Exploring Innovative High-Gain Ignition Concepts for Inertial Fusion Energy

Stephan Maclaren | 23-ERD-023

Project Overview

While the National Ignition Facility (NIF) has recently demonstrated fusion target gain > 1, Inertial Fusion Energy (IFE) for commercial power generation will require at a minimum a scheme that employs fusion targets that produce many times more energy than is used to drive them. In addition, the repetition rate requirement of such a concept requires these targets to be robust to variations in both their fabrication as well as the delivery of the driver energy, and economically feasible to mass produce. This project leveraged current state-of-the-art codes together with advances in modeling the ICF-relevant physics and brought them to bear on the IFE problem. The work focused on indirect-drive targets that reach high gain through central hot-spot (CHS) ignition of an isobaric hot-spot as well as "fast" ignition (FI) of an isochoric fuel assembly using relativistic electron or ion beams to separate the compression and heating.

The objectives were to identify and computationally assess technologies that can be applied to increase the gain of the current highest-performing ICF targets and/or adapt to the repetition rates that will be required for IFE. As part of this assessment, hypotheses associated with high gain or repetition rate that could be tested at some level in the laboratory using current facilities were prioritized for further study. Liquid layers emerged as a common denominator in almost every IFE target design, with additively manufactured CH foams being the most promising way to suspend the layer.  Concepts for experiments to test both the microphysics as well as the integrated performance in a fusion implosion of such a wetted foam fuel layer were developed. Improvements to the coupling of the IFE driver energy to the capsule in the indirect-drive scenario were examined, and concepts testable with current fabrication and laser facility capabilities were identified.  Ultimately, a larger team was identified to include the specialized experimental and fabrication expertise necessary to execute the experiments that could deliver a dataset of extremely high value to the further development of IFE technologies.  This team, together with the experimental plans outlined above, became a Strategic Initiative launched in FY24 with scope sufficient to address the hypotheses developed in FY23.

Mission Impact

The development of IFE is distinct, yet highly synergistic with NNSA's Stockpile Stewardship Program (SSP) mission through the ICF program, and this ER seeks to leverage the immense volume of knowledge and increased understanding gained over the past decade of ICF research to pursue innovative ideas for high gain targets, a pursuit that if successful will yield dividends for both SSP and IFE in the U.S. Findings that improve understanding of reaching higher target yield or increasing the efficiency of target fabrication will enhance the effectiveness of any ICF facility, and benchmarking of the radiation-hydrodynamics and PIC codes against a broader data set will only serve to improve the predictive capability for high-gain ICF design. The results of this LDRD, including potential near-term laboratory studies, directly address objectives in the 2023 Investment Strategy for Science and Technology for the IFE Institutional Initiative, which describes IFE as "a potential game-changing technology whose pursuit will bolster American competitiveness and energy and climate security." The Initiative seeks to leverage decades of investment at Lawrence Livermore National Laboratory into ICF science, investment that defines Livermore as the organization most qualified to critically examine high-gain target technologies. The technologies identified by this LDRD are foundational for a broad range of approaches to IFE and further investigation to better understand both their promise and limitations will be necessary for the Laboratory to continue its role as a leader in this field as envisioned by the Investment Strategy. By maintaining its position as the center of IFE technical expertise within the government, Livermore will serve as a trusted partner for DOE and independent assessor of critical IFE technologies.

Publications, Presentations, and Patents

A. J. Kemp et al., "Laser to Proton Conversion Efficiency Studies for Proton Fast Ignition" (Paper Presentation, International Conference on Inertial Fusion Sciences and Applications 2023, Denver, CO, September 2023).

D. P. Higginson et al., "Fast Ignition Research and Goals at Lawrence Livermore National Laboratory" (Paper Presentation, US-Japan Workshop on Inertial Fusion Energy, Denver, CO, September 2023).