Time-resolved x-ray diffraction diagnostic development with ultrafast hCMOS sensors at the National Ignition Facility*

We present details of an experimental platform that collects time-resolved x-ray diffraction (XRDt) data from laser-driven dynamically compressed materials at the National Ignition Facility. XRDt probes the atomic structure of phase transformations at extreme thermodynamic conditions in-situ. To record phase transitions, we use high speed (~1 ns) gated hybridized CMOS sensors (hCMOS), which collect multiple frames of data over a timescale of a few to tens of ns.  We record both time-resolved (hCMOS) and time-integrated (image plate) XRD and the direct x-ray beam.

The drive-laser is used to ramp compress thin samples, sandwiched between tamper layers. A pinhole limits the sample size to 400 µm.  High-precision velocimetry measurements monitor the pressure history of the sample. A temporally uniform, quasi monochromatic x-ray source of ~10 ns duration is produced by irradiating a ~250 µm thick Ge foil with < ~50 kJ of laser energy at 2x10¹⁵ W/cm². We use dedicated filters to mitigate x-ray florescence and hard x-rays from hot electrons. The platform has been used to collect XRD from ambient Sn and Pb at 1 Mbar. We discuss challenges with background mitigation and accuracy/resolution of diffraction data. 

Prepared by LLNL under Contract DE-AC52-07NA27344. LLNL-ABS-828064.