Hydrodynamic instability experiments at GEKKO XII

Hydrodynamic instabilities play an important role in inertial confinement fusion implosions. Target surface perturbations will grow, primarily owing to the Rayleigh-Taylor (R-T) instability and finally resulting in fuel-pusher mixing that degrades the implosion performance. Good understanding of the instabilities is necessary to limit the mixing to a tolerable level. At the GEKKO XII laser facility, an extensive series of direct drive experiments has been conducted on the effect of rippled shock propagation, initial imprinting and its suppression by X ray pre-irradiation, and the R-T instability in the linear regime. As to the drive laser, partially coherent light achieves the state-of-the-art uniformity by which spurious imprints are minimized. For the initial imprinting experiments, a single mode perturbation was introduced on the foot pulse for imprint, followed by a uniform main pulse for R-T amplification. The experimental R-T growth rate was significantly reduced in comparison to the classical growth rare.