Inferring temperature from x-ray diffraction of Pb ramp-compressed to 840 GPa

We will report x-ray diffraction measurements of body-centered-cubic lead (Pb) compressed quasi-isentropically, with ramp-shaped laser pulses at the National Ignition Facility, to pressures between 190 and 840 GPa. We have used the Debye-Waller attenuation of diffraction peak intensities relative to an ideal, unperturbed lattice to determine mean squared displacement of the atoms about their ideal positions, and have related this to temperature, using quantum molecular dynamics calculations of the Debye temperature at high pressure and temperature. We will comment on the general prospects for diagnosing temperature in dynamic-compression experiments from x-ray diffraction, and the associated systematic uncertainties.