Emery, M. H.
Overview
Works:  17 works in 22 publications in 1 language and 23 library holdings 

Roles:  Author 
Publication Timeline
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Most widely held works by
M. H Emery
A Fully TwoDimensional Equilibrium and Transport Model of the Poloidal Divertor by M. H Emery(
Book
)
2 editions published in 1981 in English and held by 2 WorldCat member libraries worldwide
We have developed a fully twodimensional EulerianLagrangian nonideal MHD simulation model of tokamak discharges. The code is designed to simultaneously follow the resistive diffusion transport and gross dynamics of a magnetically confined plasma of arbitrary shape. It uses as a finitedifference mesh a general connectivity triangular grid. the triangular grid is the natural choice for a finitedifference mesh for modeling complicated geometries with interfaces, multiple magnetic axes and separatrices. We present here the methods we have developed to calculate equilibria and transport in a fully twodimensional geometry. The model is sufficiently general that is capable of calculating equilibria and transport given rather general plasma geometries and coil structures. Here we apply the model to the poloidal divertor system and describe the results
2 editions published in 1981 in English and held by 2 WorldCat member libraries worldwide
We have developed a fully twodimensional EulerianLagrangian nonideal MHD simulation model of tokamak discharges. The code is designed to simultaneously follow the resistive diffusion transport and gross dynamics of a magnetically confined plasma of arbitrary shape. It uses as a finitedifference mesh a general connectivity triangular grid. the triangular grid is the natural choice for a finitedifference mesh for modeling complicated geometries with interfaces, multiple magnetic axes and separatrices. We present here the methods we have developed to calculate equilibria and transport in a fully twodimensional geometry. The model is sufficiently general that is capable of calculating equilibria and transport given rather general plasma geometries and coil structures. Here we apply the model to the poloidal divertor system and describe the results
Lagrangian Simulation of TaylorCouette Flow by M. H Emery(
Book
)
2 editions published in 1981 in English and held by 2 WorldCat member libraries worldwide
We report on the development of a hydrodynamics code designed for the Lagrangian simulation of transient rotational flow phenomena. The code solves the incompressible, inviscid fluid equations in an axisymmetric, cylindrical coordinate system. The equations of motion are finite differenced on a general connectivity triangular mesh. Here we apply the model to the study of the transition from laminar Couette flow to Taylor vortex flow and obtain very good agreement with the linear theory. (Author)
2 editions published in 1981 in English and held by 2 WorldCat member libraries worldwide
We report on the development of a hydrodynamics code designed for the Lagrangian simulation of transient rotational flow phenomena. The code solves the incompressible, inviscid fluid equations in an axisymmetric, cylindrical coordinate system. The equations of motion are finite differenced on a general connectivity triangular mesh. Here we apply the model to the study of the transition from laminar Couette flow to Taylor vortex flow and obtain very good agreement with the linear theory. (Author)
Stability and symmetry in inertialconfinement fusion(
Book
)
2 editions published in 1982 in English and held by 2 WorldCat member libraries worldwide
The asymmetries of spherical implosions driven by direct laser illuminations are of fundamental concern to the inertial confinement fusion community because they provide severe limitations on high gain pellet designs. Theoretical progress on several fronts has recently been made through numerical simulations in providing a more complete understanding of the physical processes involved in these asymmetries and instabilities. The results also suggest methods of controlling these processes and their implications for laser fusion systems design. Stability and symmetry issues have been investigated. Laser matter coupling and scaling laws relating the asymmetry results to spherical pellet designs have been investigated. Principle results include finding (1) the requirements for thermal smoothing of laser nonuniformities, (2) reduced RayleighTaylor growth rates and saturation via the nonlinear KelvinHelmholtz rollup, (3) that perturbation wavelengths greater than the shell thicknesses are most likely to cause an asymmetric implosion, (4) a new theory based on vortex shedding that explains the reduced linear RayleighTaylor growth rates and (5) a possible wavelengthintensity window for direct illumination where the requirements of pellet velocity, symmetry, and efficiency necessary for high gain can be simultaneously met
