Design and modeling of ignition targets for the National Ignition Facility

TLDR

Simulations indicate that indirectly driven targets can yield 1–30 MJ using 0.9–2 MJ of 0.35 µm laser light, and all designs rely on a cryogenic fuel layer, making ignition at this scale difficult without cryogenic capsules. The article aims to describe target designs, the modeling used to develop them, and the modeling that sets laser system specifications for the proposed National Ignition Facility. Capsules with beryllium or polystyrene ablators are enclosed in gold hohlraums, and multiple illumination bands plus a low‑Z gas fill are employed to achieve uniform x‑ray irradiation and limit gold plasma filling, while critical issues include hohlraum design and optimization, Rayleigh–Taylor instability modeling, and laser–plasma interactions.

Abstract

Several targets are described that in simulations give yields of 1–30 MJ when indirectly driven by 0.9–2 MJ of 0.35 μm laser light. The article describes the targets, the modeling that was used to design them, and the modeling done to set specifications for the laser system in the proposed National Ignition Facility. Capsules with beryllium or polystyrene ablators are enclosed in gold hohlraums. All the designs utilize a cryogenic fuel layer; it is very difficult to achieve ignition at this scale with a noncryogenic capsule. It is necessary to use multiple bands of illumination in the hohlraum to achieve sufficiently uniform x-ray irradiation, and to use a low-Z gas fill in the hohlraum to reduce filling of the hohlraum with gold plasma. Critical issues are hohlraum design and optimization, Rayleigh–Taylor instability modeling, and laser–plasma interactions.