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Low aspect ratio double shell targets for high density and high gain and a comparison with ultra thin shells

Description: Double shell targets may have decisive advantages over single shells for achieving a number of goals in the laser fusion program. With 0.2 ..mu.. light, such designs achieve 500 to 1000 times liquid density at 2 kJ absorbed; 10 percent or more of breakeven at 15 kJ absorbed, and gains of 10 or more at 200 kJ absorbed. These targets are relatively insensitive to preheat, laser pulse shape, and hydrodynamic instability. A double shell in which the outer pusher is fuel may achieve a gain of 1000 for lasers in the 1 to 10 megajoule size. Ultra thin targets have only about a factor of two reduction in power shells with aspect ratios of 2 to 4 while requiring about the same input energy and achieving about the same gain. Their extreme sensitivity to preheat, symmetry, and hydrodynamic instability makes them unattractive for targets in advanced lasers systems.
Date: September 20, 1977
Creator: Lindl, J.D.
Partner: UNT Libraries Government Documents Department

Progress on achieving the ICF conditions needed for high gain

Description: Progress during the past two years has moved us much closer to demonstrating the scientific and technological requirements for high gain ICF in the laboratory. This progress has been made possible by operating at the third harmonic of 1..mu..m light which dramatically reduces concern about hot electrons and by advances in diagnostics such as 100 ps x-ray framing cameras which greatly increase the data available from each experiment. Making use of many of these new capabilities, major improvements in confinement conditions have been achieved for ICF implosions. In particular, in an optimized hohlraum on Nova, radiation driven implosions with convergence ratio in excess of 30 (volume compression /approximately/3 /times/ 10/sup 4/) have performed essentially as predicted by spherical implosion calculations. This paper presents these results as well as examples of advances in several other areas and discusses the implications for the future of ICF with lasers and heavy ion beam drivers. 8 refs., 10 figs.
Date: December 23, 1988
Creator: Lindl, J.D.
Partner: UNT Libraries Government Documents Department

Models of electron conductivity which lead to ablation stabilization of fluid instabilities in laser-driven implosions

Description: LASNEX calculations with a modified electron conductivity show the existence of a firepolishing stabilization effect. By modifying the thermal conductivity so that K $alpha$ T/sup n//rho/sup m/, one is able to construct a situation in which the electrons deposit their energy in a thin layer at the ablation surface and closely match the zero order solutions assumed earlier. The firepolishing effect appears to require that a significant fraction of the total pressure be due to the ablation process itself rather than the thermal pressure in the corona gas. It also requires KL approximately 1 where L is the scale height for decay of thermal perturbations generated at the ablation surface. For classical electron conductivity, because the thermal flux depends linearly on the grams/cm$sup 2$ necessary to stop the electrons, (1/rho) nabla rho approximately (1/T) nabla T near the ablation surface so that the pressure is nearly constant across the ablation surface. Hence there is no ablation pressure as such and no firepolishing effect for electron-driven implosions. (auth)
Date: October 17, 1975
Creator: Lindl, J.D. & Mead, W.C.
Partner: UNT Libraries Government Documents Department

Low power multiple shell fusion targets for use with electron and ion beams

Description: Use of double shell targets with a separate low Z, low density ablator at large radius for the outer shell, reduces the focusing and power requirements while maintaining reasonable aspect ratios. A high Z, high density pusher shell is placed at a much smaller radius in order to obtain an aspect ratio small enough to protect against fluid instability. Velocity multiplication between these shells further lowers the power requirements. Careful tuning of the power profile and intershell density results in a low entropy implosion which allows breakeven at low powers. Ion beams appear to be a promising power source and breakeven at 10-20 Terrawatts with 10 MeV alpha particles appears feasible. Predicted performance of targets with various energy sources is shown and comparison is made with single shell targets. (auth)
Date: October 10, 1975
Creator: Lindl, J.D. & Bangerter, R.O.
Partner: UNT Libraries Government Documents Department

Behavior of fluid instabilities in laser fusion pellets: results of 2-D calculations