2 editions published in 1982 in English and held by 2 WorldCat member libraries worldwide
The asymmetries of spherical implosions driven by direct laser illuminations are of fundamental concern to the inertial confinement fusion community because they provide severe limitations on high gain pellet designs. Theoretical progress on several fronts has recently been made through numerical simulations in providing a more complete understanding of the physical processes involved in these asymmetries and instabilities. The results also suggest methods of controlling these processes and their implications for laser fusion systems design. Stability and symmetry issues have been investigated. Laser matter coupling and scaling laws relating the asymmetry results to spherical pellet designs have been investigated. Principle results include finding (1) the requirements for thermal smoothing of laser nonuniformities, (2) reduced RayleighTaylor growth rates and saturation via the nonlinear KelvinHelmholtz rollup, (3) that perturbation wavelengths greater than the shell thicknesses are most likely to cause an asymmetric implosion, (4) a new theory based on vortex shedding that explains the reduced linear RayleighTaylor growth rates and (5) a possible wavelengthintensity window for direct illumination where the requirements of pellet velocity, symmetry, and efficiency necessary for high gain can be simultaneously met
Comparison of various numerical solutions to the nonlinear vlasov equation by M. H Emery(
Book
)
1 edition published in 2013 in English and held by 2 WorldCat member libraries worldwide
1 edition published in 2013 in English and held by 2 WorldCat member libraries worldwide
Simulation of Laser Beam Nonuniformity Effects(
Book
)
2 editions published in 1981 in English and held by 2 WorldCat member libraries worldwide
We investigate the effect of a nonuniform beam on the ablative acceleration of thin foils using the FAST2D lasershell simulation code. The results show that laser nonuniformities with scalelengths greater than the distance from the ablation surface to the critical surface would have a severe impact on drive pressure symmetry and hence on pellet gain. (Author)
2 editions published in 1981 in English and held by 2 WorldCat member libraries worldwide
We investigate the effect of a nonuniform beam on the ablative acceleration of thin foils using the FAST2D lasershell simulation code. The results show that laser nonuniformities with scalelengths greater than the distance from the ablation surface to the critical surface would have a severe impact on drive pressure symmetry and hence on pellet gain. (Author)
The nonlinear aspects of the RayleighTaylor instability in laser ablation by M. H Emery(
Book
)
2 editions published in 1982 in English and held by 2 WorldCat member libraries worldwide
We report on our investigation of the RayleighTaylor (RT) and KelvinHelmholtz (KH) instabilities in laser ablatively accelerated targets for single mode perturbations for a series of wavelengths in the parameter regime 1/2 less than or equal to lambda/delta R less than or equal to 10, where lambda is the wavelength of the perturbation and delta is the cold foil thickness. We find linear growth rates well below classical values (by a factor on the order of 34). We also find a cutoff in the growth rates for wavelengths less than the foil thickness. The striking result is the dominance of nonlinear effects; i.e., the KH instability for short wavelength perturbations. Although the linear growth rates increase as k1/2 up to the cutoff, the KH rollup dominates at large k, drastically reducing the penetration rate of the dense spike below its free fall value and effectively doubling the aspect ratio of the foil. In other words, it is the long wavelength perturbations that are most effective in destroying the symmetric implosion of the shell
2 editions published in 1982 in English and held by 2 WorldCat member libraries worldwide
We report on our investigation of the RayleighTaylor (RT) and KelvinHelmholtz (KH) instabilities in laser ablatively accelerated targets for single mode perturbations for a series of wavelengths in the parameter regime 1/2 less than or equal to lambda/delta R less than or equal to 10, where lambda is the wavelength of the perturbation and delta is the cold foil thickness. We find linear growth rates well below classical values (by a factor on the order of 34). We also find a cutoff in the growth rates for wavelengths less than the foil thickness. The striking result is the dominance of nonlinear effects; i.e., the KH instability for short wavelength perturbations. Although the linear growth rates increase as k1/2 up to the cutoff, the KH rollup dominates at large k, drastically reducing the penetration rate of the dense spike below its free fall value and effectively doubling the aspect ratio of the foil. In other words, it is the long wavelength perturbations that are most effective in destroying the symmetric implosion of the shell
