A modeling of smoothing of nonuniform pressure in laser driven ablative plasmas

A theoretical model that studies smoothing of non-uniform ablation pressure is presented. The 'cloudy day' model that is widely used to estimate the smoothing considers only thermal waves in homogeneous plasmas. However, sound waves caused by temperature perturbation, and steep ablation structure are considered in the present model. The work of [Manheimer et al.: Phys. Fluids 25 (1982) 1644] attempted to include these. However, we newly 1) consider an ablation structure with a finite density ratio between sonic point and ablation surface; 2) solve eigenvalue problem to initialize the variables consistently with fluid equations in the shock compression region; 3) impose different boundary condition at the sonic point; and 4) consider higher mode (kyx0 ≥ 30). A nonlinear relation between the perturbed ablation pressure ratio between sonic point and ablation surface, and transverse wave number of perturbation kyx0 is shown. As kyx0 becomes larger, the smoothing becomes more efficient. (author)