A new model for the instability of a steady ablation front based on the sharp boundary approximation is presented. It is shown that a self-consistent dispersion relation can be found in terms of the density jump across the front. This is an unknown parameter that depends on the structure of the front and its determination requires the prescription of a characteristic length inherent to the instability process. With an adequate choice of such a length, the model yields results, in excellent agreement with the numerical calculations and with the sophisticated self-consistent models recently reported in the literature.

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A fully nonlinear sharp-boundary model of the ablative Rayleigh-Taylor instability is derived and closed in a similar way to the self-consistent closure of the linear theory. It contains the stabilizing effect of ablation and accurately reproduces the results of 2D DRACO simulations. The single-mode saturation amplitude, bubble and spike evolutions in the nonlinear regimes, and the seeding of long-wavelength modes via mode coupling are determined and compared with the classical theory without ablation. Nonlinear stability above the linear cutoff is also predicted.

The highly nonlinear evolution of the single-mode Rayleigh-Taylor instability (RTI) at the ablation front of an accelerated target is investigated in the parameter range typical of inertial confinement fusion implosions. A new phase of the nonlinear bubble evolution is discovered. After the linear growth phase and a short constant-velocity phase, it is found that the bubble is accelerated to velocities well above the classical value. This acceleration is driven by the vorticity accumulation inside the bubble resulting from the mass ablation and vorticity convection off the ablation front. While the ablative growth rates are slower than their classical values in the linear regime, the ablative RTI grows faster than the classical RTI in the nonlinear regime for deuterium and tritium ablators.

The model presented overcomes past inconsistencies by applying matching asymptotic techniques.The obtained growth rate, y =a(k)&kg -2kv, (where v, is the ablation velocity), could reproduce numerical simulations and experiments in a more complete way than the Takabe formula [Phys. Fluids 28, 3676 (1985)] y =0.9&kg -3k v, . Here a(k)-: [1 -(k/k, )" ]',represents the stabilization heat conduction effect and the cutoff wave number k, is much smaller than the inverse of the density scale length at the ablation front. Such a rigorously derived stabilization mechanism clarifies many of the numerical, analytical, and simulation results found in the literature. PACS number(s): 52.35.Py, 52.40.Nk