Predictions of novel features in x-ray Thomson scattering spectra for temperature diagnosis

Warm dense matter experiments often diagnose temperature by analyzing the relative prominence of red- and blue-shifted plasmon features in x-ray Thomson scattering spectra. However, this procedure loses sensitivity as the temperature exceeds the plasmon energy, and it does not provide information on the extent to which the sample is in thermal equilibrium. We summarize recent predictions from both time-dependent density functional theory (TDDFT) and a modified average atom model which show clear signatures of scattering into thermally depleted bound states in aluminum and iron heated to 20eV. These prominent bound-bound features can allow determination of electron temperature in conditions beyond the sensitivity range of plasmon-based approaches. The TDDFT results also contain signatures of atomic order within the bound-free portion of the scattering spectra, which may be used to distinguish isochorically heated and thermalized matter and perhaps even infer ion temperature in studies of ultrafast melting. These theoretical insights advance the capabilities of x-ray scattering diagnostics as more extreme conditions become experimentally accessible.