30 Novembre – Thesis defense - Corentin Mailliet

14 h Amphi GAMA - Building A33 (University of Bordeaux / Talence)

Highly non-linear study of the ablative Rayleigh-Taylor Instability in Direct Drive.

Hydrodynamic instabilites growth ais the major obstacle to achieve ignition conditions in inertial confinement fusion. It is thus crucial to understand, predict and possibly control those instabilities. Ablation front instability is particularly studied in the direct drive scheme, because of the laser imprint phenomenon. However highly non-linear stage of the ablative Rayleigh-Taylor instability remains poorly investigated. This study aims to analyze this regime.
First a new direct drive experimental platform is developped on the NIF.
It enables to study hydrodynamics up to thirty nanoseconds of laser drive. This experimental con figuration is then benchmarked with the study of the growth of a 2D preimposed ripple under the e ffect of Rayleigh-Taylor instability. A 2D numerical platform is also developed using CHIC hydrocode to reproduce experimental results.
The study of a highly non-linear Rayleigh-Taylor instability regime is realised with a 3D broadband laser imprinted perturbation. Initial conditions impact is studied by using both a smoothed and a raw imprint beam.
Face-on radiography data are analyzed in real and Fourier space in order to estimate all the parameters of the instability : linear growth rates, saturation velocity, bubble-merging rate and self-similar growth parameter. All those values are compared to existing models. The important role of initial conditions at highly non-linear stage of the perturbation is demonstrated.

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