Hydrodynamic Scaling of tHe deceleration-PHaSe rayleigH-taylor inStabiliity

LLE Review, Volume 143 125 Introduction In inertial confinement fusion (ICF),1 a shell of cryogenic deuterium (D) and tritium (T) filled with DT gas is imploded with direct laser illumination (direct drive)2 or through an x-ray bath produced inside a laser-irradiated hohlraum (indirect drive).3 Energy from the laser or x ray is absorbed in the plasma near the outer surface of the target, causing mass ablation. The ablation pressure pushes the shell inward by the “rocket effect.” In addition to the Rayleigh–Taylor (RT) unstable outer surface during the acceleration phase, the inner surface of the shell is also unstable to the Rayleigh–Taylor instability (RTI) during the deceleration phase. The RT spikes stream into the hot spot, decreasing the burn volume and increasing the surface-to-volume ratio of the hot spot. This, in turn, increases the conduction losses,4 resulting in a reduction in hot-spot temperature. The perturbations rapidly become nonlinear, and a significant fraction of the shell’s kinetic energy is used to feed lateral motion, instead of contributing to the hot-spot pressure through radial compression.5,6 The effective areal density tR of the shell is expected to decrease and degrade the confinement time, burn volume, hot-spot pressure and temperature, and, therefore, the neutron yield. The yield-over-clean (YOC) is used as a measure of the effect of hydrodynamic instabilities on the implosion performance:7