Shock-Release Studies in Spherical Geometry

Direct-drive inertial confinement fusion implosions employ shocks to set up favorable compressibility and stability for optimal fusion yield and areal density. When these shocks traverse material interfaces, a process known as rarefaction causes the release of material upstream of the shock. This release happens multiple times in multiple locations in a typical high-performance cryogenic implosion—in particular, at the fuel/vapor interface where excess deuterium–tritium fuel is released into the center of the target, thereby setting the initial density and temperature conditions of the compression. Therefore, understanding rarefaction is critical in understanding fusion performance. Dedicated experiments to study the release of material in spherical geometry have been performed to directly measure the kinetic energy in the release. Comparisons of these experiments with simulation predictions and synthetic diagnostics will be presented. The physics implications of these comparisons for accurately modeling rarefaction will also be briefly discussed.