Rayleigh-Taylor instability analysis of targets with a low-density ablation layer

Irregularities on the outer surface of Inertial Confinement Fusion (ICF) ca psules accelerated by laser irradiation are amplified by the Rayleigh-Taylo r instability (RTI), which occurs at the ablation front (ablative RTI), whe re density gradient and acceleration have the same direction. The analytic stability theory of subsonic ablation fronts, for Froude number larger than one, shows that the main stabilization mechanisms are blowoff convection ( rocket effect equilibrating the gravity force) and ablation (Sanz 1993; Bet ti er al. 1996). Blowoff convection and ablation are enhanced if the ablato r material is mixed with high-Z dopants. The latest enhances radiation emis sion setting the ablator on a higher adiabat, lowering its density, and inc reasing the ablation velocity. When such an ablator is used to push a solid deuterium-tritium (D-T) shell, the D-T-ablator interface becomes classical ly unstable. The aim of this paper is to investigate the stability of such a configuration, represented by a low-density ablator pushing a heavier she ll, and study the interplay between the classical and ablative RTIs occurri ng simultaneously. The stability analysis is carried out using a sharp boun dary model (Piriz er al. 1997), which contains all the basic physics of the RTI in ICF.