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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...

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.

A significant challenge for the successful implosion of direct-drive inertial fusion energy targets is the repeated alignment of multiple laser beams on moving targets with accuracy on the order of 20 ?m. Adding to the difficulty, targets will be traveling up to 100 m/s through a chamber environment that may disturb their trajectories. In the High Average Power Laser program, we have developed a target tracking and engagement system that is capable of meeting the goals for an inertial fusion power plant. The system consists of separate axial and transverse target detection techniques and a final correction technique using a short-pulse laser to interrogate the target's position 1-2 ms before a chamber center. Steering mirrors are then directed to engage the target at the chamber center. Over the past few years, we have constructed and improved upon an integrated tabletop demonstration operating at reduced speeds and path lengths. In August 2007, initial engagement of moving targets in air using a simulated driver beam was 150- ?m rms. Since then, we have taken an encompassing look at all error sources that contribute to the overall engagement error. By focusing on those individual component errors that have the most influence and improving their accuracy, we have substantially reduced the overall engagement error. In August 2008, we had achieved an engagement of 42-?m rms in air by using this approach, and in March 2009, 34-?m rms in vacuum. The final elements, which we believe are necessary to meet our goal, necessitate engaging lightweight targets in a prototypic vacuum environment with an understanding of the scalability of demonstration-scale errors to full-scale errors. In this paper, we present the latest improvements from the identification and reduction of errors and the resulting engagement data demonstrating near completion of the viability demonstration of direct-drive target engagement to 20 ?m.

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 target for an Inertial Fusion Energy (IFE) power plant is compressed and heated to fusion conditions by the driver beams. The “Target Fabrication Facility” (TFF) of a 1000 MW(e) IFE power plant must supply over 500,000 targets per day. The target is then 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 104 less than current costs) is a critical issue for inertial fusion. The technologies for producing Heavy Ion Fusion (HIF) targets have significant overlaps and synergisms with current-day inertial fusion experimental targets and with laser fusion (direct drive) IFE targets. Capsule formation and characterization, permeation filling, and layering of the DT using a cryogenic fluidized bed are common methodologies shared between laser fusion and HIF. Specific to HIF targets are the techniques for fabricating and assembling the hohlraum components. We will report on experimental progress with the Laser-assisted Chemical Vapor Deposition (LCVD) technique to produce “micro-engineered” low-density metallic foams for the hohlraum, and calculations of hohlraums materials performance during handling. Fiber growth by LCVD in arrays has been demonstrated for the first time, important to achieve the volume production needed for IFE. We have also evaluated a variety of hohlraum material selections, with consideration of target physics, cost, ES&H, activation, and compatibility with the molten salt coolant. These materials include selections for once-through and for recycle scenarios. We have performed a cost analysis for an “nth-of-a-kind” Target Fabrication Facility using our current assumptions about the production processes. Some of these scenarios result in future target manufacturing costs consistent with economical electricity production.

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

A zero-dimensional model that describes the evolution of plasma and gas parameters during the afterglow phase of cyclic operation of an inertial fusion energy chamber is developed. The afterglow phase determines the conditions for next fuel-target injection and therefore its thorough analysis is very important for conceptual design of inertial fusion power plants. The model incorporates important effects of intrinsic impurity ion radiation on plasma cooling as well as of chamber opacity with respect to resonance radiation on plasma recombination in the working chamber. The decay times for the plasma and gas energy and, in particular, their dependence on initially stored energy, chamber size, and background gas concentration are analyzed. The heat power load onto the cryogenic fuel target due to residual plasma, gas, and radiation field is calculated. It is found that the higher the background gas density, the longer is the time into the afterglow phase necessary to reduce the heat flux on the target to an acceptable level.

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 (

A coordinated, focused effort is underway to develop Laser Inertial Fusion Energy. The key components are developed in concert with one another and the science and engineering issues are addressed concurrently. Recent advances include: target designs have been evaluated that show it could be possible to achieve the high gains (>100) needed for a practical fusion system.These designs feature a low-density CH foam that is wicked with solid DT and over-coated with a thin high-Z layer. These results have been verified with three independent one-dimensional codes, and are now being evaluated with two- and three-dimensional codes. Two types of lasers are under development: Krypton Fluoride (KrF) gas lasers and Diode Pumped Solid State Lasers (DPSSL). Both have recently achieved repetitive 'first light', and both have made progress in meeting the fusion energy requirements for durability, efficiency, and cost. This paper also presents the advances in development of chamber operating windows (target survival plus no wall erosion), final optics (aluminium at grazing incidence has high reflectivity and exceeds the required laser damage threshold), target fabrication (demonstration of smooth DT ice layers grown over foams, batch production of foam shells, and appropriate high-Z overcoats), and target injection (new facility for target injection and tracking studies).

