Time-resolved spectroscopic measurements of high density in Ar-filled microballoon implosions

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×${10}^{24}$ ${\mathrm{cm}}^{\mathrm{-}3}$ 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 ${\mathrm{He}}_{\mathrm{\alpha }}$ line.