Comparison between x-ray free electron laser phase contrast imaging and hydrodynamical simulations of void collapse in PETN single crystals*

Much is still unknown about how detonation in high explosives initiates from insults such as shock, especially when the energy from the shock is lower than the energy barrier of the chemical reaction. The current hypothesis is that void collapse or other heterogeneity interactions with the shock form hot spots that initiate the chemical reaction needed to sustain shock wave propagation. Single-shot X-ray Free Electron Laser (XFEL) phase contrast imaging (PCI) was performed at the Matter in Extreme Conditions (MEC) Instrument at the Linac Coherent Light Source (LCLS). Pentaerythritol tetranitrate (PETN) high explosive single crystals with laser milled 10 micron voids were shocked with 5 GPa and probed with 40 fs, 5.822 keV X-ray pulse from the LCLS. Here, we compare hydrocode simulations of the experiment to PCI detector images. The hydrocode simulation density is converted to index of refraction and then summed along the optical axis into a 2D exit surface wave, and computationally propagated to the detector. The results of this proof of principle experiment represent the highest resolution imaging of shocked high explosives and will improve our understanding of hot spot formation in high explosives.