Shallow Bubble Collapse Mechanism: A demonstrated high-areal mass, high-temperature ejecta production mechanism with rapid atomization

The Shallow Bubble Collapse (SBC) mechanism was proposed to explain anomalous 2^nd shock ejecta measurements that the Richtmyer-Meshkov Instability growth model fails to capture. In the SBC regime, the first shock condition results in a melted state persisting after release. Release waves interact to result in subsurface cavitation shallow to the surface. A sufficiently strong 2^nd shock then generates substantial entropy as the cavitated metal foam gets recompacted. When the 2^nd shock breaks out at the free surface, the material rapidly expands resulting in a low-density cloud of liquid droplets. This results in temperatures that can be over 2-times higher than expected with a simple shock physics understanding of the two shocks. We observe areal masses over 1 g/cm², temperatures over 5000 K, and estimate atomization fractions at over 15% of the ejected material. A modeling approach is developed enabling us to capture many of the salient aspects of SBC production. We have observed SBC in tin and cerium target samples on gun platforms.

 

LLNL-ABS-832552. Work performed under the auspices of the U.S. DOE by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344. Lawrence Livermore National Security, LLC.