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.

A linear stability theory of double ablation fronts is developed for direct-drive inertial confinement fusion targets. The so-called electron radiative ablation front [S. Fujioka et al., Phys. Rev. Lett. 92, 195001 (2004)] is studied with a self-consistent model. Numerical results are presented as well as an analytical approach for the radiation dominated regime of very steep double ablation front structure. Dispersion relation formula is tackled by means of a sharp boundary model.

The expression for electron impact ionization rate by a Maxwellian electron population drifting with respect to a uniform neutral atom background is derived. Depending on electron temperature, drift speeds between one to five times electron thermal velocity produce increments in the ionization rate from two to seven orders of magnitude. Local ionization takes place over shorter distances than predicted for nondrifting electron populations and the results agree with previous experimental evidence on ionizing plasma double layers and electron attracting sheaths.

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