Description: Two-dimensional Lagrangian hydrodynamics simulation techniques were used to study fluid instability in laser fusion pellets. A slab geometry comparison with classical Rayleigh-Taylor theory shows good agreement, as do other slab and spherical test problems over a wide range of accelerations and wavelengths. Isentropic ablative accelerations exhibit growth rates 50 percent-100 percent of classical values, while non-isentropic cases show suppressed growth. Design optimization at 100 kJ input energy has led to an impulsively accelerated, low- aspect-ratio shell which operates successfully with a surface perturbation of a few tens of angstroms. Comparison of simulations with present experiments indicates that current neutron-producing targets are insensitive to damage from fluid instability. (auth)
Date: July 1, 1975
Creator: Mead, W.C. & Lindl, J.D.
Partner: UNT Libraries Government Documents Department

Physics of ignition for ICF capsules

Description: The implosion of an ICF capsule must accomplish both compression of the main fuel to several hundred grams per cubic centimeter and heating and compression of the central region of the fuel to ignition. This report discusses the physics of these conditions.
Date: March 13, 1989
Creator: Lindl, J.D.
Partner: UNT Libraries Government Documents Department

Introduction to the physics of ICF capsules

Description: Inertial Confinement Fusion is an approach to fusion which relies on the inertia of the fuel mass to provide confinement. To achieve conditions under which this confinement is sufficient for efficient thermonuclear burn, high gain ICF targets designed to be imploded directly by laser light. These capsules are generally a spherical shell which is filled with low density DT gas. The shell is composed of an outer region which forms the ablator and an inner region of frozen or liquid DT which forms the main fuel. Energy from the driver is delivered to the ablator which heats up and expands. As the ablator expands and blows outward, the rest of the shell is forced inward to conserve momentum. In this implosion process, several features are important. We define the in-flight-aspect-ratio (IFAR) as the ratio of the shell radius R as it implodes to its thickness {Delta}R. Hydrodynamic instabilities during the implosion impose limits on this ratio which results in a minimum pressure requirement of about 100 Mbar. The convergence ratio is defined as the ratio of the initial outer radius of the ablator to the final compressed radius of the hot spot. This hot spot is the central region of the compressed fuel which is required to ignite the main fuel in high gain designs. Typical convergence ratios are 30--40. To maintain a nearly spherical shape during the implosion, when convergence ratios are this large, the flux delivered to the capsule must be uniform to a few percent. The remainder of this paper discusses the conditions necessary to achieve thermonuclear ignition in these ICF capsules.
Date: March 13, 1989
Creator: Lindl, J.D.
Partner: UNT Libraries Government Documents Department

Symmetry issues in a class of ion beam targets using sufficiently short direct drive pulses

Description: Controlling asymmetries in direct drive ion beam targets depends upon the ability to control the effects of residual target asymmetries after an appropriate illumination scheme has already been utilized. A class of modified ion beam targets where residual asymmetries are ameliorated is considered. The illumination scheme used is an axially symmetric one convenient for reactor designs. Residual asymmetries are controlled by limiting the radial motion of the radius R/sub dep/ of peak ion energy deposition. Limiting the motion of R/sub dep/ is achieved by lengthening the time scale t/sub s/ where changes in R/sub dep/ adversely affect asymmetries. In our example, t/sub s/ becomes longer than the duration ..delta..t/sub D/ of the entire direct drive pulse train (t/sub s/ > ..delta..t/sub D/).
Date: October 23, 1986
Creator: Mark, J.W.K. & Lindl, J.D.
Partner: UNT Libraries Government Documents Department

Symmetry issues in a class of ion beam targets using short direct drive pulses

Description: We address a class of modified ion beam targets where the symmetry issues are ameliorated in the regime of short bursts of direct drive pulses. Short pulses are here defined so that the fractional change in target radii of peak beam energy deposition are assumed to be small (during each such direct drive burst with a fixed beam focal radius). This requirement is actually not stringent on the temporal pulse-length. In fact we show an explicit example where this can be satisfied by a greater than or equal to 60 ns direct drive pulse-train. A new beam placement scheme is used which systematically eliminated low order spherical harmonic asymmetries. The residual asymmetries of such pulses are studied with both simple model and numerical simulations.
Date: May 27, 1986
Creator: Mark, J.W.K. & Lindl, J.D.
Partner: UNT Libraries Government Documents Department

The Edward Teller medal lecture: The evolution toward Indirect Drive and two decades of progress toward ICF ignition and burn

