John D. Sheliak

The Science and Technologies for Fusion Energy With Lasers and Direct-Drive Targets

We are carrying out a multidisciplinary multi-institutional program to develop the scientific and technical basis for inertial fusion energy (IFE) based on laser drivers and direct-drive targets. The key components are developed as an integrated system, linking the science, technology, and final application of a 1000-MWe pure-fusion power plant. The science and technologies developed here are flexible enough to be applied to other size systems. The scientific justification for this work is a family of target designs (simulations) that show that direct drive has the potential to provide the high gains needed for a pure-fusion power plant. Two competing lasers are under development: the diode-pumped solid-state laser (DPPSL) and the electron-beam-pumped krypton fluoride (KrF) gas laser. This paper will present the current state of the art in the target designs and lasers, as well as the other IFE technologies required for energy, including final optics (grazing incidence and dielectrics), chambers, and target fabrication, injection, and tracking technologies. All of these are applicable to both laser systems and to other laser IFE-based concepts. However, in some of the higher performance target designs, the DPPSL will require more energy to reach the same yield as with the KrF laser.

Demonstrating a Target Supply for Inertial Fusion Energy

Abstract A central feature of an Inertial Fusion Energy (IFE) power plant is a target that has been compressed and heated to fusion conditions by the energy input of the driver. The technology to economically manufacture and then position cryogenic targets at chamber center is at the heart of future IFE power plants. For direct drive IFE (laser fusion), energy is applied directly to the surface of a spherical CH polymer capsule containing the deuterium-tritium (DT) fusion fuel at approximately 18K. For indirect drive (heavy ion fusion, HIF), the target consists of a similar fuel capsule within a cylindrical metal container or ’’hohlraum’’ which converts the incident driver energy into x-rays to implode the capsule. For either target, it must be accurately delivered to the target chamber center at a rate of about 5-10Hz, with a precisely predicted target location. Future successful fabrication and injection systems must operate at the low cost required for energy production (about

Developing a commercial production process for 500 000 targets per day : A key challenge for inertial fusion energy

0.25/target, about 104 less than current costs). Z-pinch driven IFE (ZFE) utilizes high current pulses to compress plasma to produce x-rays that indirectly heat a fusion capsule. ZFE target technologies utilize a repetition rate of about 0.1 Hz with a higher yield. This paper provides an overview of the proposed target methodologies for laser fusion, HIF, and ZFE, and summarizes advances in the unique materials science and technology development programs.

Ultrasonic Characterization of Inertial Confinement Fusion Targets

As is true for current-day commercial power plants, a reliable and economic fuel supply is essential for the viability of future Inertial Fusion Energy (IFE) [Energy From Inertial Fusion, edited by W. J. Hogan (International Atomic Energy Agency, Vienna, 1995)] power plants. While IFE power plants will utilize deuterium-tritium (DT) bred in-house as the fusion fuel, the “target” is the vehicle by which the fuel is delivered to the reaction chamber. Thus the cost of the target becomes a critical issue in regard to fuel cost. Typically six targets per second, or about 500 000∕day are required for a nominal 1000MW(e) power plant. The electricity value within a typical target is about

High-resolution optical measurements of surface roughness for beta-layered deuterium-tritium solid inside a re-entrant copper cylinder

3, allocating 10% for fuel cost gives only 30 cents per target as-delivered to the chamber center. Complicating this economic goal, the target supply has many significant technical challenges—fabricating the precision fuel-containing capsule, filling it with DT, cooling it to cryogenic temperatures, layering the DT into a unifo...

Overview of recent tritium target filling, layering, and material testing at Los Alamos national laboratory in support of inertial fusion experiments

Inertial confinement fusion (ICF) targets designed to achieve ignition must meet strict surface smoothness and sphericity requirements. One potentially valuable method for evaluating the quality of these targets is resonant ultrasound spectroscopy (RUS). When applied to simple geometries, such as layered spheres or rectangular parallelepipeds, RUS may yield significant information about alloy homogeneity, elastic constants, cavity geometry the presence of gross defects such as cracking or hemishell bonding problems, and properties of interior fluids. The strengths of RUS techniques for ICF target characterization include applicability at all temperatures of interest with a single apparatus, high sensitivity in frequency spectral measurements, and the inherent acoustic indifference to optically opaque samples. Possible applicational and the limitations of RUS methods for examining layer geometry and material properties are addressed. Preliminary room temperature experiments with a deuterium-filled aluminum shell are used to evaluate the utility of many of the described applications. The frequency spectrum compares favorably with theory and displays measurable mode splitting, acoustic-mode resonance widths indicative of cavity. boundary dissipative mechanisms, and low-Q elastic modes. The acoustic cavity resonance structure confirms the internal gas density and is used to calculate the two lowest even-order cavity boundary perturbation amplitudes.