Comparison of RayleighTaylor Growth with 1.0 Micrometers and 0.25 Micrometers Lasers(
Book
)
1 edition published in 1986 in English and held by 1 WorldCat member library worldwide
It is shown, through numerical simulation that the RayleighTaylor growth rate in laserablatively accelerated targets is reduced below the classical value (kg) to the 1/2 power, by factors of 34 with 0.25 micrometer laser light. The simulation results are supported by an analytical expression for the growth rates. These results provide further evidence for the viability of highaspect ratio shells in directdrive laser fusion. Keywords: Laser ablation, Hydrodynamic instability
1 edition published in 1986 in English and held by 1 WorldCat member library worldwide
It is shown, through numerical simulation that the RayleighTaylor growth rate in laserablatively accelerated targets is reduced below the classical value (kg) to the 1/2 power, by factors of 34 with 0.25 micrometer laser light. The simulation results are supported by an analytical expression for the growth rates. These results provide further evidence for the viability of highaspect ratio shells in directdrive laser fusion. Keywords: Laser ablation, Hydrodynamic instability
Experimental Methods for Studying the RayleighTaylor Instability of Ablatively Accelerated Targets(
Book
)
1 edition published in 1983 in English and held by 1 WorldCat member library worldwide
The authors describe new diagnostic methods for the study of hydrodynamic instabilities in ablatively accelerated targets. These methods include faceon xray backlighting that does not require a backlighting laser beam (for growth rate measurement), and a tracer dot technique (for tracking ablation plasma flow). The targets in the experiments are periodically perturbed to provide initial conditions for the growth of the RayleighTaylor instability. (Author)
1 edition published in 1983 in English and held by 1 WorldCat member library worldwide
The authors describe new diagnostic methods for the study of hydrodynamic instabilities in ablatively accelerated targets. These methods include faceon xray backlighting that does not require a backlighting laser beam (for growth rate measurement), and a tracer dot technique (for tracking ablation plasma flow). The targets in the experiments are periodically perturbed to provide initial conditions for the growth of the RayleighTaylor instability. (Author)
The RayleighTaylor and KelvinHelmholtz instabilities in targets accelerated by laser ablation by M. H Emery(
Book
)
1 edition published in 1981 in English and held by 1 WorldCat member library worldwide
1 edition published in 1981 in English and held by 1 WorldCat member library worldwide
Hydrodynamic Target Response to an Induced Spatial IncoherenceSmoothed Laser Beam(
Book
)
1 edition published in 1991 in English and held by 1 WorldCat member library worldwide
One of the critical elements for high gain target designs is the high degree of symmetry that must be maintained in the implosion process. The induced spatial incoherence (ISI) concept has some promise for reducing ablation pressure nonuniformities to about 1%. The ISI method produces a spatial irradiance profile that undergoes large random fluctuations on picosecond time scales but is smooth on long time scales. The ability of the ISI method to produce a nearly uniform ablation pressure is contingent on both temporal smoothing and thermal diffusion. In the startup phase of a shaped reactorlike laser pulse, the target is directly illuminated by the laser light and thermal diffusion is not effective at smoothing residual nonuniformities in the laser beam. During this period in the laser pulse, the target response is dominated by the initial shock generated by the laser pulse and the results indicate that this first shock can be the determining factor in the success or failure of the implosion process. The results of numerical simulations of several target/laser pulse designs which were investigated in an attempt to mitigate the impact of the initial shock structure stemming from the early temporal phase of an ISI smoothed laser beam are presented. It is shown that foam like layers, multiple laser wavelengths and shallow angles of incidence can sharply reduce the perturbation level stemming from the first shock
1 edition published in 1991 in English and held by 1 WorldCat member library worldwide
