D. T. Goodin

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.

Direct drive target survival during injection in an inertial fusion energy power plant

In inertial fusion energy (IFE) power plant designs, the fuel is a spherical layer of frozen DT contained in a target that is injected at high velocity into the reaction chamber. For direct drive, typically laser beams converge at the centre of the chamber (CC) to compress and heat the target to fusion conditions. To obtain the maximum energy yield from the fusion reaction, the frozen DT layer must be at about 18.5 K and the target must maintain a high degree of spherical symmetry and surface smoothness when it reaches the CC. During its transit in the chamber the cryogenic target is heated by radiation from the hot chamber wall. The target is also heated by convection as it passes through the rarefied fill-gas used to control chamber wall damage by x-rays and debris from the target explosion. This article addresses the temperature limits at the target surface beyond which target uniformity may be damaged. It concentrates on direct drive targets because fuel warm up during injection is not currently thought to be an issue for present indirect drive designs and chamber concepts. Detailed results of parametric radiative and convective heating calculations are presented for direct-drive targets during injection into a dry-wall reaction chamber. The baseline approach to target survival utilizes highly reflective targets along with a substantially lower chamber wall temperature and fill-gas pressure than previously assumed. Recently developed high-Z material coatings with high heat reflectivity are discussed and characterized. The article also presents alternate target protection methods that could be developed if targets with inherent survival features cannot be obtained within a reasonable time span.

A cost-effective target supply for inertial fusion energy

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. This is true whether the driver is a laser system, heavy ion beams or Z-pinch system. The IFE target fabrication, injection and tracking programmes are focusing on methods that will scale to mass production. We are working closely with target designers, and power plant systems specialists, to make specifications and material selections that will satisfy a wide range of required and desirable target characteristics. One-of-a-kind capsules produced for today’s inertial confinement fusion experiments are estimated to cost about US

OPERATIONAL WINDOWS FOR DRY-WALL AND WETTED-WALL IFE CHAMBERS

2500 each. Design studies of cost-effective power production from laser and heavy-ion driven IFE have suggested a cost goal of about

Demonstrating a Target Supply for Inertial Fusion Energy

0.25–0.30 for each injected target (corresponding to ∼10% of the ‘electricity value’ in a target). While a four orders of magnitude cost reduction may seem at first to be nearly impossible, there are many factors that suggest this is achievable. This paper summarizes the design, specifications, requirements and proposed manufacturing processes for the future for laser fusion, heavy ion fusion and Z-pinch driven targets. These target manufacturing processes have been developed—and are proposed—based on the unique materials science and technology programmes that are ongoing for each of the target concepts. We describe the paradigm shifts in target manufacturing methodologies that will be needed to achieve orders of magnitude reductions in target costs, and summarize the results of ‘nth-of-a-kind’ plant layouts and cost estimates for future IFE power plant fuelling. These engineering studies estimate the cost of the target supply in a fusion economy, and show that costs are within the range of commercial feasibility for electricity production.

Tritium Inventory of Inertial Fusion Energy Target Fabrication Facilities: Effect of Foam Density and Consideration of Target Yield of Direct Drive Targets

Abstract The ARIES-IFE study was an integrated study of inertial fusion energy (IFE) chambers and chamber interfaces with the driver and target systems. Detailed analysis of various subsystems was performed parametrically to uncover key physics/technology uncertainties and to identify constraints imposed by each subsystem. In this paper, these constraints (e.g., target injection and tracking, thermal response of the first wall, and driver propagation and focusing) were combined to understand the trade-offs, to develop operational windows for chamber concepts, and to identify high-leverage research and development directions for IFE research. Some conclusions drawn in this paper are (a) the detailed characterization of the target yield and spectrum has a major impact on the chamber; (b) it is prudent to use a thin armor instead of a monolithic first wall for dry-wall concepts; (c) for dry-wall concepts with direct-drive targets, the most stringent constraint is imposed by target survival during the injection process; (d) for relatively low yield targets (<250 MJ), an operational window with no buffer gas may exist; (e) for dry-wall concepts with indirect-drive targets, a high buffer gas pressure would be necessary that may preclude propagation of the laser driver and require assisted pinch transport for the heavy-ion driver; and (f) generation and transport of aerosols in the chamber is the key feasibility issue for wetted-wall concepts.

A CONTINUOUS, IN-CHAMBER TARGET TRACKING AND ENGAGEMENT APPROACH FOR LASER FUSION

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

TARGET TRACKING AND ENGAGEMENT FOR INERTIAL FUSION ENERGY - A TABLETOP DEMONSTRATION -

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.

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

The tritium inventory of direct drive inertial fusion energy (IFE) target filling facilities is examined in the interest of minimizing the tritium inventory. A model is described that has been developed to evaluate the tritium inventory of the target filling process as a function of filling and layering parameters, as well as target design parameters. Previous studies by A. Nobile et al. showed that the temperature and the fill system void fraction have a significant effect on the tritium inventory. The current study uses the model to examine the effect of deuterium-tritium (DT) ice layering time and density of the CH foam in the target on the tritium inventory. The study shows that increasing the foam density and decreasing the DT ice layering time significantly reduce the tritium inventory. Fortunately, one-dimensional target design calculations indicate that the foam density in the direct drive target can be increased to ~200 mg/cm3 without significant degradation of the target yield. Having evaluated and minimized the theoretical tritium inventory, calculations were performed with more realistic batch filling scenarios. The inventories associated with “real” filling scenarios approach the theoretical minimum inventory as the number of batches is increased, resulting in tritium inventories that seem acceptable for future IFE target DT filling facilities.

Cost modeling for fabrication of direct drive inertial fusion energy targets

Abstract Target engagement is the process of measuring the target trajectory and directing the driver beams to hit the target at a position that is predicted based on these measurements. New target engagement concepts have been proposed in the last few years to continuously track the targets and to verify that the tracking system is aligned with the driver beams for each shot. For transverse position, a laser beam continuously backlights the target and the position of the Poisson spot in the center of the target’s shadow is measured. Axial target displacement is measured using a laser interferometer and counting interference fringes as the target moves away from the laser source. Final steering corrections use a “glint” reflected off the target ˜1 ms prior to firing the laser beams and collected in a separate Position Sensitive Detector (PSD) for each driver beamlet. The position of the glint on the PSD is compared to the position of an alignment beam that is collinear with the driver beam. Steering corrections are then made based on the difference in position of the two spots reaching the PSD.