Progress towards ignition on the National Ignition Facility

TLDR

The National Ignition Facility, a 1.8 MJ/500 TW laser system operational since 2009, supports national security, fundamental science, and inertial fusion energy research with nearly 60 diagnostics and requires compressing deuterium‑tritium fuel to ~1000 g cm⁻³ and a ρR of ~1.5 g cm⁻² to achieve ignition. The National Ignition Campaign aims to implode a low‑Z deuterium‑tritium capsule via indirect‑drive inertial confinement fusion to achieve ignition and a net energy gain of 5–10. This requires precise control of laser and target parameters to achieve a low‑adiabat, high‑convergence implosion with minimal ablator‑fuel mix. Measured nuclear yields are 3–10 times lower than simulations and fall short of the alpha‑dominated regime.

Abstract

The National Ignition Facility (NIF) at Lawrence Livermore National Laboratory includes a precision laser system now capable of delivering 1.8 MJ at 500 TW of 0.35-μm light to a target. NIF has been operational since March 2009. A variety of experiments have been completed in support of NIF's mission areas: national security, fundamental science, and inertial fusion energy. NIF capabilities and infrastructure are in place to support its missions with nearly 60 X-ray, optical, and nuclear diagnostic systems. A primary goal of the National Ignition Campaign (NIC) on the NIF was to implode a low-Z capsule filled with ∼0.2 mg of deuterium-tritium (DT) fuel via laser indirect-drive inertial confinement fusion and demonstrate fusion ignition and propagating thermonuclear burn with a net energy gain of ∼5–10 (fusion yield/input laser energy). This requires assembling the DT fuel into a dense shell of ∼1000 g/cm3 with an areal density (ρR) of ∼1.5 g/cm2, surrounding a lower density hot spot with a temperature of ∼10 keV and a ρR ∼0.3 g/cm2, or approximately an α-particle range. Achieving these conditions demand precise control of laser and target parameters to allow a low adiabat, high convergence implosion with low ablator fuel mix. We have demonstrated implosion and compressed fuel conditions at ∼80–90% for most point design values independently, but not at the same time. The nuclear yield is a factor of ∼3–10× below the simulated values and a similar factor below the alpha dominated regime. This paper will discuss the experimental trends, the possible causes of the degraded performance (the off-set from the simulations), and the plan to understand and resolve the underlying physics issues.