Observation of radiative burnthrough in x-ray heated beryllium by time-resolved spectroscopy

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Abstract
A 0.5-μm-thick beryllium foil is heated by thermal x rays from a laser-irradiated converter foil up to temperatures of a few 10 eV. During the transformation of the solid Be into an ionized gas time-resolved absorption spectra have been measured in the region 100 eV ≲hν≲250 eV. The measurements agree well with calculations of the radiation transport, for which electron-impact line broadening was found to be essential. Smoothing of the Be K edge observed in the beginning of the heating, when the foil is still in a partially degenerate state, is attributed to thermal smoothing of the Fermi edge.