Deuterium-tritium beta-layering within a national ignition facility scale polymer target in the lanl cryogenic pressure loader

A high-resolution optical imaging system and custom-designed image analysis software are used to make surface roughness measurements for deuterium-tritium (D-T) solid layers, equilibrated inside a 2-mm-inside-diameter re-entrant copper cylinder. Several experiments are performed that yield D-T layer thicknesses of between 75 and 139 {mu}m, with equilibration temperatures between 17.4 and 18.8 K. A 1024- x 1024-pixel charge-coupled-device imaging camera, coupled with a Maksutov-Cassegrain long-range microscope, produces a 2.5-{mu}m (single-pixel) image resolution. The error function fitting of the image analysis data produces submicron resolution of the layer interior surface finish. The length scale for the cylinder inner bore is just over 6 mm, and the final layer surface roughness for this length ranges from 3- to 1.7-{mu}m root-mean-square. The feasibility is being explored of using these highly uniform and smooth D-T solid layers inside future targets for inertial confinement fusion reactors to produce surface finishes that will meet target design requirements for the National Ignition Facility. Techniques for improving the D-T solid layer surface finish are examined, limitations of the current D-T cell configuration and fuel mix are discussed, and cell configurations for future experiments are described. 10 refs., 8 figs.

A Robotic System for High-Throughput-Rate Target Assembly

Abstract The Tritium Science and Engineering (AET-3) Group at Los Alamos National Laboratory (LANL) performs a variety of activities to support Inertial Fusion (IF) research - both to further fundamental fusion science and to develop technologies in support of Inertial Fusion Energy (IFE) power generation. Inertial fusion ignition target designs have a smooth spherical shell of cryogenic Deuterium-Tritium (DT) solid contained within a metal or plastic shell that is a few mm in diameter. Fusion is attained by imploding these shells under the symmetric application of energy beams. For IFE targets the DT solid must also survive the process of injecting it into the power plant reactor. Non-ignition IF targets often require a non-cryogenic DT gas fill of a glass or polymeric shell. In this paper an overview will be given of recent LANL activities to study cryogenic DT layering, observe tritium exposure effects on IF relevant materials, and fill targets in support of IF implosion experiments.

Acoustic cavity resonances as a probe of the interior surface geometry of nearly spherical closed shells

Abstract Beta-layering, the process of beta-decay heat-driven mass redistribution, has been demonstrated in a deuterium-tritium (D-T)-filled polymer sphere of the type required for fusion ignition experiments at the National Ignition Facility. This is the first report, to the best of the authors’ knowledge, of a D-T layer formed in a permeation-filled sphere. The 2-mm-diam sphere was filled with D-T by permeation; cooled to cryogenic temperatures while in the high-pressure permeation vessel; and, while cold, removed to an optical axis where the D-T was frozen, melted, and beta-layered in a series of experiments over several weeks’ time. This work was performed in the Los Alamos National Laboratory cryogenic pressure loader system. The beta-layering time constant was 24.0 ± 2.5 min, less than the theoretical value of 26.8 min, and not showing the significant increase due to build-up of 3He often observed in beta-layered samples. Supercooling of the liquid D-T was observed. Neither the polymer target nor its tenting material showed visual signs of degradation after 5 weeks of exposure to D-T. Small external thermal gradients were used to shift the D-T material back and forth within the sphere.

Characterization of inertial confinement fusion targets.

Abstract A system for automated assembly and mounting of targets at high throughput rates has been developed at General Atomics. Major components of the system include two, six-axis industrial robot arms; a high-precision glue-dispensing system; a vision system; and a piezoelectric translation stage for precise positioning of parts. All operations are controlled by computer, with feedback from the vision system to the piezoelectric stage and robots. Assembly and mounting of cone-in-shell targets is described. A key requirement for these targets is that the virtual cone tip (the projection of the cone sides to a single point in space) must be aligned to the shell center to within ±10 μm. Major steps in the process include (a) gluing capsules to zirconia handling posts with water-soluble glue; (b) cutting holes in the tops of the capsules to accept cones; (c) assembling the cones to the capsules, forming a target; (d) gluing carbon fiber “stalks” to carriers on which the targets are mounted; and (e) removing targets from the handling posts and gluing them to stalks on carriers. The system has been demonstrated to be capable of assembling and mounting on the order of 500 targets per week. With further optimization, throughput rates of 1000 per week appear achievable.