Gardner, John H.Overview
Publication Timeline
Most widely held works about
John H Gardner
Most widely held works by
John H Gardner
Contributions in chemistry
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Book
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1 edition published in 1932 in English and held by 1 library worldwide
The First Presbyterian Church of Baltimore
by John H Gardner
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Book
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1 edition published in 1962 in English and held by 1 library worldwide
Fusion : power program at Brigham Young University
by John H Gardner
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Book
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1 edition published in 1974 in English and held by 1 library worldwide
Book review of] The faith of a scientist, by Henry Eyring
by John H Gardner
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Book
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1 edition published in 1968 in English and held by 1 library worldwide
book review of] Population, resources, and the future: non-Malthusian perspective
by John H Gardner
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Book
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1 edition published in 1973 in English and held by 1 library worldwide
Reduction of Early-Time Perturbation Growth in Ablatively Driven Laser Targets Using Tailored Density Profiles
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Book
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1 edition published in 1999 in English and held by 1 library worldwide We investigate analytically and numerically the effects of tailoring the density profile in a laser target in order to decrease imprinting of mass perturbations due to the long-wavelength modes. Inverting the acceleration of the ablation front during the shock transit time could reduce the early-time mass perturbation amplitudes developed in the target after the shock transit. This principle was first suggested for mitigating the RT instability of imploding Z-pinches [Velikovich et al., Phys. Rev. Lett. 77, 853 (1996); Phys. Plasmas 5, 3377 (1998)]. As the shock wave slows down propagating into higher density layers, the effective gravity near the ablation front has the same direction as the density gradient. This makes the mass perturbations near it oscillate at a higher frequency and at a lower amplitude than they normally would due to the "rocket effect" caused by mass ablation [Sanz, Phys. Rev. Lett. 73, 2700 (1994); Piriz et al., Phys. Plasmas 4, 1117 (1997)]. So, tailoring density profiles instead of using flat densities is demonstrated to reduce the "seed" mass perturbation amplitude at the onset of the exponential RT growth.
Feedout and Richtmyer-Meshkov Instability at Large Density Difference
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Book
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1 edition published in 2001 in English and held by 1 library worldwide The feedout process transfers mass perturbations from the rear to the front surface of a driven target, producing the seed for the Rayleigh-Taylor (RT) instability growth. The feedout mechanism is investigated analytically and numerically for the case of perturbation wavelength comparable to or less than the shock-compressed target thickness. The lateral mass flow in the target leads to oscillations of the initial mass non-uniformity before the reflected rippled rarefaction wave breaks out, which may result in RT bubbles produced at locations where the areal mass was initially higher. This process is determined by the evolution of hydrodynamic perturbations in the rippled rarefaction wave, which is not the same as the Richtmyer-Meshkov (RM) interfacial instability. An exact analytical formula is derived for the time-dependent mass variation in a rippled rarefaction wave, and explicit estimates are given for the time of first phase reversal and frequency of the oscillations. The limiting transition from the case of RM perturbation growth at large density difference "low ambient density behind the rear surface" to the case of feedout "zero density" is studied, and it is shown that the latter limit is approached only if the ambient density is extremely low, less than 1/1000 of the pre-shock target density.
Laser Imprint Reduction with a Short Shaping Laser Pulse Incident Upon a Foam-Plastic Target
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Book
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1 edition published in 2002 in English and held by 1 library worldwide In the previous work [Metzler et al., Phys. Plasmas 6, 3283 "1999"] it was shown that a tailored density profile could be very effective in smoothing out the laser beam non-uniformities imprinted into a laser-accelerated target. However, a target with a smoothly graded density is difficult to manufacture. A method of dynamically producing a graded density profile with a short shaping laser pulse irradiating a foam layer on top of the payload prior to the drive pulse is proposed. It is demonstrated that the intensity and the duration of the shaping pulse, the time interval between the shaping pulse and the drive pulse, and the density ratio between the foam and the payload can be selected so that the laser imprint of the drive pulse is considerably suppressed without increasing the entropy of the payload. The use of the foam-plastic target and a shaping pulse reduces the imprinted mass perturbation amplitude by more than an order of magnitude compared to a solid plastic target. The requirements to the smoothing of the drive and shaping laser beams and to the surface finish of the foam-plastic sandwich target are discussed.
