Optimizing the Fabrication of Polyimide Shells

196 LLE Review, Volume 88 Introduction Polyimide is being developed as an ablator material for inertial confinement fusion (ICF) targets because of its superior mechanical and thermal properties.1 A typical target design for the OMEGA laser system consists of a spherical shell, 1 mm in diameter and 1 μm in wall thickness, with a 100-μm-thick layer of solid deuterium and tritium (DT) uniformly deposited on the inner surface. To achieve this, the shells must be both strong and permeable so that they can be filled quickly with DT gas and survive the pressure gradient created in subsequent treatments, including cooling to below 18.9 K and layering by differential heating. Material properties that determine the performance of shells as targets include gas permeability, Young’s modulus, tensile strength, and elongation at break.2