One of the critical elements for high gain target designs is the high degree of symmetry that must be maintained in the implosion process. The induced spatial incoherence (ISI) concept has some promise for reducing ablation pressure nonuniformities to about 1%. The ISI method produces a spatial irradiance profile that undergoes large random fluctuations on picosecond time scales but is smooth on long time scales. The ability of the ISI method to produce a nearly uniform ablation pressure is contingent on both temporal smoothing and thermal diffusion. In the startup phase of a shaped reactorlike laser pulse, the target is directly illuminated by the laser light and thermal diffusion is not effective at smoothing residual nonuniformities in the laser beam. During this period in the laser pulse, the target response is dominated by the initial shock generated by the laser pulse and the results indicate that this first shock can be the determining factor in the success or failure of the implosion process. The results of numerical simulations of several target/laser pulse designs which were investigated in an attempt to mitigate the impact of the initial shock structure stemming from the early temporal phase of an ISI smoothed laser beam are presented. It is shown that foam like layers, multiple laser wavelengths and shallow angles of incidence can sharply reduce the perturbation level stemming from the first shock
Observation of RayleighTaylorLike Structures in a LaserAccelerated Foil(
Book
)
1 edition published in 1984 in English and held by 1 WorldCat member library worldwide
Laseraccelerated targets have been predicted to be subject to the RayleighTaylor hydrodynamic instability. The development of the instability was studied by introducing mass thickness variations in foil targets and observing the development of the target nonuniformities by sideon flash x radiography. Observations were made of target structures and mass redistribution effects which resemble RayleighTaylor bubbles and spikes, including not only advanced broadening of the spike tips on the laserirradiated side of the foil but also projections of mass on the unirradiated side. The observations compare well with numerical simulations. (Author)
1 edition published in 1984 in English and held by 1 WorldCat member library worldwide
Laseraccelerated targets have been predicted to be subject to the RayleighTaylor hydrodynamic instability. The development of the instability was studied by introducing mass thickness variations in foil targets and observing the development of the target nonuniformities by sideon flash x radiography. Observations were made of target structures and mass redistribution effects which resemble RayleighTaylor bubbles and spikes, including not only advanced broadening of the spike tips on the laserirradiated side of the foil but also projections of mass on the unirradiated side. The observations compare well with numerical simulations. (Author)
Measurement of Areal Mass Variation in RayleighTaylor Unstable Targets(
Book
)
1 edition published in 1984 in English and held by 1 WorldCat member library worldwide
We present the first measurements of Rayleigh Taylor caused mass redistribution resolved in two spatial dimensiona. Bubble and spike formation and two dimensional effects have been observed. Results are consistent with theory which claims that the Rayleigh Taylor growth rate is about 1/2 of classical
1 edition published in 1984 in English and held by 1 WorldCat member library worldwide
We present the first measurements of Rayleigh Taylor caused mass redistribution resolved in two spatial dimensiona. Bubble and spike formation and two dimensional effects have been observed. Results are consistent with theory which claims that the Rayleigh Taylor growth rate is about 1/2 of classical
The RayleighTaylor and KelvinHelmholtz Instabilites in Targets Accelerated by Laser Ablation(
Book
)
1 edition published in 1981 in English and held by 1 WorldCat member library worldwide
Using the FAST2D lasershell simulation model we have accelerated a 20 micrometer thick plastic foil up to 160 km/s. The foil maintained its integrity up to 10 ns giving an aspect ratio of 40. We are able to follow the RayleighTaylor bubbleandspike development far into the nonlinear regime and beyond the point of foil fragmentation. Strong shear flow develops at the interface between the bubbleandspike which leads to the development of the KelvinHelmholtz instability. The KH instability causes the tips of the spikes to widen and as a result reduce their rate of 'fall.' (Author)
1 edition published in 1981 in English and held by 1 WorldCat member library worldwide
