LLE Review 77

Review 77


LLE Review 77 begins with two articles addressing issues applicable to direct-drive ICF on the National Ignition Facility (NIF): laser–plasma interactions and laser-irradiation uniformity. The experimental results of the first article indicate the parametric instabilities—stimulated Raman scattering and stimulated Brillouin scattering—are not likely to have a significant impact on target performance at the peak of the NIF direct-drive laser pulse. Laser-irradiation uniformity on OMEGA and the NIF is investigated in the second article, and improvements in irradiation uniformity planned for the OMEGA laser during 1999, which will reduce the rms nonuniformity to less than 1% when the intensity is averaged over 300 ps, are outlined. A novel charged-particle diagnostic has been developed that performs simultaneous rR measurements of the fuel, shell, and ablator regions of a compressed ICF target [which consists of an inner DT-fuel region, a plastic (CH) shell, and an ablator (CD)] by measuring the knock-on deuteron spectrum. Stress-inhibited laser-driven crack propagation and stress-delayed damage-initiation experiments in fused silica at 351 nm revealed a 70% increase in the damage initiation threshold when a modest amount of mechanical stress was applied to the optic. An analytic theory of the ablative Richtmyer–Meshkov instability shows that the main stabilizing mechanism of the ablation-front perturbations is the dynamic overpressure of the blowoff plasma with respect to the target material. Two articles outside of the scope of ICF research conclude this volume: (1) a triplet state of rose bengal—a dye used in photodynamic therapy—has been characterized; and (2) single-picosecond switching of a high-temperature-superconductor Josephson junction was observed.

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