Description: In 1972, I joined the Livermore ICF Theory and Target Design group led by John Nuckolls, shortly after publication of John`s seminal Nature article on ICF. My primary role, working with others in the target design program including Mordy Rosen, Steve Haan, and Larry Suter, has been as a target designer and theorist who utilized the LASNEX code to perform numerical experiments, which along with analysis of laboratory and underground thermonuclear experiments allowed me to develop a series of models and physical insights which have been used to set the direction and priorities of the Livermore program. I have had the good fortune of working with an outstanding team of scientists who have established LLNL as the premier ICF laboratory in the world. John Emmett and the LLNL Laser Science team were responsible for developing a series of lasers from Janus to Nova which have given LLNL unequaled facilities. George Zimmerman and the LASNEX group developed the numerical models essential for projecting future performance and requirements as well as for designing and analyzing the experiments. Bill Kruer, Bruce Langdon and others in the plasma theory group developed the fundamental understanding of laser plasma interactions which have played such an important role in ICF. And a series of experiment program leaders including Mike Campbell and Joe Kilkenny and their laser experimental teams developed the experimental techniques and diagnostic capabilities which have allowed us to c increasingly complex and sophisticated experiments.
Date: December 1, 1993
Creator: Lindl, J. D.
Partner: UNT Libraries Government Documents Department

Progress on the physics of ignition for radiation driven inertial confinement fusion (ICF) targets

Description: Extensive modeling of proposed National Ignition Facility (NIF) ignition targets has resulted in a variety of targets using different materials in the fuel shell, using driving temperatures which range from 250-300 eV, and requiring energies from < 1 MJ up to the full 1. 8 MJ design capability of NIF. Recent Nova experiments have shown that hohlraum walls composed of a mixture of high-z materials could result in targets which require about 20% less energy. Nova experiments are being used to quantify benefits of beam smoothing in reducing stimulated scattering processes and laser beam filamentation for proposed gas-filled hohlraum targets on NIF. Use of Smoothing by Spectral Dispersion with 2-3 {Angstrom}of bandwidth results in <4-5% of Stimulated Raman Scattering and less than about 1% Stimulated Brillouin Scattering for intensities less than about 2x10{sup 15}W/cm{sup 2} for this type of hohlraum. The symmetry in Nova gas- filled hohlraums is affected by the gas fill. A large body of evidence now exists which indicates that this effect is due to laser beam filamentation which can be largely controlled by beam smoothing. We present here the firs 3-D simulations of hydrodynamic instability for the NIF point design capsule. These simulations, with the HYDRA radiation hydrodynamics code, indicate that spikes can penetrate up to 10 {mu}m into the 30{mu}m radius hot spot before ignition is quenched. Using capsules whose surface is modified by laser ablation, Nova experiments have been used to quantify the degradation of implosions subject to near NIF levels of hydrodynamic instability.
Date: September 1, 1996
Creator: Lindl, J.D. & Marinak, M.M.
Partner: UNT Libraries Government Documents Department

Wavelength scaling of implosion symmetry, ablation pressure, and hydrodynamic efficiency in laser fusion

Description: We examine the scaling of implosion symmetry, ablation pressure, and hydrodynamic efficiency with the wavelength of the laser, using a recent theoretical analysis of ablative laser driven implosions as a tool. Symmetrization by a hot atmosphere is most effective for long wavelength lasers, whereas ablation pressure and hydrodynamic efficiency are best for shorter laser wavelengths.
Date: July 31, 1981
Creator: Max, C.E.; Lindl, J.D. & Mead, W.C.
Partner: UNT Libraries Government Documents Department

Stability and symmetry requirements of electron and ion beam fusion targets

Description: Considerations of hydrodynamic stability impose severe restrictions on the design of electron and ion beam imploded fusion targets. Furthermore, in order to obtain a sufficiently spherical implosion, many target designs require electron or ion beams having a high degree of spherical symmetry. The stability and symmetry requirements of several recently proposed target designs were studied by numerical simulation using the computer program LASNEX. The ion beam targets studied are more vulnerable to instability than the electron beam targets. (auth)
Date: October 14, 1975
Creator: Bangerter, R.O.; Lindl, J.D.; Max, C.E. & Mead, W.C.
Partner: UNT Libraries Government Documents Department