Using the FAST2D lasershell simulation model we have accelerated a 20 micrometer thick plastic foil up to 160 km/s. The foil maintained its integrity up to 10 ns giving an aspect ratio of 40. We are able to follow the RayleighTaylor bubbleandspike development far into the nonlinear regime and beyond the point of foil fragmentation. Strong shear flow develops at the interface between the bubbleandspike which leads to the development of the KelvinHelmholtz instability. The KH instability causes the tips of the spikes to widen and as a result reduce their rate of 'fall.' (Author)
RayleighTaylor instability in ablatively accelerated targets with 1, 1/2, and 1/4 um laser light by M. H Emery(
Book
)
1 edition published in 1987 in English and held by 1 WorldCat member library worldwide
1 edition published in 1987 in English and held by 1 WorldCat member library worldwide
Analysis of Stability and Symmetry Implications for ICF(
Book
)
1 edition published in 1983 in English and held by 1 WorldCat member library worldwide
Pellet gains in excess of 100 will probably be necessary for most applications of inertial fusion. In order to achieve these high gains a number of critical physics elements must be controlled. These include (1) high coupling efficiency, (2) low fuel preheat, (3) implosion symmetry, (4) implosion stability (ablation pressure) and (5) an ignition scheme. These factors interact with each other providing conflicting requirements. The purpose of this paper is to report on the theoretical and computational work that has been carried out in connection with the experimental work at NRL in evaluating the design constraints that are imposed primarily by the symmetry and stability requirements on directly driven laser fusion targets
1 edition published in 1983 in English and held by 1 WorldCat member library worldwide
Pellet gains in excess of 100 will probably be necessary for most applications of inertial fusion. In order to achieve these high gains a number of critical physics elements must be controlled. These include (1) high coupling efficiency, (2) low fuel preheat, (3) implosion symmetry, (4) implosion stability (ablation pressure) and (5) an ignition scheme. These factors interact with each other providing conflicting requirements. The purpose of this paper is to report on the theoretical and computational work that has been carried out in connection with the experimental work at NRL in evaluating the design constraints that are imposed primarily by the symmetry and stability requirements on directly driven laser fusion targets
Vortex Shedding and Laser Ablation(
Book
)
1 edition published in 1983 in English and held by 1 WorldCat member library worldwide
Through a critical examination of the vortex dynamics of laser ablatively accelerated targets the author was able to explain the inhibited linear RayleighTaylor growth rates, clarify the role fo the KelvinHelmholtz rollup, explain the short wavelength cutoff, explain and theoretically reproduce dynamically stabilized growth rates and predict magnetic field structures throughout the overdense region which lead to a physically motivated model of thermal flux inhibition
1 edition published in 1983 in English and held by 1 WorldCat member library worldwide
Through a critical examination of the vortex dynamics of laser ablatively accelerated targets the author was able to explain the inhibited linear RayleighTaylor growth rates, clarify the role fo the KelvinHelmholtz rollup, explain the short wavelength cutoff, explain and theoretically reproduce dynamically stabilized growth rates and predict magnetic field structures throughout the overdense region which lead to a physically motivated model of thermal flux inhibition
SelfGenerated Magnetic Fields and Thermal Flux Inhibition(
Book
)
1 edition published in 1984 in English and held by 1 WorldCat member library worldwide
We show that the observed thermal flux inhibition in high intensity, short pulse laserplasma interaction experiments can stem directly from the strong magnetic fields generated at the ablation layer as a result of laser asymmetries. The selfconsistent modeling of magnetized thermal transport in this environment shows strong thermal flux inhibition as manifested by reduced ablation pressures, reduced implosion velocities, reduced classical absorption, density profile flattening and reduced mass ablation rates. (Author)
1 edition published in 1984 in English and held by 1 WorldCat member library worldwide
We show that the observed thermal flux inhibition in high intensity, short pulse laserplasma interaction experiments can stem directly from the strong magnetic fields generated at the ablation layer as a result of laser asymmetries. The selfconsistent modeling of magnetized thermal transport in this environment shows strong thermal flux inhibition as manifested by reduced ablation pressures, reduced implosion velocities, reduced classical absorption, density profile flattening and reduced mass ablation rates. (Author)
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