We report on the analysis of time-resolved x-ray spectra from direct-drive, Ar-filled polymer
shell implosion experiments in which we trace the time evolution of the electron density
through stagnation. Very high electron densities in the range 2–8× 10 24 cm− 3 are inferred.
We also discuss several novel spectral features, including large Stark broadening of satellite
line emission, optical thicknesses for resonant transitions lower than expected, and the
onset of density-dependent ''blue satellites''on the high-energy wing of the He α line.

In current high-density, laser-driven implosion experiments the determination of core
conditions at stagnation is of great importance. This is particularly true of fusion experiments
(D2-or DT-filled targets) where nuclear diagnostics have been developed to estimate final
core conditions.',* A complementary approach, relying on x-ray spectroscopy of high-Z
gases (as total fill gas or as dopant), provides values of the electron density and
temperature. 3-6 This technique has the added advantage that, with the inclusion of x-ray …