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Capsule fill-tube target assemblies (CFTAs) for direct drive have been demonstrated in the past for Laboratory for Laser Energetics (LLE) cryogenic layering studies, evolving and building upon successful deliveries for the National Ignition Facility [Saito et al., Fusion Sci. Tech., Vol. 55, p. 337 (2009); Johal et al., Fusion Sci. Tech., Vol. 55, p. 331 (2009); Saito et al., Fusion Sci. Tech., Vol. 59, p. 271 (2011); Moreno et al., Fusion Sci. Tech., Vol. 59, p. 46 (2011); and Rice et al., High Power Laser Sci. Eng., Vol. 5, p. 7 (2017)]. The current 100 Gigabar (GBar) Campaign requires tighter specifications over prior CFTA work in terms of robustness and reduced fill-tube diameter and glue spot size, which impact the survivability of the CFTA. To tackle these challenges, General Atomics and LLE are developing a direct-drive CFTA that survives all fabrication activities, from assembly and qualification testing to transport, cryogenic layering, and target chamber insertion at the Omega Laser Faci...

Various methods for accelerating targets to be injected into an Inertial Fusion Energy (IFE) power plant have been considered such as gas gun, rail gun and electromagnetic induction. One method that could also be used for direct drive targets is electrostatic acceleration. We have been using electrostatic steering to improve target placement accuracy. We optically track the motion of a charged target, and feed back appropriate steering voltage to four steering electrodes. We have also completed fabrication and begun testing of an electrostatic accelerator that advances the electric field each time the charged target passes one of the 96 accelerating electrodes. Many of the accelerating electrodes are segmented to allow transverse position correction based on transverse position measurements during the acceleration process. Calculations indicate that this "first step" accelerator will achieve 10-15 m/s target velocity in 0.9 m with ±4 kV accelerating voltage. Updated target steering results as well as the accelerator design, fabrication, and early experimental results are presented.

To achieve high gain in an Inertial Fusion Energy (IFE) power plant, driver beams must hit direct drive targets with ±20 μm accuracy. For driver beams to arrive at the target with sufficient simultaneity, the targets must be placed to ±5 mm from chamber center. Better placement accuracy simplifies driver beam steering by reducing the distance that steering mirrors must reposition the beam aim point in the last few ms. Current best target placement experimental accuracy is 0.22 mrad standard deviation which corresponds to 3 mm at 13 m. A factor of two improvement is required to achieve 3 a accuracy in ±5 mm, and even greater accuracy is desired. General Atomics has recently embarked on a program to improve target placement accuracy through electrostatic steering. Preliminary experiments have improved accuracy of falling charged spheres. We optically track the motion, and feed back appropriate voltage to steering electrodes. A steering algorithm was prepared to steer targets with placement accuracy limited primarily by rate and accuracy of target tracking. Substantial accuracy improvement is expected with higher-frequency tracking and voltage amplification equipment. The results will be reported.

Successful ignition of direct drive targets in an IFE power plant requires a reliable system for tracking the location of the target in flight and illuminating it by many separate laser beams with a high degree of precision. As part of a coordinated effort in the High Average Power Laser (HAPL) program, we have developed and tested an interferometric technique for measuring the position and velocity of targets along their axis of motion. The technique involves reflecting light from the moving target and combining it with a reference beam in order to produce interference fringes at a rate corresponding to the movement of the target. A scaled benchtop experiment has been built and tested to characterize the performance of this technique of axial target tracking. Results are presented here together with recommendations on improvements needed for a fullscale performance demonstration.

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.

The High Average Power Laser (HAPL) Program, directed by the Naval Research Laboratory (NRL) in Washington, DC, is pursuing an all-systems approach to inertial fusion energy (IFE) with lasers. Systems that will be needed for an IFE power plant, such as the laser drivers, cryogenic targets, target factory, target injection, target tracking and engagement, chamber design, and chamber materials to name a few, are all being developed in parallel at various laboratories, universities, and companies across the U.S. While all such systems in an IFE power plant are essential, at the heart of the energy production is the fuel, the cryogenic target. The emphasis at General Atomics is the development of cryogenic targets within physics specifications, the economical mass production of targets, and the delivery of the targets to the center of the chamber within tight tolerances.

Mechanical response of DT targets to acceleration was analyzed using the finite element method for Inertial Fusion Energy (IFE) targets and for smaller targets that have been proposed for an upcoming Fusion Test Facility (FTF). Analysis was done in the temperature and acceleration regions of interest for Inertial Fusion Energy (14-19 K and 1,000-10,000 m/s2). In these ranges, von Mises stress distribution, axial deflection, and the minimum value of support membrane attachment angle as well as free vibrations of the target after it leaves the injector were calculated. The role of the outer polymer coating, the support membrane attachment angle and the DT void pressure in the mechanical response of a DT target to acceleration was considered. Analysis shows, assuming that DT mechanical properties are equivalent to D2, that IFE and FTF targets should withstand acceleration of up to 10,000 m/s2 with negligible deformation.

