Absolute x-ray spectra measurements at the Dynamic Compression Sector*

The x-ray properties at the Dynamic Compression Sector can be tailored in peak energy, bandwidth, and spot size to accommodate a broad range of real-time, in-situ, x-ray measurements during dynamic compression experiments for addressing the scientific needs of each research campaign.  Accurate characterization of the x-ray beam properties used for each campaign is critical for performing quantitative analysis of the x-ray data obtained. We provide each DCS experimentalist with an accurate measurement of the beam profile on target as well as the full x-ray energy spectral profile – using a small, Si (220) double crystal monochromator and photodiode – to aid in the analysis of their data. However, we have not been able to provide our users with quantitative flux measurements, and the total number of x-ray photons per pulse have been estimated using simulations. Using a newapproach  that accounts for the monochromator characteristics, electronic equipment response, and photodiode calibration, we can now quantitively determine the absolute flux for each spectral measurement. The measurements are in good agreement with calorimetry data and with x-ray ray trace simulations that account for the beamline optics setup. These measurements constitute a significant enhancement to our x-ray diagnostics capabilities and are critical for real-time evaluation of the performance of the beamline, accurate forward simulations of experimental results, and predictive calculations for future experiments.