Compact, Efficient, Low-cost Lasers (CELL) Project (Final Report)

Abstract

Development of clean, sustainable and affordable energy sources is a national and international challenge. Inertial Fusion Energy (IFE) may provide a transformational solution that is scalable, proliferation-resistant, and that generates negligible nuclear waste. To produce energy economically competitive with alternative power plants, the IFE laser drive must operate at a high repetition rate (≥10 Hz) with high efficiency (>10%), while maintaining beam quality suitable for focusing to a small spot suitable for compressing the fusion target. The NIF laser system meets the beam quality requirements using a solid-state gain medium pumped by flashlamps. Scaling from NIF to IFE requires increases of ~10 5 in rep rate and ~20X in efficiency, which adds significant challenges to the laser design. The increased repetition rate results in much more waste heat generated in the system, and the prevention of thermal beam quality degradation (through phenomena such as thermally-induced birefringence) becomes a critical issue. While thermal issues are mitigated by increasing the system volume, a major size increase renders the system less economical and less easy to site. LIFE laser efficiency targets can be achieved at high rep rate without reliability degradation by using diode lasers as pumps. An IFE plant requires ~10 8 diode laser bars. At current costs the diodes dominate the overall laser cost and render IFE less cost-effective. Thus, designing a compact and cost-effective laser system with the repetition rate, efficiency, and beam quality required for IFE presents a significant technical challenge. The goal of the CELL strategic initiative was to develop new laser architectures to address these challenges by leveraging recent advances in optical technology. New laser design options have become potentially feasible due to improvements in laser gain media, diode pumps, large aperture nonlinear optics, and damage-resistant optics that have occurred since NIF’s conception. The project investigated designs that take advantage of these advances, combining them with advanced and novel subsystem concepts to achieve laser designs with significantly improved performance, size, and cost.