LTE absorption spectroscopy of an X-ray heated boron plasma

Time-resolved K-shell spectroscopy of an X-ray driven boron sample is reported. A small cavity irradiated by two frequency-doubled Nd:glass laser beams is used as an X-ray heating source, allowing to reach electron temperatures in the 10-25 eV range, in conditions close to local thermodynamic equilibrium. Synthetic spectra obtained from detailed atomic calculations are fitted to the experimental data to determine the electron temperature and the density of plasma. We compare the resulting data to radiative hydrodynamic simulations of the heating and expansion of the sample, and find lower densities and higher temperatures than predicted by the code. The reason for this discrepancy is attributed to difficulties in maintaining the boron sample homogeneity and to take into account properly the expansion of the plasma walls with such small-size cavities.