RT growth are studied in planar and cylindrical geometries under conditions relevant to the National Ignition Facility(NIF)and Omega experiments.The magnetohydrodynamic(MHD)and resistive-MHD capabilities of the FLASH code are used to model imploding cylinders and planar blast-wave-driven targets.Realistic target and laser parameters are presented that suggest the occurrence of morphological differences in late-time RT evolution in the cylindrical NIF case and a measurable difference in spike height of single-mode growth in the planar NIF case.The results of this study indicate the need for target designs to utilize an RT-unstable foam–foam interface in order to achieve sufficient magnetic field amplification to alter RT evolution.Benchmarked FLASH simulations are used to study these magnetic field effects in both resistive and ideal MHD.展开更多
The problem of finding optimum semijoin sequ4ence of an arbitrary query under linear cost function for the transmission cost is NP.hard.Hence heuristic algorithms with desirable properties are explored.In this paper f...The problem of finding optimum semijoin sequ4ence of an arbitrary query under linear cost function for the transmission cost is NP.hard.Hence heuristic algorithms with desirable properties are explored.In this paper four properties of semijoin programs for distributed query processing are identified,The use of these properties in constructing semijoin sequence is justified.An existing algorithm is modified incorporating these properties.Empirical comparison with existing algorithms shows the superiority of the proposed algorithm.展开更多
基金This work used resources provided by Los Alamos National Laboratory,supported by the U.S Department of Energy National Nuclear Security Administration,operated by Los Alamos National Security,LLC(Contract No.DE-AC52-06NA25396)until November 2018and currently operated by Triad National Security,LLC(Contract No.89233218CNA000001).
文摘Hydrodynamic instabilities such as the Rayleigh–Taylor(RT)and Richtmyer–Meshkov instabilities disrupt inertial confinement fusion(ICF)implosions through the growth of 3D perturbations.Growth of these 3D imperfections at the interfaces of an ICF capsule during implosion lead to mixing between materials that is detrimental to performance.These instabilities have been studied extensively in planar geometry,but such experiments lack the effects of convergence in spherical implosions.While several studies have been performed in spherical geometry,these often lack a direct means to measure perturbation growth.Experiments in cylindrical geometry include convergence effects while maintaining direct diagnostic access.Although cylinders have less compression than spheres,they do provide an excellent platform to validate modeling for convergent geometries.The problem with previous cylindrical implosion experiments was that the convergence ratios were limited to∼4.With the National Ignition Facility(NIF),larger cylindrical targets can be driven to convergences of 10–15 while maintaining a large enough final diameter to measure perturbation growth.This paper reviews the design process used to both benchmark radiation hydrodynamics codes and enable 1D post-processed simulations to explore design space to separate compression effects from acceleration/deceleration RT instability.Results from 1D simulations suggest that cylindrical implosions on the NIF can produce high-convergence experiments to validate RT instability growth for ICF implosions.
基金This work was supported by the Office of Science of the U.S.Department of Energy under Award Nos.DE-SC0018993,DE-SC0016515,and DE-SC0022319the High Energy Density Laboratory Plasmas subprogram of the Fusion Energy Sciences program and under Award No.DE-SC0020055 by the Financial Assistance ProgramThis work was also supported through a Los Alamos National Laboratory subcontract to Virginia Tech under Contract No.463281.
文摘Experiments have identified the Rayleigh–Taylor(RT)instability as one of the greatest obstacles to achieving inertial confinement fusion.Consequently,mitigation strategies to reduce RT growth and fuel–ablator mixing in the hotspot during the deceleration phase of the implosion are of great interest.In this work,the effect of seed magnetic fields on deceleration-phase RT growth are studied in planar and cylindrical geometries under conditions relevant to the National Ignition Facility(NIF)and Omega experiments.The magnetohydrodynamic(MHD)and resistive-MHD capabilities of the FLASH code are used to model imploding cylinders and planar blast-wave-driven targets.Realistic target and laser parameters are presented that suggest the occurrence of morphological differences in late-time RT evolution in the cylindrical NIF case and a measurable difference in spike height of single-mode growth in the planar NIF case.The results of this study indicate the need for target designs to utilize an RT-unstable foam–foam interface in order to achieve sufficient magnetic field amplification to alter RT evolution.Benchmarked FLASH simulations are used to study these magnetic field effects in both resistive and ideal MHD.
文摘The problem of finding optimum semijoin sequ4ence of an arbitrary query under linear cost function for the transmission cost is NP.hard.Hence heuristic algorithms with desirable properties are explored.In this paper four properties of semijoin programs for distributed query processing are identified,The use of these properties in constructing semijoin sequence is justified.An existing algorithm is modified incorporating these properties.Empirical comparison with existing algorithms shows the superiority of the proposed algorithm.
