Growth rates of the Rayleigh-Taylor instability in foils accelerated with a laser beam smoothed by induced spatial incoherence were measured and compared with hydrodynamic-code simulations. Modes with 150-and 100-/im wavelengths grew at predicted rates. However, no growth was experimentally observed at 50-/im wavelength. Code simulations suggest that induced spatial incoherence can influence the 50-/im Rayleigh-Taylor mode by delaying the start of its growth.
We report on our continued development of high resolution monochromatic x-ray imaging system based on spherically curved crystals. This system can be extensively used in the relevant experiments of the inertial confinement fusion (ICF) program. The system is currently used, but not limited to diagnostics of the targets ablatively accelerated by the Nike KrF laser. A spherically curved quartz crystal (2d=6.687 03 Å, R=200 mm) has been used to produce monochromatic backlit images with the He-like Si resonance line (1865 eV) as the source of radiation. Another quartz crystal (2d=8.5099 Å, R=200 mm) with the H-like Mg resonance line (1473 eV) has been used for backlit imaging with higher contrast. The spatial resolution of the x-ray optical system is 1.7 μm in selected places and 2–3 μm over a larger area. A second crystal with a separate backlighter was added to the imaging system. This makes it possible to make use of all four strips of the framing camera. Time resolved, 20× magnified, backlit monochromatic images of CH planar targets driven by the Nike facility have been obtained with spatial resolution of 2.5 μm in selected places and 5 μm over the focal spot of the Nike laser. We are exploring the enhancement of this technique to the higher and lower backlighter energies.
Measurements of the 3ω0/2 emission from laser-irradiated targets at 0.53 μm were made at three angles over a wide range of laser bandwidths with and without induced spatial incoherence (ISI) echelons. The 3ω0/2 emission was found to be correlated with hard x rays but not Raman spectra, suggesting that the 3ω0/2 radiation was due to two-plasmon decay. Reduction of both 3ω0/2 emission and the accompanying hard x rays by ISI required five to ten times larger bandwidths than needed to suppress stimulated Raman scattering and stimulated Brillouin scattering.
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