Single-mode, Rayleigh-Taylor growth-rate measurements on the OMEGA laser system

The results from a series of single-mode, Rayleigh-Taylor (RT) instability growth experiments performed on the OMEGA laser system [T. R. Boehly et al. , Opt. Commun. 133, 495 (1997)] using planar targets are reported. Planar t argets with imposed mass perturbations were accelerated using five or six 3 51 nm laser beams overlapped with total intensities up to 2.5 X 10(14) W/cm (2). Experiments were performed with both 3 ns ramp and 3 ns flat-topped te mporal pulse shapes. The use of distributed phase plates and smoothing by s pectral dispersion resulted in a laser-irradiation nonuniformity of 4%-7% o ver a 600 mu m diam region defined by the 90% intensity contour. The tempor al growth of the modulation in optical depth was measured using throughfoil radiography and was detected with an x-ray framing camera for CH targets. Two-dimensional (2-D) hydrodynamic simulations (ORCHID) [R. L. McCrory and C. P. Verdon, in Inertial Confinement Fusion (Editrice Compositori, Bologna , 1989), pp. 83-124] of the growth of 20, 31, and 60 mu m wavelength pertur bations were in good agreement with the experimental data when the experime ntal details, including noise, were included. The amplitude of the simulati on optical depth is in good agreement with the experimental optical depth; therefore, great care must be taken when the growth rates are compared to d ispersion formulas. Since the foil's initial condition just before it is ac celerated is not that of a uniformly compressed foil, the optical density m easurement does not accurately reflect the amplitude of the ablation surfac e but is affected by the initial nonuniform density profile. (C) 2000 Ameri can Institute of Physics. [S1070-664X(00)02801-9].