G. W. Flint

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.

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

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.

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

Abstract In the High Average Power Laser program, we have developed an integrated target tracking and engagement system designed to track an inertial fusion energy target traveling 50-100 m/s in three dimensions and to steer driver beams so as to engage it with ±20 μm accuracy. The system consists of separate axial and transverse detection techniques to pre-steer individual beamlet mirrors, and a final fine-correction technique using a short-pulse laser “glint” from the target itself. Transverse tracking of the target uses the Poisson spot diffraction phenomenon, which lies exactly on axis to the centroid of the target. The spot is imaged on a digital video camera and its centroid is calculated in ˜10 ms with 5 μm precision. In our tabletop demonstration, we have been able to continuously track a target falling at 5 m/s and provide a fast steering mirror with steering commands. We are on the verge of intercepting the target on-the-fly and of verifying the accuracy of engagement. Future work entails combining transverse tracking, axial tracking, triggering and the final “glint” system. We also will implement a verification technique that confirms successful target engagement with a simulated driver beam. Results and integration progress are reported.

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

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

Completing the Viability Demonstration of Direct-Drive IFE Target Engagement and Assessing Scalability to a Full-Scale Power Plant

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...

Completing the viability demonstration of direct-drive inertial fusion energy target engagement

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 targets 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.

Glint system integration into an IFE target tracking and engagement demonstration

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.