Ablative Rayleigh-Taylor instability with strong temperature dependence ofthe thermal conductivity

An asymptotic analysis of Rayleigh-Taylor unstable ablation fronts encountered in inertial confinement fusion is performed in the case of a strong temperature dependence of the thermal conductivity. At leading order the nonlinear analysis leads to a free boundary problem which is an extension of the classical Rayleigh-Taylor instability with unity Atwood number and an additional potential flow of negligible density expelled perpendicular to the front. The nonlinear evolution of the front is analysed in two-dimensional geometry by a boundary integral method. The shape of the front develops a curvature singularity within a finite time, as for the Birkhoff-Rott equation for the Kelvin-Helmholtz instability.