Comparison of LASNEX calculations with experimental results of parylene disc irradiations at 1.06 $mu$m

Description: Calculations are discussed using the 2D Lagrangian code LASNEX to simulate irradiation of Parylene discs. Using a representation of the experimental beam profile, geometric optics propagation, and an absorption model based on plasma simulations, the scattered light angular intensity distribution can be obtained. The use of a suprathermal electron heating spectrum and thermally generated magnetic fields with Braginskii transport coefficients leads to agreement with time-integrated x-ray spectra and x-ray spatial distributions. Details of the calculations and comparisons with other models are discussed. (auth)
Date: November 1, 1975
Creator: Mead, W.C.; Kruer, W.L.; Lindl, J.D. & Shay, H.D.
Partner: UNT Libraries Government Documents Department

Inertial fusion energy development approaches for direct and indirect-drive

Description: Consideration of different driver and target requirements for inertial fusion energy (IFE) power plants together with the potential energy gains of direct and indirect-drive targets leads to different optimal combinations of driver and target options for each type of target. In addition, different fusion chamber concepts are likely to be most compatible with these different driver and target combinations. For example, heavy-ion drivers appear to be well matched to indirect=drive targets with all-liquid-protected-wall chambers requiring two-sided illuminations, while diode-pumped, solid- state laser drivers are better matched to direct-drive targets with chambers using solid walls or flow-guiding structures to allow spherically symmetric illuminations. R&D on the critical issues of drivers, targets, and chambers for both direct and indirect-drive options should be pursued until the ultimate gain of either type of target for IFE is better understood.
Date: August 20, 1996
Creator: Logan, B.G.; Lindl, J.D. & Meier, W.R.
Partner: UNT Libraries Government Documents Department

An IFE development strategy

Description: The development of inertial fusion as a power source will require achieving four principal milestones: ignition and propagating burn; high gain at low drive energy for the reactor driver; pulse repetition rates of a few Hz; and long-term reliability and economics of a reactor. To keep development time and costs to a minimum, these should be accomplished with as few major facilities as possible. A viable scenario for the Inertial Fusion Energy (IFE) Program would include establishing the first milestone in a Nova Upgrade for ignition and gain and the latter three in an upgradable, low-power Engineering Test Facility (ETF)/Demonstration Power Plant (DPP), i.e. two major facilities. To be successful in as short a time as possible operations at the major facilities would have to be supported by off-line reactor driver and other reactor technology development efforts. These efforts would evaluate and prioritize the myriad of options available at present for power plant and subsystem concepts. This paper describes the elements of such a program that could make the first commercial power available in the decade of the 2020s and estimates the resources needed. This program would be carried out in phases with major go/no-go decision points before each large funding change. It is estimated that an IFE evaluation phase in the early 1990s would cost $100--150 M, a concept development phase in the latter 1990s would cost $500--850 M, and an engineering test and demonstration phase after the year 2000 would cost $6--8 over 20 years.
Date: July 16, 1991
Creator: Hogan, W.J.; Storm, E. & Lindl, J.D.
Partner: UNT Libraries Government Documents Department

Research with high-power short-wavelength lasers

Description: Three important high-temperature, high-density experiments were conducted recently using the 10-TW, short-wavelength Novette laser system at the Lawrence Livermore National Laboratory. These experiments demonstrated successful solutions to problems that arose during previous experiments with long wavelength lasers (lambda greater than or equal to 1..mu..m) in which inertial confinement fusion (ICF), x-ray laser, and other high-temperature physics concepts were being tested. The demonstrations were: (1) large-scale plasmas (typical dimensions of up to 1000 laser wavelengths) were produced in which potentially deleterious laser-plasma instabilities were collisionally damped. (2) Deuterium-tritium fuel was imploded to a density of 20 g/cm/sup 3/ and a pressure of 10/sup 10/ atm. (3) A 700-fold amplification of soft x rays by stimulated emission at 206 and 209 A (62 eV) from Se/sup +24/ ions was observed in a laser-generated plasma. Isoelectronic scaling to 155 A (87 eV) in Y/sup +29/ was also demonstrated.
Date: March 5, 1985
Creator: Holzrichter, J.F.; Campbell, E.M.; Lindl, J.D. & Storm, E.
Partner: UNT Libraries Government Documents Department