Laboratory Measurements Of Geometrical Effects In The X-Ray Emission Of Optically Thick Lines For Icf Diagnostics

Understanding the effects of radiative transfer in High Energy Density Physics experiments is critical for the characterization of the thermodynamic properties of highly ionized matter, in particular in Inertial Confinement Fusion (ICF). We report on non-Local Thermodynamic Equilibrium experiments on cylindrical targets carried out at the Omega Laser Facility at the Laboratory for Laser Energetics, Rochester NY, which aim to characterize these effects. In these experiments, a 50/50 mixture of iron and vanadium, with a thickness of 2000 angstrom and a diameter of 250 mu m, is contained within a beryllium tamper, with a thickness of 10 mu m and a diameter of 1000 mu m. Each side of the beryllium tamper is then irradiated using 18 of the 60 Omega beams with an intensity of roughly 3x10(14) W cm(-2) per side, over a duration of 3ns. Spectroscopic measurements show that a plasma temperature on the order of 2keV was produced. Imaging data show that the plasma remains cylindrical, with geometrical aspect ratios (quotient between the height and the radius of the cylinder) from 0.4 to 2.0. The temperatures in this experiment were kept sufficiently low (similar to 1-2keV) so that the optically thin Li-like satellite emission could be used for temperature diagnosis. This allowed for the characterization of optical-depth-dependent geometric effects in the vanadium line emission. Simulations present good agreement with the data, which allows this study to benchmark these effects in order to take them into account to deduce temperature and density in future ICF experiments, such as those performed at the National Ignition Facility.