2.B X-Ray Conversion Measurements from High-Z Spherical Targets

Quantitative measurements of the x-ray emission from laser-produced plasmas have been a subject of considerable interest since the early 1970s.l With the fabrication of large, in some cases multibeam, highpower laser systems, much work has been performed on the analysis of x-ray emission from laser-produced plasmas of high-atomic-number materiak2 Measurements of soft x-ray emission from the plasmas of high-Z materials, particularly Au targets, are not only of considerable interest for inertial confinement fusion applications but are also relevant to a number of potential applications of laser-produced x rays. For these reasons, there is a need for the quantitative understanding,. through hydrodynamic and atomic physics numerical codes, of soft x-ray production from laser-irradiated solid targets. This is particularly the case for interaction experiments with high-power, short-wavelength laser radiation. Such experiments exhibit not only high overall coupling efficiency but also produce, for high-Z targets, greater soft x-ray emission. However, experiments to date have all been performed with planar targets, irradiated by single or nonuniform multiple-laser beams. A number of studies have been performed at Lawrence Livermore National Laboratory (LLNL) with the ARGUS3 and NOVETrE4 laser systems to compare the experimentally determined conversion efficiencies to x rays and those estimated from numerical simulations performed with the laser-fusion hydrodynamic code LASNEX. At low intensities (< 8 x 1 013 W/cm2), the measured x-ray conversion efficiency3 is lower than that predicted by LASNEX.