Saturation effects in K alpha absorption spectroscopy of laser-produced plasmas

L-band x-ray absorption of radiatively heated nickel

Absorption of L-M and L-N transitions of nickel has been measured using point projection spectroscopy. The x-ray radiation from laser-irradiated gold cavities was used to heat volumetrically nickel foils "tamped with carbon" up to 20 eV. Experimental spectra have been analyzed with calculations based on the spin-orbit split arrays statistical approach and performed for each ionic species Ni5+ to Ni11+. Using a least-squares fit, this method provides an ion distribution broader than at local thermodynamic equilibrium, which is explained by spatial and temporal temperature gradients. A major improvement in the simulation of the absolute value of transmission is obtained with a resolved transition array statistical calculation that reproduces the experimental spectrum with the nominal areal mass density by taking into account the saturation of narrow lines.

Effect of shock heating on the stability of laser-driven targets

The shock heating of a laser-driven, direct-drive target can determine its stability by affecting Rayleigh-Taylor growth rates through target decompression and ablative stabilization. Measurements indicate that pulses that rise rapidly to 10(14) W/cm(2) produce shock-induced temperatures of approximately 25 eV, whereas more slowly rising pulses show less heating. Analysis of the observed target behavior produced by these two pulses demonstrates that shock heating improves hydrodynamic stability because ablative stabilization increases when the targets are preheated by shocks.