Measurement of Rayleigh–Taylor instability in a laser-accelerated target

Abstract

The classical Rayleigh–Taylor (R–T) instability of a fluid supporting a higher-density fluid^1,2 in a gravitational field is expected to occur in laser-driven compression³. A laser produces a high-pressure plasma that accelerates a higher-density solid shell of thickness Δr at a rate a. The effective gravitational acceleration–a would cause shell perturbations of wavenumber k to grow at the R–T rate γ = (ka)^½. However, ablation effects^3–5 are predicted to damp short-wavelength modes, giving rise to a maximum growth rate at k ∼ 1/Δr and implying a maximum aspect ratio r/Δr for a stable implosion. We present here the first clear experimental evidence for the growth of the R–T instability in a laser-accelerated plane target. These results were obtained by a novel technique using a target with an initial corrugation of known k. Streak X-ray radiography allows direct measurement of the growth of mass modulations in the target caused by this initial perturbation. The time-averaged growth rate of an imposed perturbation is measured as (0.3±0.05) × (ka)^½, in close agreement with a numerical simulation.