Rayleigh--Taylor Growth Measurements of 3-D Modulations in Nonlinear Regime

The nonlinear growth of 3-D broadband nonuniformities was measured near saturation levels\footnote{S. W. Haan, Phys. Rev. A, Gen. Phys. \textbf{39}, 5812 (1989).}$^{,}$\footnote{ V. A. Smalyuk\textit{ et al.}, Phys. Rev. Lett. \textbf{81}, 5342 (1998).} using x-ray radiography in planar foils accelerated by the OMEGA laser. An understanding of the nonlinear evolution of the Rayleigh--Taylor instability is essential in inertial confinement fusion and astrophysics. The initial target modulations were seeded by laser nonuniformities and subsequently amplified by the Rayleigh--Taylor instability. The nonlinear saturation velocities are measured in Fourier space and are found to be in excellent agreement with Haan predictions.\footnote{V. A. Smalyuk \textit{et al.}, ``Fourier-Space, Nonlinear Rayleigh--Taylor Growth Measurements of 3-D Laser-Imprinted Modulations in Planar Targets,'' submitted to Phys. Rev. Lett.} The measured growth of long-wavelength modes is in good agreement with models of enhanced, nonlinear, long-wavelength generation in ablatively-driven targets.$^{3}$ In a real space analysis, bubble merger is quantified by the evolution of distributions of the bubble size, amplitude, and velocity. A self-similar evolution of the distribution of bubble sizes is measured and the bubble-merging rate inferred. This talk will describe the nonlinear evolution of the 3-D modulations and compare them with theoretical models. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC52-92SF19460. Contributors: J. A. Delettrez, D. D. Meyerhofer, S. P. Regan, and T. C. Sangster; O. Sadot (also Ben Gurion University); D. Shvarts, Negev, Israel.