A Simple Model for Dissociation of Diatomic Molecules
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Book
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1 edition published in 1997 in English and held by 1 library worldwide A simple model for dissociation of diatomic molecules was implemented in the equation of state which is currently in use in the 'FAST' code at NRL. Hugoniot curve, obtained with this equation of state is compared with experimental results.
LCPFCT-A Flux-Corrected Transport Algorithm for Solving Generalized Continuity Equations
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Book
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1 edition published in 1993 in English and held by 1 library worldwide Flux-Corrected Transport has proven to be an accurate and easy to use an algorithm to solve nonlinear, time-dependent continuity equations of the type which occur in fluid dynamics, reactive, multiphase, and elastic plastic flows, plasmadynamics, and magnetohydrodynamics. This report updates and supersedes a previous report entitled Flux-Corrected Transport Modules for Solving Generalized Continuity Equations. It can be used as a user manual for subroutines and test programs included in the appendices. The entire LCPFCT library in its most recent from is presented and discussed in detail. There are, in addition, discussions of more general topics such as the application of physical boundary conditions, physical positivity and numerical diffusion which help to put the numerical aspects to this subroutine library in context.
Shock-Free Acceleration of Laser Driven Targets
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Book
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1 edition published in 1992 in English and held by 1 library worldwide The ability of recently developed laser smoothing techniques to produce uniform ablation pressures is strongly contingent on the degree of thermal smoothing. Thermal smoothing is not effective at reducing residual laser nonuniformities during the start up phase of a shaped, reactor-like laser pulse. The impact of the first shock can be diminished by adiabatically compressing the target with a temporally long, slowly rising laser pulse. This Memorandum Report discusses an elastic-plastic laser-matter-interaction model and shows that a shock-free, induced spatial incoherence-smoothed laser pulse can accelerate a target to nearly the conditions required for uniform implosion.
Numerical Simulations of Flowfields in a Central-Dump Ramjet Combustor. 3. Effects of Chemistry
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Book
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1 edition published in 1990 in English and held by 1 library worldwide This report is the third in a series which presents the results of numerical simulations performed to isolate and study acoustic-vortex-chemical interactions in an idealized ramjet consisting of an axisymmetric inlet and combustor and a choked nozzle. Both reactive and nonreactive flows have been simulated. The nonreactive flow calculations show complex interactions among the natural instability frequency of the shear layer at the inlet-combustor junction and the acoustics of both the inlet and the combustor. The entire flow oscillates at a low frequency which corresponds to that of a quarter-mode in the inlet. For the reactive flow cases studied, energy release alters the flow field substantially. Energy release in a large vortex is in phase with the pressure oscillation over a substantial region of the combustor and results in the observed amplification of the low-frequency oscillations and leads to combustion instability. The large pressure oscillation also modifies the vortex shedding process. Keywords: Ramjet, Turbulence, Combustion instability. (jes).
The Rayleigh-Taylor Instability in Ablatively Accelerated Targets with 1, 1/2 and 1/4 Micrometers Laser Light
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Book
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1 edition published in 1987 in English and held by 1 library worldwide The results of a series of detailed numerical simulations are presented for the Rayleigh-Taylor instability in laser ablatively accelerated targets for a fairly wide range of initial conditions. It is shown that the Rayleigh-Taylor growth rate in an ablative environment is a strong function of the laser wavelength. For perturbation wavelengths about 3 times the inflight target thickness, the ratios of the numerical growth rates to the classical growth rates are of the order of 1/1.5, 1/2.5 and 1/3.5 for 1, 1/2 and 1/4 micrometer laser light respectively. The numerical results are in good agreement with out theoretical based on the ablative convection of vorticity away from the unstable ablation front. These results provide strong evidence for the viability of high aspect ratio shells in direct drive laser fusion. Keywords: Laser ablation; Inertial confinement fusion; Hydrodynamic instabilities.
Hydrodynamic Aspects of the Split-Foil Laser Target Design
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Book
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1 edition published in 1986 in English and held by 1 library worldwide Hydrodynamic simulations of exploding copper foils, which are irradiated on one side by 1.06 micron laser light, indicated that peak axial electron number density is more easily controlled with split-foil target design. Results from a series of simulations with solid copper foils that range in width from 500A to 1500A show that while peak electron temperature and time of burnthrough can be varied, evolved electron number densities are approximately bounded from above by 3 X 10 to the 20th power particles/cc. By increasing foil thickness to 1 micron and introducing aa slit on the foil axis of 100 micron width, uniform plasmas with electron number densities on the order of 6 X 10 to the 20th power particles/cc can be generated. Essentially the same results are obtained from simulations with split selenium foils. Keywords: X-ray lasers, Laser-matter interactions, Hydrodynamic simulation.
