Alternate Approaches/Direct Drive in Inertial-Confinement Fusion

Direct-drive inertial confinement fusion provides a true alternative to the indirect-drive concept. It couples 7 to 9× more energy to the compressed core allowing higher margin and gain for the same laser energy. A new variant, shock ignition, shows promise for increasing the gains even further. Significant progress has been made in direct-drive research over the past decades, suggesting it provides a viable path toward inertial fusion energy. The Omega Laser Facility at the Laboratory for Laser Energetics (LLE) is used to study direct-drive inertial confinement fusion (ICF) ignition concepts. The baseline symmetric-illumination ignition target design consists of a 1.5-MJ multiple-picket laser pulse that generates four shock waves [similar to the National Ignition Facility (NIF) baseline indirect-drive design] and produces a 1-D gain of 48. Re‑optimized for polar-drive (PD) illumination (with beams in the x-ray-drive configuration), ignition and significant gain are predicted. Verification of the physics basis of these simulations is a major thrust of implosion experiments on both OMEGA and the NIF. Many issues can be examined with symmetric beam irradiation. OMEGA cryogenic-DT target experiments with symmetric irradiation have produced areal densities of ~0.3 g/cm², ion temperatures up to 3 keV, and neutron yields above 10¹³ that are up to 20% of “clean” 1-D simulations. Physics issues unique to PD are being examined on OMEGA by turning off the equatorial beams and closely approximating the NIF polar-illumination geometry. Initial PD “exploding-pusher” experiments on the NIF, designed and tested on OMEGA, have produced neutron yields up to 6 x10¹⁴. This talk describes progress in direct-drive ICF in both symmetric and PD configurations.

This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No DE-FC52-08NA28302, the University of Rochester, and the New York State Energy Research and Development Authority. The support of DOE does not constitute an endorsement by DOE of the views expressed in this article.