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.

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.

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.

We have demonstrated that in-flight electrostatic steering can substantially improve target placement accuracy. We optically track the motion of a charged target and feed back appropriate steering voltage to four steering electrodes. Target placement accuracy of falling ∼1.8 mg shells with 0.5 m stand off from steering electrodes is improved from ∼ 500 to 10 µm standard deviation in each transverse direction. It might be possible to replace current-day positioning systems for target shots with a system such as this, resulting in substantial debris reduction. We also completed fabrication and started testing 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. The accelerator operation has now transitioned to vacuum acceleration of 1.8 mg hollow shells. Calculations indicate that this “first step” accelerator could achieve 10–15 m/s target velocity in 0.9 m with −0.5 nC target charge and ±4 kV accelerating voltage. Demonstrating this capability is still underway. Additional experimental work and updated acceleration results will be presented.

A significant challenge for the successful implosion of direct-drive inertial fusion energy (IFE) targets is the repeated alignment of multiple laser beams on moving targets with accuracy on the order of 20 µm. Adding to the difficulty, targets will be traveling up to 100 m/s through a chamber environment that may disturb their trajectories.

We have defined the characteristics of a target injection and tracking facility to validate the science and technology of full-scale components for a laser inertial fusion energy (IFE) power plant. This facility will be a key element of the plan to develop laser IFE with direct drive targets and solid wall chambers. It is the final step before construction of an engineering test facility. Elements of the facility include mass production (in batch mode) of cryogenic targets that meet the specifications of high gain, target injection into the chamber and target tracking in the chamber. The chamber will simulate the environment (background gas, wall temperature, etc.) envisioned for a laser IFE power plant, and the facility will include steering of a low-energy pulsed laser onto the target in flight. In this paper we describe the program goals and key science and technology issues which will be addressed in the facility, quantitative requirements for successful target injection, major characteristics of the various subsystems, and R&D which will be needed in order to prepare for its construction and operation.

The authors performed 1-D coupled, neutron-gamma transport calculations for lithium-vanadium blankets and lithium-sodium cauldron pot blankets in cylindrical and spherical geometries. Parametric fits to the data are supplied for subsequent use in systems code models. Scaling relationships are given for various neutronics parameters of interest, including: tritium breeding ratio, neutron energy multiplication, magnet dose rates, magnet heating rates, and integrated magnet fluence.

In the High Average Power Laser (HAPL) program, we are developing an integrated target tracking and engagement system designed to track in three dimensions an IFE target traveling 50-100 m/s and to steer simulated driver beams so as to engage it at chamber center with ±20 μm accuracy. The system consists of separate axial and transverse target detection techniques, and a short-pulse 'glint' laser to provide final steering instructions for beamlet alignment and target engagement by using the target itself as the final reference point. The glint laser overfills the target with a pulsed illumination beam 1-2 ms before chamber center, thus reflecting a 'glint' off the target in all directions. The glint return propagates back through the driver beamline and is collinear to the outgoing driver beam except for an offset determined by a wedged dichroic mirror. The wedged mirror accounts for the predefined transit distance of the target between the glint location and the driver beam arrival. This technique allows both the glint return and the driver beam to share a common path. Thus, the glint return represents the target's final position, but at a small discrete offset from chamber center, and therefore can be used to steer the driver beams to intercept the target at chamber center. We are currently prototyping this tracking and engagement system on the tabletop at reduced speeds and dimensions to verify feasibility. All subsystems have been characterized and currently we are integrating the glint system into the tabletop demo and using the glint return signal to provide the final steering instructions for the mirror. The glint system's integration into the tracking and engagement demo and current engagement results are reported.

One of the most significant "grand challenges" for inertial fusion is to develop robust processes capable of manufacturing Inertial Fusion Energy (IFE) targets with ignition-quality specifications in large quantities and at low cost. In addition, these DT-filled, cryogenic targets must be rapidly delivered to the center of a target chamber with high placement accuracy, and tracked on their journey into the chamber with high precision to permit steering of the driver beams for the implosion. Plant designs typically are based on repetition rates of 5 to 10 shots per second (∼500,000 targets per day for a 1000MW(e) power plant). Laser fusion designs typically require alignment of the driver beams with the targets at chamber center to ten's of microns. While much progress has been made, reliably fueling an IFE power plant with high-yield, low-cost, targets will remain a significant "grand challenge" of inertial fusion over the next decade.

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 $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 uniform layer, characterizing the finished product, accelerating it to high velocity for injection into the chamber, and tracking the target to steer the driver beams to meet it with micron-precision at the chamber center.

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...