Experimental studies of material strength in the high energy density regime*

A solid material can be placed in the high energy density regime by compressing it to pressures > 1 Mbar using a laser driven plasma piston drive. We create a ramped laser drive that avoids shock melting, maintaining the material in the solid state during the full compression. Understanding plastic deformation dynamics of materials under these extreme conditions is of great interest in a number of fields, including meteor impact dynamics and advanced inertial confinement fusion. We infer the strength of Ta, Pb [1,2] and Fe at high pressures (up to 8 Mbar), high strain rates (~10⁷ s⁻¹) and high strains (> 30%) by measuring the growth of Rayleigh-Taylor instabilities (RTI) under ramped compression. We find that the RTI growth for materials in the solid state, compressed under high pressure and high strain rates, is reduced compared to the no-strength case. We describe recent experimental results from NIF and compare them to various strength models. [1] H. -S. Park et al., Phys. Rev. Lett. 114, 065502 (2015). [2] A. Krygier et al., Phys. Rev. Lett., accepted (2019).