Observation of Secular Growth Dominated Dynamics in X-Ray Driven Foils.

Understanding and controlling the seeding of hydrodynamic perturbations are crucial for achieving ignition and high gain in inertial confinement fusion (ICF). In this Letter, we present face-on radiography of planar foil with preimposed sinusoidal ripples, revealing a novel phenomenon that the perturbation inverts its phase during the acceleration of the ablation front. With radiation-hydrodynamic simulations and a simple model, we can identify a secular (nonexponential) growth dominated regime before the quasisteady acceleration of the foil is fully established. Further evaluation reveals another novel freeze-out-like phenomenon, in which the growth of the ablation front perturbation ceases for a substantial duration relative to the acceleration phase. Our results advance the understanding of the Rayleigh-Taylor seeding in ICF implosions and inspire new designs for high-gain ICF targets.