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Non-modal hydrodynamic stability analysis of ablation flows relative to inertial confinement fusion

Analyse non normale de stabilité hydrodynamique d'écoulements d'ablation en fusion par confinement inertiel

Résumé : A non-modal linear hydrodynamic stability analysis of ablation waves is carried out for the first time. This analysis is performed for unsteady self-similar solutions in slab symmetry of the Euler equations with nonlinear heat conduction, using a direct-adjoint method that results from a Lagrangian-based optimization problem. Such solutions are considered in connection with inertial confinement fusion (ICF) experiments where the hydrodynamic stability of ablative flows has been identified as a key issue to the achievement of thermonuclear burn. Inherently unsteady, these flows are compressible, highly nonuniform with a steep heat front, and bounded by a material surface and a shock front — features that are possible sources of non-modal thermo-acoustics effects. Non-modal effects are presently exhibited on a particular ablation wave solution. This finding raises the question of the existence and consequences of such effects in configurations of X-ray driven ablation that are more representative of ICF experiments, which is the object of an ongoing investigation.