David B. Harris

Design and modeling of ignition targets for the National Ignition Facility

Several targets are described that in simulations give yields of 1–30 MJ when indirectly driven by 0.9–2 MJ of 0.35 μm laser light. The article describes the targets, the modeling that was used to design them, and the modeling done to set specifications for the laser system in the proposed National Ignition Facility. Capsules with beryllium or polystyrene ablators are enclosed in gold hohlraums. All the designs utilize a cryogenic fuel layer; it is very difficult to achieve ignition at this scale with a noncryogenic capsule. It is necessary to use multiple bands of illumination in the hohlraum to achieve sufficiently uniform x‐ray irradiation, and to use a low‐Z gas fill in the hohlraum to reduce filling of the hohlraum with gold plasma. Critical issues are hohlraum design and optimization, Rayleigh–Taylor instability modeling, and laser–plasma interactions.

Ignition target design and robustness studies for the National Ignition Facility

Recent results are presented from two‐dimensional LASNEX [G. B. Zimmerman and W. L. Kruer, Comments Plasmas Phys. Controlled Thermonucl. Fusion 2, 51 (1975)] calculations of the indirectly driven hohlraum and ignition capsules proposed for the National Ignition Facility (NIF). The calculations concentrate on two capsule designs, the baseline design that has a bromine‐doped plastic ablator, and the beryllium design that has a copper‐doped beryllium ablator. Both capsules have a cryogenic fuel layer. Primary emphasis in these calculations is placed upon robustness studies detailing various sensitivities. Because of computer modeling limitations these studies fall into two categories: those performed with integrated modeling where the capsule, hohlraum, and laser rays all are modeled simultaneously with the laser power levels as the only energy input; and those performed in a capsule‐only mode where an externally imposed radiative flux is applied to the exterior of the capsule, and only the capsule performan...

Symmetry experiments in gas‐filled hohlraums at NOVA

Understanding drive symmetry in gas‐filled hohlraums is currently of interest because the baseline design of the indirect drive ignition target for the planned National Ignition Facility uses a gas‐filled hohlraum. This paper reports on the results of a series of experiments performed at the Nova laser [C. Bibeau et al. Appl. Opt. 31, 5799 (1992)] facility at Lawrence Livermore National Laboratory with the goal of understanding time‐dependent drive symmetry in gas filled hohlraums. Time‐dependent symmetry data from capsule implosions and reemission targets in gas‐filled hohlraums are discussed. Results of symmetry measurements using thin wall gas‐filled hohlraums are also discussed. The results show that the gas is effective in impeding the motion of the wall blowoff material, and that the resulting implosion performance of the capsule is not significantly degraded from vacuum results. The implosion symmetry in gas differs from vacuum results with similar laser pointing indicating a shift in beam position...

The role of symmetry in indirect‐drive laser fusion

Good radiation drive symmetry will be crucial for achieving ignition in laboratory inertial fusion experiments. The indirect‐drive inertial confinement fusion (ICF) method utilizes the soft x‐ray field in a radiation‐containing cavity, or hohlraum, to help achieve a high degree of symmetry. Achievement of the conditions necessary for ignition and gain will require experimental fine tuning of the drive symmetry. In order to make tuning possible, a significant effort has been devoted to developing symmetry measurement techniques. These techniques have been applied to a series of experiments that give a graphic picture of the symmetry conditions in the complex hohlraum environment. These experiments have been compared with detailed, fully integrated theoretical modeling. The ultimate goal of this work is the detailed understanding of symmetry conditions and the methods for their control. Comparison with experiments provides crucial benchmarking for the modeling—a key element in planning for ignition.

Review of drive symmetry measurement and control experiments on the Nova laser system (invited)

Good radiation drive symmetry is crucial for achieving ignition in laboratory inertial fusion experiments. X‐ray drive symmetry in hohlraums has been the subject of investigation for more than four years and a great deal of progress has been made. Over the last two to three years, a concerted series of (indirect) drive symmetry experiments has been performed on the Nova laser system and is the subject of the present paper. The goals of this work have been to develop measurement techniques and to apply them to symmetry variation and control experiments. The principal diagnostic has utilized the symmetry signature impressed on the dense core of a target imploded by the hohlraum x‐ray environment. The core is distorted by drive asymmetries and x‐ray imaging of this core provides a mapping that can be compared with theoretical modeling and thus related to specific amounts of drive asymmetry. We will describe the instruments and measurement techniques used in these experiments and present representative data a...

KrF amplifier design issues and application to inertial confinement fusion system design

Los Alamos National Laboratory has assembled an array of experimental and theoretical tools to optimize amplifier design for future single-pulse KrF lasers. The next opportunity to exercise these tools is with the design of the second-generation NIKE system under construction at the Naval Research Laboratory with the collaboration of Los Alamos National Laboratory. Major issues include laser physics (energy extraction in large modules with amplified spontaneous emission) and diode performance and efficiency. Low cost is increasingly important for larger future KrF single-pulse systems (low cost and high efficiency is important for larger repetitively pulsed applications such as electric power production). In this article, we present our approach to amplifier scaling and discuss the more important design considerations for large single-pulse KrF amplifiers. We point out where improvements in the fundamental database for KrF amplifiers could lead to increased confidence in performance predictions for large amplifiers and address the currently unresolved issues of anomalous absorption near line center and the possibility of diode instabilities for lowimpedance designs. Los Alamos has applied these amplifier design tools to the conceptual design of a 100-kJ Laser Target Test Facility and a 3-MJ Laboratory Microfusion Facility.

Heavy-ion fusion target cost model

A new model for the cost of production of heavy-ion fusion targets in dedicated on-site target factories is presented for power plants. The model treats single- and double-shell direct-drive and generic indirect-drive targets. Target factory capital costs, nontritium target materials costs, and target factory operations and maintenance costs are estimated for target substructures such as fuel capsules, radiation cases, and driver energy absorption regions. These individual estimates are combined to obtain the total target cost. Realistic scaling of target costs with variations of such important performance parameters as target factory production capacity and driver pulse energy is emphasized. The model can be modified and used for other inertial fusion drivers and fuels. Typical target cost estimates fall into the range of

Improved KrF laser design for the Laboratory Microfusion Facility

0.25 to 0.45 per target. The estimated target cost contribution to the total cost of production of electric power is typically --4 to 7 mill/kW . h.

Pulsed-power considerations for electron-beam-pumped krypton-fluoride lasers for inertial confinement fusion applications

A conceptual design of the KrF laser-driven Laboratory Microfusion Facility (LMF) has been completed. LASNEX calculations predict an indirect-drive target yield of 400 MJ from the 3-MJ, 480-beam driver system. Nine final amplifiers with individual output energy of 412 kJ are used. The 480 beams are transmitted through helium to reduce losses and are delivered to target through a series of buildings designed for radiation safety. The total cost of the KrF laser-driven LMF is estimated by an independent cost assessment to be

Status of Inertial Confinement Fusion Research at Los Alamos National Laboratory

921 million in 1992 dollars.<<ETX>>