Large growth, planar Rayleigh–Taylor experiments on Nova

A set of indirect‐drive experiments to study large growth Rayleigh–Taylor instability using shaped laser pulses at the Nova laser facility has been conducted. Planar foils of fluorosilicone were accelerated by x‐ray ablation. The foil trajectory was measured using edge‐on radiography. In separate experiments using face‐on radiography, contrast in optical depth was measured as a function of time, from which the evolution of 50 μm wavelength initially sinusoidal surface perturbations was deduced. Holding other parameters fixed, the amplitude of the initial perturbation was varied by up to a factor of 30 in separate shots. The foils with the smallest initial perturbation exhibited growth factors of 75 in contrast. Foils with large initial amplitude perturbation gave growth factors of 6 or less, and displayed the ‘‘bubble‐and‐spike’’ shape characteristic of the nonlinear Rayleigh–Taylor instability. Comparisons of two‐dimensional computer simulations with both the measured foil trajectory and the perturbation growth show good agreement, provided that a suitable opacity model is chosen. In the linear regime the observed growth rates are 60%–75% of classical, the reduction attributed primarily to ablative stabilization. The observed onset of harmonic generation, signaling the transition into the nonlinear regime, is well predicted by third‐order theory.

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