Fabrication of Polyimide Shells for Use as ICF Targets

LLE Review, Volume 71 113 The current target-shell material for direct-drive experiments on OMEGA is a low-density hydrocarbon polymer fabricated using a low-pressure plasma polymerization process. This material meets the immediate requirements for an inertial confinement fusion (ICF) target shell: low density; smooth surfaces (outer and inner); spherical and concentric; and the capability of being fabricated with dopants at discrete radial positions in the shell wall. Future ICF experiments, especially those conducted at cryogenic temperatures, would benefit if the targets possessed additional properties: higher tensile strength; larger elastic moduli; greater room-temperature permeability; greater radiation resistance; higher thermal conductivity and lower electrical conductivity; and greater opacity at ~351 nm. These desirable properties will allow targets to be filled more rapidly with DT; be cooled faster to the DT triple point (19.8 K); survive higher temperature gradients in a cryostat; better resist the damaging effects of β-decay from tritium; and more readily accommodate augmented layering techniques such as RF-coupled joule heating. These properties will also allow decreasingly thin-walled shells to be used to contain the DT fuel; the goal is a 1-mm-diam target with a 1-μm-thick wall.