Measurements of early time radiation asymmetry in vacuum and methane-filled Hohlraums with the reemission ball technique

In a previous paper [Phys. Rev. E {bold 53}, 5240 (1996)], we presented experimental results of a technique for measuring time resolved symmetry in vacuum {ital Hohlraums} irradiated with the laser beams from the NOVA laser located at Lawrence Livermore National Laboratory. The experimental method involved x-ray imaging a high-Z ball placed in the center of a laser irradiated vacuum {ital Hohlraum}. The signal from the high-Z ball was measured along the {ital Hohlraum} axis, and compared with calculations. In this paper, using this experimental technique, we present time-dependent reemission measurements and calculations of the drive symmetry in vacuum and methane-filled {ital Hohlraums} for a shaped laser pulse. We also present a method for determining the time dependence of the radiation flux from the measured reemission signal ratios, and do a modal analysis to determine the values of the dominant Legendre components. {copyright} {ital 1998} {ital The American Physical Society}