The shock initiation of high explosives is believed to be controlled by hot spots that ignite, grow, and coalesce. This hypothesis is supported by the observation that single crystals of high explosive molecules are much more difficult to ignite than pressed explosive crystals. Similarly, high explosive initiability is known to be very sensitive to porosity.
These observations, however, offer only indirect support of the hot spot hypothesis. We have designed experiments to be conducted (November 2017) that will directly measure the early stages of shock initiation with spatial resolution of several microns. Supporting simulations have been conducted to optimize the experimental design and help interpret the experimental data.
The first stage of this work is to characterize the grain structure in TATB plastic-bonded samples that are 0.12 – 0.20 mm thick. We used computed tomography capabilities to examine the 3D particle structures. Further, we will investigate the response of these samples to shock waves at the 0.010 – 0.10 mm scale. Experiments will be conducted at LLNL’s Jupiter Laser Facility. Line-VISAR measurements of shocks will determine time dependent flow velocities with an appropriate spatiotemporal resolution to capture variations induced by the grain-scale structure of the materials. Microwave transmission/reflection measurements will be simultaneously conducted to characterize void collapse and ignition phenomena.
We have conducted simulations of the laser-driven experiment on TATB high explosive grain initiation. The simulations use the ALE3D hydrodynamic code and the Cheetah HE chemistry code to calculate the shock response of the high explosive grains. The simulations have been used to design the experimental drive necessary to achieve hot spot formation and chemical reactions.
This work was performed under the auspices of the U. S. Department of Energy by Lawrence Livermore National Security, LLC under Contract DE-AC52-07NA27344.