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Richtmyer–Meshkov (RM) mixing seeded by multimode initial surface perturbations in a convergent, compressible, miscible plasma system is measured on the OMEGA [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] laser system. A strong shock (Mach 12–20), created by 50 laser beams, is used to accelerate impulsively a thin aluminum shell into a lower density foam. As the system converges, both interfaces of the aluminum are RM unstable and undergo mixing. Standard x-ray radiographic techniques are employed to survey accurately the zero-order hydrodynamics, the average radius and overall width, of the marker. LASNEX [G. B. Zimmerman et al., Comments on Plasma Physics 2, 51 (1975)] simulations are consistent with the zero-order behavior of initially smooth markers. In experiments with smooth aluminum markers, the measured marker width shortly after shock passage behaves incompressibly and thickens due to Bell–Plesset effects. At high convergence (>4), the marker begins to compress as the rebounding shock passes back through the marker. When an initial multimode perturbation is introduced to the outer surface of the marker, the measured marker width is observed to increase by 10–15 μm, and is substantially smaller than as-shot simulations using RAGE [R. M. Baltrusaitis et al., Phys. Fluids 8, 2471 (1996)] would predict.

Laser beams that directly drive a cylindrical implosion are used to create a measurable region of mixed material in a compressible plasma state, for the first time in a convergent geometry. The turbulence driven by the Richtmyer–Meshkov instability by shock passage across a density discontinuity mixes marker material that is radiographically opaque. The width of the mix layer is compared between a system with large surface roughness and an initially smooth system. The experiment is described and results are compared to multi-dimensional numerical simulation, including three-dimensional turbulence calculations. The calculations adequately match the observations provided the measured initial conditions are used.

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