High Efficiency Targets for High Gain Inertial Confinement Fusion
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Book
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1 edition published in 1986 in English and held by 1 library worldwide Rocket efficiencies as high as 15% are possible using short wavelength lasers and moderately high aspect ratio pellet designs. These designs are made possible by two recent breakthroughs in physics constraints. First is the development of the Induced Spatial Incoherence (ISI) technique which allows uniform illumination of the pellet and relaxes the constraint of thermal smoothing, permitting the use of short wavelength laser light. Second is the discovery that the Rayleigh Taylor growth rate is considerably reduced at the short laser wavelengths. By taking advantage of the reduced constraints imposed by nonuniform laser illumination and Rayleigh Taylor instability, pellets using 1/4 micron laser light and initial aspect ratios of about 10 (with in flight aspect ratios of about 150-200) may produce energy gains as high as 200-250.
A Review of Research in Chemical-Acoustic Coupling
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Book
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1 edition published in 1983 in English and held by 1 library worldwide In this review we have summarized previous research in chemical-acoustic interactions and extracted from it those elements which may be most important to reactive flows of exothermic materials. (Author).
Linear Stability of Self-Similar Flow. 8. Imploding Cylindrical and Spherical Shocks in the C-C-W Approximation
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Book
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1 edition published in 1980 in English and held by 1 library worldwide Analytical and computational techniques are developed to investigate the stability of converging shock waves in cylindrical and spherical geometry. The linearized Chester-Chisnell-Whitham (C-C-W) equations describing the evolution of an arbitrary perturbation about an imploding shock wave in an ideal fluid are solved exactly in the strong-shock limit for a density profile rho(r) approx (r to the -q power). All modes are found to be relatively unstable (i.e., the ratio of perturbation amplitude to shock radius diverges as the latter goes to zero), provided that q is not too large. The nonlinear C-C-W equations are solved numerically for both moderate and strong shocks. The small-amplitude limit agrees with the analytical results, but some forms of perturbation which are stable at small amplitude become unstable in the nonlinear regime. The results are related to the problem of pellet compression in experiments on inertial confinement fusion. (Author).
Thermospheric Propagation of Sonic Booms from the Concorde Supersonic Transport
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Book
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1 edition published in 1979 in English and held by 1 library worldwide A nonlinear theory for the long-range propagation of sonic booms through the thermosphere has been developed. Arealistic atmosphere is employed, and consideration is given to such factors as nonlinear stretching and decay of the wave, the effects of the caustic, the linear acoustic attenuation, and the increase in Mach number due to the decreasing density at high altitudes, detailed results are presented for the case of the Concorde SST in straight, level and steady flight at 17.5 km and a velocity of Mach 2. We predict maximum ground level pressures of 0.3 Pa with an N-wave period of about 10 seconds. The sound level is a minimum along the flight track with the maximum signal strength occurring about 300 km off the flight track. The strongest received signal travels Initially downward and reflects off the surface of the ocean to thermosphere. The wave turns around at an altitude of 160 km and is returned back to the ground at a horizontal distance of 320 km from the launch point. The acoustic Mach number of the wave never exceeds 0.2. Ninety percent of the wave's energy is attenuated below 100 km with 99% attenuated by the time the wave reaches the turning the turning point. (Author).
The study of a method to reduce electron density in the ionospheric d-region by means of high-powered ground-based transmitters
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Book
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1 edition published in 1962 in English and held by 1 library worldwide
On the production of and scatter propagation from artificial irregularities in the ionospheric d-layer
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Book
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1 edition published in 1962 in English and held by 1 library worldwide The possibility of utilizing irregularities produced in the ionospheric D-layer by rf heating or by intense optical radiation from lasers to enhance forward scatter propagation is considered. It is shown that, on the assumption that a reduction of electron density by a factor of two can be achieved at 70 km by rf heating with a one megawatt beam of 1 degree half-power width as calculated by Molmud, forward scatter propagation with reduction in power of about 50 db from line-of-sight propagation can be achieved for a disturbed ionosphere. If lasers are used to lay out a diffraction grating in the D-layer, similar results may be achieved with the received power proportional to the square of the number of grating lines and with the additional possibility of utilizing high-order spectra of the grating. (Author). more
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