The hohlraum surrounds the fuel capsule in a heavy ion fusion (HIF) target. The hohlraum absorbs ion beam driver energy and emits this energy uniformly around the capsule in the form of X-rays. High-atomic-number materials are necessary in the walls of the hohlraum to contain the X-ray energy around the capsule during the implosion process. These high-atomic-number hohlraum materials affect many aspects of an HIF power plant operation. A systematic review of available information for all high-atomic-number elements was conducted to select candidate hohlraum materials. The effects of materials on target fabrication, energy cost, target gain, radioactivity, chemical toxicity, and potential for recycle were considered. Lead and tungsten are the lowest-cost acceptable materials in the primary coolant. The combination of lead and tungsten provide better target gain than either material alone. Seeding the primary coolant with submicron-sized tungsten particles can minimize tungsten growth in small openings in power plant components such as vacuum tritium disengagers. Concerns remain for possible tungsten particle agglomeration, settling, or erosion caused by tungsten particles. Tungsten could be replaced by several lanthanide elements if tungsten proves unacceptable.

Inertial Fusion Energy (1FE) with laser drivers is a pulsed power generation system that relies on repetitive, high-speed injection of targets into a fusion reactor. To produce an economically viable IFE power plant the targets must be injected into the reactor at a rate between 5 and 10 Hz. To survive the injection process, direct drive (laser fusion) targets (spherical capsules) are placed into protective sabots. 1 The sabots separate from the target and are stripped off before entering the reactor chamber. Indirect drive (heavy ion fusion) utilizes a hohlraum surrounding the spherical capsule and enters the chamber as one piece. 2 In our target injection demonstration system, the sabots or hohlraums are injected into a vacuum system with a light gas gun using helium as a propellant. To achieve pulsed operation a rep-rated injection system has been developed. For a viable power plant we must be able to fire continuously at 6 Hz. This demonstration system is currently set up to allow bursts of up to 12 targets at 6 Hz. Using the current system, tests have been successfully run with direct drive targets to show sabot separation under vacuum and at barrel exit velocities of ∼400 m/s. The existing revolver system along with operational data will be presented.

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 economical...

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 (

The Target Fabrication Facility (TFF) of an IFE power plant must supply about 500,000 targets per day. The targets are injected into the target chamber at a rate of 5-10 Hz and tracked precisely so the driver beams can be directed to the target. The feasibility of developing successful fabrication and injection methodologies at the low cost required for energy production (about $0.25/target, about 10 4 less than current costs) is a critical issue for inertial fusion. To help identify major cost factors and technology development needs, we have utilized a classic chemical engineering approach to the TFF. The analyses assume an nth-of-a-kind TFF and utilize standard industrial engineering cost factors. The results indicate that the direct drive target can be produced for about $0.16 each. Iterations are still underway for the indirect drive target. These cost analyses assume that the process development is accomplished to allow scaling of current laboratory methods to larger sizes, while still meeting target specifications. A development program is underway at various laboratories to support this scale-up.

During injection, inertial fusion energy (IFE) direct drive (DD) targets are subject to heating from energy exchange with the background gas and radiation from the wall. This heat deposition could lead to deuterium-tritium (DT) phase change and target deformation violating the target physics symmetry requirements. This paper assesses the thermal behavior of the target under such conditions and explores possible ways of extending the target lifetime.

The authors present an evaporative initiated chemical vapor deposition (iCVD) coater and use it to establish a submicron bonding process for millimeter-scale foils with potentially rough surface features. The coater uses a simple benchtop design suited to research labs, with pre-heated metal pins instead of hot filaments, and direct evaporation of reactants within the chamber. Coatings of poly(glycidyl methacrylate) (pGMA) with thickness 100–800 nm are achieved at rates of 10–40 nm min−1 on substrates common in high energy laser compression experiments. Coating uniformities of 10–30 nm mm−1 are demonstrated in a ≈60 × 10 mm zone under the heated pins. As an aside, the authors further show the ability to coat intentionally non-uniform layers in a monomer vapor diffusion gradient. Coatings are formed on both plastics and solids ranging from smooth, non-burred silicon or lithium fluoride to rough and burred metals (aluminum and copper). These coated substrates are then chemically bonded under mild heat and pressure. Detailed surface, thickness, and cross-sectional characterization is performed to confirm a submicron bond gap and to troubleshoot the common clearance issues from burrs, roughness, and surface curvature. Peeling and dropping bond strength tests confirm the bonds are robust, when coated and assembled under conditions to mitigate clearance issues.

The current status of the fabrication, injection, and tracking of fast ignition targets is summarized including on cryogenic technologies for direct-drive, laser fusion targets with and without a r...