Observation of transonic ionization fronts in low-density foam targets

Transonic ionization fronts have been observed in low-density chlorinated f oam targets using time-resolved K-shell absorption spectroscopy. The front was driven by an intense pulse of soft x rays produced by high-power laser irradiation of a thin foil. The density and temperature profiles inferred f rom the radiographs provided detailed measurement of the conditions at a nu mber of times. The experimental data were compared to radiation hydrodynami cs simulations and reasonable agreement was obtained. [S0031-9007(99)08879- 1].