VISAR and high-resolution Talbot X-ray diagnostics for shock breakout times in low density aerogel foams*

The description of matter in extreme conditions is an important challenge to address in High Energy Density and Materials Science research. Low-density porous media behavior under dynamic compression is of particular interest to Inertial Fusion Energy applications, for example. Equations of state (EOS) are useful in characterizing the behavior of materials as their state variables (pressure, density, temperature) change. While no universal EOS exists, an EOS can be formulated for specific materials. Little is known about the microphysics of foams and thus, we present shock-compression of foam targets and shock velocity measurements, an important parameter for determining the EOS.  Low-density foams of various densities (20,50, 100, and 500 mg/cc) were irradiated by the LCLS Matter in Extreme Conditions laser (~ 60 J, 10 ns, >10¹⁵ W/cm²). Shock breakout time and velocity were obtained from VISAR diagnostics, with a median shock velocity of ~25 km/s in 20 mg/cc foam targets and ~7 km/s in 500 mg/cc foam targets.