Symmetry control using a 2-shock pulse shape in an indirect-drive double shell implosion*

Double shell inertial confinement fusion compresses deuterium-tritium fuel to fusion conditions using a multi-shell target with a dense metal inner shell. Performance of these implosions requires approximate spherical symmetry of the implosion for efficient transfer of kinetic energy between shells.  Asymmetries may be seeded by the radiation drive as well as target fabrication artifacts, such as the outer shell assembly joint.

This work discusses the first use of a 2-shock pulse design with an indirectly-driven double shell capsule consisting of an aluminum ablator, a foam layer, and an unfilled tungsten inner shell. The goal of this shot was to delay the main pulse in order to improve symmetry control and mitigate asymmetries caused by the ablator joint. Shape analysis of backlighter images shows an oblate outer shell with a nearly symmetric (slightly oblate) inner shell. These experimental results are in agreement with corresponding hydrodynamic simulations. Results from a corresponding two-axis keyhole experiment which used the 2-shock pulse design will also be discussed.