Very-high-growth-factor planar ablative Rayleigh-Taylor experiments

The Rayleigh-Taylor (RT) instability is an important factor in bounding the performance envelope of inertial confinement fusion targets. This paper describes an experiment for ablative RT instability that for the first time achieves growth factors close to those expected to occur in indirect-drive ignition targets at the National Ignition Facility (NIF) [J. A. Paisner, J. D. Boyes, S. A. Kumpan et al., Laser Focus World 30, 75 (1994)]. The large growth allows small-seed perturbations to be detected and can be used to place an upper bound on perturbation growth at the ablation front resulting from microstructure or surface roughness in the preferred Be ablator. The experiments were performed on the Omega laser [T. R. Boehly, D. L. Brown, R. S. Craxton et al., Optics Communications 133, 495 (1997)] using a two stepped x-ray pulse consisting of an early time section to emulate the NIF foot followed by a higher-radiation-temperature drive sustained over an additional 5-7 ns. The trajectory of the ablator was measured using streaked backlit radiography, and the growth of a sinusoidal perturbation machined on the drive side of the ablator was measured using face-on radiography. The diagnostic view remained open until -11 ns with maximum growth factors measured to be -200. (C) 2007 American Institute of Physics.